Lighting circuits (full page)
A source of comfort and productivity, lighting represents 15% of the quantity of electricity consumed in industry and 40% in buildings. The quality of lighting (light stability and continuity of service) depends on the quality of the electrical energy thus consumed. The supply of electrical power to lighting networks has therefore assumed great importance.
To help with their design and simplify the selection of appropriate protection devices, an analysis of the different lamp technologies is presented. The distinctive features of lighting circuits and their impact on control and protection devices are discussed. Recommendations relative to the difficulties of lighting circuit implementation are given.
The different lamp technologies
Artificial luminous radiation can be produced from electrical energy according to two principles: incandescence and electroluminescence.
Incandescence is the production of light via temperature elevation. The most common example is a filament heated to white state by the circulation of an electrical current. The energy supplied is transformed into heat by the Joule effect and into luminous flux.
Luminescence is the phenomenon of emission by a material of visible or almost visible luminous radiation. A gas (or vapors) subjected to an electrical discharge emits luminous radiation (Electroluminescence of gases).
Since this gas does not conduct at normal temperature and pressure, the discharge is produced by generating charged particles which permit ionization of the gas. The nature, pressure and temperature of the gas determine the light spectrum.
Photoluminescence is the luminescence of a material exposed to visible or almost visible radiation (ultraviolet, infrared).
When the substance absorbs ultraviolet radiation and emits visible radiation which stops a short time after energization, this is fluorescence.
Incandescent lamps
Incandescent lamps are historically the oldest and the most often found in common use.
They are based on the principle of a filament rendered incandescent in a vacuum or neutral atmosphere which prevents combustion.
A distinction is made between:
- Standard bulbs
These contain a tungsten filament and are filled with an inert gas (nitrogen and argon or krypton).
- Halogen bulbs
These also contain a tungsten filament, but are filled with a halogen compound and an inert gas (krypton or xenon). This halogen compound is responsible for the phenomenon of filament regeneration, which increases the service life of the lamps and avoids them blackening. It also enables a higher filament temperature and therefore greater luminosity in smaller-size bulbs.
The main disadvantage of incandescent lamps is their significant heat dissipation, resulting in poor luminous efficiency.
Fluorescent lamps
This family covers fluorescent tubes and compact fluorescent lamps. Their technology is usually known as “low-pressure mercury”.
In fluorescent tubes, an electrical discharge causes electrons to collide with ions of mercury vapor, resulting in ultraviolet radiation due to energization of the mercury atoms. The fluorescent material, which covers the inside of the tubes, then transforms this radiation into visible light.
Fluorescent tubes dissipate less heat and have a longer service life than incandescent lamps, but they do need an ignition device called a “starter” and a device to limit the current in the arc after ignition. This device called “ballast” is usually a choke placed in series with the arc.
Compact fluorescent lamps are based on the same principle as a fluorescent tube. The starter and ballast functions are provided by an electronic circuit (integrated in the lamp) which enables the use of smaller tubes folded back on themselves.
Compact fluorescent lamps (see Fig. N35) were developed to replace incandescent lamps: They offer significant energy savings (15 W against 75 W for the same level of brightness) and an increased service life.
[a]-
[b]-
Fig.N35: Compact fluorescent lamps [a] standard, [b] induction
Lamps known as “induction” type or “without electrodes” operate on the principle of ionization of the gas present in the tube by a very high frequency electromagnetic field (up to 1 GHz). Their service life can be as long as 100,000 hrs.
Discharge lamps (see Fig. N36)
Fig. N36: Discharge lamps
The light is produced by an electrical discharge created between two electrodes within a gas in a quartz bulb. All these lamps therefore require a ballast to limit the current in the arc. A number of technologies have been developed for different applications.
Low-pressure sodium vapor lamps have the best light output, however the color rendering is very poor since they only have a monochromatic orange radiation.
High-pressure sodium vapor lamps produce a white light with an orange tinge.
In high-pressure mercury vapor lamps, the discharge is produced in a quartz or ceramic bulb at high pressure. These lamps are called “fluorescent mercury discharge lamps”. They produce a characteristically bluish white light.
Metal halide lamps are the latest technology. They produce a color with a broad color spectrum. The use of a ceramic tube offers better luminous efficiency and better color stability.
Light Emitting Diodes (LED)
The principle of light emitting diodes is the emission of light by a semi-conductor as an electrical current passes through it. LEDs are commonly found in numerous applications, but the recent development of white or blue diodes with a high light output opens new perspectives, especially for signaling (traffic lights, exit signs or emergency lighting).
LEDs are low-voltage and low-current devices, thus suitable for battery-supply. A converter is required for a line power supply.
The advantage of LEDs is their low energy consumption. As a result, they operate at a very low temperature, giving them a very long service life. Conversely, a simple diode has a weak light intensity. A high-power lighting installation therefore requires connection of a large number of units in series and parallel.
| Technology | Application | Advantages | Disadvantages |
| Standard incandescent |
- Domestic use - Localized decorative lighting |
- Direct connection without intermediate switchgear - Reasonable purchase price - Compact size - Instantaneous lighting |
- Low luminous efficiency and high electricity - Significant heat dissipation - Short service life |
|
Halogen incandescent |
- Spot lighting - Intense lighting |
- Direct connection - Instantaneous efficiency |
- Average luminous efficiency |
| Fluorescent tube |
- Shops, offices, workshops - Outdoors |
- High luminous efficiency - Average color rendering |
- Low light intensity of single unit - Sensitive to extreme temperatures |
| Compact fluorescent lamp |
- Domestic use - Offices - Replacement of |
- Good luminous efficiency - Good color rendering |
- High initial investment
compared to incandescent lamps |
| HP mercury vapor |
- Workshops, halls, hangars - Factory floors |
- Good luminous efficiency - Acceptable color rendering - Compact size - Long service life |
- Lighting and relighting time of a few minutes |
|
High-pressure sodium |
- Outdoors - Large halls |
- Very good luminous efficiency |
- Lighting and relighting time of a few minutes |
| Low-pressure
sodium |
- Outdoors
- Emergency lighting |
- Good visibility in foggy weather
- Economical to use |
- Long lighting time (5 min.) - Mediocre color rendering |
| Metal halide | - Large areas
- Halls with high ceilings |
- Good luminous efficiency
- Good color rendering - Long service life |
- Lighting and relighting time of a few minutes |
| LED | - Signaling (3-color traffic lights, “exit” signs and emergency lighting) |
- Insensitive to the - Low energy consumption |
- Limited number of colors - Low brightness of single unit |
| Technology | Power (watt) | Efficiency (lumen/watt) | Service life (hours) |
| Standard incandescent | 3 – 1,000 | 10 – 15 | 1,000 – 2,000 |
| Halogen incandescent | 5 – 500 | 15 – 25 | 2,000 – 4,000 |
| Fluorescent tube | 4 – 56 | 50 – 100 | 7,500 – 24,000 |
| Compact fluorescent lamp | 5 – 40 | 50 – 80 | 10,000 – 20,000 |
| HP mercury vapor | 40 – 1,000 | 25 – 55 | 16,000 – 24,000 |
| High-pressure sodium | 35 – 1,000 |
40 – 140 | 16,000 – 24,000 |
| Low-pressure sodium | 35 – 180 | 100 – 185 |
14,000 – 18,000 |
| Metal halide | 30 – 2,000 | 50 – 115 |
6,000 – 20,000 |
| LED | 0.05 – 0.1 | 10 – 30 | 40,000 – 100,000 |
Fig. N37:Usage and technical characteristics of lighting devices
Electrical characteristics of lamps
Incandescent lamps with direct power supply
Due to the very high temperature of the filament during operation (up to 2,500 °C), its resistance varies greatly depending on whether the lamp is on or off. As the cold resistance is low, a current peak occurs on ignition that can reach 10 to 15 times the nominal current for a few milliseconds or even several milliseconds.
This constraint affects both ordinary lamps and halogen lamps: it imposes a reduction in the maximum number of lamps that can be powered by devices such as remote-control switches, modular contactors and relays for busbar trunking.
Extra Low Voltage (ELV) halogen lamps
- Some low-power halogen lamps are supplied with ELV 12 or 24 V, via a transformer or an electronic converter. With a transformer, the magnetization phenomenon combines with the filament resistance variation phenomenon at switch-on. The inrush current can reach 50 to 75 times the nominal current for a few milliseconds. The use of dimmer switches placed upstream significantly reduces this constraint.
- Electronic converters, with the same power rating, are more expensive than solutions with a transformer. This commercial handicap is compensated by a greater ease of installation since their low heat dissipation means they can be fixed on a flammable support. Moreover, they usually have built-in thermal protection.
New ELV halogen lamps are now available with a transformer integrated in their base. They can be supplied directly from the LV line supply and can replace normal lamps without any special adaptation.
Dimming for incandescent lamps
This can be obtained by varying the voltage applied to the lampere
This voltage variation is usually performed by a device such as a Triac dimmer switch, by varying its firing angle in the line voltage period. The wave form of the voltage applied to the lamp is illustrated in Figure N38a. This technique known as “cut-on control” is suitable for supplying power to resistive or inductive circuits. Another technique suitable for supplying power to capacitive circuits has been developed with MOS or IGBT electronic components. This techniques varies the voltage by blocking the current before the end of the half-period (see Fig. N38b) and is known as “cut-off control”.
Fig. N38: Shape of the voltage supplied by a light dimmer at 50% of maximum voltage with the following techniques:
a] “cut-on control”
b] “cut-off control”
Switching on the lamp gradually can also reduce, or even eliminate, the current peak on ignition.
As the lamp current is distorted by the electronic switching, harmonic currents are produced. The 3rd harmonic order is predominant, and the percentage of 3rd harmonic current related to the maximum fundamental current (at maximum power) is represented onFigure N39.
Fig. N39: Percentage of 3rd harmonic current as a function of the power applied to an incandescent lamp using an electronic dimmer switch
Note that in practice, the power applied to the lamp by a dimmer switch can only vary in the range between 15 and 85% of the maximum power of the lampere
According to IEC standard 61000-3-2 setting harmonic emission limits for electric or electronic systems with current y 16 A, the following arrangements apply:
- Independent dimmers for incandescent lamps with a rated power less than or equal to 1 kW have no limits applied
- Otherwise, or for incandescent lighting equipment with built-in dimmer or dimmer built in an enclosure, the maximum permissible 3rd harmonic current is equal to 2.30 A
Fluorescent lamps with magnetic ballast
Fluorescent tubes and discharge lamps require the intensity of the arc to be limited, and this function is fulfilled by a choke (or magnetic ballast) placed in series with the bulb itself (see Fig. N40).
Fig.N40: Magnetic ballasts
This arrangement is most commonly used in domestic applications with a limited number of tubes. No particular constraint applies to the switches.
Dimmer switches are not compatible with magnetic ballasts: the cancellation of the voltage for a fraction of the period interrupts the discharge and totally extinguishes the lampere
The starter has a dual function: preheating the tube electrodes, and then generating an overvoltage to ignite the tube. This overvoltage is generated by the opening of a contact (controlled by a thermal switch) which interrupts the current circulating in the magnetic ballast.
During operation of the starter (approx. 1 s), the current drawn by the luminaire is approximately twice the nominal current.
Since the current drawn by the tube and ballast assembly is essentially inductive, the power factor is very low (on average between 0.4 and 0.5). In installations consisting of a large number of tubes, it is necessary to provide compensation to improve the power factor.
For large lighting installations, centralized compensation with capacitor banks is a possible solution, but more often this compensation is included at the level of each luminaire in a variety of different layouts (see Fig.N41).
| Compensation layout |
Application | Comments |
| Without compensation | Domestic | Single connection |
| Parallel [a] | Offices, workshops, superstores | Risk of overcurrents for control devices |
| Series [b] | Choose capacitors with high operating voltage (450 to 480 V) | |
| Duo [c] | Avoids flicker |
Fig.N41: The various compensation layouts: a] parallel; b] series; c] dual series also called “duo” and their fields of application
The compensation capacitors are therefore sized so that the global power factor is greater than 0.85. In the most common case of parallel compensation, its capacity is on average 1 µF for 10 W of active power, for any type of lampere However, this compensation is incompatible with dimmer switches.
Constraints affecting compensation
The layout for parallel compensation creates constraints on ignition of the lampere Since the capacitor is initially discharged, switch-on produces an overcurrent. An overvoltage also appears, due to the oscillations in the circuit made up of the capacitor and the power supply inductance.
The following example can be used to determine the orders of magnitude.
Assuming an assembly of 50 fluorescent tubes of 36 W each:
- Total active power: 1,800 W
- Apparent power: 2 kVA
- Total rms current: 9 A
- Peak current: 13 A
With:
- A total capacity: C = 175 µF
- A line inductance (corresponding to a short-circuit current of 5 kA): L = 150 µH
The maximum peak current at switch-on equals:
[math]\displaystyle{ Ic = V_max \sqrt{\frac{c}{L}}= 230 \sqrt 2 \sqrt{\frac{175 \times 10^{-6}{150 \times 10^{-6}}= 350 A }[/math]
The theoretical peak current at switch-on can therefore reach 27 times the peak current during normal operation.
The shape of the voltage and current at ignition is given in Figure N42 for switch closing at the line supply voltage peak.
Fig.N42: Power supply voltage at switch-on and inrush current
There is therefore a risk of contact welding in electromechanical control devices (remote-control switch, contactor, circuit-breaker) or destruction of solid state switches with semi-conductors.
In reality, the constraints are usually less severe, due to the impedance of the cables.
Ignition of fluorescent tubes in groups implies one specific constraint. When a group of tubes is already switched on, the compensation capacitors in these tubes which are already energized participate in the inrush current at the moment of ignition of a second group of tubes: they “amplify” the current peak in the control switch at the moment of ignition of the second group.
The table in Figure N43, resulting from measurements, specifies the magnitude of the first current peak, for different values of prospective short-circuit current Isc. It is seen that the current peak can be multiplied by 2 or 3, depending on the number of tubes already in use at the moment of connection of the last group of tubes.
|
Number of tubes already in use |
Number of tubes connected |
Inrush current peak (A) | ||
| Isc = 1,500 A | Isc = 3,000 A | Isc = 6,000 A | ||
| 0 | 14 | 233 | 250 | 320 |
| 14 | 14 | 558 | 556 | 575 |
| 28 | 14 | 608 | 607 | 624 |
| 42 | 14 | 618 | 616 | 632 |
Fig. N43: Magnitude of the current peak in the control switch of the moment of ignition of a second group of tubes
Nonetheless, sequential ignition of each group of tubes is recommended so as to reduce the current peak in the main switch.
The most recent magnetic ballasts are known as “low-loss”. The magnetic circuit has been optimized, but the operating principle remains the same. This new generation of ballasts is coming into widespread use, under the influence of new regulations (European Directive, Energy Policy Act - USA).
In these conditions, the use of electronic ballasts is likely to increase, to the detriment of magnetic ballasts.
Fluorescent lamps with electronic ballast
Electronic ballasts are used as a replacement for magnetic ballasts to supply power to fluorescent tubes (including compact fluorescent lamps) and discharge lamps. They also provide the “starter” function and do not need any compensation capacity.
The principle of the electronic ballast (see Fig.N44) consists of supplying the lamp arc via an electronic device that generates a rectangular form AC voltage with a frequency between 20 and 60 kHz.
Fig.N44: Electronic ballast
Supplying the arc with a high-frequency voltage can totally eliminate the flicker phenomenon and strobe effects. The electronic ballast is totally silent.
During the preheating period of a discharge lamp, this ballast supplies the lamp with increasing voltage, imposing an almost constant current. In steady state, it regulates the voltage applied to the lamp independently of any fluctuations in the line voltage.
Since the arc is supplied in optimum voltage conditions, this results in energy savings of 5 to 10% and increased lamp service life. Moreover, the efficiency of the electronic ballast can exceed 93%, whereas the average efficiency of a magnetic device is only 85%.
The power factor is high (> 0.9).
The electronic ballast is also used to provide the light dimming function. Varying the frequency in fact varies the current magnitude in the arc and hence the luminous intensity.
Inrush current
The main constraint that electronic ballasts bring to line supplies is the high inrush current on switch-on linked to the initial load of the smoothing capacitors (see Fig. N45).
| Technology | Max. inrush current | Duration |
| Rectifier with PFC | 30 to 100 In
|
y 1 ms |
| Rectifier with choke | 10 to 30 In | y 5 ms |
| Magnetic ballast | y 13 In | 5 to 10 ms |
Fig. N45: Orders of magnitude of the inrush current maximum values, depending on the technologies used
In reality, due to the wiring impedances, the inrush currents for an assembly of lamps is much lower than these values, in the order of 5 to 10 In for less than 5 ms.
Unlike magnetic ballasts, this inrush current is not accompanied by an overvoltage.
Harmonic currents
For ballasts associated with high-power discharge lamps, the current drawn from the line supply has a low total harmonic distortion (< 20% in general and < 10% for the most sophisticated devices). Conversely, devices associated with low-power lamps, in particular compact fluorescent lamps, draw a very distorted current (see Fig. N46). The total harmonic distortion can be as high as 150%. In these conditions, the rms current drawn from the line supply equals 1.8 times the current corresponding to the lamp active power, which corresponds to a power factor of 0.55.
Fig.N46: Shape of the current drawn by a compact fluorescent lamp
In order to balance the load between the different phases, lighting circuits are usually connected between phases and neutral in a balanced way. In these conditions, the high level of third harmonic and harmonics that are multiple of 3 can cause an overload of the neutral conductor. The least favorable situation leads to a neutral current which may reach 3 times the current in each phase.
Harmonic emission limits for electric or electronic systems are set by IEC standard 61000-3-2. For simplification, the limits for lighting equipment are given here only for harmonic orders 3 and 5 which are the most relevant (seeFig. N47).
| Harmonic order |
Active input power y 25W |
Active input power > 25W one of the 2 sets of limits apply: | |
| % of fundamental current |
% of fundamental current | Harmonic current relative to active power | |
| 3 |
30 | 86 | 3.4 mA/W |
| 5 | 10 | 61 | 1.9 mA/W |
Fig. N47:Maximum permissible harmonic current
Leakage currents
Electronic ballasts usually have capacitors placed between the power supply conductors and the earth. These interference-suppressing capacitors are responsible for the circulation of a permanent leakage current in the order of 0.5 to 1 mA per ballast. This therefore results in a limit being placed on the number of ballasts that can be supplied by a Residual Current Differential Safety Device (RCD).
At switch-on, the initial load of these capacitors can also cause the circulation of a current peak whose magnitude can reach several amps for 10 µs. This current peak may cause unwanted tripping of unsuitable devices.
High-frequency emissions
Electronic ballasts are responsible for high-frequency conducted and radiated emissions.
The very steep rising edges applied to the ballast output conductors cause current pulses circulating in the stray capacities to earth. As a result, stray currents circulate in the earth conductor and the power supply conductors. Due to the high frequency of these currents, there is also electromagnetic radiation. To limit these HF emissions, the lamp should be placed in the immediate proximity of the ballast, thus reducing the length of the most strongly radiating conductors.
The different power supply modes (see Fig. N48)
| Technology | Power supply mode | Other device |
| Standard incandescent | Direct power supply | Dimmer switch |
| Halogen incandescent | ||
| ELV halogen incandescent | Transformer | Electronic converter |
| Fluorescent tube | Magnetic ballast and starter |
Electronic ballast Electronic dimmer + |
| Compact fluorescent lamp | Built-in electronic ballast | |
| Mercury vapor | Magnetic ballast | Electronic ballast |
| High-pressure sodium | ||
| Low-pressure sodium | ||
| Metal halide |
Fig. N48:Different power supply modes
The current actually drawn by luminaires
The risk
This characteristic is the first one that should be defined when creating an installation, otherwise it is highly probable that overload protection devices will trip and users may often find themselves in the dark.
It is evident that their determination should take into account the consumption of all components, especially for fluorescent lighting installations, since the power consumed by the ballasts has to be added to that of the tubes and bulbs.
The solution
For incandescent lighting, it should be remembered that the line voltage can be more than 10% of its nominal value, which would then cause an increase in the current drawn.
For fluorescent lighting, unless otherwise specified, the power of the magnetic ballasts can be assessed at 25% of that of the bulbs. For electronic ballasts, this power is lower, in the order of 5 to 10%.
The thresholds for the overcurrent protection devices should therefore be calculated as a function of the total power and the power factor, calculated for each circuit.
Overcurrents at switch-on
The risk
The devices used for control and protection of lighting circuits are those such as relays, triac, remote-control switches, contactors or circuit-breakers.
The main constraint applied to these devices is the current peak on energization.
This current peak depends on the technology of the lamps used, but also on the installation characteristics (supply transformer power, length of cables, number of lamps) and the moment of energization in the line voltage period. A high current peak, however fleeting, can cause the contacts on an electromechanical control device to weld together or the destruction of a solid state device with semi-conductors.
Two solutions
Because of the inrush current, the majority of ordinary relays are incompatible with lighting device power supply. The following recommendations are therefore usually made:
- Limit the number of lamps to be connected to a single device so that their total power is less than the maximum permissible power for the device
- Check with the manufacturers what operating limits they suggest for the devices. This precaution is particularly important when replacing incandescent lamps with compact fluorescent lamps
By way of example, the table in Figure N49 indicates the maximum number of compensated fluorescent tubes that can be controlled by different devices with 16 A rating. Note that the number of controlled tubes is well below the number corresponding to the maximum power for the devices.
| Tube unit power requirement (W) |
Number of tubes corresponding to the power 16 A x 230 V |
Maximum number of tubes that can be controlled by | ||
|
Contactors GC16 A CT16 A |
Remote control switches TL16 A |
Circuit- breakers C60-16 A | ||
| 18 | 204 |
15 | 50 | 112 |
| 36 |
102 | 15 | 25 | 56 |
| 58 |
63 | 10 | 16 | 34 |
Fig.N49:The number of controlled tubes is well below the number corresponding to the maximum power for the devices
But a technique exists to limit the current peak on energization of circuits with capacitive behavior (magnetic ballasts with parallel compensation and electronic ballasts). It consists of ensuring that activation occurs at the moment when the line voltage passes through zero. Only solid state switches with semi-conductors offer this possibility (see Fig. N50a). This technique has proved to be particularly useful when designing new lighting circuits.
More recently, hybrid technology devices have been developed that combine a solid state switch (activation on voltage passage through zero) and an electromechanical contactor short-circuiting the solid state switch (reduction of losses in the semi-conductors) (see Fig. N50b).
a b c
Fig.N50:“Standard” CT+ contactor [a], CT+ contactor with manual override, pushbutton for selection of operating mode and indicator lamp showing the active operating mode [b], and TL + remote-control switch [c] (Merlin Gerin brand)
Choice of relay rating according to lamp type
| Modular contactors and impulse relays do not use the same technologies. Their rating is determined according to different standards. For example, for a given rating, an impulse relay is more efficient than a modular contactor for the control of light fittings with a strong inrush current, or with a low power factor (non-compensated inductive circuit). |
Figure 51 shows the maximum number of light fittings for each relay, according to the type, power and configuration of a given lamp. As an indication, the total acceptable power is also mentioned.
- These values are given for a 230 V circuit with 2 active conductors (single-phase phase/neutral or two-phase phase/phase). For 110 V circuits, divide the values in the table by 2.
- To obtain the equivalent values for the whole of a 230 V three-phase circuit, multiply the number of lamps and the total acceptable power:
- by 3 (1.73) for circuits without neutral;
- by 3 for circuits with neutral.
Note: The power ratings of the lamps most commonly used are shown in bold.
Fig. N51:Maximum number of light fittings for each relay, according to the type, power and configuration of a given lamp (Continued on opposite page)
(1) Circuits with non-compensated ferromagnetic ballasts consume twice as much current for a given lamp power output. This explains the small number of lamps in this configuration.
(2) The total capacitance of the power factor correction capacitors in parallel in a circuit limits the number of lamps that can be controlled by a contactor. The total downstream capacitance of a modular contactor of rating 16, 25, 40 or 63 A should not exceed 75, 100, 200 or 300 µF respectively. Allow for these limits to calculate the maximum acceptable number of lamps if the capacitance values are different from those in the table.
(3) High-pressure mercury vapour lamps without ignitor, of power 125, 250 and 400 W, are gradually being replaced by high-pressure sodium vapour lamps with integral ignitor, and respective power of 110, 220 and 350 W.
Fig. N51:Maximum number of light fittings for each relay, according to the type, power and configuration of a given lamp (Concluded)
Protection of lamp circuits: Maximum number of lamps and MCB rating versus lamp type, unit power and MCB tripping curve
During start up of discharge lamps (with their ballast), the inrush current drawn by each lamp may be in the order of:
- 25 x circuit start current for the first 3 ms
- 7 x circuit start current for the following 2 s
For fluorescent lamps with High Frequency Electronic control ballast, the protective device ratings must cope with 25 x inrush for 250 to 350 µs.
However due to the circuit resistance the total inrush current seen by the MCB is lower than the summation of all individual lamp inrush current if directly connected to the MCB.
The tables below (see Fig. N52 to NXX) take into account:
- Circuits cables have a length of 20 meters from distribution board to the first lamp and 7 meters between each additional fittings.
- MCB rating is given to protect the lamp circuit in accordance with the cable cross section, and without unwanted tripping upon lamp starting.
- MCB tripping curve (C = instantaneous trip setting 5 to 10 In, D = instantaneous trip setting 10 to 14 In).
| Lamp power (W) |
Number of lamps per circuit | ||||||||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | ||
| MCB rating C & D tripping curve | |||||||||||||||||||||
| 14/18 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 14x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 14x3 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | |
| 14x4 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | |
| 18x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 18x4 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | |
| 21/24 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 21/24 x 2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 28 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 28x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | |
| 35/36/39 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 35/36 x 2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | |
| 38/39 x 2 | |||||||||||||||||||||
| 40/42 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | |
| 40/42 x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | |
| 49/50 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 6 | 6 | 6 | 6 | 6 | |
| 49/50 x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 16 | |
| 54/55 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | |
| 54/55 x2 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 16 | 16 | 16 | |
| 60 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | |
Fig. N52:Fluorescent tubes with electronic ballast - Vac = 230 V
| Lamp power (W) |
Number of lamps per circuit | ||||||||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | ||
| MCB rating C & D tripping curve | |||||||||||||||||||||
| 6 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 9 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 11 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 13 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 14 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 15 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 16 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 17 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 18 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 20 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 21 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 23 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | |
| 25 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | |
Fig. N53:Compact fluorescent lamps - Vac = 230 V
| Lamp power (W) |
Number of lamps per circuit | ||||||||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | ||
| MCB rating C tripping curve | |||||||||||||||||||||
| 50 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | |
| 80 | 6 | 6 | 6 |
6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | |
| 125 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 16 | 16 | 16 | 16 | 20 | 20 | |
| 250 | 6 | 10 | 10 | 16 | 16 | 16 | 16 | 16 | 16 | 20 | 20 | 25 | 25 | 25 | 32 | 32 | 32 | 32 | 40 | 40 | |
| 400 | 6 | 16 | 20 | 25 | 25 | 32 | 32 | 32 | 32 | 32 | 32 | 40 | 40 | 40 | 50 | 50 | 50 | 50 | 63 | 63 | |
| 1000 | 16 | 32 | 40 | 50 | 50 | 50 | 50 | 50 | 63 | - | - | - | - | - | - | - | - | - | - | - | |
| MCB rating D tripping curve | |||||||||||||||||||||
| 50 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | |
| 80 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 16 | |
| 125 | 6 | 6 | 6 | 6 | 6 | 6 | 10 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 16 | 16 | 16 | 16 | 20 | 20 | |
| 250 | 6 | 6 | 10 | 10 | 10 | 10 | 16 | 16 | 16 | 20 | 20 | 25 | 25 | 25 | 32 | 32 | 32 | 32 | 40 | 40 | |
| 400 | 6 | 10 | 16 | 16 | 20 | 20 | 25 | 25 | 25 | 32 | 32 | 40 | 40 | 40 | 50 | 50 | 50 | 50 | 63 | 63 | |
| 1000 | 10 | 20 | 25 | 32 | 40 | 40 | 50 | 63 | 63 | - | - | - | - | - | - | - | - | - | - | - | |
Fig. N54:High pressure mercury vapour (with ferromagnetic ballast and PF correction) - Vac = 230 V
Fig. N55:Low pressure sodium (with PF correction) - Vac = 230 V
Fig. N56:High pressure sodium (with PF correction) - Vac = 230 V
Fig. N57:Metal halide (with PF correction) - Vac = 230 V
| Lamp power (W) |
Number of lamps per circuit | ||||||||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | ||
| MCB rating C tripping curve | |||||||||||||||||||||
| 1800 | 16 | 32 | 40 |
50 | 50 | 50 | 50 | 63 | 63 | - | - | - | - | - | - | - | - | - | - | - | |
| 2000 | 16 | 32 | 40 |
50 | 50 | 50 | 50 | 63 | 63 | - | - | - | - | - | - | - | - | - | - | - | |
| MCB rating D tripping curve | |||||||||||||||||||||
| 1800 | 16 | 20 | 32 | 32 | 32 | 32 | 50 | 63 | 63 | - | - | - | - | - | - | - | - | - | - | - | |
| 2000 | 16 | 25 | 32 | 32 | 32 | 32 | 50 | 63 | - | - | - | - | - | - | - | - | - | - | - | - | |
Fig. N58:Metal halide (with ferromagnetic ballast and PF correction) - Vac = 400 V
Overload of the neutral conductor
The risk
In an installation including, for example, numerous fluorescent tubes with electronic ballasts supplied between phases and neutral, a high percentage of 3rd harmonic current can cause an overload of the neutral conductor. Figure N59 below gives an overview of typical H3 level created by lighting.
| Lamp type |
Typical power | Setting mode | Typical H3 level |
| Incandescend lamp with dimmer | 100 W | Light dimmer | 5 to 45 % |
| ELV halogen lamp | 25 W | Electronic ELV transformer | 5 % |
| Fluorescent tube | 100 W | Magnetic ballast |
10 % |
| < 25 W | Electronic ballast | 85 % | |
| > 25 W | + PFC |
30 % | |
| Discharge lamp | 100 W | Magnetic ballast | 10 % |
| Electrical ballast | 30 % |
Fig. N59:Overview of typical H3 level created by lighting
The solution
Firstly, the use of a neutral conductor with a small cross-section (half) should be prohibited, as requested by Installation standard IEC 60364, section 523–5–3.
As far as overcurrent protection devices are concerned, it is necessary to provide
4-pole circuit-breakers with protected neutral (except with the TN-C system for which the PEN, a combined neutral and protection conductor, should not be cut).
This type of device can also be used for the breaking of all poles necessary to supply luminaires at the phase-to-phase voltage in the event of a fault.
A breaking device should therefore interrupt the phase and Neutral circuit simultaneously.
Leakage currents to earth
The risk
At switch-on, the earth capacitances of the electronic ballasts are responsible for residual current peaks that are likely to cause unintentional tripping of protection devices.
Two solutions
The use of Residual Current Devices providing immunity against this type of impulse current is recommended, even essential, when equipping an existing installation
(see Fig.N60).
Fig.N60:s.i. residual current devices with immunity against impulse currents (Merlin Gerin brand)
For a new installation, it is sensible to provide solid state or hybrid control devices (contactors and remote-control switches) that reduce these impulse currents (activation on voltage passage through zero).
Overvoltages
The risk
As illustrated in earlier sections, switching on a lighting circuit causes a transient state which is manifested by a significant overcurrent. This overcurrent is accompanied by a strong voltage fluctuation applied to the load terminals connected to the same circuit.
These voltage fluctuations can be detrimental to correct operation of sensitive loads (micro-computers, temperature controllers, etc.)
The Solution
It is advisable to separate the power supply for these sensitive loads from the lighting circuit power supply.
Sensitivity of lighting devices to line voltage disturbances
Short interruptions
- The risk
Discharge lamps require a relighting time of a few minutes after their power supply has been switched off.
- The solution
Partial lighting with instantaneous relighting (incandescent lamps or fluorescent tubes, or “hot restrike” discharge lamps) should be provided if safety requirements so dictate. Its power supply circuit is, depending on current regulations, usually distinct from the main lighting circuit.
Voltage fluctuations
- The risk
The majority of lighting devices (with the exception of lamps supplied by electronic ballasts) are sensitive to rapid fluctuations in the supply voltage. These fluctuations cause a flicker phenomenon which is unpleasant for users and may even cause significant problems. These problems depend on both the frequency of variations and their magnitude.
Standard IEC 61000-2-2 (“compatibility levels for low-frequency conducted disturbances”) specifies the maximum permissible magnitude of voltage variations as a function of the number of variations per second or per minute.
These voltage fluctuations are caused mainly by high-power fluctuating loads (arc furnaces, welding machines, starting motors).
- The solution
Special methods can be used to reduce voltage fluctuations. Nonetheless, it is advisable, wherever possible, to supply lighting circuits via a separate line supply.
The use of electronic ballasts is recommended for demanding applications (hospitals, clean rooms, inspection rooms, computer rooms, etc).
Developments in control and protection equipment
The use of light dimmers is more and more common. The constraints on ignition are therefore reduced and derating of control and protection equipment is less important.
New protection devices adapted to the constraints on lighting circuits are being introduced, for example Merlin Gerin brand circuit-breakers and modular residual current circuit-breakers with special immunity, such as s.i. type ID switches and Vigi circuit-breakers. As control and protection equipment evolves, some now offer remote control, 24-hour management, lighting control, reduced consumption, etc.
Lighting of public areas
Normal lighting
Regulations governing the minimum requirements for buildings receiving the public in most European countries are as follows:
- Installations which illuminates areas accessible to the public must be controlled and protected independently from installations providing illumination to other areas
- Loss of supply on a final lighting circuit (i.e. fuse blown or CB tripped) must not result in total loss of illumination in an area which is capable of accommodating more than 50 persons
- Protection by Residual Current Devices (RCD) must be divided amongst several devices (i.e. more than on device must be used)
Emergency lighting and other systems
When we refer to emergency lighting, we mean the auxiliary lighting that is triggered when the standard lighting fails.
Emergency lighting is subdivided as follows (EN-1838):
Emergency lighting and safety signs for escape routes
The emergency lighting and safety signs for escape routes are very important for all those who design emergency systems. Their suitable choice helps improve safety levels and allows emergency situations to be handled better.
Standard EN 1838 ("Lighting applications. Emergency lighting") gives some fundamental concepts concerning what is meant by emergency lighting for escape routes:
"The intention behind lighting escape routes is to allow safe exit by the occupants, providing them with suffi cient visibility and directions on the escape route …"
The concept referred to above is very simple:
The safety signs and escape route lighting must be two separate things.
Functions and operation of the luminaires
The manufacturing specifi cations are covered by standard EN 60598-2-22, "Particular Requirements - Luminaires for Emergency Lighting", which must be read with EN 60598-1, "Luminaires – Part 1: General Requirements and Tests".
Duration
A basic requirement is to determine the duration required for the emergency lighting. Generally it is 1 hour but some countries may have different duration requirements according to statutory technical standards.
Operation
We should clarify the different types of emergency luminaires:
- Non-maintained luminaires
- The lamp will only switch on if there is a fault in the standard lighting
- The lamp will be powered by the battery during failure
- The battery will be automatically recharged when the mains power supply is
restored
- Maintained luminaires
- The lamp can be switched on in continuous mode
- A power supply unit is required with the mains, especially for powering the lamp, which can be disconnected when the area is not busy
- The lamp will be powered by the battery during failure.
Design
The integration of emergency lighting with standard lighting must comply strictly with electrical system standards in the design of a building or particular place.
All regulations and laws must be complied with in order to design a system which is up to standard (see Fig.N61).
Fig. N61:The main functions of an emergency lighting system
European standards
The design of emergency lighting systems is regulated by a number of legislative provisions that are updated and implemented from time to time by new documentation published on request by the authorities that deal with European and international technical standards and regulations.
Each country has its own laws and regulations, in addition to technical standards
which govern different sectors. Basically they describe the places that must be provided with emergency lighting as well as its technical specifi cations. The designer's job is to ensure that the design project complies with these standards.
EN 1838
A very important document on a European level regarding emergency lighting is the Standard EN 1838, "Lighting applications. Emergency lighting".
This standard presents specifi c requirements and constraints regarding the operation and the function of emergency lighting systems.
CEN and CENELEC standards
With the CEN (Comité Européen de Normalisation) and CENELEC standards (Comité Européen de Normalisation Electrotechnique), we are in a standardised environment of particular interest to the technician and the designer. A number of sections deal with emergencies. An initial distinction should be made between luminaire standards and installation standards.
EN 60598-2-22 and EN-60598-1
Emergency lighting luminaires are subject to European standard EN 60598-2-22, "Particular Requirements - Luminaires for Emergency Lighting", which is an integrative text (of specifi cations and analysis) of the Standard EN-60598-1, Luminaires – "Part 1: General Requirements and Tests".
