Other lamp technologies - constraints and recommendations

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 recommendation

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 and specific control offer this possibility but the important heat due to permanent current requires the use of heater not compatible with conventional electrical distribution system for building (cumbersome has to be limited).

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 (cancellation of losses in the semiconductors) during permanent state (see Fig. N50a). Additionally that concept allows to reduce the current peak at the switch-on in a ratio 4 to 5.

Fig. N50a – Examples of control devices (Schneider Electric brand)

• 

  [a] “zero crossing” contactor iCT+

• 

  [b] “standard” contactor iCT

• 

  [c] impulse relay iTL

• 

  [d] remote controlled MCB

Overload of the neutral conductor

The risk

LED luminaires and fluorescent tubes with electronic ballasts are characterized as nonlinear loads, generating harmonic currents. When a number of such luminaires are supplied between phase and neutral on a 3-phase circuit, the 3rd harmonics (and multiples of 3) in each phase are adding together in the neutral, which can cause an overload of the neutral conductor. Figure N50b 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 %
Led lamps	10 to 200 W	Electrical driver	10 to 20 %

Fig. N50b – 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.

The effects concern the thermal consequences on switchgear and controlgear, cables and equipment. They are due to harmonic levels maintained for durations equal to or greater than 10 minutes.

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 or driver 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. N50c).

Fig. N50c – s.i. residual current devices with immunity against impulse currents (Schneider-Electric brand)

For a new installation, it is sensible to provide zero crossing devices (contactors or impulse relay) 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.

The installation of protective devices such as “surge arrester” type is recommended for exposed installations such as public lighting, lighting for car park, or industrial facilities.

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, LED 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. LED lighting is also an alternative to overcome that constraint

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 Schneider Electric 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.