Tabulated functional capabilities of LV switchgear
From Electrical Installation Guide
After having studied the basic functions of LV switchgear (Figure H1) and the different components of switchgear, Figure H19 summarizes the capabilities of the various components to perform the basic functions.
Fig. H19 – Functions fulfilled by different items of switchgear
| Switchgear item | Isolation | Control | Electrical protection | |||||
|---|---|---|---|---|---|---|---|---|
| Functional | Emergency switching | Emergency stop (mechanical) | Switching for mechanical maintenance | Overload | Short-circuit | Electric shock | ||
| Isolator (or disconnector)[a] | ☑ | |||||||
| Switch[b] | ☑ | ☑ | ☑[c] | ☑[c][d] | ☑ | |||
| Residual device (RCCB)[b] | ☑ | ☑ | ☑[c] | ☑[c][d] | ☑ | ☑ | ||
| Switch- disconnector | ☑ | ☑ | ☑[c] | ☑[c][d] | ☑ | |||
| Contactor | ☑ | ☑[c] | ☑[c][d] | ☑ | ☑[e] | |||
| Remote control switch | ☑ | ☑[c] | ☑ | |||||
| Fuse | ☑ | ☑ | ☑ | [f] | ||||
| Circuit breaker | ☑ | ☑[c] | ☑[c][d] | ☑ | ☑ | ☑ | [f] | |
| Circuit-breaker disconnector[b] | ☑ | ☑ | ☑[c] | ☑[c][d] | ☑ | ☑ | ☑ | [f] |
| Residual and overcurrent circuit-breaker (RCBO)[b] | ☑ | ☑ | ☑[c] | ☑[c][d] | ☑ | ☑ | ☑ | ☑ |
| Point of installation (general principle) | Origin of each circuit | All points where,for operational reasons it may be necessary to stop the process | In general at the incoming circuit to every distribution board | At the supply point to each machine and/or on the machine concerned | At the supply point to each machine | Origin of each circuit | Origin of each circuit | Origin of circuits where the earthing system is appropriate TN-S, IT, TT |
- ^ In certain countries a disconnector with visible contacts is mandatory at the origin of a LV installation supplied directly from a MV/LV transformer
- ^ 1 2 3 4 Certain items of switchgear are suitable for isolation duties (e.g. RCCBs according to IEC 61008) without being explicitly marked as such
- ^ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Where cut-off of all active conductors is provided
- ^ 1 2 3 4 5 6 7 It may be necessary to maintain supply to a braking system
- ^ If it is associated with a thermal relay (the combination is commonly referred to as a “discontactor”)
- ^ 1 2 3 Circuit breaker and fuse can ensure also protective measure in case of fault by automatic disconnection of the supply
