Earth leakage relay protective device

Question

Due to a change in earthing arrangement, I need to add overall earth leakage protection to a 400 A LV distribution board. The board has an incoming switch disconnector, with overcurrent protection provided by fuses upstream.

What's providing ADS to the submain cable? I would have though it more conventional to have the "RCD" element at the start of each circuit - that also avoids any difficulties in making the incoming cables double/reinforced insulation before the incomer device.

- Andy.

mapj1 · Accepted Answer

Only if the disconnector is rated to open under the current that may be flowing when at the time - not always clear, as a switch disconnector is generally not rated for breaking against a heavy fault - does it have arc chutes for example ? 
 However, if the power will be removed in the case of a short circuit fault by something else, the upstream fuse or a breaker suitable for the PSSC, then you may argue that the switch disconnector is protected by that, and it is acceptable for the switch disconnector to be sacrificed then, as the back-up device does the ADS. 
 Generally, to have the earth fault detection operate a proper breaker is vastly preferred. Mike

AJJewsbury · Answer

Due to a change in earthing arrangement, I need to add overall earth leakage protection to a 400 A LV distribution board. The board has an incoming switch disconnector, with overcurrent protection provided by fuses upstream. 
 
 What's providing ADS to the submain cable? I would have though it more conventional to have the "RCD" element at the start of each circuit - that also avoids any difficulties in making the incoming cables double/reinforced insulation before the incomer device. 
 - Andy.

Earth leakage relay protective device

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