RCD Board Consumer Unit

[Nigelk]

Hi is it OK to switch the mains off and use a generator with a lead with plugs both ends to supply electric ;ighting when heres a power cut with a RCD Board Consumer Unit

 

[johnstantine]

Hi
This can be done but you need something like a changeover switch to ensure that you can't feed mains power and generator into same system, just turning of the main switch isn't sufficient.

 

[Nigelk]

Thanks John but would the RCD work OK backwards that's what I'm worried about. I don't want to damage the consumer unit.

 

[johnstantine]

Thanks John but would the RCD work OK backwards that's what I'm worried about. I don't want to damage the consumer unit.

I assume you're saying that the RCD is the main switch, the generator would have to be connected on the same side as the mains tails which is why you would need a changeover switch.
Hard to say exactly what you need because every situation is different but, you'd probably want to connect mains tails onto switched terminals of changeover, connect generator onto other switched terminals and have RCD connected via tails onto common of changeover, (my changeover terminals naming mght be slightly inaccurate).

 

[NoSparks]

An RCD is in fact a bi-directional device. The only thing is that the detection circuitary in on one side of the switch (normally the "bottom" side). The convention of power in at top and out at bottom means that if anything goes wrong with the RCD circuitary, it is isolated from the supply when the the RCD switches off.

What you are suggesting will work, but is very dangerious. In my nieve youth I wired a battery into a lighting circuit during the pit strikes, and I've seen another electrician do it!!! Your method of using a double plug connection also means the pins of the second plug would be live when the generator was running! Really you should wire it like jonstantine says. Put a two way, break before make, switch before your main supply with the common connected to the load, one way to the alternate supply, and the other way to the normal supply. I repeat, this must be a break before make switch. and needs to be rated at the full load of the CU.

You must also consider the load to which the generator may be subjected. In your solution any connected accessories on the socket circuit will be connected, eg electric fires!

If you only want emergency lighting then one solution might be to use another ISO bar container (CU without a main switch) by the first. Feed the lighing output of the normal CU into the normally closed way of an isolator in the second box. Isolators are normally two way break before make but you need to specify this when purchasing. Wire the generator into the normally open way in the isolator, and wire the coil of the isolator from the generator (I assume the generator has an output fuse). The common of the iosolator should go to one or more mcbs and then to the lighting load. When the generator is started it will switch the isolator to use its own supply for the lights automatically, and isolate it from the rest of the instalation. I know it sounds a lot, but the cost would only be about £60, far less than the generator!