Can you have a full load RCD CU rather than split load ?

[dmccormick]

We recently had our old CU replaced by a new split load RCD one. The split part seems to mean ring main circuits are on RCD side and lighting circuits are on non-RCD side. I understand the reasoning goes "if you've just tripped your RCD, perhaps having touched a live conductor, you don't want to make a dangerous situation worse by having no lights so put them on a non RCD protected circuit".

I was wondering if it is actually a regulation to use a split load or if you wanted, you could have everything RCD protected. I would prefer RCD protection for everything rather than keeping the lights on - where we live there is a power cut about every 2-3 weeks anyway so we're used to the lights going off.

 

[Adam_151]

There is a regulation that states that socket outlets of 32A or below that can reasonably be expected to supply equipment outside need protecting with RCD

There is also a regulation that states that circuits should be arranged to cause minimum inconvenience in the event of a fault, a split load board is pushing the boaunds of this as it is, a board with a 30ma rcd main incommer would be even worse in terms of this.

Best solution is a board with a switch incommer and a mixture of MCBs and RCBOs as appropiate

Why do you want RCD protection for the lights anyway

Edit: When I wrote this I was assuming TNS or TNC-S, things are a bit different if you have TT

 

[Qedelec]

Yes you can have the whole installation protected by an RCD and this is a requirement where your supply is TT (with an earth spike).

Change your incommer (main switch) for a type 'S' 500mA RCD.
Type 'S' will have the effect of ensuring that the 30mA RCD trips before the main switch and keeps your lights on.

 

[ban-all-sheds]

where we live there is a power cut about every 2-3 weeks anyway so we're used to the lights going off.

Why not fit some emergency lighting?

 

[Steve]

where we live there is a power cut about every 2-3 weeks anyway so we're used to the lights going off.

Why not fit some emergency lighting?

or a couple of UPS's on the lighting circuits? (make sure you turn all but a couple of lights off though when the power goes off - or it wont last very long!)

 

[securespark]

There is a regulation that says any socket outlet that could reasonably be expected to supply equipment for use outdoors should be protected by a 30mA RCD. The OSG interpret this as all G/F sockets. At the same time, there is another reg that says if an RCD trips, any lighting circuits should remain unaffected.

 

[ban-all-sheds]

or a couple of UPS's on the lighting circuits?

Because emergency lighting is the proper purpose-designed solution?

 

[baldelectrician]

You could have a split rcd unit and if say sockets trip then you still have lights.

 

[JohnD]

If you like RCD protection, you can have the whole installation protected by a 100mA or greater RCD, with a 30mA on the sockets. The 100mA is better if time-delayed, otherwise they will probably both trip at the same time unless you have a conveniently precise amount of leakage. Depending on your make of CU you might be abe to get an RCD that wiull fit in place of the main switch, or you may need to have it between the meter and the CU.

Some people will say that lights don't need an RCD, but you never know when someone will be changing a bulb or fitting and make a mistake.

 

[Steve]

or a couple of UPS's on the lighting circuits?

Because emergency lighting is the proper purpose-designed solution?

in a house? EM lights are one thing: ugly.

UPS's allow you to use normal lights for a short time after power has gone off - used with energy saver bulbs, i bet they could last a while (not knowing specific battery sizes, i cant say how long exactly!!!)

 

[ebee]

If we make an assumption that 50mA can kill and a 6A MCB can run 8Amps for ages then you can be killed 160 times over by a humble lighting circuit.
Replacing a MCB with a RCBO would make you feel safer

 

[Big_Spark]

Lights should never be on a 30mA RCD except in exceptional circumstances.

If you want total RCD protection for your home, then you should fit the main incomer as a 300mA 100A Type S RCD, leave all lighting circuits on MCB's, but all other circuits put on 30mA RCBO's of the appropriate rating for that circuit.

 

[plugwash]

a couple of issues with your suggestion.

1: time delay rcds are damn expensive
2: many single module rcbos do not isolate the neutral. therefore there is a good chance of a fault tripping both rcds even if you use a time delay main rcd.

a better arrangment would be to use a split load kit and have the RCBO cuircuits on switch only and then a 100/300ma rcd on the lights. but even this arrangement won't be cheap.

 

[JohnD]

I saw a design sketch intended for TT installations where there was a set of MCBs on a busbar fed from the 30mA RCD for sockets, and another set fed from a 100mA RCD for everything else. I liked the idea but it takes a big CU and you still need an Main Switch as well to feed both the RCDs. I don't think ordinary CUs have a busbar arrangement to achieve this.

 

[dmccormick]

Thanks to everyone for your replies and advice.

The reason for wanting RCD on the lights is to help reduce the risk of death by electric shock. In the past year there have been two occassions where I thought there was a risk of getting a shock from the lights - changing an upstairs light fitting; despite switching off the upstairs lights MCB and then testing each terminal on the existing with a multimeter to ensure 0 V I was startled to find that as I removed one of the neutral wires from the fitting, the bulb started to glow dimly and so did a couple of others from outside the room. I now realise this was due to a borrowed neutral. When I measured the voltage on the remaining connected neutral wires against earth it read 70V.

Second incident was simply replacing a bulb - as I pushed and twisted the bulb, the whole fitting turned instead and the wires inside, including the earth, became disconnected. Maybe not an issue as the lights were turned off, but having experienced the borrowed neutral it was disconcerting.

In an ideal world I would have a full re-wire to modern standards and when I can addord that I will (with a proper registered electrician). However in the meantime I would take some comfort from knowing that the whole house was covered by RCD protection. I know it might not be perfect, but it is better than nothing.

I am also thinking about getting some emergency lights installed in a couple of locations - hall and the conveniently located outside CU that we have to traipse along to every time a light bulb goes.

It sounds like replacing the main switch with an RCD is the way to go so I will set about contacting a local electrician as it's not something I can do.