To RCD or not.

[electronicsuk]

I'm not sure where all this has come from.. the OP is having problems with an old voltage operated circuit breaker, .

I am not sure where you got that impression. At no point has the OP said he is having any problems with anything at all. All he asked is should he RCD it. To which the answer is yes.

Really?

It is my understanding that where a earth rod is used all circuits must run off a RCD. However we get regular power cuts and I want the freezer on when the power comes back. 17th edition combined with a TT system appears to mandate the use of RCDs on all circuits. Which would prove to be a pain.

If I replace the CU I will need to purchase an active 100mA RCD so that it won't trip when the power fails? The sockets would need to be active as well? On one hand I want to update it on the other hand leave well alone.

My understanding was that the OP is having problems with the VOCB failing to automatically restore the supply after a power cut. He/she does not want an RCD specifically for the protection that it offers. Replacing it with a passive 100mA RCD should not only overcome that problem, but also offer a greater degree of protection than that already present.

Would you use an electric shower knowing there is an EFLI of 60 ohms or more with no 30mA RCD in place? I wouldn't.
I doubt that any equipotential bonding has been carried out. that would mean that fault current could light up the copper pipework.

Do you think an electric shower with 100mA RCD upfront is going to be, by any significant degree, any more or less safe than a TN-C-S install to the 16th edition with no RCD protection on the shower circuit at all?

I stand by what I said before, it is advisable to 30mA RCD the shower circuit, but the OP is under no impetus to do so.

 

[aptsys]

The OP doesn't have a voltage operated ELCB, it's a current operated one. There's no earth wires going into or out of it to measure the voltage on earth.

 

[dickmurray]

Thank you for the replies much appreciated. I now know the difference between an active and passive RCD amongst other things. I also get the general concensus that "it" could be better.

Having read about ELCB's I think the one I have is a current one which means its an ELCB by name because of its age but actually an RCD? They measure current balance using a differential current transformer and if its not zero they trip. You use an active RCD if the devices connected might be a hazard when power is restored.

An RCD does not protect against overload but an RCBO does because it is a combined RCD and MCB.

A split load CU with a DP main switch and RCD would allow the RCD to trip but not the main switch. But as I have a TT circuit the main switch would be a time delay RCD and I need RCD's anyway?

Would a CU with a main switch and 3 RCBO's be the "best"?

I was going to have a shower this evening but not sure I want to now...

 

[AndyPRK]

Yes that is not an ELCB.

It is an RCD (probably 500mA)

 

[flameport]

To comply with regulations today, the shower and socket outlets should have 30mA RCDs to provide additional protection against electric shock. Yours do not have these, simply because they were installed some time ago and RCDs were not required then.
There is no requirement to upgrade these to meet current regulations, however nothing stopping you doing this either.

The main RCD / black box is there to ensure disconnection times are met in the event of a line-earth fault. This is required on a TT system, as without it, most/all of the circuits would never disconnect under fault conditions.

As for a new install or replacement CU, there are various options:

Dual RCD board, with various MCBs for the circuits. Allegedly complies, however there is still the issue of 50% or more of the installation failing when there is a single fault. (although the same applies if that board was installed in any property).
Could alternatively have a dual RCD board with one or more RCBOs (bizzarely called 'high integrity' by manufacturers).
The consumer unit would need to be insulated (plastic)

Main switch board fitted with RCBOs only. Some people might prefer double pole devices, but there is no regulation which requires this. Plastic CU only.

Split load board with a 30mA RCD for sockets, showers and so on, and another set of MCBs for the lighting circuits. A separate front end RCD will be required, and this must be time delayed to provide discrimination with the 30mA device. A metal CU could be used.
This is a poor solution, since a single fault can result in the entire installation being disconnected.

What you definitely don't want is a front end time delay RCD with single pole RCBOs fitted in the main board.

 

[ericmark]

It is very easy to miss quote the regulations as there are many exceptions. If there is no danger should the lights trip then there is no need to split between two circuits. This may be as with caravans that street lighting provides enough back-up light or that emergency lighting is fitted or standard/bedside lamps running from sockets which have different RCD.

Sorry if I was wrong about voltage operated ELCB but better to talk about it and not be a problem than other way around.

As all ready stated there is no rule saying you must up-grade however I am sure you would not ask question if you did not intend to upgrade.

Part P is a problem and because likely it will be cheaper to get upgrade done by registered electrician than DIY anything you want to do must be agreed by him. Use of single pole switching RBCO's and metal enclosures is very much down to the electrician doing the job and I think you really need to ask guy doing the job what he will accept.