Time delay RCCB

[Andypease1]

Hello

Have bought a small consumer unit to power an out house. Unit will be sited in the house next to the main board. Will replace the double pole disconnector
Switch with an RCCB for safety. Can you please tell me the difference between a time delay RCCB and a non time delay. Board is Square d qwikline II proposed RCCB is SQOE 100100s type delay s ( which already have)

Thank you

 

[deadshort]

Hi, time delayed rcd's are required on a TT earthing system. If the property has an earth rod ? And the earthing is not provided by the DNO.

This will NOT reduce the risk of electric shock you would require a 30ma RCD in the out building consumer unit, which will provide a faster disconection time.

Regards,

DS

 

[Andypease1]

Thanks for that. Yes we do run on an earth rod (Very rural)

Why would you also need an rccb in the out house as well. Surely protection is provided by the rccb unit in the small cu at the house. The cu in the out house is really just a distribution box using mcb,s

Sorry if sound a bit thick

 

[deadshort]

No, sorry misread that. If the outhouse wiring is protected by a 30ma rcd in the house that's fine.

If you are using machinery please be aware if a fault occurs your lights will go out in the outbuilding which is an obvious concern.


Regards,

ds

 

[ban-all-sheds]

Hi, time delayed rcd's are required on a TT earthing system.

They are not required.

They were traditionally used upstream of an RCD covering the circuits which needed a fast disconnection time, the idea being that a trip caused by a fault on a socket circuit wouldn't take out the lights, for example.

Depending on how a CU is divided, and how many RCCBs are used, there may be no need for a time delayed one upstream of the others.

 

[AndyPRK]

A picture if what u have in the house at present would help

 

[Andypease1]

Thanks guys

Think I will fit a non time delay unit in the cu for the outhouse situated in the house and leave the cu in the outhouse (distribution box) with just a disconnector switch and the MCB' s .

No worries on the lighting front as installing emergency lighting over the bench just in case.

All three boards in the house . Lighting board, power board and outhouse board ( yes is a very big house) are protected by a 100amp 30ma mains switch.

Does that lot sound ok.

Will all be checked and certified before use.

Thanks

 

[JohnW2]

No, sorry misread that. If the outhouse wiring is protected by a 30ma rcd in the house that's fine. If you are using machinery please be aware if a fault occurs your lights will go out in the outbuilding which is an obvious concern.

Indeed, but that is obviously not an issue only related to RCDs. A fault on the sockets circuit can obviously take out the lights if (as is usually the case) both outhouse circuits are protected by the same over-current device (MCB or fuse) at the house end, regardless of RCDs. If loss of lighting could present a hazard, the only true solution is to install emergency (battery backed-up) lighting (as the OP has done).

Kind Regards, John

 

[JohnW2]

Think I will fit a non time delay unit in the cu for the outhouse situated in the house and leave the cu in the outhouse (distribution box) with just a disconnector switch and the MCB' s . ... No worries on the lighting front as installing emergency lighting over the bench just in case. ... All three boards in the house . Lighting board, power board and outhouse board ( yes is a very big house) are protected by a 100amp 30ma mains switch. ... Does that lot sound ok.

Assuming that the "100amp 30mA mains switch" you refer to is actually a RCD (RCCB), then that sounds fine, protection-wise. Having just a single RCD does, of course, mean that any fault on any circuit will take out your entire installation (which would probably not be allowed by current regulations, but there is no requirement for you to comply retrospectively).

Kind Regards, John

 

[ericmark]

It is a historical thing years ago we started with the ELCB-v these were outlawed and replaced with the ELCB-c better know as the RCCB or RCB which were very likely to trip in electric storms and the like, so the delayed type was used.

As time has gone on other methods have been found to stop a RCD tripping with electrical storms X-Pole by Moeller is a good example of how this has been done.

There is still a place for the 100mA RCD delayed but very little used in domestic now.

 

[Andypease1]

Thanks guys

It won't take out everything as the rccb in outhouse cu situated in the house should blow first intend to fit. 63 amp unit. Cover provided by the emergency lighting.

Should therefore be fine I think.

Cheers

 

[ban-all-sheds]

Have bought a small consumer unit to power an out house. Unit will be sited in the house next to the main board.

The place for it is in the outbuilding.

Why on earth put it in the house and then have to run multiple armoured cables to the outbuilding for the final circuits?

 

[Andypease1]

Hi

Am running one swa cable 6mm ( mcb at house end cu is 40a )and using a cu in the outhouse as a distribution box with mcb's 16 a for power and 6a for lighting a bit OTT but think is ok. Already have the cu's so cost not an issue

Putting the rccd on the house end will protect the cable if damaged unlikely I know but an idiot with a long shovel may turn up!!!

Cheers

 

[JohnW2]

It won't take out everything as the rccb in outhouse cu situated in the house should blow first intend to fit. 63 amp unit. Cover provided by the emergency lighting.

Sorry, I misunderstood. Even though you wrote otherwise, I thought that you were going to feed your outhouse CU via that "100A 30mA" device (presumably RCD) you mentioned and not have an additional RCD in the outhouse CU (which would then be unnecessary). If you were going to feed the outhouse CU via that 30mA RCD, unless the latter were time-delayed, there is no guarantee at all that an RCD in your outhouse CU would operate before the other one 'took out your entire installation'.

As BAS has said, I don't understand why you are talking about having the outhouse CU in the house, rather than the outhouse. What were you planning to have in that outhouse CU?

Kind Regards, John

 

[JohnW2]

Am running one swa cable 6mm ( mcb at house end cu is 40a )and using a cu in the outhouse as a distribution box with mcb's 16 a for power and 6a for lighting a bit OTT but think is ok. Already have the cu's so cost not an issue

Areyou saying that you're planning to have an 'outhouse CU' in the house and another 'outhouse CU' in the outhouse? If so, why - and what is the one in the house being fed from

Putting the rccd on the house end will protect the cable if damaged unlikely I know but an idiot with a long shovel may turn up!!!

As with everything else in a TT installation, the SWA has to have RCD protection - but if (I'm not sure, I'm getting confused!) it is being fed via that 100A 30mA RCD, then that is adequate.

Kind Regards, John