RCD to RCd

[stidge]

Running a feed to garage from dual RCD CU.Would like to fit RCD CU in garage but have heard that this might cause nuisance tripping( RCDs acting against each other)???????? Have seen this before on various jobs ie RCD controlled radial to RCD socket !!! Would like your opinions/answers on this. Thanks lads

 

[Hawk81]

You need to have discrimination between RCD's. What is the point in having a 30mA RCD covering another 30mA RCD for both to trip?

 

[SPARTYKUS]

You need to have discrimination between RCD's. What is the point in having a 30mA RCD covering another 30mA RCD for both to trip?

extra extra safe

 

[nickblake]

fit a CU in the garage with out the RCD alls covered by the main RCD

 

[Hawk81]

extra extra safe

Good point lol

 

[SPARTYKUS]

stidge

it's called in series, and can be a pain. Not such a pain if both RCD's are next to each other physically but it depends what else they cover. Basically it is a bad idea.

To discriminate the usual answer is a time delayed RCD (type "S").


The point to understand is that discrimination is achieved for RCD's in series by modifying the TIME value. Not the mA value.

If you had two RCDs in series and one was 100mA and the other was 30mA you might think you had discrimination but you'd be mistaken.

As soon as you get a large fault, well, it's anybodys guess which one will pop. And that is the problem.

 

[stidge]

So would be fine nickblake to run swa from non protected side to RCD CU in garage ???

 

[truckster]

That would be a good way to do it

 

[telectrix]

as long as the cable doesn't itself need |RCD protection.

 

[just add water sparks]

stidge

it's called in series, and can be a pain. Not such a pain if both RCD's are next to each other physically but it depends what else they cover. Basically it is a bad idea.

To discriminate the usual answer is a time delayed RCD (type "S").


The point to understand is that discrimination is achieved for RCD's in series by modifying the TIME value. Not the mA value.

If you had two RCDs in series and one was 100mA and the other was 30mA you might think you had discrimination but you'd be mistaken.

As soon as you get a large fault, well, it's anybodys guess which one will pop. And that is the problem.

I came across this problem a while ago i.e 2 30mA RCDs on a radial.I'm sure i enquired about a time delayed 30mA RCD and was told they do not make such a device ? On a 100mA yes, but not 30mA

 

[nickblake]

So would be fine nickblake to run swa from non protected side to RCD CU in garage ???

Eh , sorry if im miss reading here , you said you had a dual RCD board or is the board a hi integrety board with some unprotected circuits if this is the case then you can install the SWA without RCD protection as the armour protects the cable as long as its been terminated using the correct glands and the SWA is earthed , un less like tel has said it requires RCD protection then you can use an RCD board in the garage , if its just a dual board then there is no need for the RCD in the board in the garage as it will be protected by the RCD in the house SWA as well

 

[SPARTYKUS]

you can get a 30mA time delayed RCD. I have seen one.

But there is still a problem.

x1 requirement is usually 200milli seconds, yes? (300 for RCBO's 61009 )

So - time delayed 30mA RCD at front, followed by a normal one downstream. say they are in the remit of a 35mA fault and the one thats non time delayed is a bit slow but still compliant, and trips at 135ms, and the other one (which is time delayed by 100mS, but is a bit quicker, and goes off in 35mS on top of that) ...... so which one will pop

Same problem.

(I think, more learn-ed members please feel free to mock me)

 

[just add water sparks]

I have just googled time delayed 30mA rcd's and found the same thing no one can find one????? according to other forum's.Also states same on Voltium forum and stated from Select even if there was one it would not be compliant.I don't wish to point score but see for yourself

 

[pushrod]

Apart from the discrimination problems ie fault in garage possibly taking out half the house circuits by tripping main CU's rcd - you also have the problem with testing the rcd for EIC/PIR

If you can run from an unprotected way in main CU (with some CUs you can rearrange them to get an unprotected way) with swa to a little rcd garage unit that is a good way to go

 

[SPARTYKUS]

I have just googled time delayed 30mA rcd's and found the same thing no one can find one????? according to other forum's.Also states same on Voltium forum and stated from Select even if there was one it would not be compliant.I don't wish to point score but see for yourself

'Googling' and not finding something does not therefore mean it does not exist

Yes, you are right, it would not be compliant. (x5 trip time)

I was using it as a vehicle to explain a point.

RCDs > Time Delayed > 100-30-4TD - Protek Circuit Protection


Dock yourself 10 points!

 

[steve-the-bruce]

Stidge,

Came across this in Wiring Matters, goes through your scenario. Hope it helps.

http://electrical.------.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf

Steve

 

[just add water sparks]

Deduct yourself 20 points for bad observation Spartykus When i said i googled 30mA RCD'S i did not specifically say i was just sourceing them i was also merely seeking other forum sites comments.Of which i stated other members had tried to source them without success.I was refering to 32amp 30mA RCD'S Although to be fair i did not stipulate this in my post.I am still certain there is no device in this range,although i sure you will try to earn your brownie points to prove me wrong

 

[SPARTYKUS]

Nope, I won't.

where's that beer

 

[just add water sparks]

The forman apparently phoned the wholesalers today and yes you can get a 30mA 32amp time delayed rcd but not a R.C.B.O of this denomination