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time delay RCD

Discuss time delay RCD in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Hi guys, Got a TT system. Do I need to install a time delay RCD on an old Wylex board that is supplying off-peak night storage heaters. The unrestricted board has been changed to 17th last year but the restricted board has not been changed.
Cheers. The external Ze is very good at 0.18.
 
I think e54 installed that earth pit. If it is tt, it should have one too cover both boards, don't need two. On the incoming tails before wiggles off in all directions..
 
even by flying eng54 all the way from china to install a TT earthing system, i'd be amazed at that Ze. must have a rod down to Oz to get 0.18.
 
The TT system, if that's what you've got, doesn't require a RCD as long as the disconnection times can be met, 41.1, then 411.5.2 can be considered as sufficient.

As for E54 flying over to inspect a pit, he'll probably condemn it for using a twigg - lol
 
That's why I'm going out to check it later this week. One of our other sparks did an EICR on it last week, gave me the cert to sign off, as QS, and I refused. He wondered why! Also noticed other discrepancies like 2.5 lives and 2.5 cpc with him specifying PVC/PVC type used. Challenged, it now appears type C.
 
I just thought as might not be stable , just use rcd even 30mA on the board without. But I ain't a electrical legend yet , just a chancer.
 
I just thought as might not be stable , just use rcd even 30mA on the board without. But I ain't a electrical legend yet , just a chancer.

I am with you 100 % . It may be a first class Ra at the moment but no matter how deep you go , unforeseen external circumstances may change this far before its next inspection ( Unlikely , but not impossible ) ! I am not advocating the reliance of an rcd , but for TT systems it just makes sense to have as a added security !
 
there's no way he's got a Ze of 0.18 on a TT system. someone's telling porkies.either that or his pi$$ is marketable.
 
I am with you 100 % . It may be a first class Ra at the moment but no matter how deep you go , unforeseen external circumstances may change this far before its next inspection ( Unlikely , but not impossible ) ! I am not advocating the reliance of an rcd , but for TT systems it just makes sense to have as a added security !

I can't understand why people do not believe what's written in BS7671. If its a TT system with a Ze of 0.18 Ohms after the MPB have been disconnected then 411.5.2 (ii) is sufficient. We used to work to that all the time 20 odd years ago.

However, I've never seen a TT system as low as that. Maybe 0.5 - 1.5 Ohms.
 

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