RCD on a TT System

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Can anyone tell me the in regs wether or not a on a TT system with a 10mm main Earth (not buried) to the rod and consumer unit with a split load, if you need or when you need an overall protection of an RCD, or is the 30mA RCD on the sockets enough. I dont know, but could find out the Ze if required. It looks like in the OSG, that it does need the overall RCD but the regs say that sockets on a TT system need to be protected by an RCD.
Please enlighten me. :oops:
 
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Why don't you look in the regs? It's got a pretty good index, and the more you look up answers like this yourself, the more familiarity you will gain with the regs - surely a good thing.
 
Take a look at 531-04-01 hence the use of split load cu 30mA will trip you loose all circuits, so main isolation switch 100A 100mA td rcd.
Remember the regs are open to your interpretation of them, they don't give you how to answers

Efli is to high rcd is required(Page 20 osg / 413-02-19 in regs)
personally I go by the osg & use split load cu with td rcd as main isolation switch on TT systems, because dry weather = dry ground = high resistance possibly giving high efli (until it rains again).

Thats my answer anyway but i'm sure someone can elaborate or correct me.
 
The only situation when TT does not require RCD protection of some kind on all circuits, is if you can show the ZE is low enough to operate the trip (MCB/Fuse) of the non-RCD protected circuits.
With a typical rod impedance of perhaps ~100 ohms or so in dry weather, a normal earth rod will not do for any normal fuse or MCB size.
So, in practice either a 100mA slow triping RCD is used as the incomer for all, and this feeds a fast tripping 30mA RCD for sockets, or there is one double insulated main switch, and then the power is split to 2 RCDs, one for sockets, one for the rest. Take you pick.
 
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Thanks very much Mapj1 and comms for your personal views, as I had said in the original post Ban, I looked in the regs but hadn't been able to answer the question myself so thought one of you "oracles" may be able to help me. Ban if everyone were told to read the OSG or regs we wouldn't need the forum would we!!!!?? Cheers guys and thanks again.
 
Newspark said:
Ban if everyone were told to read the OSG or regs we wouldn't need the forum would we!!!!??
Not everyone - just professional electricians.
 

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