TT system / Zone 3

30 Jan 2008
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United Kingdom
I have a suitable light fitting located in zone 3 of a bathroom. As its a TT system, the light circuit is on a 100ma RCD. I am told that a fixed light fitting in zone 3 of a TT system has to be on a 30ma RCD. Is that correct?
Many thanks,
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There is no such requirement under bs7671:2001(2004) afaik, under BS7671:2008 the light will be required to have 30ma rcd protection but it won't be in zone 3 anymore (and it would be the same on a TN system) ;)
Thanks, I didn't think so either. My 'Practical Guide to Testing...' states that "any current using equipment in a TT system in Zone 3 requires 30ma personal protection". Regards, Mike.
No reg number or anything?

It does seem odd, the extra RCD requirements with TT are concerning protection against indirect contact; the ADS bit of EEBADS simply wouldn't work if we installed as if it were a TN system!, but where an RCD is installed for extra personal protection, its normally to do with risks of direct contact involving things like mowed flexes or wet folk, etc and would normally apply to both TN or TT systems
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I agree. No reg reference (not helpful). I cant find anything that relates either. Regards, Mike.
In Zone 3 current-using equipment other than fixed current using equipment shall be protected by a residual current device not exceeding 30mA.
If it is fixed it doesn't need 30mA protection.

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