metal enclosures on tt

[jstephens251]

hi all,

been looking at an outbuilding supply on a tt arrangement.
i usually gland the swa near the ccu in a metal enclosure but whats peoples thoughts on using a metal enclosure on tt?

cheers

 

[jstephens251]

forgot to say swa will not be rcd protected for descrimination

 

[i=p/u]

not reccomended

 

[jstephens251]

plastic ip box then?

 

[yellowvanman]

531.4.1 is the reg number applicable.

If you think about it, if there is a fault between the phase and the metal enclosure and the metal enclosure is earthed. Because its TT it'll have a Zs of >10ohms. So if it is 10ohms and there is a dead short between phase and enclosure - 23A will flow, not enough to trip a 20A breaker, might work on smaller breakers. If Ze is higher then dead short wouldn't even trip a 6A breaker.

 

[Deleted member 9648]

Generally the metal enclosure should be RCD protected....if the only RCD is within the metal enclosure it wont be protectd against a fault between the incoming supply and the enclosure .
If you take additional steps to ensure the incomer cant short onto the enclosure this is deemed satisfactory....but IMO it is not and an insulated enclosure should always be used.

 

[Spudnik]

Its the tails that should be RCD protected that are feeding a metal CU.

 

[jstephens251]

thanks guys i agree with all comments. it was the high zs that made me think about it. ill just make a neat job with a insulated enclosure

thanks again

 

[Guest123]

forgot to say swa will not be rcd protected for descrimination

I think you'll find it wil HAVE to be.....

 

[keniff]

As Lenny says, think the whole instalation has to be on at least a 100ma rcd could be wrong aint got the brb with me