Metal Fuseboard on TT

[somersetsparks]

On one of my 'other jobs' which I mentioned the other day,
One building which is TT and fed by an SWA, although the earths are isolated and this building is protected by a rod, has single insulated cores feeding the incomer (100ma rcd).
However the whole installation is protected by a 300ma Time delay at source, so would the double insulation of the incoming cores still be necessary?

cheers

 

[sparks1973]

i mean could you not do deep with the submains....or even go to the efforts of running em in protective pipework?....its all about consultation with the clients and intended use isn`t it....

 

[JD6400]

Just thinking , if the only stake is on the cowshed then would you not have to that rcd , to much whisky and cider to think properly !

 

[JD6400]

i mean could you not do deep with the submains....or even go to the efforts of running em in protective pipework?....its all about consultation with the clients and intended use isn`t it....

Ye , but that pipe work / mesh grid wil not just cost but be a royal pain in the !
As a rule we just TT all out going subs , but have often wondered what others think ?

 

[sparks1973]

Just thinking , if the only stake is on the cowshed then would you not have to that rcd , to much whisky and cider to think properly !

well would not the metal framework of the building (a barn in this case) not also provide adequate earthing?....so lets say you had final circuits within the barn not exeeding 32A...i would say they needed 30mA protection....

 

[sparks1973]

you could of course have a mix of both....30 mA for finals not exeeding 32A....anything more put on 100mA...so a split load board would provide this.....

 

[sparks1973]

as you do....you could also TT the subs going out to the barn/outbuildings....and use the structural localy....

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so for a barn with multiple struts....loads of parrallel paths there.....

 

[JD6400]

Sorry it should read " should you not have to have that rcd "

 

[sparks1973]

what?...for a TT?....

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isn`t that the requirements for TT systems DP?

 

[JD6400]

Apparently you are unable to use the structure of a metal building as a means of main earth , checked this only a few weeks ago with the ECA teck line .

 

[JD6400]

what?...for a TT?....

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isn`t that the requirements for TT systems DP?

Ye , but it was mentioned earlier in the thread that the faulty rcd could be replaced for just a main switch , well at least i think it was ?

 

[sparks1973]

well i dont know about that....542.2.3 would suggest otherwise...

 

[sparks1973]

Ye , but it was mentioned earlier in the thread that the faulty rcd could be replaced for just a main switch , well at least i think it was ?

well i think that was the 300mA feeding the lot....i would put a 100mA in at the barn end...for finals exeeding 32A of course....

 

[sparks1973]

i think the idea was to use the 300mA RCD as protection for the lot.....

 

[JD6400]

Whats that one , regs are in the van across the yard and i am buggered if i could manage that stagger at the moment !:54:

 

[sparks1973]

well for a start i would say that doesn`t satisfy 705.411.1