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sub main?


musicspark

Question

Hi chaps,

I visited a house the other day which has a granny flat. this is supplied by a 16mm T&E On a 50A Breaker with 30mA RCD from the CU in the house. There would not appear to be any extra earthing run along with the submain for the granny flat.

would i be right in thinking that the 6mm in the T&E is inadequate for the main earth between the two CUs?

Should I run a 10mm alongside the T&E?

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is there any main bonding is the granny flat? its own water supply?

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is there any main bonding is the granny flat? its own water supply?

This is the key question for me, if there's no main bonding taken from the sub-main CU, what's the difference between this an a fixed load requiring 16mm cable - so long as Zs values are acceptable obviously.

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kinda what I figured. I will have access to the granny flat later this week and will check the bonding situation

incidentally , can someone explain the adiabatic equation to me?

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If we do any sub mains in 16mm twin and earth we also run a seperate 16mm earth alongside.

I did some work on two flats a few weeks ago where all the flats are supplied by 16mm twin and earth with no additional earthing, not really very good practice and I am amazed they got away with doing it this way.

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if there are no metallic services the T&E is fine, but if there are metallic services and you want to include the flat into the equipotential zone then a 10mm earth will be required

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unless the flat is already attached to the main building and the services to there are shared with main building and already bonded.

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