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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> A 3ph Problem https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1425241228 Message started by get_it_done on Mar 1^st, 2015, 8:20pm

Title: A 3ph Problem
Post by get_it_done on Mar 1^st, 2015, 8:20pm

OK here is the situation. The premises - A Hairdresser shop.

3P supply to shop. Split L1 - Dist board for Shop, L2 - Dist Board for Annex (Supplied by 3 core 10mm SWA), L3 - Sunbed room next to annex (1P 63A) (Supplied by 3-core 10mm SWA).

The owner requires a second sunbed and the fitting co need 3P supply in Annex and wish the original sunbed converted back to 3P. Both beds to supplied with 25A type C MCB and 63A RCD. That's the easy bit.

Question - Instead of laying a new 5core cable is there anything wrong with using the existing two 3 Core to provide the 3P supply. Assuming the calcs where correct and everything was correctly labelled. A bit unorthodox but does it comply? All comments suggestions welcome.

And welcome back

Title: Re: A 3ph Problem
Post by Lectrician on Mar 1^st, 2015, 8:35pm

If you mean use the three core as 3phases and no neutral (if the beds don't require one), then yes.

However, I would say a neutral would be required.

If so, all lives and neutral need to be contained in the same armoured cable as the armour is magnetic. You cannot put the phases down one cable and the neutral down another.

Title: Re: A 3ph Problem
Post by get_it_done on Mar 1^st, 2015, 9:35pm

I knew it would not be that easy. Yup a neutral is required.
I did look up the big green book and Reg 521.5.1 explains it all.

Back to plan A

Title: Re: A 3ph Problem
Post by get_it_done on Mar 2^nd, 2015, 1:04pm

Is there any sparky available in the Slough area to do a bit of 3p work ASAP?