Spliting 3 phase (shop & house)

[Norv]

Right, I'm not going to take this job on because I have almost no experience of 3 phase.

I was chatting to the owner of a small printing shop earlier & they asked if the 3 phase could be split so the bills for the house & shop are separate. (The house has been converted so the shop is part of it). I didnt see how it had been wired but she said the incoming 3 phase is in the main house & split for the shop.

I'm curious to know how this would be split & how do you make sure it is balanced. Do you work out the max demand on each phase ?

 

[plugwash]

Do they actually need two seperate bills? That would require having the supply split by the DNO which would be expensive and would mean they had to pay two lots of standing charges/higher intial rates. If the DNO split it they would probablly fit a second service head and meter fed off the incoming supply to the first.

If they just want to know how much is being used in each area for tax or budgetory reasons I would suggest fitting a private meter to the submain that leads off to the shop. Meters are not terriblly expensive (e.g. http://www.tlc-direct.co.uk/Products/RDCRED3slash100.html is a 3 phase 100A meter for less than £100 )

Unfortunately meters are designed for use with tails and don't have enough space to terminate a multicore cable without exposing the individual single insulated cores (which is a NO-NO). A common way arround this is to butt an adaptable box with a slot cut in the top against the bottom of the meter to provide more wiring roo.

As for balance you need to try and keep the demand on each phase as similar as you can. It is virtually impossible to get perfect in many cases though because of varying loads and the need to keep phases seperate if you don't want warning labels everywhere.

 

[Norv]

ok plugwash. Good answer, thanks