3phase but using only 2

[oac9211]

Hi. Just having a moment and doubting some work that I have done. Although discussed with a couple of other sparks and niceic tech line and they said was the right way.

House had a single phase board and a 3phase for old storage heaters. Storage heaters out and replaced for lower cost haverlands. Total load less than 50amps. Have replaced both boards for 2 single phase board running from just 2 of the phases ( have put a central 4pole isolator ) upgraded neutral from the isolator to 35mm then 25mm to each board but used existing dno tails from the meter (25mm)

Can anybody see any wrong doing in this?

Be gentle if I have made a cock up but just sat here doubting things!!

 

[davesparks]

It's poor design to put a three phase supply so far out of balance.

I don't understand why you're mixing 35mm and 25mm tails? You would normally only reduce cable size with appropriate fusing.

 

[oac9211]

this is y I'm sat here doubting my self. I spoke to the niceic to discuss what I was doing and the chap was very helpful with it and couldn't see any problem with it. the original design was out of balance using one phase for the whole house and 3 for the heating. The 35mm was recommended by the chap I spoke to but I struggled to see the need due to only 25mm coming in and before was split between the 2 boards. I've got to install 2 ovens and a induction hob so I could install another board of the other phase. this would then balance things up. peed of with my self as no better but just got caught up with bad advise

 

[oac9211]

thought I replied but not sure where it went.

I completely hear what you are saying hence y I am doubting my self. I should have listened to my gut instinct that it didn't sound rite advise after talking to niceic and other sparks. ive got to install 2 ovens and a induction hob so will install another consumer from the other phase for these to help balance things up. so wound up with my self

 

[Leesparkykent]

That's not really going to balance things up though...

 

[oac9211]

will also put the kitchen ring main on it to help balance things

 

[oac9211]

I'm an idiot having a bad day, go easy guys!

 

[davesparks]

Oh dear, don't just randomly pick circuits to dump onto another phase! You need to think about what the loads actually are and how you are distributing them across the phases aswell as where each phase ends up physically located in the installation.

Any answer on why the mixture of 25 and 35 mm

 

[oac9211]

The 35mm I can not answer I'm holding my hands up on that one, cant blame anyone even the bad advise but me for that.

I'm sat down now working things out and loads locations etc and will install an additional board to help things

 

[oac9211]

I appreciate your feed back thankyou

 

[HandySparks]

If you're not overloading the two boards, then I wouldn't bother adding a third. After all, there's no financial penalty for out of balance loading on a domestic supply. If you take a row of three houses, one on each phase, then they're not going to be 'balanced' most of the time anyway.

 

[oac9211]

I take your point. The house has never been balanced as one phase had the whole house plus 4 s/heaters and the other 2 phase only had a couple of heaters on each. I haven't rewired the house just alterations and with adding sockets to the old heater points wanted 30ma protection but the cost of 3 phase board and robos had the customer sweating so I thought this was the best way after talking it through with the help line and a couple of sparks

 

[Darkwood]

Is this a big house with a larger than normal calculated demand, if not then run of 1ph and get the energy provider to blank 2 phases and charge a single phase tarriff.

If it is a big house then like has been said, its good design to balance but not usually essential in domestic, when you get to Commercial and Industrial then thats a whole new ball game and balance can be an essential part of design.

 

[oac9211]

It's not overly big but demands slightly more than 100 amps in the winter especially

just having a moment conte plaiting things as hate doing things wrong

 

[Darkwood]

You have already installed 2 boards so just balance across them, next time you come across this situe' you maybe better forgetting multiple CU's and fitting a 3ph board then all cicuits can be easily balanced accordingly.

Don't spend all night beating yourself up about it, as long as the circuits are safe, the CU are not going to overload and it looks neat then wrap it up and move on while taking the advice given onboard for future.