Overload. Help Please

[Anonomoose]

I am currently doing a job for perhaps the tightest builder ever. The job consists of

Three Ring Mains
Two lighting circuits
One 9.5KW shower
Two x 12.5KW boilers
one x Smoke alarm
One x 32a Cooker supply
one x 32a Hob supply.

He is getting EDF to put in a new supply (complicated story) so thats obviously going to be a 100a main fuse. this is far too much.

What do you lot suggest. Obviously 3 phase is going to ramp the cost up somewhat. Im confused and builder is having a fit.

 

[ezzzekiel]

doing a rough calc it came out at about 100a max demand (although i would check this)
now depending on how you think the circuits will be loaded and used then maybe the supply would be ok (providing the max demand is around the 100a ish then i wouldnt worry too much.

scrap that, miscalculated your hitting a 130a after diversity (using rule of thumb) - 3 phase supply in or reduce the circuits.

 

[High Tower]

Is the oven going to be 32a??? if there is a seperate hob i doubt it??? ovens on their own normally only pull about 10a unless its a brute. hob might be 32a alright!

 

[Jimmyb]

can you not ask for a 2nd phase to be installed instead of a 3 phase supply

 

[GrannySmiff]

MD I really find a grey area, I know if you work it out correctly it comes out over 100a however realistically is he going to have all that on at the same time, but then would you want to risk it. A good understanding of how often those boilers are going to be used would help make a decision.

Even though if you look at your time current characteristics which I have just tried to do pg 244 brb but can't remember how to work it out but I remember going by that a 100a would need to pull something like 140 a for 45 mins for it to go, obviously we don't want to plan for this.

If edf are putting a new supply in it would just be simpler to bring in a second phase, as if you were to install this all on a single phase then that will be pretty much it if he wants to add anything.

 

[pushrod]

That is 2 electric boilers in one property?

 

[telectrix]

one boiler is for heating. the other is his mother-in-law

 

[Marvo]

I don't see a problem. If the max demand calc comes to 130A and the builder doesn't want to install a 3-phase supply then he can give it to you in writing he understands the risks of overload tripping and he can sort out any future problems for his account.

You could install a load shedding relay on one of the boilers as well depending how critical it is.

 

[IQ Electrical]

You need to look at the load characteristics and make your own assessment, the good book states: "The use of other methods of determining maximum demand is not precluded where specified by a competent person"