electric combi

[tombennetts]

just been asked to connect up a 12kw electric combi boiler. run is about 13mm through floorboards. dont want to sound stupid but does this have to be 16mm? its for an old guy who is scared of gas so having everything changed to electric (cooker, shower etc.)
cheers guys

 

[Rockingit]

Before worrying about cable sizes, you need to think about loading!! 12kW of instantaneous water heating is a massive current load, and you may find the DNO have an interest as well if there's pumps involved at the same time.

12kW @ 230 = 52A with no diversity allowable. So if you have the heating running and a power shower both together there'll be a loud popping noise and it will go dark very quickly. DNO probably wouldn't replace the fuse either until changes are made.

 

[tombennetts]

i did wonder that, have persuaded the client to have a mixer shower installed to reduce the loading, that means its just the boiler and oven with the big loads, ill tell him he can only use 1 hob in the winter when the heating is on!
surely this is a pretty common problem in houses when electric combi's are being installed? The plumber has specced everything for this, is a 12kw nescesary for a small 3 bed house? could it be dropped to 10?

 

[UNG]

surely this is a pretty common problem in houses when electric combi's are being installed?

Haven't seen one installed any where and with the cost of electricity and potential load issues with the service fuse it wouldn't be my first choice

The plumber has specced everything for this, is a 12kw nescesary for a small 3 bed house? could it be dropped to 10?

This says it all everything specced bar the electric supply. I would think that 12Kw could be on the low side for heating a 3 bed house and providing hot water. A lot of gas combi's have outputs much greater

 

[GT1]

Cost of gas is going up more than electricity every time. Seen a few plumbers starting to train up on electric boilers. Not quite cheaper yet than gas. But I don't think it will be long.
Notifiable too as I remember ?

 

[BlueToBits]

Electric CH systems are often require 3 phase supplies

 

[UNG]

Cost of gas is going up more than electricity every time. Not quite cheaper yet than gas. But I don't think it will be long.

Don't know what tariffs your looking at but gas has a long way to go to get close to electric prices

One thing with going all electric the DNO's have not got the capacity to supply everyone, that'll be power cuts on the way

 

[tombennetts]

so we are looking at 16mm t and e? joy, I love making off 16mm t and e in enclosed spaces!

 

[Rockingit]

10mm method C = 64A with a vd of 4.4
16mm method C = 85A with a vd of 2.8

only 16mm will go to 12kW with other methods. Table 4D5 BGB.

 

[mogga]

Iv fitted these in the past It MAY be an option to split the system 6Kw and 6Kw seen that done
BIL had 2 big ones fitted AGAINST ALL ADVICE but he hes a plonker he then phoned DNO to come n see about upgrading the supply as during a snowy period there was a nice clear developed line in the snow leading from house to pole where transformer was mounted
he then opted to get it our and fit a nice oil burning combie outside in a heated cupboard
other time iv seen them fitted was a development of a BIG old house into flats the buyers all liked the Idea TILL one of first electricity meter reading when the meter guy told them that the faster the wee red light flashes the more electricity your using "Mine stays on " said woman

 

[tombennetts]

added point, he recently had a 2.8 kw pv system installed (i did the wiring) and believes it will be free heating as its electric. I have tried explaining to him that this is in no way correct but he is an old boy, bit of a geezer and doesnt pay any attention to me. what would silly little sparky know?!

 

[holmes571]

We have installed several electric boilers of this size and have always had to have fuses/ supply upgraded to 100amp at customers expense. When we first fitted one it was fired up and hob and oven were put on at same time and it was drawing 82amps so upgrade is a must. 12kw is usually ok for three bedroom semi and hot water but anymore than that and it will struggle. If you use an Amptec boiler you can purchase a relay that cuts power to the boiler if an electric shower is turned on which can be useful. You also need to bear in mind that any isolators need to be able to cope with the 52 amps the boiler will draw as well. Hopefully you will be as amused as we were to see the speed the meter wheel spins at when the boiler is in use. If it is a combined boiler and hot water system, eg Heatrae Sadia Electromax, the hot water is provided via two immersion which heaters and an unvented cylinder which will add more demand supply.

 

[tombennetts]

We have installed several electric boilers of this size and have always had to have fuses/ supply upgraded to 100amp at customers expense. When we first fitted one it was fired up and hob and oven were put on at same time and it was drawing 82amps so upgrade is a must. 12kw is usually ok for three bedroom semi and hot water but anymore than that and it will struggle. If you use an Amptec boiler you can purchase a relay that cuts power to the boiler if an electric shower is turned on which can be useful. You also need to bear in mind that any isolators need to be able to cope with the 52 amps the boiler will draw as well. Hopefully you will be as amused as we were to see the speed the meter wheel spins at when the boiler is in use. If it is a combined boiler and hot water system, eg Heatrae Sadia Electromax, the hot water is provided via two immersion which heaters and an unvented cylinder which will add more demand supply.

just checked my cert from the pv installation, its on 16mm tails with an 80 amp fuse at the moment, so will be cutting it fine with electric boiler and oven! any bright ideas anyone?! how much do dno generally charge for an upgrade like that?

 

[Rockingit]

I've just been quoted £4.5k to uprate a pole transformer to cope with a 50A ground source heat pump. Same problem as OP just different technology.

 

[tombennetts]

christ, the amount the old boy smokes i doubt he will be around by the time they get round to replacing the transformer anyway! seems there is a bit more than meets the eye to installing these electric combi boilers!