Domestic 3 phase advice

[Aok1]

I would appreciate some advice on the following as i am not a full time spark and most of my electrical work is normally limited to minor works.

I was at a clients house in the week and while talking she mentioned that she needed to get a 3 phase supply installed at a cost of £6.5K + for her under floor heating which apparently draws 80A. The spark who done the re-wire in January thinks the total load is going to be around 135A which includes everything in the house.

He has said all the db's need changing to 3 phase.

There house is large but there are no electric showers, cooker is gas so the only items are really pull any current are on the ring and kitchen appliances.

I had a look quick look at the current system which has a 60A fuse on the incoming and then 2 x 12 way boards, 1 of which is for the underfloor 4 x 20a mcbs - Hall, living room, kitchen and small bathroom.

I think the figure of 135A is way out and no diversity has been allowed and there would be no need to change the db's either.

Would i be correct in thinking that no diversity is allowed for the underfloor heating but more common sense in that she has said that there would only ever be a maximum off 2 x areas on and never all 4.

I am due back on Friday to finish some AV and security stuff so i was thinking of advising possibly getting the 60A upgraded to 80A or 100A and also clamp testing the supply with the 2 x areas of the underfloor on and some other items to get some sort of idea on the actual load.

Thanks

 

[Engineer54]

If as you state the house is large then an upgrade to an 80A service fuse should be more than sufficient for the present installation and future additions.

As Dave suggested i'd bring these four UFH mats on gradually, i bet as others here say, that you'll not see 135A or anywhere near it....


BTW what's the total square meterage of UFH mats. Oh and i'm sure the installing electrician left the homeowner with all the details of the systems to register the them for warranty purposes etc!! loll!!

 

[shanky887614]

sorry that guy is a muppet?

having 3 single phase boards each fed by a different phase would be fine

i could say the total load in my house is over 100amps

both showers pull 40 amps and the hob 50 acording to the manufacturer

but i doubt it would get anywhere near that

 

[mark_]

Slightly off point but £6.5k for a three phase supply! Did the client not ask this question before they put in the uf heating to begin with. If there are not cooking with electric I take it there is gas on site so for £6.5k they could have put a wet uf system is with far lower running costs. Sounds odd to me.

 

[SIIVION]

Hopefully there are bills/receipts for the underfloor heating somewhere? Or a contact number for the installers?

With a quick bit of research I am sure you will find the loading.
ie. An average sized room of say 20m² X a few examples found via google at 200w/m²

 

[davesparks]

Why guess it when a quick resistance measurement will give a much better idea?

 

[trev]

Hopefully there are bills/receipts for the underfloor heating somewhere? Or a contact number for the installers?

With a quick bit of research I am sure you will find the loading.
ie. An average sized room of say 20m² X a few examples found via google at 200w/m²

Oh dear me!
Perhaps I've been doing things wrong all these years, I rely on this machine thingy that measures resistances.

 

[Engineer54]

Oh dear me!
Perhaps I've been doing things wrong all these years, I rely on this machine thingy that measures resistances.

Shouldn't need to test these UHM's the homeowner should be in receipt of all the product documentation that will state total areas installed and W/m2 values!!!

But thinking about it, it's more likely that the homeowner has been given nothing apart from the bill for the installation!! .... lol!!

 

[davesparks]

It has already been stated that the installer hasn't given over any paperwork.
So it's a case of simply testing the mats and calculating the power, granted it may not be spot on to the nearest watt, but a lot better than the other suggestion of guessing the watts per square metre!