3 phase domestic job

[The Mains Man]

I fully accept that having swapped trades half way through my life I don't have the years of experience that many of you guys have and maybe I should have put my time in as an apprentice, but that isn't how it all turned out for me!

I am a qualified electrician with Stroma, but find their technical support patronising and unhelpful to say the least.

I do a lot of standard domestic work but I haven't done a lot of 3 phase. I have a friend who has a domestic 3phase installation which needs re-designing as they are upgrading their old night storage as well as getting new immersion heaters and aga etc. An extension is pending too!

I really want to help them out with project as this as the work lies awkwardly between your average domestic and commercial and they can't find anyone who can deal with it. It would be interesting and push my knowledge but it wouldn't be something I would be prepared to take on without having someone more experienced check my plans.

It would be quite a mission to put it all in a post so I was hoping maybe someone experienced would be willing to chat on the phone or meet up for an hour to talk it through. Happy to pay for the time.

 

[The Mains Man]

Currently the

Not sure if I'm understanding the heater question, are you intending to run 1 circuit as say, a radial for all the heaters? Probably misunderstood your statement

No, even I know that is a bad idea they are all on separate mcbs, currently distributed across the three phases and I would maintain that. I was considering the merit of splitting the three phases by location as that suggested or whether I run all three phases to both locations to aid balancing and possibly flexibility.

Sorry if my explanation and choice of words isn't clear.

 

[The Mains Man]

Currently the

Not sure if I'm understanding the heater question, are you intending to run 1 circuit as say, a radial for all the heaters? Probably misunderstood your statement

No, even I know that is a bad idea they are all on separate mcbs, currently distributed across the three phases and I would maintain that. I was considering the merit of splitting the three phases by location as that suggested or whether I run all three phases to both locations to aid balancing and possibly flexibility.

Sorry if my explanation and choice of words isn't clear.

Coming off of the economy tariff and replacing storage heaters with electric radiators will increased their electricity bill, not reduce it.

Why are you selecting a cable size of 16mm when you don’t yet know the load? And why do you want to put a 30mA RCD on this circuit? This sounds like a terrible design to me.

What is a ‘nominal breaker potential’? That total heating load is not the best part of a whole phase because you balance the load across the phases of a three phase supply.

30mA RCD is already there, presumably to protect the distribution circuit. I would use a 100mA RCD, i don't know why it isn't.

This was one of the points I was questioning... See reply to previous question above.

Maximum breaker potential is the kind of nonsense I come up with when trying to explain something I am finding challenging at 11:30pm after a long day. I guess I meant the sum of Ib for heating circuits.

 

[Andy78]

Why would you want to put an rcd of any type on a distribution circuit ?
To work out diversity it would be best to start with total connected loads allowing a sensible amount for socket circuits. Load division across phases also needs balancing as best as possible.
The electric heating plan sounds very costly to run. Have they no gas ?

 

[westward10]

Could be incorrect but that rcd setup says TT to me.

 

[The Mains Man]

Could be incorrect but that rcd setup says TT to me.

I see your thinking, but no. TN, TNCS I believe. The RCD is before the contactor and did turn out to be handy when there was a short before on the contactor connections!

 

[The Mains Man]

Why would you want to put an rcd of any type on a distribution circuit ?
To work out diversity it would be best to start with total connected loads allowing a sensible amount for socket circuits. Load division across phases also needs balancing as best as possible.
The electric heating plan sounds very costly to run. Have they no gas ?

The T&E distribution runs through the walls of the house. I can't see it. So I guess that is why?

Yes, it is costly and no, they don't have gas. Out in the countryside!

 

[Pete999]

Currently the


No, even I know that is a bad idea they are all on separate mcbs, currently distributed across the three phases and I would maintain that. I was considering the merit of splitting the three phases by location as that suggested or whether I run all three phases to both locations to aid balancing and possibly flexibility.

Sorry if my explanation and choice of words isn't clear.

Is it possible to install a poly phase DB, as opposed to three separate SP DBs? the poly phase way allows you to split the loads in a more beneficial way, imo

 

[The Mains Man]

I hadn't thought too much about the current installation as I am essentially starting again but having been asked about the RCD and thought about it, the current 3ph feed from the RCD is off peak only and only powers the heaters which are on mcb. The RCD near the origin provides additional protection to all the heating radial circuits.

 

[UKMeterman]

If they are out in the sticks try selling them a ground source heat pump and thermal store for most of their heat. Ground Source Heat Pumps | GSHPA is the focal point of the ground source heat pump industry | Renewable Heat | Renewable Cooling | GSHP | Ground Source Heat Pump Systems - https://www.gshp.org.uk/ as for the distribution side, I would suggest make provison for 3 phase distributon to any garrage so if need be they can install pumps and so on.

As for the heating, ask can their improve the insulation, improve the controls, and tactfully suggest they need to think like what it was like before central heating, in other words in a big house you made one room tosty warm and the others were cooler.

Other ways also look at all loads that could be run off E7 / E10 The supplier should provide a time clock, or radio switch, both can appear to "drift". To make sure the switching is done at the correct time for loads which are remote, use a 6A MCB on the offpeak board to control remote contactors fed from the 24Hr supply, that way you only need to supply an extra 1.5mm T+E but mark up the contactor enclosure dual supply! or use a 240V to 24V transformer and 24V contactor coils subject to voltage drop.

 

[The Mains Man]

If they are out in the sticks try selling them a ground source heat pump and thermal store for most of their heat. Ground Source Heat Pumps | GSHPA is the focal point of the ground source heat pump industry | Renewable Heat | Renewable Cooling | GSHP | Ground Source Heat Pump Systems - https://www.gshp.org.uk/ as for the distribution side, I would suggest make provison for 3 phase distributon to any garrage so if need be they can install pumps and so on.

As for the heating, ask can their improve the insulation, improve the controls, and tactfully suggest they need to think like what it was like before central heating, in other words in a big house you made one room tosty warm and the others were cooler.

Other ways also look at all loads that could be run off E7 / E10 The supplier should provide a time clock, or radio switch, both can appear to "drift". To make sure the switching is done at the correct time for loads which are remote, use a 6A MCB on the offpeak board to control remote contactors fed from the 24Hr supply, that way you only need to supply an extra 1.5mm T+E but mark up the contactor enclosure dual supply! or use a 240V to 24V transformer and 24V contactor coils subject to voltage drop.

Thanks. Will look into GSHP. Potentially a good idea.

 

[The Mains Man]

Is it possible to install a poly phase DB, as opposed to three separate SP DBs? the poly phase way allows you to split the loads in a more beneficial way, imo

I believe I could do either. I was hoping for help deciding which was the better method. Sounds like you agree that it is worth running 3 phase to both locations for the benefit of the flexibility. When you say a Polyphase board, is that different from a 3phase board? If so, can you give me a link to an example? Thanks.

 

[Pete999]

I believe I could do either. I was hoping for help deciding which was the better method. Sounds like you agree that it is worth running 3 phase to both locations for the benefit of the flexibility. When you say a Polyphase board, is that different from a 3phase board? If so, can you give me a link to an example? Thanks.

Poly phase is a posh way of saying 3 phase, no I dont mean take 3 phase to each location, what I mean is have 1 3phase DB so you can ballance the SP loads more easily at one point of connection, taking 3 phase to different locations will mean running sub mains to each position, sounds like my 1st suggestion is a non starter on this occasion.

 

[Pete999]

I believe I could do either. I was hoping for help deciding which was the better method. Sounds like you agree that it is worth running 3 phase to both locations for the benefit of the flexibility. When you say a Polyphase board, is that different from a 3phase board? If so, can you give me a link to an example? Thanks.

Poly phase is a posh way of saying 3 phase, no I dont mean take 3 phase to each location, what I mean is have 1 3phase DB so you can ballance the SP loads more easily at one point of connection, taking 3 phase to different locations will mean running sub mains to each position, sounds like my 1st suggestion is a non starter on this occasion.

 

[Pete999]

Poly phase is a posh way of saying 3 phase, no I dont mean take 3 phase to each location, what I mean is have 1 3phase DB so you can ballance the SP loads more easily at one point of connection, taking 3 phase to different locations will mean running sub mains to each position, sounds like my 1st suggestion is a non starter on this occasion.

In my opinion the best and easiest way would be to have one central DB, this will allow you to, balance the loads easier, save you money by not having to run sub mains to remote locations, the only difficulty I can foresee is being able to extend the final circuits to the central DB, but without eyes on it's difficult to give any practical advice.

 

[naylorpd]

Yes, that us definitely an option. No 3ph equipment.

Some hobs have the ability to connect to two phases of a 3ph supply. Might be useful to help spread the load as the hob is going to be one of the highest power consumers.

But I'm not based in the UK, different rules and different gear in the shops. My hob is AEG.