2 phases into a domestic dwelling

[blastcleaner]

To run 2 single phases into a domestic property, do I need 2 seperate switch fuses off the main bus bar, or can I use 2 phases out of an unused 3 phase 63amp switch fuse that is already there?

I am a learner, so cut me a little slack guys if this is a silly question.

Using two legs of a 3 phase switch fuse does not sound quite right but on the other hand seems like a good idea, it would ensure isolation of all supply during maintenance, no chance of confusion (but of course one would always use a proving unit) Doing a bit of planning to upgrade the power supply to my bungalow that sort of keeps growing.

The proposed underfloor electric heating is going to throw the loading calculation all to hell if lots of things come on together and the existing 60's overhead private wiring will glow !!!

The farm has a 200 amp 3 phase PME supply. I want to run 2 phases into the dwelling underground from the distribution board. Its all a bit cluttered on the incomer board, so I am trying to plan and use what is there if possible.

Thanks.

 

[Robojin]

Are you sure about this, 3 phase might be considered in a very large dwelling e.g Beckingham Palace, but a bungalow?, if you detail the likely loads we can give you further advice

Also remember that you apply diversity to any final design load calc, if you think about it, it's not unusual for CB's in a CU to add up to over 100A

 

[Andy™]

ideally they should all be on one interlinked switch. you can use a 3 phase switch and ignore phase 3 terminals

 

[kme]

Being domestic, it may be more beneficial to use a "summation" supply - two heads; both from the same phase - load being shared across the supply fuses. However, As stated above, max dem. may not require such a large supply.

 

[blastcleaner]

Thank you for the replies gentlemen. Beckingham palace, yer I wish!

I have done a spread sheet and made it into a JPG but cant see how to attach it here without starting a new thread, need practice with the forum tools. The total load is 57,000 watts approx if you put everything on that is hard wired, and assumes nothing plugged into the 43 socket outlets on the various ring mains. I am going to try and do the diversity calculation, but the underfloor elec heating allows no diversity and that the real killer.

"Summation supply-two heads", not entirely clear what that is, but also not sure it would work if my load calculation is even close to right, I cant see 1 phase doing the job even if I split the load across the 2 x 17 way consumer units, the heating load has a potential for 50 odd amps, add the oven and hobb on the other consumer unit, it would surely cause a big phase inbalance, it will be bad enough over two phases.

Thanks again for the input, I will see how it calculates out and report back for more guideance.

 

[Apache]

I have done a spread sheet and made it into a JPG but cant see how to attach it here without starting a new thread, need practice with the forum tools.

You need to either save the file to somewhere like www.photobucket.com (free account) and then link from there or check the size of the jpg, if it's less than 97.7kb you can attach it using the paperclip icon next to the smilie face.

You have more options clicking the reply button at the left hand side after the last post than the quick reply box.

http://www.talk.electricianforum.co.uk/showthread.php?t=2752

 

[blastcleaner]

Thanks Apache , and admin, upload achieved.... I think

Load calculation sheet, roughly, with 50M run for the supply to the dwelling from the main incomer board.

 

[batty]

Blastcleaner

If you have 3 phase supply I would take that into the house and spread load across phases. Problem you may have is pme. Unusual to get pme on farm installs. Boards don't usually like to give it are you sure its not tns. I think you would have to tt house to make it safe it it is pme. Are you going to be doing this work yourself if you are a learner as you say I would think is a bit out of your depth

Batty

 

[Robojin]

Thanks Apache , and admin, upload achieved.... I thinkLoad calculation sheet, roughly, with 50M run for the supply to the dwelling from the main incomer board.

Realistically all this is not going to be on at once, 57kW = 247A load, aside that you may likely only have 16kW at the supply (if memory serves me right)

You need to work with the OSG on diversity calcs, you may have 45x13amp but likely loads will be highest in Kitchen, Utility, followed by lounge, all the rest beds etc would be low usage, so you may end up with only 5-6 devices with 3A+ load and again would these be on at once?

BTW when calculating lamps you would use 100W with a 10 pendant per circuit rule, max demand 4.3A, with diversity of 66% you get 3A, having said that 1 in 4 lamps must now be Energy Saving, so further reducing the load

As Batty mentioned this might be a big project for a learner so might be worth working with an experienced sparky and learning from it

 

[blastcleaner]

Hi Robojin,

Thanks for the message.

Yes, I realise the 43 socket outlets come into the diversity calc but dont necessarily add greatly, but had to set it all out on paper somehow to get an outline. Will use OSG to do calculation. Thanks for reminding me of the low energy bulbs.

It is the underfloor heating loads that are really causing the problem, with, quite rightly, no diversity, and likely to be on demand when the cooker etc are also on demand.

Batty raised some thought provoking questions and I am certainly going to need help on this and bigger issues it raises on the distribution around the site.

Thanks again for your input.

 

[kme]

To clarify:

A summation supply uses two service heads and main fuses, from THE SAME phase.

Therefore, you only have single phase, but twice the load allowance.

I haven`t looked at your jpg yet ( too late, too much Guinness ), but 57KW is a VERY large load, even for 3phase.

I`m with the guys here mate. Get someone in. No offence, but this is a biggie to get wrong

 

[SPECIAL LOCATION]

To clarify:A summation supply uses two service heads and main fuses, from THE SAME phase.

Therefore, you only have single phase, but twice the load allowance.

I haven`t looked at your jpg yet ( too late, too much Guinness ), but 57KW is a VERY large load, even for 3phase.

I`m with the guys here mate. Get someone in. No offence, but this is a biggie to get wrong

And would prevent problems of simultaneously accessible live parts across two phases!

 

[blastcleaner]

Thanks for all the contributions, many minds collectively come up with solutions.

Still have not done the diversity calc on my load figure because Batty came up with some much more serious issues in his post.

Been reading up on stuff, and if I am right that this is a PME installation to the main board, and Batty is right that the dwelling should be TT'd for safety reasons, and that makes sense to me from what I have read, it is not the case at the moment because there is an overhead private wiring with neutral and earth to the dwelling and has been for the 25 years I have lived here.

But reading on that there are special installation requirements for the use of a PME supply, and Batty tells me they dont like it for farm type buildings, gives me greater cause for concern. I have steel containers with supplies to them for a start.

Of all the electricians that have done work here over the years, none has identified these issues and merrily whacked in stuff. Question is - do they know any better?

A kitchen installer who came to do the wiring up on my kitchen did not even know of the on site guide when I questioned something he had done, and another bigger company of serious electricians did not know socket outlets in kitchens are a special case and can be outside the normal height conditions.

So how do I find a competent electrician who is going to know this stuff, there is no substitute for 20 years experience and as a learner I am having to learn fast but this is serious stuff as you have pointed out, and out of my league.

Anyone know a time served sparks in the Guildford area who could sort this out? Or how do I vet someone from an advert, is there a particular qualification relating to heavy installation.

Thanks again for all the input, it has been really important to identify these issues, although the downside may be the cost of sorting it out.

 

[batty]

Blastcleaner.

I would TT installation to be on safe side. With the 17th they like you to RCD everything. I am not saying you cannot export the earth but for the cost of an earth rod etc I would do it.

Batty

 

[kme]

As far as finding someone suitable....

Firstly, there is this forum. You can look in the directory of sparx, and see who is in your area. If that fails, and you have to "ring round", (and I`m going to duck after this one), Go for an approved contractor (not domestic installer), with one of the larger governing bodies ( ECA, NIC).

Or ask them some of these questions, posing as a diy bob, and see what they say...........

HTH

KME

 

[Andy™]

(and I`m going to duck after this one), Go for an approved contractor (not domestic installer), with one of the larger governing bodies ( ECA, NIC).

not everyone is registered with a larger governing body.

If it wasnt for part p, i probably wouldnt be registered with anyone

 

[Evans Electric]

not everyone is registered with a larger governing body.If it wasnt for part p, i probably wouldnt be registered with anyone

Neither would I Andy !!

Deke

 

[batty]

Blastcleaners best bet would be to get someone who is recommended. You don't have to be NICEIC approved to be a top class electrician. I am with British Standards and registered to do commercial work. This may not get me certain work but most of my work comes from recommendation anyway.

Batty

 

[kme]

See. I knew I`d have to duck.....

I`m NOT decrying anyone who isn`t with one of the aforementioned; just pointing out generalities. I meant no offence to my esteemed colleagues, who are, in all likelihood, as competent or more than myself.

KME. (can I have a "group hug" smiley????)