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Hi people.

My first post on this forum - many thanks in advance for the commitment to it, hopefully I may be able to contribute as well. For anyone who is interested, I was an Electrical Maintenance Engineer for 10 years at BAE Systems, doing anything and everything - then i chose a completely different career path, but I still try to remain as current and active in Electrical installations as feasibly possible.

I have just bought a 3 story house that is converted into 5 self-contained flats. Re-wired within the last decade as a guess, however, whoever did it forgot about the 100A Single phase cut out being upgraded. The set up isn't ideal to say the least - in Brief - A CU with 5x 45A type B breakers, 10mm T&E to each flat, local CU's and landlord meters, then all the other junk (landlord supply’s, fire alarms etc etc are fed from the remaining available ways). Some flats have Gas, allowing smaller supplies than 45A. Over time I want all electric, economy 7 heating, check meters in the basements, SWA to each flat and everything else you would expect. My initial design considerations lead me to wanting a 60A supply in each flat after all diversity considerations.

The DNO - I have no experience dealing with these chaps so I have some questions I would appreciate help for.

1. What supply do I ask for - (60A x 5 = 300A, x 230v = 69kva x 75% for diversity = 52kva?) would this be acceptable or am I way off? how do THEY calculate maximum demand based on what you tell them?

2. I don’t want to cut my own arm short asking for a supply that will end up limiting me - however the price seems to increase considerably over 60kva?

3. I have attached an image "plan" of the site - I have a few questions regarding the plan. my property is highlighted in RED (No 556). Adjacent Properties No.558 and No.2 have recently had supplies upgraded to suit what I require. However the DNO isnt able to tell me what they have been given (why they can’t do this I don’t know). BUT, on the drawing i can see they have installed a "1x150" and a "1x117" electrical ducts to encase the new supply cable which is "3C 95 SAC XC TP" Cable. I assume "3-core 95mm2 Solid Aluminum Conductor" - I don’t know what "XC TP" is referring to - maybe Capacitive reactance or twisted pairs - but this makes no sense to me?? you can also see the OLD supplies "3C 25 SAC PSC OOC" - which I currently have supplying the flats.

4. What does "3C 95 SAC XC TP" equate too and what supply is this likely to be giving?

5. I assume the most the DNO will give me on my 3c 25 SAC will be a 100A cut out?

6. Ultimately - I think I am expecting to be asking for a 3 phase supply (100a x 400v x root3 / 1000 = 69kva) - but this still gives me issues balancing the phases if no further diversity is allowed - so then it would be a 120a (83kva) - and this sounds ridiculous!

Many thanks for your help in advance

Kind regards
Distribution plan.jpg
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Sorry made a mistake - carry on

Messed formulas up
Last edited by a moderator:


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Nicholas, I don't think you've really understood any of the OP's question.
I'm not going to jump in with a reply without giving it some thought. Others here will be much more experienced with this type of question.
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Hi tomomac,

Apologies for some other users treating you like an idiot.
The dno will be awkward to deal with, they have no competetition so have no 'need' for your business,
I can't answer all of your points but I can help you with a couple!

1- You are going the right way with your diversity, however as a side note all E7 heating must be enquired about with DNO and they usually use a 100% figure of any heating load.
4- That is the cable size, basically 3 core 95mm2 concentric cable.
5- Yes that is 25mm single concentric, you may even find its an 80A fuse, certain DNO's always supply an 80A unless 100a is specifically asked for.
6- Unfortunately you may to have to bite the bullet on this, the DNO may be helpful and may let you have unbalanced phases in your installation depending on what they have elsewhere on the network.

I think it may be better to get the DNO to run 60A supplies to each individual flat with a ryfield unit downstairs, that way they can provide timeclocks etc. to each flat as if you are having off-peak. Then the supplies/metering are are no longfer your problem,
As if you have off-peak it gets complicated with timeclocks for each flat etc. possibly 2x SWA's etc to each flat (o/p and day rate)

Hope this helps!
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Responses in red

What I am trying to work out is if the flats got rewired only about 10 years back why change it now! Dont fix something that is not broken!
You have made a few vital mistakes so I am not sure if you know what your doing, also flats are notifiable so you will have to inform LABC or get an electrician in to do it - again from the mistakes you have made get a pro in from stage 1!

Your also looking into the whole thing to much that is not your problem!

If the install has been there for about 10 years then there is probably nothing wrong with it!

Nicolas, for once this is someone who DOES know what they are doing, and judging by your responses, I don't think you do, How is 5x 60A 60A?
The OP has carefully considered these plans, provided good relevant information, and just wants advice before approaching the big nasty DNO!

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