Hi all, I will be doing a kitchen rewire in a domestic house which i want to use for my Napit inspection. Existing consumer unit has not enough spare ways for the new circuits to be installed for the new kitchen and its a bit untidy. So i will be adding an additional 10 way consumer unit with 25mm tails to a Henley block and installing earth bonding to the gas and water pipes as there is not any at the moment. The existing consumer unit is fed by 16mm tails and the house hold fuse is a 60 Amp TN-S supply. The property's a standard 3 bedroom house with a loft conversion. The new kitchen has an electric hob, oven, fridge freezer and dishwasher and some led down lights and around 5 socket outlets. I've calculated the max diversity for the circuits i will be installing to be around 63 amps which is highly unlikely that it will ever reach that level. My only concern is that will the inspector get funny over adding an additional consumer unit to a 60 amp incoming fuse on time of inspection? As the client needs to work to been done asap and I have told him he may need to contact the DNO about a possible fuse change, but the only thing i can see that draws a lot of current is an electric shower which is connected the existing distribution board.
Suggestions will be appreciated many thanks Anthony
Hi Anthony - inspections are always fun aren't they. If you have reasons for the design Inspector should be ok.
Some thoughts ...
- existing fuse has never blown, no sign of heat damage to fuse holder and perhaps you don't really know what size the fuse is?
- new kitchen does not add new load, are just changing how the load is delivered with the new board.
- re examining the diversity calcs for new circuits as it may be less (?)
Thanks for reply Wilko much appreciated! Na theirs no signs of over heating to fuse holder, haha true, but my Xray vision is telling me its 100% a 60 amp . Yea calculated diversity from the onsite guide and the new appliances he has but yea like you said its probably much lower only real addition would be that he is now having a electric hob and oven where before it was just an oven and a few more appliances extra dishwasher + fridge freezer. Also on the certificate is it classed as an addition to an existing installation even with the new consumer unit and new circuits? And supply protective device on the certificate do i just state not verified or put down 60 Amp ?
Thanks mate
Mhar in case the fuse does get upgraded to 100amp fuse in the future its called covering myself.. Telectrix i know but try to tell the client that a full periodic inspection needs to be taken place on the existing circuits and rectification of any faults if found i'll think you find many wont want to pay out, so an additional board for only my work makes sense. Geordie well i could of installed a 6 way but one rcd ? or would you pay for 6 rcbo's on a tight budget, so a 10 way duel rcd consumer unit makes sense Regards Ant
Why all the appliances on there own circuit ?
Rcbos can be had for around £10 each
You can get 6 way split boards.
Does the current board have an rcd installed ?
Given that most 3 bed houses have less than 10 circuits this seems a bit much.
For what its worth I doubt VERY much that many houses EVER get any where near 40A load let alone enough to take out a suppliers 60A fuse.
Maybe you should reconsider your design as your Napit Inspector will be grilling you about what you did and why....
Just saying
PS: The diversity calculations in the OSG were probably thought up when fused boards had no more than 4 circuits..... so using the "rules" is simply not realistic in the 21st Century.
About 15 years ago had a colleague who was an electrical consultant and he said for a new housing estate they would allow 4-6A per dwelling. Don't know if this would still be the case.
Yea westward i think they still use the same system. Cheers Murdoch i think ill just amp clamp the line meter tail to my consumer unit and see what ampage the kitchen pulls with appliances on. Do you reckon the inspector will get funny about the two consumer units? I've labelled both consumer units with Warning Multiple Supplys ect.. all tested and is fine i know there is plenty of spare ways on the c/u..
Cheers Ant
Yea was thinking that westward but there was a existing Henley block that was direct under the meter and the tails to the meter are really short. So cant really alter them as that is part of the DNO's side
I seem to remember that the issue for a singular isolator in a domestic property has been raised before here, and that the recommendation given in Guidance note 2, says something like;
'It is permitted for a dwelling to have more than one electrical installation. Therefore one 'main switch' is not required to isolate all consumer units simultaneously provided the consumer units have an integral main switch'. (from quick google)
This would not be the case perhaps, if the CU's were in different locations within the property.
Perhaps someone could have a quick look in GN2, page 40ish I believe, I haven't got a copy
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