Overload Protection - Major Renovation

omega750 · Apr 1, 2017

Hi All,

First post on this forum, but I've been reading the great questions and answers for years, so I hope someone can help me out?

I've renovated a few houses in my time and done some of the basic wiring myself, but my latest 1940's house is a real project and needs a professional's attention. Unfortunately my usual electrician of choice is in hospital (no he didn't electrocute himself) so I have had to find another.

Overview
Old house, very poor 1940's wiring all needs replacing! From what I can tell there seem to be effectively 3 sub mains currently installed, all connected directly to DNO supply via a set of Henley Blocks.

Main CU (old fuse based unit)
Summer House 10mm2 SWA to 60A MCB CU
Garage 10mm2 SWA to 80A MCB CU

Electricians Proposal
The electrician has pointed out that there is no overload protection on the circuit in the summer house and garage which are more than 3m away from the DNO supply and connected via Henley Block. He has proposed the following setup, again all connected to DNO supply via existing (probably replaced) Henley Blocks.

Replace existing main fuse based CU with 100A MCB CU
Install 1x Wylex 60A SF connect to 10mm2 SWA for Summer House, retain existing 60A MCB CU installed in Summer House
Install 1x Wylex 80A SF connect to 10mm2 SWA for Garage, retain existing 80A MCB CU installed in Garage

Question:
Please bear in mind we are way past my level of expertise, but I am not sure how this is providing overload protection for the DNO supply as there is still only one set of tails to the meter and the DNO fuse behind that, presumably rated at 100A.

Whilst I see it protects the individual sub mains, what is preventing overload of the DNO supply other than its 100A fuse, given we have potential 100A + 80A + 60A draw via the Henley Blocks?

I was wondering if someone could just sanity check this proposal for me, hopefully it will just be a case of me not understanding overload protection otherwise I might need to consider finding myself another electrician?

Many thanks in advance.
Jason

EDIT: Garage has a car lift and some other machinery hence 80A CU

HandySparks · Apr 2, 2017

westward10 said:
Any idea what current these cables would have to draw to reach 70 degrees

I usually use the tables for 70 deg PVC SWA when sizing 90 deg XLPE SWA.

davesparks · Apr 2, 2017

westward10 said:
Any idea what current these cables would have to draw to reach 70 degrees

The best estimate we have are the tables for 70degree cable, there may be a very slight difference, but not enough to cause any practical difference

omega750 · Apr 2, 2017

UPDATE

BIG THANK YOU to everyone who gave me the benefit of their time and experience to answer my question, most appreciated!

After a few beers last night, I actually re-read the quote (RTFM), and realised the sparks did actually recommend the replacement of both 60A and 80A CU's in Summer House and Garage at the bottom of the quote.

Not sure of the regs regarding the requirements for him to carry out such remedial work on the parts of the installations he is not touching, but based on all your feedback I think I will have him do that as well!

@Midwest
Just so there is no confusion for you...

Thanks to all the time and helpful advice given by others on this forum, it would seem the sparks really knows what he's doing and will definitely be getting the job!

I will pull all the cable runs and make first and second fixes for lighting and power along with installing structured cabling switches and servers for the network and telephony (one of many IT jobs I have done and something I have provided free help and advice to many of my mates on doing it in their own homes), Sparks will do all the other stuff, test and sign off.

To help, to share, to advise and to learn is how we grow and become better human beings!

Andy78 · Apr 2, 2017

omega750 said:
Thanks to all the time and helpful advice given by others on this forum, it would seem the sparks really knows what he's doing and will definitely be getting the job!

I will pull all the cable runs and make first and second fixes for lighting and power along with installing structured cabling switches and servers for the network and telephony (one of many IT jobs I have done and something I have provided free help and advice to many of my mates on doing it in their own homes), Sparks will do all the other stuff, test and sign off.

Doesn't sound like he is getting a job at all.

Your electrician has okayed this ? You doing all the work and them signing the certification ? Who is doing all the design work ?

Midwest · Apr 2, 2017

@ omega750

I'm assuming this installation is being carried out in England & Wales, in a domestic property, and therefore possibly subject to the Part P building regulations?

As the property is being rewired, a new Consumer Unit being installed and work carried out in special locations, then it will be subject to notification to local building control.

It appears, you are carrying out some of the electrical installation work yourself, and intend to use a registered 'Third Party Certifier' (TPC) as one of the methods of notification as prescribed in Part P?

A TPC has to be enrolled into one of the government approved schemes, currently only operated by two of these schemes. The TPC would have to be involved in the inspection & testing of the installation (as it progresses), that he/she would be certifying & notifying to LBC.

The government approved schemes were set up and envisaged to prevent incorrect and unsafe installation of electrical work in domestic properties, aka DIY'ers etc.

I have no idea of your competence, you say you are an electrician in your profile, but then you say you are an IT geek in one of your posts?

There are many electricians on this forum, who believe Part P registration and schemes are not fit for purpose.

This week, I went to a property to replace a bathroom extractor fan. My client had had a consumer unit replaced, by a friend who was an alarm engineer. There was no certificate, and aspects were non compliant with BS7671. My work to replace the fan, was extended to put right the poor workmanship in the bathroom wiring, which they had only recently been refurbished.

I note that you have given free help and advice to mates, who have renovated their own homes. Whilst this is admirable, I hope this doesn't extend to electrical installation advice; this is not quite what Part P had in mind. I also note that you have renovated other house, doing some of the basic wiring yourself. Presumably other people now own and live in these houses?

Please tell me you are a qualified competent electrician, who has the skills, knowledge and suitable tools to carry out this work.

If you are trying to sooth me with your last sentence, you will only do so if you are a competent qualified electrician, or this project is carried out by one.