Sub Fuse Box Wiring to BS7671

[o.karel]

Hello all
Can anyone please let me know, if BS7671 clearly specifies the wiring requirements for sub fuse boxes?

A builder's electrician upgraded an existing fuse box of a house and from the same single main supply also installed another (sub) fuse box for upstairs, to the notionally separate flat for her daughter. He issued a completion certificate about 6 months ago.

However, another electrician stated SWA cable had to be installed for the sub fuse box wiring to meet the BS.

A third electrician said it is not needed to meet the BS as one of the experts sitting on the BS board confirmed in a Webinar a week ago - we could not find the link to the webinar.

About 2,5m length of cable is buried in the wood floor and wood stud partition (inaccessible without cutting floor and wall linings). The first 2,5m or so length of the double insulated cable is in the under-stair storage and easier to access. No part of the wiring is underground.

So, if 5m or so double insulated cable is not acceptable, is it possible to use SWA cable for the first 2.5m to an isolator and keep the last 2.5m as installed - I have heard there is a mention of 3m max distance acceptable in the BS?

Of course the safety is first but we also wish to avoid works, cutting, chasing, on the statement of one electrician, if it is based on an over cautious interpretation of BS7671 and not strickly essential or necessary.

Any other explanation or solution avoiding the replacement of cable needing chasing, cutting in etc. will be most welcomed.

 

[Murdoch]

So, if said cable is deeper than 50mm in a wall the need for SWA isn’t mandatory - that said there is no way to prove the depth.

how thick is the stud wall ?

what certificates were you given for the work ?

 

[Fleeting]

Does this second supply have circuit protection, e.g. a fuse or mcb.
Show a pic where it is connected from.

 

[o.karel]

Thank you for your response, most appreciated, even it does not look like good news.

The studs are 100mm (including lath and plaster 130mm) therefore min 50mm distance reqirement doesn not appear technically possible.

The certificate given is

Electrical Installation Condition Report
Requirements for Electrical Installations - BS
7671:2018
(IET Wiring Regulations 18th Edition)

 

[Fleeting]

You should have got an Electrical Installation Certificate what they have supplied is incorrect. Unless you are in Scotland it also needs notification to Building Control under Part P of the Building Regulations.

 

[o.karel]

Does this second supply have circuit protection, e.g. a fuse or mcb.
Show a pic where it is connected from.

Thank you. It is not my property but I was sent the attached photos of the ground floor (main) fusebox. I was told the sub fuse box is identical.

 

[o.karel]

You should have got an Electrical Installation Certificate what they have supplied is incorrect. Unless you are in Scotland it also needs notification to Building Control under Part P of the Building Regulations.

Thanks, getting more worrying. I will enquire further.

 

[Fleeting]

Does one of those circuit breakers turn the upstairs board off.

 

[Andy™]

submain or not is irrelevant, its dependant on where the cable is installed. it may need to be an SWA, it may not. not enough info here

 

[o.karel]

Thanks, getting more worrying. I will enquire further.

PS Unlikely to be agreeable but is a stainless steel sheet cover is acceptable as alternative to SWA cable?

 

[o.karel]

Does one of those circuit breakers turn the upstairs board off.

Sorry I do not have the answer to this question. I will try to find out but it will take time. If it is, would it eliminate the need for a replacement SWA Cable? Can circuit breaker be added if not there already?

 

[Murdoch]

Can you post a picture of the second fuseboard / consumer unit ?

 

[o.karel]

submain or not is irrelevant, its dependant on where the cable is installed. it may need to be an SWA, it may not. not enough info here

Thank you, I do appreciate I do not have full information. Sorry.

 

[o.karel]

Can you post a picture of the second fuseboard / consumer unit ?

please see the attached

 

[Fleeting]

please see the attached

That's the same as the other pic which one is this.

 

[o.karel]

That's the same as the other pic which one is this.

Sorry for the late confirmation. The one below id the ground floor and the previous photos are the first floor. They are identical boxes.

 

[Fleeting]

Where is the upstairs board connected from.

 

[Luckyboy]

So the upstairs consumer unit is not fed from the downstairs consumer unit.
The meter tails going to the upstairs consumer unit should either be redone with SWA, or a switched fuse installed at the origin, such as:
Fused Switch

 

[Murdoch]

So the upstairs consumer unit is not fed from the downstairs consumer unit.
The meter tails going to the upstairs consumer unit should either be redone with SWA, or a switched fuse installed at the origin, such as:
Fused Switch

there isn’t enough information on this thread to conclude this

 

[o.karel]

So the upstairs consumer unit is not fed from the downstairs consumer unit.
The meter tails going to the upstairs consumer unit should either be redone with SWA, or a switched fuse installed at the origin, such as:
Fused Switch

Thank you,

I was told the upstairs box is supplied from the ground floor box. There is no new main supply, just one existing going into the ground floor box. But I will double check. However, if Fused Switch will eliminate the need for rewiring with SWA cable , it sounds promising. Just one clarification please: when you say "a switched fuse installed at the origin" do you mean the start of the cable feeding to upper floor box?