16mm tails on 100A cut out

[Kingers]

Hello everyone,

I have recently qualified, though yet to start practising, as an electrician.

I have noticed, at my home, the tails from the (single phase) 100A mains cut out to the 100A rated meter, from the meter, to a 60A isolator and from the isolator to the antiquated fusebox are all 16mm. I have looked up on this forum and elsewhere about 16mm tails on 100A supplies, so I am fairly up to speed on the debate, but ...

• My mains cut out was upgraded in January 2015 (long, long before I ever thought of becoming an electrician) to a Henley Series 8 with a type II 100A fuse.
• I know the DNO’s last point of responsibility is the exit point of the cut out.
• The DNO (in my case Western Power) claims (maybe quite reasonably) not to be obliged to have to conform to IEE (and hence BS7671) regulations

Q1 But, when the cut out was replaced and the tails then reconnected, wasn’t whoever replaced the cut out subject to IEE regulations for the domestic installation at that point?

This is my thinking: BS 7671 110.2 (i) excludes systems for the distribution of electricity to the public from 7671, but would not BS 7671 regulations still apply when reconnecting meter tails as these would be part of the domestic installation even if the cut out fuse was regarded as part of the distribution system? (NB at this point I am not saying necessarily that the 16mm tails would be a violation of BS7671, it’s more an academic question as to whether the person/organisation replacing the cut out is subject to IEE regulations when reconnecting the meter tails.)

• BS 7671 Table 4D1A provides no data on the current carrying capacity of 16mm Single-core 70°C Thermoplastic Insulated, Non-Armoured, Sheathed Cables (i.e. 16mm 6181Y meter tails) for Reference Method F (in free air) both touching and spaced by 1 diameter.
• I do find the odd reference from retailers to the current carrying capacity being 87A, such as this: 6181Y 16.0mm² Tails Brown 50M - Cut to Length - https://www.tlc-direct.co.uk/Products/CA16TBRslash50.html, but that is for Reference Method C, clipped direct.

Q2 Is there any published data anywhere on the actual current carrying capacity of a 16mm meter tail for Reference Method F? Or, is there an accurate and reliable way of calculating this from the data that is published? (All the tails at my home are ‘in free air’.)

• Western Power have a policy document (MI13A/8 to be precise!) which says that all main current carrying conductors should be a minimum of 16mm2 and a fuse of up to 100A will give adequate overload protection for this size of conductor. WPD do not publish this policy document for the public or electricians to see.
• Western Power say their policies are strictly regulated.
• However, on their website they do have a document (Company Directive SD5D/2: https://www.westernpower.co.uk/downloads/3347) which refers to 'Arrangements for LV Cut-Outs'. That, states “The service cable and the tails connected to the cut-out shall be rated at, or above, the cut-out fuse rating, taking account of the installation method.” This is dated February 2013, so almost two years before my cut out was upgraded.
• I have asked Western Power if they have any definitive data on the current carrying capacity of 16mm tails. They did not directly answer that query. All I got was a quote from their unpublished policy document stating 16mm tails conductors were permitted.

Q3 Given that Western Power are unable to provide a reference or source to the cable rating for a 16mm tail installed according to Reference Method F, and the only data that is actually available is for Reference Method C, namely 87A, do you think WPD are complying with their published Company Directive SD5D/2 which requires tails connected to the cut out to be rated at or above the cut out fuse rating?

 

[snowhead]

As you've stated, the tails are not the responsibility of W-P, they're the responsibility of the Energy Supplier along with the meter.
If they weren't happy with the 16mm or whatever size the tails were, then W-P would not reconnect them.

 

[R-fur]

Also the point of the cutout fuse is not to protect the tails, it is to protect the service cable from overload.

 

[davesparks]

Can you be more specific about the 60A isolator fitted at the meter position, that's an unusual piece of equipment. Are you sure it's not a switchfuse or other protective device?

 

[Kingers]

I appreciate WPD were happy with the 16mm tails when the cut out was upgraded and that the tails are now the responsibility of the supplier. However, what I am trying to establish - or at least get you guys' opinions on - is whether they should have upgraded them, or at the point of reconnecting been subject to 7671.

You see, at some point, whether it was when the cut out was upgraded to a 100A fuse or the meter was replaced (not to a smart meter) - both were done around the same time but not at the same time - someone installed a 60A isolator between the meter and fusebox. That effectively protects the tails from overload but doesn't necessarily mean the installation of the cut out (or the meter for that matter) was 7671 compliant.

It's not just a pedantic squabble. I need to replace the decades old fusebox. To do that i need to move the 60A isolator. Some of the tails are going to have to be replaced and the main cut out pulled in order for me to be able to do the work. Of course the DNO will want to charge but perhaps not if they have to replace the tails anyway.

 

[Lister1987]

Re; 16mm2 6181Y you should be able to obtain data sheets from producers (Doncaster, Eland and the like), the cables will be to BS6004 (iirc) and not BS7671. I can't find any enabling legislation re:BS6004

Cutout positions and equipment don't fall in the SCOPE of BS7671 (consumer tails being the exception), ESQCR is likely the be overriding legislation that will dictate what DNOs have to use as a minimum, but I could be wrong

 

[Kingers]

Can you be more specific about the 60A isolator fitted at the meter position, that's an unusual piece of equipment. Are you sure it's not a switchfuse or other protective device?

Please see attached photos. As mentioned in another reply, I have to move this isolator thingy (or whatever it turns out to be) in order to upgrade the fusebox to an 18th Edition CU.
[automerge]1587489119[/automerge]

Re; 16mm2 6181Y you should be able to obtain data sheets from producers (Doncaster, Eland and the like), the cables will be to BS6004 (iirc) and not BS7671. I can't find any enabling legislation re:BS6004

Cutout positions and equipment don't fall in the SCOPE of BS7671 (consumer tails being the exception), ESQCR is likely the be overriding legislation that will dictate what DNOs have to use as a minimum, but I could be wrong

I found various producers' data sheets online and they all seem just to reproduce Table 4D1A. I would love to lay my hands on a copy of BS6004 but it's rather expensive!

My understanding of the scope of 7671 is that it starts at the point of exit from the cut out. At least, the DNO stated their responsibility ends at that point. Yes, the IEE regulations aren't themselves legislation but - again my understanding - they are used to interpret the legislation i.e. to determine what is 'safe' etc.
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Sorry, I'm still getting used to how this works. I replied to your comment above but didn't quote the original.

 

[davesparks]

someone installed a 60A isolator between the meter and fusebox. That effectively protects the tails from overload but doesn't necessarily mean the installation of the cut out (or the meter for that matter) was 7671 compliant.

An isolator does not protect anything from overload, you need an overload protective device for that.

If however it is not an isolator and does incorporate an OCPD then the tails are protected at 60A and so they could probably safely be 10mm.

 

[Kingers]

Thank you for correcting me. It is indeed NOT an isolator but a 60A circuit breaker. I was being sloppy with my terminology and really should know better. I think of it as an isolator because I need an isolator (minimum) to be able to replace the fusebox (except, in this case I have to move it as there isn't enough space).

 

[R-fur]

A 60A MCCB is unlikely to be owned by the DNO or energy supplier. I would think that you own the MCCB and the point of supply is the outgoing meter terminals. 16mm tails on a 100A fuse is fairly common in many parts of the UK, I wouldn't worry about it.

 

[davesparks]

Thank you for correcting me. It is indeed NOT an isolator but a 60A circuit breaker. I was being sloppy with my terminology and really should know better. I think of it as an isolator because I need an isolator (minimum) to be able to replace the fusebox (except, in this case I have to move it as there isn't enough space).

That is unusual to have a circuit breaker there, but not impossible.
So the 16mm tails are perfectly fine as everything is limited to 60A.

Do you have a picture of this circuit breaker?
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Please see attached photos. As mentioned in another reply, I have to move this isolator thingy (or whatever it turns out to be) in order to upgrade the fusebox to an 18th Edition CU.
[automerge]1587489119[/automerge]


I found various producers' data sheets online and they all seem just to reproduce Table 4D1A. I would love to lay my hands on a copy of BS6004 but it's rather expensive!

My understanding of the scope of 7671 is that it starts at the point of exit from the cut out. At least, the DNO stated their responsibility ends at that point. Yes, the IEE regulations aren't themselves legislation but - again my understanding - they are used to interpret the legislation i.e. to determine what is 'safe' etc.
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Sorry, I'm still getting used to how this works. I replied to your comment above but didn't quote the original.

Ive only just seen this post, now it's clear from the pictures that this is not an isolator or a circuit breaker.
As is clearly written on the front of it that is a voltage operated earth leakage circuit breaker (VOELCB)

So obviously this is, or must have originally been a TT supply.

Don't bother moving it, just chuck it in the bin.

 

[7029 dave]

That is VOELCB

 

[R-fur]

As above, bin it. And that is not an ancient consumer unit, I installed dozens of them.

 

[ferg]

As above, bin it. And that is not an ancient consumer unit, I installed dozens of them.

That only makes you more ancient than the consumer unit.

 

[Timbo]

Just to give an idea of age of installation, I think VOELCB's were deleted from the 15th Edition around 1985.

 

[Simon47]

Ive only just seen this post, now it's clear from the pictures that this is not an isolator or a circuit breaker.
As is clearly written on the front of it that is a voltage operated earth leakage circuit breaker (VOELCB)

As a point of pedantry ...
As the VOELCB is only rated at 60A, wasn't it a bit naughty of the DNO to fit a 100A fuse ?

 

[davesparks]

As a point of pedantry ...
As the VOELCB is only rated at 60A, wasn't it a bit naughty of the DNO to fit a 100A fuse ?

No, as far as I know there is no requirement for the DNO to make their equipment suit the customers installation. They provide a standard size and type of supply and it is up to the customer to ensure that their installation is suitable.

 

[pc1966]

I think you will find it cheaper to replace the tails than buy a copy of BS6004!

Have you got a photo of the other side (DNO / meter / etc)? Having an isolator fitted is a good idea as it makes future work much easier.

Yes, that type of breaker is ancient and you really could do with a new incomer RCD (and a new board with RCBO or whatever) but don't bin it, there will be folk on here willing to pay postage to get an example I'm sure!