16mm SWA tails maybe 9 mtrs from isolator on a 100a supply, and other concerns - EICR opinions

[S P]

This has come up many times before and after a couple of hours reading previous posts I'm no closer to deciding on a code, note or nothing at all.

BS7671 allows 16mm tails on 100A fuse if demand is less than the cables CCC, I have 16mm at 94amps and the max demand is 60a.

From a previous post I've read UKPN state switched fuse OR ISOLATOR within 3mtrs.

Would you code, mention or no mention this?

 

[Dillb]

You are assesong the job as per BS7671, nithing else so UKPN has no bearing on it. What you have to ask yourself is will the maximum demand ever chamge in the future seeing as the incoming fuses will allow it.

 

[Wes1000]

Surely if the cable after de rating is at 94A and your max demand is 60A an 80A fuse would be more appropriate?

 

[Dillb]

Surely if the cable after de rating is at 94A and your max demand is 60A an 80A fuse would be more appropriate?

Yeah but we cant change that init, beside thats not the question.

 

[S P]

Thanks Guys,

I agree Dillb, and it is feasible as separate 6mm cable has been run for hob and oven, new home owners may decide to install induction hob and higher rating oven.

It is a gas hob atm and 13amp SFS for oven.
Oven at higher rating is probably unlikely as most modern ones are 16A max.

Either way it didn't sit right with me as I would have installed switched fuse at 80A. Still unsure on code though?

 

[Dillb]

Well its your call as the one signing the EICR. From what you have said as its just my opinion I would give it a C2 as you never what they may do in the future.

 

[S P]

Im going to try to attach photos..
Other areas of concern are:

1) Un-enclosed SWA conductors - I guess it could be argued the meter cabinet is an enclosure opened by key. so maybe C3 not C2?

2) Main earth uses gas supply = C2
From suppliers terminal they have 10mm to first earth terminal, the 2x 10mm goes to water bond, the 2x 2.5mm go to SWA amour. Nothing connects to the other earth terminal! Which holds the 2x 16mm from the SWA and 2x 10mm Gas bonds. Therefore other than the gas the earth path is the 2x2.5mm to the amour.

 

[S P]

 

[westward10]

What provides fault protection for the cable.

 

[S P]

Just the cut out as is

 

[westward10]

So you have a possible 9m cable run with the service head fuse providing overcurrent and fault protection?

 

[johnduffell]

new home owners may decide to install induction hob and higher rating oven.

I'm not a sparky but surely the person installing the hob would have to assess the demand, assuming they are competent to do so. You would probably do well to make the installation owner aware of the limit though.

 

[johnduffell]

You are assesong the job as per BS7671, nithing else so UKPN has no bearing on it.

I was under the impression for BS7671 you have to have fault protection for all cables, and overcurrent where necessary.
Overcurrent has been dealt with through assessement of max demand for the installation.
The fault protection for the tails is only by permission with UKPN, so if UKPN has no bearing, surely that means it would be unsatisfactory by default due to no valid fault protection? If they only allow 3m if they are happy for their fault protection to be used, then that's that?

 

[S P]

So you have a possible 9m cable run with the service head fuse providing overcurrent and fault protection?

Correct - or not so!

I'd have installed metal switched fuses at 80A to enclose SWA conductors and offer protection.

How would you code?

 

[S P]

I was under the impression for BS7671 you have to have fault protection for all cables, and overcurrent where necessary.
Overcurrent has been dealt with through assessement of max demand for the installation.
The fault protection for the tails is only by permission with UKPN, so if UKPN has no bearing, surely that means it would be unsatisfactory by default due to no valid fault protection? If they only allow 3m if they are happy for their fault protection to be used, then that's that?

I thought the same until I read through a load of posts.

IET Forums - EICR - https://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=70233

"
Not BS7671 as such, but in the paperwork from a well know DNO..
If you want connection, you need ot do what they ask for.

4.6 Meter Tails
Standard 25mm2 copper double-insulated conductors (meter tails) from the meter to the cut-out shall be provided and installed by the appointed meter operator.
Standard 25mm2 copper double-insulated conductors shall be provided and installed by the customer from the consumer unit for connection by the meter operator into the outgoing (load side) of the meter.
BS 7671 Regulation 433.2.2 requires a maximum three metres distance between overload protection devices and their source, therefore the customer shall provide and install an intermediate switch fuse or isolating switch if the distance between the meter and consumer unit is greater than three metres.
The customer should seek professional electrical advice to determine the protection equipment that is appropriate for the customer given the impedance at the cut-out and the design of their installation as UK Power Networks is unable to advise on these aspects.
Meter tails shall not be installed or run inside the cavity wall of a building other than passing directly through the wall.
Tri-rated cables shall not be terminated onto UK Power Networks equipment.



quoted from page 6 of the
ENGINEERING DESIGN STANDARD EDS 08-0129
LV CUSTOMER SUPPLIES UP TO 100A SINGLE PHASE
"

 

[S P]

BDzs is low at 0.22
ZE 0.14

 

[johnduffell]

maximum three metres distance between overload protection devices and their source, therefore the customer shall provide and install an intermediate switch fuse or isolating switch if the distance between the meter and consumer unit is greater than three metres.

Yeah I've always thought that's ridiculous too, basically the DNO just want a way to remove all load before pulling their fuse. Then someone got confused about something else, and decided to imply that an "isolating switch" gives overcurrent protection.
In this case, there is an isolating switch, so the DNO's requirements have been met technically...

 

[Dillb]

I was under the impression for BS7671 you have to have fault protection for all cables, and overcurrent where necessary.
Overcurrent has been dealt with through assessement of max demand for the installation.
The fault protection for the tails is only by permission with UKPN, so if UKPN has no bearing, surely that means it would be unsatisfactory by default due to no valid fault protection? If they only allow 3m if they are happy for their fault protection to be used, then that's that?

But there is potential for overcurrent as there isnt just OCPD before the DB where there are several, so as it stands the cable coild become overloaded.

 

[Dillb]

I was under the impression for BS7671 you have to have fault protection for all cables, and overcurrent where necessary.
Overcurrent has been dealt with through assessement of max demand for the installation.
The fault protection for the tails is only by permission with UKPN, so if UKPN has no bearing, surely that means it would be unsatisfactory by default due to no valid fault protection? If they only allow 3m if they are happy for their fault protection to be used, then that's that?

But there is potential for overcurrent as there isnt just OCPD before the DB where there are several, so as it stands the cable coild become overloaded.

 

[johnduffell]

But there is potential for overcurrent as there isnt just OCPD before the DB where there are several, so as it stands the cable coild become overloaded.

good point (I'm not a spark) so both would need to be dealt with by the grace of the DNO.
I'm glad I don't have to do EICRs, it's one thing knowing what will definitely comply and installing it, but it's completely different judging whether something already there complies.

 

[westward10]

Correct - or not so!

I'd have installed metal switched fuses at 80A to enclose SWA conductors and offer protection.

How would you code?

This is a rudimentary issue and how I would Code it is not important. How are you assessing circuit protection for a distribution circuit is provided considering you do not know the characteristics of the protective device and whether this device is recommended for circuit protection of the consumers supply.

 

[The Ghost]

Main earth uses gas supply

Sorry bit confused with that. Looks like the main earth is coming from the cut out? And the SWA are you absolutely sure it is 16mm and not 10mm? I know it is difficult sometimes to assess cable size especially through a piccy. I agree I would have fitted a couple of maybe Lewden fused isolators maybe 63a cartridge fuses apart from a lack of room and location.

 

[Wilko]

I also do not like to see single insulated cables in the meter box. Ordinary folks open that to read the meter.

 

[Octopus]

(I'm not a spark).

What are you?

 

[johnduffell]

just a homeowner (i.e. diy knowledge)
Just wanted to be clear that my answers don't have the weight of training or job experience

 

[Ian1981]

A ze of 0.14 ohms will ‘blow’ the fuse whether it be rated at 60,80 or 100 amp bs1361 or bs 88.
I find it harsh to say a C2 as the fuse would blow in less than 5 seconds on a TN system.
However you are only allowed to rely upon the distributors fuse where they allow that it can afford protection to the part of the installation between the origin and the main distribution point where overload and fault protection is provided at your DB.
So if they only allow 3 meters then you need to code accordingly in my opinion.

As for 16 mm on a 100amp fuse.
My opinion is that is the demand of the installation at time of inspection reveals that overload isn’t likely then I’d assess it on that basis.
If the demand was to change in the future then before any alterations in the future by an electrician, they would need to assess the existing demand and decide if it is acceptable to determine if the proposed alterations comply Which is what’s always required anyway.

 

[spinkieieie]

Providing it is 16mmSQ as in the pics it looks like 10. 16mmSQ armoured Is good at 35m clipped direct for 100a. And providing the ZsDB is ok which you have proven there is not code relevent.
However I Disagree with only basic insulation in the meter enclosure, as meter readers have access and as such aren't competent. I'd C2 it on this count under section 526.

Could of staggered the isolators in the box, glanded the inner sheath to a small enclosure box flush with the bottom of the isolator with the top cut out.

 

[Gavin John Hyde]

Sorry bit confused with that. Looks like the main earth is coming from the cut out? And the SWA are you absolutely sure it is 16mm and not 10mm? I know it is difficult sometimes to assess cable size especially through a piccy. I agree I would have fitted a couple of maybe Lewden fused isolators maybe 63a cartridge fuses apart from a lack of room and location.

If i recall correctly the dno around here get right funny if you install something in the meter / cutout cabinet. I fitted a switched fuse for a cu change as the customer wanted it moved somewhere out of sight and they went right off on one when they came to pull the fuse so i coudl fit it in and do the change.... telling me we arent allowed to put stuff in the cabinet. its different if its indoors on a wall then its a free for all.

 

[The Ghost]

install something in the meter / cutout cabinet

Oh yes very much so, quite aside from the fact that it would be physically impossible to fit in there. But I would have found a way to incorporate protection for the SWA on its way to the CU.