Unusual voltage measurements

The electrician has used through crimps (so he says on the phone), to join a 25mm armoured and meter tails in a metal junction box. He stated this was inside of the meter cupboard on the outside wall, but it isn‘t. I think this is OK as a setup, however the builder has whacked the joint into the cavity of the wall behind the built in meter cupboard so it isn’t accessible - this of course isn’t acceptable. 

Crimped joints (i.e. ones made by a compression tool) are one of the few acceptable means of making a joint that doesn't have to be left accessible for future inspection (526.3) - so superficially at least the arrangement might well comply.

The connection to the armour might still be questionable (it would be unusual to crimp directly to the steel armour wires) - more than likely it's a threaded gland and either a banjo or earthing nut to which the PE is bolted - which strictly speaking should indeed be accessible.  If however something like a constant force spring has been used (as often done with underground SWA joints) it might be less of an issue.

The underlying issue is probably down to the DNOs/suppliers objecting to consumer equipment in the meter boxes - typically you're just allowed the tails and that's it. Something like a switchfuse for a SWA submain isn't allowed the room, so we often end up with problems like this. The typical answer when there's no room indoors directly behind the meter box, is a 2nd enclosure next to the original meter box (often a duplicate meter box) - that houses the switchfuse and connection to the SWA and then the ordinary meter tails run the short distance from there to the original meter box. But such considerations are often left rather late.

Arguably, if it's the builder that's caused the issue by moved things, it might seem a hit harsh to blame the electrician for the problem. 

   - Andy.

AJJewsbury: 
 

The electrician has used through crimps (so he says on the phone), to join a 25mm armoured and meter tails in a metal junction box. He stated this was inside of the meter cupboard on the outside wall, but it isn‘t. I think this is OK as a setup, however the builder has whacked the joint into the cavity of the wall behind the built in meter cupboard so it isn’t accessible - this of course isn’t acceptable. 

Crimped joints (i.e. ones made by a compression tool) are one of the few acceptable means of making a joint that doesn't have to be left accessible for future inspection (526.3) - so superficially at least the arrangement might well comply.

The connection to the armour might still be questionable (it would be unusual to crimp directly to the steel armour wires) - more than likely it's a threaded gland and either a banjo or earthing nut to which the PE is bolted - which strictly speaking should indeed be accessible.  If however something like a constant force spring has been used (as often done with underground SWA joints) it might be less of an issue.

The underlying issue is probably down to the DNOs/suppliers objecting to consumer equipment in the meter boxes - typically you're just allowed the tails and that's it. Something like a switchfuse for a SWA submain isn't allowed the room, so we often end up with problems like this. The typical answer when there's no room indoors directly behind the meter box, is a 2nd enclosure next to the original meter box (often a duplicate meter box) - that houses the switchfuse and connection to the SWA and then the ordinary meter tails run the short distance from there to the original meter box. But such considerations are often left rather late.

Arguably, if it's the builder that's caused the issue by moved things, it might seem a hit harsh to blame the electrician for the problem. 

   - Andy.

That said, the cable from the DNO cupboard and the DB inside is at least 6m in length maybe longer. 

It should have a fuse after the meter and it’s doesn’t. Obviously the DNOs fuse does protect the cable, albeit not completely aligned with the regulations. 

If you mean “would the DNO accept responsibility if their cutout fuse did not clear a fault”, then I suspect the answer is no. Two reasons, one is the cabling is too long, secondly, SWA is not meter tails. When they say their fuse protects a maximum of 3m of meter tails, that is exactly what they mean. 

Regards,

Alan. 

Why would their fuse not protect equivalent-sized SWA Alan?

Alan Capon: 
 

If you mean “would the DNO accept responsibility if their cutout fuse did not clear a fault”, then I suspect the answer is no. Two reasons, one is the cabling is too long, secondly, SWA is not meter tails. When they say their fuse protects a maximum of 3m of meter tails, that is exactly what they mean. 

Regards,

Alan. 

The DNOs fuse would protect a 25mm armoured. A fuse is a fuse surely? 

Maybe they won’t guarantee it this I appreciate. 

Maybe they won’t guarantee it this I appreciate. 

I suspect that's more of the issue. A generation ago most houses had 60A fuses - after which 100A and 80A got more common. What's likely to happen in the lifetime of current services? An even bigger upgrade (to cope with EVs and heat pumps) or perhaps a change from fuses to some kind of circuit breaker (like they usually have in France) - which may or may not have the same Zs requirement as the original HBC fuse. I guess the DNOs have enough foresight not to want to be in the position of having to ensure that things will still be safe if they're faced with an unknown length of an unknown type of cable with an unknown Zs at the end of it. 

   - Andy.

Exactly. If you want to use the DNO fuse for protection, you need to play by their rules. My employer’s rule is 2.5m of 25mm insulated & sheathed meter tails. Our network design uses this as part of the calculation. 

Regards,

Alan.