Strange off peak meter setup??

[ljb123]

Firstly this is my first post so be nice

I got called out to a burnt out switch for an electric boiler (Standard 45A switch) on a relatively new estate (2005)

The boiler is a 9.5KW system, and does hot water and central heating.

it is supplied via a 10mm feed (northing wrong with that), what I noticed is there was a spur under the 45A switch labelled up as "off peak supply, isolate in meter box". I believe this just gives the boiler a live" supply signal at off peak times so it can heat water on an off peak rate.

I have attached pictures of what I found in the meter box and unless I'm being stupid, how is this aloud!!! 1.5mm T&E out of the meter to a spur only protected by a 100A fuse with the CPC cut out??

Has anyone else seen this sort of thing, is there maybe a small fuse in the meter ? (obviously I didn't want to open the meter)

Thanks Luke

Untitled

• ljb123
• 16 Apr 2015
• 1

Untitled

• ljb123
• 16 Apr 2015
• 1

Untitled

• ljb123
• 16 Apr 2015
• 1

 

[333rocky333]

strangest thing is the way its all mounted sideways

 

[JohnW2]

I have attached pictures of what I found in the meter box and unless I'm being stupid, how is this aloud!!! 1.5mm T&E out of the meter to a spur only protected by a 100A fuse with the CPC cut out??

It's effectively being protected (against anything other than a fault in the very short length of cable itself) by the downstream fuse (obviously 13A at most) in the FCU.

Kind Regards, John

 

[ljb123]

Sorry about the sideways pics

Yes John it is protected by a 3A fuse at the spur but i just don't understand how the DNO/meter guys get away with connecting the short piece of cable from the meter to the spur, i know the chances of cutting it by accident are slim but if it did get damaged would the 100A fuse blow? I have never heard of 1.5 being able to carry a fault current to take out a 100A fuse

thanks Luke

 

[Iggifer]

Presumably the wiring for the boiler is connected to the cpc from the peak supply and hopefully, there is continuity throughout so that t&e is earthed right up to where it's cut

If the t&e were to get cut, I suspect it would be molten before any fuse operated

 

[JohnW2]

Yes John it is protected by a 3A fuse at the spur but i just don't understand how the DNO/meter guys get away with connecting the short piece of cable from the meter to the spur, i know the chances of cutting it by accident are slim but if it did get damaged would the 100A fuse blow? I have never heard of 1.5 being able to carry a fault current to take out a 100A fuse

The regs allow downstream overload protection of a cable (433.2.2) and downstream fault protection of a cable (434.2.1) provided it is installed in a manner which minimises the risk of a fault in the cable to a minimum. That's obviously somewhat of a subjective call, but I think many/most would be happy that the risk of a fault arising in that very short length of cable, close to the meter backboard, would be 'minimal'.

The DNO-installed cable from my meter to my E7 timeswitch looks like a 2.5mm² single (conceivably 4mm²) and has no downstream OPD (unless there is one inside the timeswitch) and so is protected only by the cutout fuse.

Kind Regards, John

 

[333rocky333]

The old school way would have been 6mm Double insulated, sometimes via a slydelock fuse holder, usually meter sealed.

 

[JohnW2]

The old school way would have been 6mm Double insulated, sometimes via a slydelock fuse holder, usually meter sealed.

If you're talking about my timeswitch ... yes, I think it's a DI single, no fuse holder in sight, and sealed at both meter and timeswitch ends. However, I really don't think its 6mm² - it certainly looks tiny next to the 16mm² tails. Admittedly it's very high up, hence difficult to see properly - If I remember, I'll stand on something tomorrow and measure it's outer sheath!

Of course, in the context of this discussion, the chances of a DI single developing/suffering a fault (to N or E) is much smaller (almost non-existant!) than the corresponding risk with the OP's T&E (which I believe also is a negligible risk).

Kind Regards, John

 

[333rocky333]

Just talking in general John nothing specific.

We do a lot of old sites and its common to see smaller tails bunched in meters, usually for off peak contol stuff

 

[JohnW2]

Just talking in general John nothing specific. ... We do a lot of old sites and its common to see smaller tails bunched in meters, usually for off peak contol stuff

Fair enough. At least that shows that DNOs (and meter operators) seem happy for the small cables to be protected only by the cutout fuse.

Kind Regards, John

 

[ericmark]

We are allowed 3 meters to the fuse but to me any cores visible should be double insulated. Had both the line and neutral wires been sleeved then maybe but seems to be single insulated wires and more to the point no earth connection.

Since inside the meter cupboard it may be acceptable but seems odd.

 

[JohnW2]

We are allowed 3 meters to the fuse ...

As has often been pointed out, if there is adequate fault protection for the cable, the 3m limit for downstream over-current protection does not have to be satisfied.

...but to me any cores visible should be double insulated.

That is obviously always a requirement, regardless of any considerations of over-current protection. Touchable single-insulated LV conductors are never acceptable.

Kind Regards, John

 

[JohnW2]

Since inside the meter cupboard it may be acceptable but seems odd.

I'm not too sure what you (or anyone else) is thinking of as an alternative - one could not connect 16mm² conductors to an FCU.

Kind Regards, John

 

[ban-all-sheds]

Sorry guys - I will go to my grave being in no doubt whatsoever that work like that does not count as good workmanship and therefore does not comply with the Wiring Regulations.

 

[JohnW2]

Sorry guys - I will go to my grave being in no doubt whatsoever that work like that does not count as good workmanship and therefore does not comply with the Wiring Regulations.

As I've just asked, what alternative are you considering - would you want to see a mini-CU (with main switch and B3 MCB), fed with fat tails, instead of the FCU?

Knd Regards, John