Terminating SWA in Meter Box?

[mfarrow]

I wouldn't say 'limited to' PME. Even without PME, the other considerations, particularly for long runs, are the adequacy of the 'CPC' CSA for (a) achieving an acceptable Zs and/or (b) serving as a PMB conductor if there are extraneous-c-ps to be bonded in the outhouse.

Which is all accomplished via good circuit design.

I wouldn't have been surprised if the regs did insist on a single MET (although I've yet to find evidence that such is the case!).

But the unreliability you describe would be true of every connection in an installation, and if we started limiting ourselves to designing circuits with the least number of terminations then we would have houses on single ring mains with a double socket in every room, one lighting circuit, and cooker/shower circuit.

As it is, we are encouraged to split our installation into more, shorter circuits which contain an increasing number of outlet points, terminations and switchgear components. If the screw terminal was that unreliable as to require regulation of the type you're searching for in BS 7671, then we are surely limiting inconvenience at the expense of the safety of our installations.

 

[JohnW2]

I wouldn't say 'limited to' PME. Even without PME, the other considerations, particularly for long runs, are the adequacy of the 'CPC' CSA for (a) achieving an acceptable Zs and/or (b) serving as a PMB conductor if there are extraneous-c-ps to be bonded in the outhouse.

Which is all accomplished via good circuit design.

Yes, it can be. However, if cable length is long and there are extraneous-c-ps in the outhouse, 'good circuit design' may well indicate the need for appreciably bigger (more expensive) cable if one exports the earth (and hence has to main bond back to the house).

I wouldn't have been surprised if the regs did insist on a single MET (although I've yet to find evidence that such is the case!).

But the unreliability you describe would be true of every connection in an installation, and if we started limiting ourselves to designing circuits with the least number of terminations then ...

Sure, I don't disagree with any of that. However, I'm talking specifically about MPB conductors, which a fair number of people seem to believe (despite the absence of any regulatory requirement) shouldn't even have any joints. When I've suggested in discussions here that someone should use an earth block to faciliate bonding to a second service when the existing MPB conductor to the first service was not long enough to reach the second, some people have been unhappy with that - but you, presmably, would be happy, regarding the block as 'another MET'?

...If the screw terminal was that unreliable as to require regulation of the type you're searching for in BS 7671, then we are surely limiting inconvenience at the expense of the safety of our installations.

Even though that's probably intended as a tongue-in-cheek (or Devil's Advocate) suggestion, given that screw terminals are certainly not 'perfect', I suppose that what you say actually has to be, to some extent, true!

Kind Regards, John

 

[mfarrow]

Yes, it can be. However, if cable length is long and there are extraneous-c-ps in the outhouse, 'good circuit design' may well indicate the need for appreciably bigger (more expensive) cable if one exports the earth (and hence has to main bond back to the house).

I can't disagree with that. Not many submains require the size of cable required for the bonding conductor.

Sure, I don't disagree with any of that. However, I'm talking specifically about MPB conductors, which a fair number of people seem to believe (despite the absence of any regulatory requirement) shouldn't even have any joints. When I've suggested in discussions here that someone should use an earth block to faciliate bonding to a second service when the existing MPB conductor to the first service was not long enough to reach the second, some people have been unhappy with that - but you, presmably, would be happy, regarding the block as 'another MET'?

As long as it's accessible, and obvious, why would I? It seems to be the trade bodies (NICEIC?) which want continuous bonds; it's certainly not the regulations.

Even though that's probably intended as a tongue-in-cheek (or Devil's Advocate) suggestion, given that screw terminals are certainly not 'perfect', I suppose that what you say actually has to be, to some extent, true!

More devil's advocate than tongue in cheek I'm afraid. Though I suggest it's a discussion for another forum. I think if a problem were to be identified, I would think the first step to come out of the discussion and the industry's tackling of the problem, would most likely be the use of proper torque screwdrivers, clear instructions from manufacturers, the training for electricians to recognise the difference between Philips, pozidriv, and JIS (!), rather than limiting the scope of our installations.

 

[JohnW2]

I can't disagree with that. Not many submains require the size of cable required for the bonding conductor.

Exactly - which takes me back to how this started. If the run to an outhouse is long and there are extraneous-c-ps in the outhouse, this can be a good practical reason for not exporting the main installation's earth, even if it's not PME.

As long as it's accessible, and obvious, why would I? It seems to be the trade bodies (NICEIC?) which want continuous bonds; it's certainly not the regulations.

As you say, it's certainly not the regulations - but it's an indication that at least some people consider main bonding conductors to have 'special status' in this respect!

More devil's advocate than tongue in cheek I'm afraid. Though I suggest it's a discussion for another forum. I think if a problem were to be identified, I would think the first step to come out of the discussion and the industry's tackling of the problem, would most likely be the use of proper torque screwdrivers, clear instructions from manufacturers, the training for electricians to recognise the difference between Philips, pozidriv, and JIS (!), rather than limiting the scope of our installations.

There's obviously scope for screw terminal connections to be improved by attention to all such issues but they (just like any other type of connection) are never going to be perfect - so there's always going to be some truth in what your Devil's Advocate said - that some of the steps we take to reduce 'inconvenience' inevitably increase the risk of things going wrong, which could in some cases have a detrimental effect on safety!

Kind Regards, John

 

[m5kgk]

I just had WPD come and do a service renewal for me at a property I was renovating for a friend. The old overheads had no insulation left where they were attached to the walls.

Untitled

• m5kgk
• 12 Sep 2013
• 1

Anyway, they installed a new meter box with cutout on the outside of the property. Then Haste came to do the wire back and move the meter.

They installed a switch fuse in the meter box and then 3 core SWA to the CU.
The SWA armour is not earthed. At either end they placed a jacket over the cores and heat shrunk it down.

 

[sparkwright]

I just had WPD come and do a service renewal for me at a property I was renovating for a friend. The old overheads had no insulation left where they were attached to the walls.

Untitled

• m5kgk
• 12 Sep 2013
• 1

Anyway, they installed a new meter box with cutout on the outside of the property. Then Haste came to do the wire back and move the meter.

They installed a switch fuse in the meter box and then 3 core SWA to the CU.
The SWA armour is not earthed. At either end they placed a jacket over the cores and heat shrunk it down.

Interesting pic.

Have you a picture of the switch fuse they installed by any chance?

 

[m5kgk]

I will get one, I will be there tomorrow finishing a few things off

 

[Spark123]

Are you sure it is SWA?, the distribution network operators tend to use concentric or split concentric cables, as seen in the original pic, the DNOs stuff is tiny in comparison to what the OP installed!

 

[gazfen]

I was thinking of terminating the SWA into an adaptable box, directly below a KMF fused switch, which admittedly are much smaller.

You mean something like this:
View media item 66091 ?

It's probably best having the adaptable box on top as it's easier to obtain IP4X.

That's along the lines I was thinking of, although you appear to have the tails exiting through different holes in the metal box?? Or have you just removed the whole of that side of it?

No wonder they left it , e.on need to fit an isolator in there as well
Here's a picture of it - I admit it is tight, but the DNO said it would be fine and there is enough room for another meter I measured.

View media item 66096

 

[ban-all-sheds]

Did he?