From SWA to meter tails

[sparc]

I have to link make a temporary supply to a building that's going to get demolished shortly. Coming into the meter cupboard on 3 core 6.0mm2 SWA I need to hook up to the existing 25mm2 meter tails, so existing meter and REC switch can be disconnected and be removed by SSE.

There's not a lot of space, so ideally I want a single box. Can't find anything that will do it in one box, so plan to terminate SWA in one housing, then take the L and N from 6mm T&E to a 100A main switch in a second enclosure, with the tails to consumer unit coming from that. The earths can go to an existing MET, which is currently earthed via spike. (The new supply is PME).

Could find anything already posted on this, so wondering if anyone has any suggestions please.

 

[Amp David]

Why not use an adaptable box to gland to SWA into, then mount henley blocks inside this to terminate both the cables into.

 

[sparc]

That will probably do the trick - just need to check available space.

 

[Guitarist]

Any reason why you can't gland the swa straight into the CU, and feed the main isolator with your 6mm? All you need to do later is put a blanking plug into the hole you cut.

 

[sparc]

Thanks Amp David - that worked a treat. Shame it's all going to get torn down in a couple of weeks ...

Guitarist's suggestion would have worked, but in this case the tails and main earth are plastered into inside wall, with CU high up near ceiling.

 

[Des 56]

Be prepared sparc
Someone might moan about eddie currents :earmuffs:

 

[ashrow]

lol, im glad someone else noticed, i did not have the nerve to mention it !

Also i liked the brown tape on the mcb

Other then that tidy job in a tight space

 

[johnboy6083]

agreed, thats a potentially dangerous error sparc! all live conductors of a circuit must go through the same hole in a ferrous enclosure. You can send the CPC through a different hole if you want.

 

[Knobhead]

The heat generated by eddy currents is directly proportional to the load current (1 to 1). If the entire load is being carried by a 6mm SWA it won’t be much.

Had this been a permanent job I would have had a rant about it.

 

[sparc]

agreed, thats a potentially dangerous error sparc! all live conductors of a circuit must go through the same hole in a ferrous enclosure. You can send the CPC through a different hole if you want.

This is a new one on me - must have been away the day they covered that :-( I've just searched BGB for 'eddy currents' but not found anything so far- can you direct me to appropriate bits please?

Frankly, I was finding it tough getting a single tails bent and through a 20mm hole - but 2!! aaaghh

 

[Bobster]

Could of drilled a bigger 32mm hole. For future reference.

Reg 521.5.1.

 

[sparc]

Could of drilled a bigger 32mm hole. For future reference.

Reg 521.5.1.

Thanks for inputs guys - good learning point. The meter, supply and switch are going to be removed tomorrow, and rest of building demolished over the next week. The SWA supply will get moved to the mobile home, so I'll replace the metal adaptable box with a plastic one at that point.

 

[Bobster]

No need to make It plastic, if your using the 6mm to supply the mobile home, I'm guessing your not going to be contending with the same issues.

 

[sparc]

Won't the issues be the same? The max load will be a bit lower, but the supply will still come in on the 6mm SWA, and need to go into the tails for the home's CU.

 

[Bobster]

Sorry thaught you would be taking the supply straight from the swa not using the tails. Where is the feed coming from?

 

[Knobhead]

This is a new one on me - must have been away the day they covered that :-( I've just searched BGB for 'eddy currents' but not found anything so far- can you direct me to appropriate bits please?

You won't find it in the BGB. Eddy currents cause a magnetic flux around a hole in ferus material that has a single conductor through it. If you have 20 amps flowing through the conductor you will have the equivalent of 20A flowing around it, all be it a very low power as it's a dead short.
They only really become a problem when you have say 500A coming from a transformer. By cutting a slot between the holes the magnetic path is broken.



View attachment 14616

 

[sparc]

Presumably having the metal enclosure earthed would limit the risk anyway - at least in cases with current in the tails of around the 20A you suggest?

 

[sparc]

Sorry thaught you would be taking the supply straight from the swa not using the tails. Where is the feed coming from?

Opening myself up for more drubbing here but here's the other end of that SWA. As the house is getting demolished a temporary new supply and meter was installed in garage. This is to supply the house (via SWA) for a week, then the SWA will get moved to supply the mobile home while new house is being built. The second CU is to supply power for site. So straight away you'll see I've done same thing with tails going into CU on right via separate holes. Won't be doing that again in a hurry! Bit on left is temporary waiting on builders to say what they want. All this will get torn down when new house completed in a few months time.

 

[Guitarist]

As already said, if you cut a slot between the 2 holes you will stop the eddy currents occurring.

 

[Des 56]

Looks nice and neat sparc,a credit to our trade,(but why have you painted that lid black) :joker: