SWA selection

ccrowe · 6 Jan 2009

Customer has a new meter and isolator installed about 10 meters from his CU. I need to connect the isolator to the CU and will use a length of SWA. I'm leaning towards using 3 core SWA so I can use one of the cores to connect to the MET.

However, is there any reason why I couldn't use 2-core with the armour to provide the earth?

Spark123 · 6 Jan 2009

What size SWA, do the PEBs connect into the consumer unit or to the MET?
Do you also have a fuse to protect the SWA? Sometimes the eleccy board don't allow you to use their fuse to protect tails over 3m.

ccrowe · 6 Jan 2009

Thanks for the reply.

I've been looking in to this a bit more and the rules on using the armour as the earthing conductor are quite tough. The CSA required is higher than provided by the armour so it looks like I'll go with my original plan of using a third core for the earthing conductor.

Thanks for the pointer on the fuse, I'd overlooked that.

RF Lighting · 6 Jan 2009

How were you planning on glanding your SWA into the meter?

ccrowe · 6 Jan 2009

The meter's in an IP66 wall box outside the house. I was going to gland to that and put my tails in the DNO's isolator.

RF Lighting · 6 Jan 2009

Wouldn't that have left you with single insulated cores on show?

ccrowe · 6 Jan 2009

Not if I strip the armour back to fit the gland but leave the inner sleeving on until I need to expose the cores at the isolator.

RF Lighting · 6 Jan 2009

Nice

ccrowe · 6 Jan 2009

The

has confused me. I can't tell whether you're being ironic with your "nice".

Is there a better way of doing it? Genuine question, always keen to learn.

RF Lighting · 6 Jan 2009

Replace the DNO isolator with a metalclad switch fuse, and gland directly into it.

You might wan't to add the switchfuse after their isolator if there is room in the meter cabinet.

Don't forget you need to earth the armour, so a metal enclosure is by far the easiest way to do it.

ccrowe · 6 Jan 2009

I was considering that because it also addresses the fuse issue raised further up the thread. As long as I sealed the entry hole to the box I wouldn't break the integrity of the IP rating.

Replacing the DNO isolator raises the sticky issue of breaking the seal on the DNO's fuse, although that does seem to be a fairly minor issue if you let the DNO know you're doing it. In fact, now I think about it, I'm not sure they remembered to put a seal on the fuse when they left.

Seems like overkill to have a DNO isolator and my own switch fuse.

Hadn't forgotten about earthing the armour, in fact, I think that's more or less where all this started.

Excellent help though, thanks very much.

sjwkmje · 6 Jan 2009

ccrowe said:
Thanks for the reply.

I've been looking in to this a bit more and the rules on using the armour as the earthing conductor are quite tough. The CSA required is higher than provided by the armour so it looks like I'll go with my original plan of using a third core for the earthing conductor.

Thanks for the pointer on the fuse, I'd overlooked that.

Last time I did this we used two core SWA into a metal clad hager switch fuse and ran a seperate 16mm g/y for the earth cable tied to the SWA. All the PEBs was connected to the CU earth bar so I connected my g/y to that. We used 25mm2 SWA and thats good for 100A. We also earthed the sheath on the armour.

One thing I cannot remember is how we ran the tales into the metal clad switch fuse due to eddy currents. I remember we used stuffing glands.

To gland the other end into the house we used a hager metal clad consumer unit, looked a bit commerical, but the hager stuff blended into the domestic setting quite well.

Adam

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SWA selection

sjwkmje

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