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Upside Down Fused Switch and Cable Entry?

Postby rogerk110 » Fri May 15, 2020 7:24 am

I need to install a double pole 80A fused switch to feed a granny flat via SWA.
All of the fused switches I've seen have the supply cable entering at the bottom and the load cable leaving from the top. I'm working with 25mm2 tails from the consumer unit and 25mm2 SWA going to the granny flat, and manipulating such heavy cables to do this is really inconvenient. I would prefer not to mount the fused switch upside down, so can I reverse the cable entry-exit such that the supply arrives at the top and the load leaves from the bottom of the fused switch?
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Postby ericmark » Fri May 15, 2020 10:03 am

With most yes, the switch normally has some anti flash system, the big problem is ionisation of the atmosphere when the air becomes conductive, and the anti flash is designed to reduce this, so there are some switches where it does matter, but in the main it is AC so it does not matter, but there may be one or two exceptions.

All isolators should switch down for off, idea is if anything falls on the switch, it switches off, however domestic tradition has been up for off, so there is a real mixture.

However the main problem you will likely have is getting the LABC to let you do it. OK we all do the odd job where we have not notified when we should, but clearly with a granny flat LABC will be involved, so may be less hassle to get a scheme member electrician to do the job.

Some LABC inspectors are very helpful, my son found Liverpool very easy to work with inspectors, Cheshire not quite so easy, and Flintshire was a real problem. So can't really say what they will allow you to do, also this house had a granny flat built, and we are now struggling to get it combined with the house for rates, at first they wanted to charge us 40% extra for granny flat as not always occupied, we could not rent it out even if we wanted, as it shares electric, water, and heating with main house, and we need access at all times to reset any electrical breakers, or central heating, we got the 40% extra dropped but still one house is considered as two properties, at least we get two sets of bins.
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Postby rogerk110 » Fri May 15, 2020 2:17 pm

Thanks for your reply.
I've always been taught that before turning off an isolator you should turn off ALL loads that are downstream from the isolator, i.e. trip all the MCBs and RCDs first, and only when everything is off should you trip the isolator. This is specifically to prevent arcing of the contacts.
The isolator that I have bought is a Click double pole 80A fused switch, and the bottom terminals are labelled Lin and Nin, while the top terminals are labelled Lout and Nout.
All I was hoping to do is to swap them around. I'm basically looking for anyone to provide me with any reasons why this is not a good idea.
You talked about arcing, and that is somewhat of a consideration, but the Click isolator that I'm installing has absolutely nothing in their design that makes me think they've designed and catered to reduce/eliminate arcing.
Regarding the LABC, I don't plan on involving them. I have an electrician friend who will be doing the full testing of the granny flat before connecting it to the main house. He will be pulling the DNO's fuse and connecting the Henley splitter. I'm doing all the grunt work of pulling cables and mounting boxes. It was while trying to find a suitable housing for the Click isolator that I noticed the inconvenient orientation of the cables. If they were 2.5mm2 instead of 25mm2, it wouldn't be an issue, but 25mm2 cables are a pain in the rear end to work with, especially if you want the end result to look neat and compact.
Any/all thoughts/considerations welcome.
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