Electrical Question

Adding a new swa cable feeding a new flat

Hi there,

If anyone out there could help me get my head around this I would be very grateful.

I own a property, shop/flat above (new), the shop has 3 phase coming in from the road and the flat above was powered via a fuse board in the shop coming off one of the phases (my electrician didn't tell me which phase).

Basically the electrician has run a new 16mm SWA cable from downstairs where the 3 phases come into the shop and run it straight up to the fuse board in flat, not connected yet, not sure what he's got to do because I'm sure it needs to into the meter first then out of the meter to the board, that's what I've been told, I'm no expert, office worker......

I would just like to know, the correct way, if the electrician is doing the job correct, if someone could explain what is needed (materials and how it works) from start to finish I would be over the moon.

Thanks a lot.

2 Answers

Best Answer

The supply arrangement you have detailed is known as a "submain" or "rising & lateral main" The SWA cable should be the low smoke zero halogen type in order to comply with fire regulations. Standard PVC or XLPE Steel Wire Armoured cable is inadequate.

At the shop (supply end), there should be a 100amp fused isolator that the SWA cable connects to. At the flat (remote end) the SWA cable should be made off using a proprietary brass SWA gland into a short section of 100mm steel trunking. The top surface of the trunking should have a slot cut into it so that the inner cores of the SWA can pass up from the trunking to the electricity meter directly above. The short exposed section of cable between the trunking and the meter should be oversleeved so that the cable becomes double insulated at that point.

Double insulated tails can then be taken from the electric meter to the fuseboard in the flat.

Answered 22nd May 2014

Electrical Safety Services

Member since 17 Oct 2011

Hi, so there is a 3 phase incoming supply and one phase supplies the shop and the a second phase is going to be used to supply the flat. The supply for the flat will have to come from the cut out incoming phase (normally a BS1361 type 2b main fuse) to feed a single phase meter and then from the meter to a 80/100A KMF switch fuse as isolation if the run from the meter to the flat is over 3 meters which I assume it will be and then to the consumer unit in the flat.

Depending on how the cable is run/installed will determine what type of cable is used as the supply. I would personally run 25mm2 double insolated tails with a 16mm2 earth if internal I.e through joists, under floor boards etc. I would only use SWA if the run was to be external at some point. Although 25mm2/16mm2 earth tails may be deemed as over kill, it will cover for every eventuality especially if you are relying on electricity for your choice of cooking, showering and heating as all af those appliances are high carrying current using appliances.

I would advise taking into consideration loading factors when deciding on cable sizing and ensure that the mains installation is capable of providing what is required of it. I would also advise to check and ensure that your electrician is current and qualified to the latest 17th edition IET Wiring Regulations and registered with an electrical governing body i.e NAPIT, NICEIC etc. I wish you luck with your project and hope all works out well.

Answered 22nd May 2014

JEM Electrical

Member since 10 Apr 2013

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