Compressor needs 15A

[Jim]

I've just been given an air compressor but it states in the instructions that it needs a 15A supply and I'm not sure what the best way of wiring this in will be.

At present I have SWA cable running from a 20A MCB on the CU into my garage, this terminates in a metal switch box which in turn has 2 supplies running from it. One is 1.5mm to the lights the other is 2.5mm to a metal socket which is mounted right next to the switch box (physically connected to it via the gland hole)

I was hoping to run a 2.5mm cable from the socket to a new 20A switch (run of about 3m) and then connect this switch to a round 16A IP44 socket.

Graphically it would look something like this

SWA----- Switch - Socket ------------Switch - IP44 Socket | Lights

The first socket currently runs a fridge freezer.

Would this set up work or am I likely to burn the house/garage down. Would I be better to connect the new 2.5mm cable direct to the SWA terminals inside the first switch (It's tight in there already) If necessary I could wire the compressor directly to the second switch but liked the idea of the versatility of being able to unplug it.

Any help much appreciated and hope my explanatipon makes sense

Jim

[Andrew Gabriel]

I guess the lights comes off the switch? (Use a constant width font when creating diagrams). I hope the switch is actually an FCU, so the light is protected at 5A and not 20A!

It would work, but it would be better to have a separate circuit. You could try it initially anyway.

How long is the SWA run? The compressor starting might create rather a voltage sag which would be noticable from the light, and might interfere with the fridge freezer momentarily if it's really bad. You might need a Type C MCB to avoid the compressor tripping the breaker when it starts up, but you also need to do a check on the earth fault loop impedance to ensure the tripping time remains in range. 20A protection on the 16A outlet is OK (it is the maximum permitted for a 16A outlet). One slight nit is that socket outlets used in the home have to be shuttered and the 16A sockets aren't -- you might at least want to position it well out of the reach of tiny fingers.

[Alan]

One slight nit

Ahhh - I have lots of these in my garage, and the 32A versions - I guess not a problem there as it's a small-person free zone. However, I also have one 16A one near the CU under the stairs, used for occasional car welding on the drive - I guess technically this should not be there?? Any easy workaround - I'd prefer to keep the socket where it is.

Alan.

[Jim]

Thanks for your input Andrew

The SWA run is about 10m so hopefully this isn't too much of a problem. I'll give the set up a go and see how I get on, if necessary I can always switch the fridge freezer off whilst running the compressor as it's only a backup and doesn't have much in it.

I plan on mounting the socket about 5 foot from ground level so hopefully that should stop my lilttle one geeting her fingers near it. Although not shuttered, the socket I'm using does have a flip down cover, which is some sort of protection at least.

Cheers

Jim

[nightjar]

You can buy interlocked sockets, which cannot be switched on unless there is a plug connected and which will not release the plug unless switched off.

Colin Bignell

[bigcat]

instructions

compliant: put it on a 15A round pin plug. Fuse the socket at 15A at the CU. I would go with fuse, not mcb, as compressors draw lots of start up surge.

non-compliant: put a standard mains plug on it. This is often done, and such goods often get past PAT, even though the plugs are only realy rated at 13A for stone cold operation. Realise the 13A appliance limit is modern-ish, and there were plenty of 15A appliances about at changeover in the 60s.

NT