Dual double pole FCU switches

[Ian]

Dear All,

I am trying to tidy up the kitchen wiring prior to fitting a new set of units and worktops. As I have a large number of fused spurs (boiler, washing machine, fridge, dishwasher, hob, extractor, 2*lights under units) I was hoping to tidy up the array of single FCU switches. I had planned to use dual metal back boxes but was wondering if anyone knows of a supplier of dual FCU switch plates?

This would be wired into the ring main and allow two fused spurs in a neat and tidy fashion.

I have looked on the BES, TLC etc www pages with no luck.

thanks

Ian

[Andy Hall]

A good solution to this would be to use grid system components, then you can build what you want. There are several brands, but MK have the most comprehensive range that I've seen.

Basically you buy the back box, and then a frame for the appropriate number of modules. The modules click into place and then there is a front plate that fits over this. Face plates are in the usual white plastic or metal patterns.

There are double pole switches (20A), neon indicators and fuses. For a double FCU, you would need as a minimum a four module plate, which is the width of a double socket. This would need two switches and two fuses. If you wanted neons as well then it would be a six module plate which is three above three and slightly larger.

You can order labelled switches if you want to be fancy.

Electrical wholesalers have this stuff and I've also seen it B&Q.

.andy

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[Christian McArdle]

You could do what I did and use a grid switch. I used a 3 module type that is the size of a double socket (4 module would also fit a double socket space). I used only 20A DP switches, running to an unswitched socket behind the appliance. There is no fuse in the switch. It is safe to do this, even on a 32A circuit, provided that the runs of 2.5mm aren't too long. This is because overcurrent protection can be assumed to be provided by the 13A fuse in the plug top. The 20A switch is protected because of this. If the 2.5mm spur isn't too long, then earth loop impedence will be fine too. This is required so that the 32A breaker can be used for short circuit protection for the cable up to the socket.

Christian.

[Ian]

Thanks Andy and Christian,

The grid system looks very useful for my needs, but I have difficulty visualising the terminals on the DP and fuse modules. I have downloaded the MK grid pdf file from TLC (I found them once I know what to look for) but despite all the useful info and pictures not one view from the rear of the modules.

I currently have the ring main going into the unswitched side of a single FCU and then continuing into another FCU (unwsitched side) and then a double socket and then a third FCU (unswitched side) before returning to the ring. So the single metal boxes containing the FCU each have

3*2.5mm2 cables (ring *2 and cable to hidden unswitched socket), these are a little cramped. These faceplates are all mounted together touching each other in a horizontal line.

Am I correct in assuming that the 20A DP switch has two input terminals and two output terminals? Earth wires all connected to the grid frame?

And that the 13A fuse module has two screw terminals?

I assume that I would make the ring main up by using links between modules?

sorry about the extra questions.

thanks

Ian

[Andy Hall]

You can get deep boxes for grid plates which will give you more room. It doesn't really matter about the order that you wire the circuit as long as you make only one spur and wire the rest as part of the ring.

Within the grid box you only need to run single conductors.

Yes they do.

Probably easiest. There is also an earth terminal on the box which you connect to the frame as well. You can run all earths to the box and a single to the frame if it's easier. Obviously sleeve all the earths.

Yes.

No problem.

.andy

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[Christian McArdle]

Yes, but you don't need the fuse module. The plug top is already fused, provided you don't attempt to hard wire the appliance flexes directly into the grid switch. The design absolutely relies on there being a 13A fuse in the system, however. This can be either the plug top and an unswitched socket, or a unswitched fused connection unit to terminate the appliance flex. The former is cheaper and more flexible, provided it can be located where it won't be used for portable appliances. (i.e. under the worktop or behind integrated appliances).

Your main issue will be ensuring that the ring is not overloaded or made lopsided. With mine, this is not an issue as the whole lot is fed from a 6mm radial on its own 32A circuit. If you have a dishwasher, washing machine and tumble dryer off a single point on the ring, you may find that calculations show the ring is overloaded, especially if it isn't near the mid point. You would certainly have to consider refraining from using too many appliances at once, especially if you have kettles, microwaves and built in ovens or dual fuel cookers on the circuit.

The terminals aren't huge on the DP switch modules. I couldn't run 2 6mm cables to them, so they are each fed with a separate 2.5mm cable to a nearby junction box where the 6mm terminates. Again, these short sections of 2.5mm are protected against overcurrent by the 13A fuse in the plug top and short circuit by measured low earth loop impedence (no RCD in the system).

Christian.