Electrical spur in utility room

[ron]

Hi, all.

At my sister-in-law's for the weekend, and we have a small electrical problem.

In the utility room, there is a fused switch spur unit above the worktop, feeding a socket in a cupboard below. This fused spur unit is directly on the ring. The washing machine sits next to the cupboard, and it's flex comes into the cupboard via a hole in the side of the carcase. So far, so good.

Now, the house owner has replaced the socket with a double socket, and is attempting to run a tumble drier off it also.

Needless to say, the 13A fuse in the switch fuse spur unit blows whenever both appliances run together. The drier has a rating plate of 2700W, I can't see the rating on the W/ M, but the element will be well up there I'd imagine.

The best solution would be to add another fused spur beside the existing one, also on the ring, and have it feed the second appliance via its own socket.

However, that would be very difficult to do due to how the wires have been installed behind the plasterboard and then tiled over.

A possible bodge comes to mind:

How about replacing the fused spur unit with a 13A single socked, making the double socket in the cupboard a regular unfused spur?

There are some issues with this. For a start, we loose the appliance isolating switch above the worktop. I understand this is not actually a requirement. Even if it were, the socket is accessible in the cupboard without needing to move the appliance, so that may fulfill this requirement if it existed. Secondly, I'm going to be drawing somewhat over 13A off this spur on the occasion both appliances run together. I'm a little unsure about how kosher that is.

Advice?

-- Ron Lowe

[Lurch]

On 17 Feb 2007 08:32:53 -0800, [e-mail] mused:

I like the sound of that!

Doesn't sound too much of a bodge actually.

It doesn't exist, but if you can get to the socket without removing the appliance then that would be fine. I fit the switched spurs for convenience so as long as the appliance can be conveniently isolated then that's all there is to it really.

I'd be a bit more concerned if the spur were from the other side of the house with the cable wrapped in insulation in the roof void but as it's probably maximum 1m and the cable is rated for 27A then it should be fine for the infrequent times that the element in the washing machine is on during a cycle and the tumble dryer is also on.

[David Hansen]

On 17 Feb 2007 08:32:53 -0800 someone who may be [e-mail] wrote this:-

What size is the cable between the switched fused spur and the socket?

[Owain]

You are allowed to do this, as the assumption is that a doubel socket will not draw more than 20A (less than 2x13A) and 20A is the normal rating of 2.5mm T&E.

However if you believe that 20A would not be sufficient for both appliances simultaneously, you should not install an unfused spur to supply them.

Could you put a single socket direct on the ring, and a *single* socket as an unfused spur?

If the cable from spur to ring is less than 2.5mm you won't be able to remove the fusing anyway.

Owain

[David Hansen]

On Sat, 17 Feb 2007 20:51:51 +0000 someone who may be Owain wrote this:-

Under what conditions is 20A the normal rating?

[ron]

blockwork wall ( dot-and-daub construction. )

-- Ron

[David Hansen]

On 18 Feb 2007 01:14:06 -0800 someone who may be [e-mail] wrote this:-

Then I'm surprised someone fitted a fuse where it joins the ring main. The reason for fitting a fuse at such a point is to make it a fused spur and thus allow smaller cable to be used. I would be on the lookout for a bodge.

However, the cable installation method is somewhere between clipped direct and in free air, depending on the space between the blockwork and plasterboard. Assuming the area is not subject to high ambient temperatures this size of cable is rated at 27 or 30A under those conditions. Thus fitting a single socket at high level and making the spur unfused should be fine no matter how the machines are used.

Note this assumes the protective devices are not rewirable fuses and any advice is worth what you paid for it.

If the house is in England or Wales beware of Mr Prescott.

[Andy Wade]

Installation method 6 (enclosed in conduit in an insulated wall). See Table 4D5A of BS 7671. The clipped direct rating is 27 A.

[David Hansen]

On Sun, 18 Feb 2007 10:48:08 +0000 someone who may be Andy Wade wrote this:-

So, not the situation here.

[Andy Wade]

True, it's actually method 16 in a duct with a large perimeter, so you use reference method 3 and Table 4D2A and come up with a rating of 23 A.

This is all a bit irrelevant though. In this situation I'd consider simply changing the switched fused spur unit for a 20 A DP switch, leaving the double socket on a short unfused spur. The design rating is now limited to 20 A by the switch. For the two appliances mentioned it's unlikely that the load will exceed 20 A for long periods. (I'm assuming normal domestic use and that it's not a commercial laundry!)

I'd be more concerned about reviewing the loading and load distribution on the ring itself in regard to reg. 433-02-04, rather than this little spur alone.

BTW that switched fused spur unit should have been a simple switch in the first place. Overload protection is provided by the appliance plug fuse and there's no point at all in a second fuse.

[David Hansen]

On Sun, 18 Feb 2007 12:15:33 +0000 someone who may be Andy Wade wrote this:-

Debatable. Given the relatively large volume of air compared to a duct, the fact that the cable is vertical and can lose heat on both surfaces and the fact that this air can then circulate vertically (and thus lose rather more heat than it could do in a horizontal duct) I would say that the cable can be rated higher than 23A.

[Lurch]

On Sun, 18 Feb 2007 12:15:33 +0000, Andy Wade mused:

Either\or really.

[Lurch]

On Sun, 18 Feb 2007 09:57:54 +0000, David Hansen mused:

The switched fused spur is fitted for convenience. Many many thousands of under counter sockets are fitted like this up and down the country and have been for many years.

I can assume then that you are in no way an electrician of any kind or have any electrical experience?

[David Hansen]

On Sun, 18 Feb 2007 13:53:32 +0000 someone who may be Lurch wrote this:-

A 20A DP switch is just as convenient.

[Lurch]

On Sun, 18 Feb 2007 16:41:39 +0000, David Hansen mused:

But is very much more less common than a switch fuse. Both methods do the same job, isolate a single socket below a worktop.

Some installations will have flex outlets rather than single sockets to allow appliances to g back and extra 20-30mm so you would have to have a fused spur in this instance. If a fused spur is installed at the outset then the transition from socket to otlet is easierif required at a later date.

[Ron Lowe]

The rating plate on the W/M is 2100w @240, and the dryer is 2700W @240. This computes to 20A, so right on the limit.

Yes, I could, but then I'd need to drill a hole in the worktop to pass the appliance flex up to one socket. ( And chop the moulded plug to pass the flex thru the hole, then fit a new plug. ) And I'm here for a social visit, not a DIY fest.

Not a problem, it's 2.5 T+E.

I just did it. As bodges go, it's reading fairly low on the bodge-o-meter. He still had the old single socket lying around which he'd replaced with the double, so I just used it to replace the fused switched spur as per my plan. Avoided a trip to a shed to buy anything, and we got on with out social nicieties.

And now 7 hours later, I'm back home.

As regards Part Pee, . They were planning to run the drier off an extension cord from the kitchen.