Spurs

[TonyW2]

Eg bedside lights.

Why is a double socket permitted as a spur from a ring final but two single sockets, with the second being a spur from spur is not acceptable?
If a fused unit were placed between the ring and first spur would it conform?
It would be very convenient if the two sockets could be spurred from the ceiling lighting circuit ; would this conform if a fused unit fitted with a 5amp fuse were used.?
(5amp plugs and sockets are not an option.).
Thanks

 

[ban-all-sheds]

Why is a double socket permitted as a spur from a ring final but two single sockets, with the second being a spur from spur is not acceptable?

Because of the (little known) fact that a double socket is rated at 20A, not 26.

If a fused unit were placed between the ring and first spur would it conform?

Yes.

It would be very convenient if the two sockets could be spurred from the ceiling lighting circuit ; would this conform if a fused unit fitted with a 5amp fuse were used.?

What's the point of the FCU? The purpose of an FCU is to protect the cable from overload, but you've already got that protection in the CU. You haven't with a 32A ring final, hence the need for FCUs to protect spur cables.

Sockets on light circuits are generally not considered a good idea, as they might be used for loads large enough to trip the circuit breaker (and a 5A FCU won't stop that happening), but that's not electrically dangerous, and there's no explicit prohibition of them. But your best bet would be to cut the plugs off <whatever> and wire them into FCUs. If they are wall-wart PSUs find replacements with trailing leads.

 

[PrenticeBoyofDerry]

So not a thread about Andre Villas Boas then?

 

[ban-all-sheds]

I believe a cantankerous old Scot has threatened to shout at anybody who talks about any footie topic except one until Monday.

 

[PrenticeBoyofDerry]

I think we can now safely wave bye bye to 20 yrs of domestic dominance.

 

[stillp]

Because of the incorrect belief that a double socket is rated at 20A, not 26.

There you are BAS, fixed it for you!

 

[TonyW2]

Using the lighting circuit still appeals, but opens the risk of somebody not realising that the spur could be live when the other room sockets have been isolated at the CU. I realise that 'prove dead' should apply, but is it not prohibited for that reason?
Fixed wiring into FCU is too limiting.

 

[ban-all-sheds]

I realise that 'prove dead' should apply, but is it not prohibited for that reason?

No.

Fixed wiring into FCU is too limiting.

Why?

How many different things do you want to plug into sockets on a lighting circuit?

 

[TonyW2]

2 bedside lamps, one clock, one removable electric blanket, vibrating "massager"' etc.

 

[DetlefSchmitz]

vibrating "massager"' etc.

Mains operated!

 

[PrenticeBoyofDerry]

Sounds orgasmic

 

[TonyW2]

And she has ,me attached to a 26 year old lad with a pair of jump leads.
Now stop it

 

[ban-all-sheds]

2 bedside lamps, one clock, one removable electric blanket, vibrating "massager"' etc.

FFS do it properly then, and put the sockets for those on a socket circuit.

I assumed (as it's almost always the case) that you wanted to plug in, for example, a TV signal booster, or a wall mounted TV or fan, and the lighting circuit was by far and away the most conveniently located for high level sockets, or sockets in the loft etc.

For all of those items you'll want sockets in the conventional place. Madness to struggle to find a way to have them on the wrong circuit.

 

[PrenticeBoyofDerry]

The solution is a simple one extend the ring final circuit are connect a fused spur.
Remember these newly installed sockets will then require 30mA RCD protection, as will any newly buried cable in walls less than 50mm deep (from both sides of wall) unless the cable is mechanically protected (metal capping is not mechanical protection). The cable should be routed if buried in permitted safe zones and there are regulations concerning depths of chase in solid walls (no greater than 1/6th depth of wall's skin/leaf horizontally and 1/3rd vertically)
//www.diynot.com/wiki/electrics:installation_techniques

Once the circuit was been constructed, the relevant inspections and tests(dead and live) for the circuit should then be performed and documented as detailed in chapters 61, 62 and 63 of BS7671

 

[ericmark]

Very early in the regulations we have:-

314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.

If you look at (iii) above that is the basic rules to say don't fit a socket to a lighting circuit. Reason is simply to stop some thing being plugged into the socket from tripping out the lights.

It was years ago illegal to use power products from the lighting circuit. There were two meters one for lights and one for power and lighting cost less than power. Not sure of dates but likely pre-first world war.

But by the time of the second world war all on same meter and my granddads house had two 15A sockets so taking power with adaptors from the lights was wide spread but by end on second world war more sockets were being fitted my dads house had 5 sockets. However the lights also had no earths so because of lack of earth talking power from lights was very dangerous.

By the 1960's they changed and fitted earths to lights but there are still many houses without earths and also RCD's were not fitted to lighting circuits until 2008 when the bathroom lights had to have an RCD.

So in general the only time when a socket is fitted to the lighting circuit is to supply TV boosters fitted in the loft and even this really breaks the rules. The only other non lighting use for lighting supply is the fan in bathroom and fire alarms. In all cases a very low current consumption.

The regulations say the protective device (fuse) should be fitted at "point of reduction of cross-sectional area" but it allows 3 meters (434.2.1) if certain rules are obeyed before the fitting of the protective device. The socket single or double or the fused connection unit is considered as the protective device since the maximum fuse size fitted is 26A and twin and earth clipped direct is rated at 27A. Clearly where ref method 100 is used then only rated at 21A but a risk assessment shows it is unlikely in real terms to exceed the 21A for enough time to allow the cable to over heat. In a plug the 13A fuse produces more heat than the modified plug since the finger protectors were added can radiate over a prolonged time.

"ban-all-sheds" 20A limit for a double sockets reflects this heat dissipation problem two plugs so close heat each other up. All fuses produce heat this is how they work. So for an immersion heater which runs for an extended time we will not use a fused plug but use a dedicated supply. We may use a unfused 15A plug so it can be unplugged for easy maintenance these should produce no heat.