one for the pro's to debate...

[chapeau]

It would appear that the spur can be >3m long but any protection eg FCU has to come in first 3m.

And there has to be a ring if it's a 30/32amp MCB and 2.5mm T/E.

 

[mfarrow]

mfarrow, are you saying that a spur from a ring final including when originating from the consumer unit should be less than 3 meters?

On a ring, it can be as long as possible or as you like and it's covered by 433.1.5.

I you want to add a single socket outlet/FCU to a spare 32A breaker in the board (i.e. no ring in there) then you're limited to 3m by 433.2.2(ii).

 

[ericmark]

that's only ONE section of 434 and the one that deals with the placement for the device for fault protection at that....


and your reading of the other reg is also flawed..

has neither branch circuits nor outlets for connection of current-using equipment

the important word there is NOR...
this means that the outlets don't HAVE to be on the branches....

Until of course you have a MCB or fuse which of course is there in a plug.

What would be the point in any cable if it does not carry current? Comparator can't think of any other cable without current?

 

[GaryMo]

mfarrow, are you saying that a spur from a ring final including when originating from the consumer unit should be less than 3 meters?

On a ring, it can be as long as possible or as you like and it's covered by 433.1.5.

I you want to add a single socket outlet/FCU to a spare 32A breaker in the board (i.e. no ring in there) then you're limited to 3m by 433.2.2(ii).

What's the difference?

I don't agree with you though.

Don't forget 434.2.2 and 434.5.2

 

[NotHimAgain]

mfarrow, are you saying that a spur from a ring final including when originating from the consumer unit should be less than 3 meters?

On a ring, it can be as long as possible or as you like and it's covered by 433.1.5.

I you want to add a single socket outlet/FCU to a spare 32A breaker in the board (i.e. no ring in there) then you're limited to 3m by 433.2.2(ii).

Am I missing something here - why are you applying 433.2.2 (ii) to a final circuit for a socket outlet?

Clause (ii) to regulation is as old as the hills and it was designed to allow the connection of small fuse units to large bus-bar systems. A typical example would be a 15A BS 3036 MEM one way fuse board for a fire alarm connected near the origin to a 300A bus bar. You will note that circuit length limitation is only one of the requirements. You also need to install it in such a manner as to reduce the risk of fire. This would traditionally usually be achieved by the use of steel enclosures such as the bus bar chamber. (see also 434.2.1)

All you need is clause (i) – the 32A mcb needs to provide fault current protection but does not have to provide overload protection. So you need to check that the let through energy of the device does not exceed the withstand of the cable.

 

[ColJack]

Until of course you have a MCB or fuse which of course is there in a plug.

What would be the point in any cable if it does not carry current? Comparator can't think of any other cable without current?

we covered that a few pages back..

as an outlet it is possible to plug something in that is NOT fused and therefore you cannot rely on the protection in the plug to prevent overload of the cable upstream..

there are "red plugs" on some equipment that require more than 13A, although to date I've only seen these on mobile x-ray machines..
however that doesn't stop joe public from bypassing a fuse in the plug.. such as the fabled tinfoil round a blown fuse or the often seen on here drillbit in a socket..
I've even known people with welders to use a welding nozel in the fuseholder to stop the 13A fuse from blowing..
then there's always the method of just swapping the live pin in a plug for a spare neutral pin and wiring direct..

 

[GaryMo]

All you need is clause (i) – the 32A mcb needs to provide fault current protection but does not have to provide overload protection. So you need to check that the let through energy of the device does not exceed the withstand of the cable.

Which is what I tried to say above:

Don't forget 434.2.2 and 434.5.2

 

[NotHimAgain]

There is no requirement to accomodate the misuse of BS 1363 accessories - read 120.1 - last three words.

 

[GaryMo]

there are "red plugs" on some equipment that require more than 13A, although to date I've only seen these on mobile x-ray machines..
however that doesn't stop joe public from bypassing a fuse in the plug.. such as the fabled tinfoil round a blown fuse or the often seen on here drillbit in a socket..
I've even known people with welders to use a welding nozel in the fuseholder to stop the 13A fuse from blowing..
then there's always the method of just swapping the live pin in a plug for a spare neutral pin and wiring direct..

We can't be held resoponsible for the actions of idiots.

 

[ColJack]

you're designing an installation that will be under the control of idiots, so you have to make it as safe as possible for and idiot to use.. or idiot proof if you prefer..

as a sparky I KNOW not to plug things into non-RCD protected sockets so it's OK for me to have a single socket near the door that is RCD protected and the rest of the house not.. but if I move then the next idiot puts the lawnmower lead through the back window instead... so ALL the socket outlets in the house have to be RCD..

I KNOW not to put nails or screws directly above, below or to either side of a switch or socket, so I don't NEED RCD protection on all my burried cables.. but the next idiot does..

 

[mfarrow]

Sorry I've spent so long looking at references to 433.2.2(ii) that I completely ignored 433.2.2(i). Yes there is no length limit.

And no I hadn't forgotten about the requirements to protect against fault current, just didn't think of mentioning it.

If not then what's the difference?

The only difference is that double sockets are only permitted as spurs off ring mains, and cannot be fed off a spur from a 32A breaker not forming part of a ring main.

 

[GaryMo]

BS3036 fuses are still listed in BS7671:2008 yet they're abused more than anything else.

 

[GaryMo]

The only difference is that double sockets are only permitted as spurs off ring mains, and cannot be fed off a spur from a 32A breaker not forming part of a ring main.

Why though, what's the difference between there being an extra two conductors in the same terminal?

 

[ColJack]

The only difference is that double sockets are only permitted as spurs off ring mains, and cannot be fed off a spur from a 32A breaker not forming part of a ring main.

Why though, what's the difference between there being an extra two conductors in the same terminal?

exactly the thought that prompted the original question..

you could just say that it's a spur form a ring of zero length..

although to qualify as a ring does it need at least 2 points of utilisation? other wise it's just a "conductors in parallel" circuit...

 

[GaryMo]

But the supplying 2.5mm2 conductors would have the same overload protection and the same fault current protection so I see no difference between the two scenarios.