Mystery spur..any ideas?

[deadshort]

So what do you call the load cable/circuit connected to it?

The 'appliance'. or "load" as you called it

DS

 

[EFLImpudence]

No, what do you call the cable/circuit?

 

[deadshort]

No, what do you call the cable/circuit?

Cable= Cable, Circuit = Circuit.

DS

 

[EFLImpudence]

I'll give you a clue:

 

[deadshort]

Mm, is that a fuse supplying that "spur"? Would that be a "fused spur" ? Oh, lets add a switch.
That would be a switched- fused- spur ideal if you don't want to use a "plug top" !

DS

 

[winston1]

Mm, is that a fuse supplying that "spur"? Would that be a "fused spur" ? Oh, lets add a switch.
That would be a switched- fused- spur ideal if you don't want to use a "plug top" !

DS

You can't use a plug top. You can however use a complete plug.

 

[EFLImpudence]

Mm, is that a fuse supplying that "spur"?

There is a fuse; it is protecting the spur.

Would that be a "fused spur" ?

No, the cable is the fused spur.

Oh, lets add a switch.
That would be a switched- fused- spur

No, the cable is the switched fused spur.
The thing with the switch and the fuse is a switched fused connection unit.
You can get connection units without a switch or fuse.

ideal if you don't want to use a "plug top" !

As Winston's reply above.
So using your logic, the plug top would also be a fused spur, would it?

 

[deadshort]

yes, you've got it !

DS

 

[EFLImpudence]

yes, you've got it !

So, you are just being silly.

 

[John D v2.0]

While we're on the topic of plug top vs fcu, Interestingly when you add a fused spur to a fixed installation you have to check disconnection times etc comply as per the example design in the osg shown above. As per deadshort, if there's a plug instead of a fused spur, since it's no longer part of the fixed installation you can have unsafe situations. Every time you plug something in you're creating a new circuit, although not writhing the regs.
Inappropriate use of extension leads can be flagged on an eicr, but it's not coded.
Not likely to be an issue on a 32a ring with 13a plug fuses, but other situations may happen.

 

[EFLImpudence]

Not likely to be an issue on a 32a ring with 13a plug fuses, but other situations may happen.

As you say, not likely.

25m of 1mm² flex is needed to increase max. Zs of the ring to max. Zs of 13A fuse.
How many sockets are already at maximum Zs?

Plus, the figures are worst case scenario:
Cmin is very unlikely to be the case.
Ia is probably less than 5 for B type MCBs.

 

[John D v2.0]

As you say, not likely.

25m of 1mm² flex is needed to increase max. Zs of the ring to max. Zs of 13A fuse.
How many sockets are already at maximum Zs?

True not many, but not everyone is a fan of rings, some people prefer 20a radials, maybe you have a 16a or 20a radial from your cu at the front to your garage at the back on 1.5mm cable, or maybe a 13a fcu supplying the garage from another final circuit, then you plug a 25m extension into that to get to your shed (that's what next door does although off the ring) then a lamp and a laptop plugged in.

As we both say, all very far fetched, but it's interesting that ordinary people can effectively design arbitrary circuits using extension leads. And never mind the other issue that outside is one large extraneous conductive part.

The only way to be really watertight and prevent arbitrary circuits would be to use a special keyed plug hole for wall sockets that would allow extension adaptors or standard plugs, and extension leads would not allow insertion of other extension leads. Then have a maximum r1+r2 for extension leads assuming a 20a socket circuit.

But presumably in amendment 3 the worry was cu fires not extension lead fires, so it's probably not worth effort.

 

[JohnW2]

As we both say, all very far fetched, but it's interesting that ordinary people can effectively design arbitrary circuits using extension leads. .... But presumably in amendment 3 the worry was cu fires not extension lead fires, so it's probably not worth effort.

"Extension lead fires" will only result from overload of the extension cable (bearing in mind the maximum safe current when wound or not wound in the case of extension reels), and that ought to be covered by the fuse in the extension lead plug. The 'maximum Zs' business is all about (negligible impedance) 'faults', not overloads, and they are very unlikely to start a fire in the cable before some protective device operates.

Although some would regard it as an 'inconvenience' (and, maybe sometimes, a 'trip hazard') one way to address the 'still on reel' issue with extension reels would be to have them made so that the extension was 'switched off' unless/until the cable was fully unwound - the plug fuse could then be guaranteed always to provide adequate overload protection for the extension lead.

Kind Regards, John

 

[Echo the husky]

It would be half a job if they stopped selling those 10A rated extension leads, where did that stupidity start from?

 

[John D v2.0]

The 'maximum Zs' business is all about (negligible impedance) 'faults', not overloads, and they are very unlikely to start a fire in the cable before some protective device operates.

Yes assuming the zs is low enough. The situation under discussion is where the zs to the end of the lead is too high for the 13a fuse in the plug. Then a fault (to earth) would not be cleared in time. I suppose that's more about the shock risk than a fire, so just hope there's no extraneous metallic parts nearby. All very unlikely, but it doesn't give eebads so wouldn't comply with the regs if it were fixed wiring.