Double socket off a 13a fused switch?

[SUNRAY]

That potential problem surely goes away if one installs a single socket for the appliance - in which case an FCU supplying it is certainly not needed, given the fuse in the {one and only} plug.

Kind Regards, John

I agree, until someone does this:

While fitting our new kitchen i replaced a single unswitched socket for a double unswitched socket

and at that point the game changes.

 

[EFLImpudence]

I agree, until someone does this:
and at that point the game changes.

I may be getting confused, but -

in such a case wouldn't the only problem be the unnecessary FCU?

 

[JohnW2]

I may be getting confused, but - in such a case wouldn't the only problem be the unnecessary FCU?

Safety-wise, yes, but presumably Sunray is talking about the the same 'problem' as the OP - two high-current appliances being run simultaneously from a double socket which, in turn, is fed from an FCU (and the FCU fuse blows).

Kind Regards, John

 

[JohnW2]

I agree, until someone does this: ... and at that point the game changes.

Yes, but as often discussed, one cannot, and does not, design on the basis of what changes some idiot may make in the future, particularly given that idiocy seemingly has no limits.

Kind Regards, John

 

[EFLImpudence]

Safety-wise, yes, but presumably Sunray is talking about the the same 'problem' as the OP - two high-current appliances being run simultaneously from a double socket which, in turn, is fed from an FCU (and the FCU fuse blows).

Yes, but that's because the FCU "shouldn't be there".

The two high current appliances in a double socket problem applies to all double sockets wherever they are.

It is nothing to do with it being on a spur.

 

[JohnW2]

Yes, but that's because the FCU "shouldn't be there". ... The two high current appliances in a double socket problem applies to all double sockets wherever they are. ... It is nothing to do with it being on a spur.

Oh - I didn't think we were talking about the 'double socket problem' (i.e. the fact that some double sockets seem to overheat when supplying two large loads) but, rather, of the problem of trying to get 20A+ (theoretically up to 26A, but I'm not sure where you'd find the appliances to achieve that) through a 13A fuse in an FCU.

Kind Regards, John

 

[EFLImpudence]

I said I might be confused. What is the subject?

 

[EFLImpudence]

This was the first reply to the OP:

It’s too much for 13A when on together
It’s also not sensible for them two items in the same double.
Some replanning required.

 

[SUNRAY]

Oh - I didn't think we were talking about the 'double socket problem' (i.e. the fact that some double sockets seem to overheat when supplying two large loads) but, rather, of the problem of trying to get 20A+ (theoretically up to 26A, but I'm not sure where you'd find the appliances to achieve that) through a 13A fuse in an FCU.

Kind Regards, John

It's not just the double socket problem, it is the whole 'design' of the spur on a ring.
I once encountered a pair of German machines which came with moulded 13A plugs on 1.5mm² cable, the ratings plate showed 220-240V drier- 3KW & W/M - 3.1KW, both were plugged into a DSSO on a 2.5mm spur, both plugs and the socket showed signs of overheating and once repaired the drier measured 14.8A on 242V, my calculation for the W/M around 15.4A. I'm convinced they would have been on together at some stage.

 

[ban-all-sheds]

I have gone through life under the impression that the ring final is a predetermined installation method which has all the circuit design principles taken into account including but not limited to derating factors.

How can it when the requirement is for an Iz of 20A but different installation methods give 2.5mm² a rating of 27A down to 13.5A, and that's before you add in any further de-rating for grouping and ambient temperature?

It's perfectly feasible that a full load of 32A may be applied at any point of a ring, by that I mean there may be several sockets in close proximity with heavy loads, such as the kitchen. Are you saying this may be outside of the design parameters and therefore unsafe?

It's not just me saying that.

Surely you've read what 433.1.204 says about that very issue?

 

[EFLImpudence]

This is what is confusing me.

It's not just the double socket problem, it is the whole 'design' of the spur on a ring.
I once encountered a pair of German machines which came with moulded 13A plugs on 1.5mm² cable, the ratings plate showed 220-240V drier- 3KW & W/M - 3.1KW, both were plugged into a DSSO on a 2.5mm spur, both plugs and the socket showed signs of overheating and once repaired the drier measured 14.8A on 242V, my calculation for the W/M around 15.4A. I'm convinced they would have been on together at some stage.

None of those things has anything to do with it being a spur.

14.8A and 15.4A should not be on 13A plugs anyway. 30.2A it is a bit high for 2.5mm² CCC but it likely will have no effect on the cable, so the problem is nothing to do with it being a spur.

 

[SUNRAY]

How can it when the requirement is for an Iz of 20A but different installation methods give 2.5mm² a rating of 27A down to 13.5A, and that's before you add in any further de-rating for grouping and ambient temperature?



It's not just me saying that.

Surely you've read what 433.1.204 says about that very issue?

It's irrelevant what the regs say.
Mrs Smith does not have a copy and she will happily plug in every device under the sun and expect it to work.

An example of Which happened at a hotel, we happened to be there derigging the morning after when a group of people entered the hall to discuss arrangements for an event. They counted 13A sockets which amounted to 20or so DSSO and customer confirmed they had enough double adapters to reach their requirements.
Being intimately familiar with the hall we asked what the event will be.
32 competitors in a hairdressing competition. All to take place on 2x 32A rings.
If we hadn't been there I can just imagine the poor maintenance guy on the day when 32 hairdryers started up.

 

[ban-all-sheds]

It's irrelevant what the regs say.

Err....

Wrong.

 

[JohnW2]

It's not just the double socket problem, it is the whole 'design' of the spur on a ring.
I once encountered a pair of German machines which came with moulded 13A plugs on 1.5mm² cable, the ratings plate showed 220-240V drier- 3KW & W/M - 3.1KW, both were plugged into a DSSO on a 2.5mm spur, both plugs and the socket showed signs of overheating and once repaired the drier measured 14.8A on 242V, my calculation for the W/M around 15.4A. I'm convinced they would have been on together at some stage.

As has been said, I don't see what that's got to do with "the 'design' of the spur on a ring".

The phenomenon you describe, of a double socket overheating when supplying two large loads, is one we hear about, but it would surely be exactly the same if the same socket, used to supply the same two loads, were part of the ring, rather than a spur, wouldn't it??

Kind Regards, John

 

[JohnW2]

This was the first reply to the OP:

Yes, I think that's where the waters started becoming a bit muddied, since Andy introduced (albeit only with an "... It's also not sensible for ...") the 'double socket problem' in addition to the OP's actual problem (that far more than 13A was being supplied via a 13A FCU), after he had addressed that latter issue.

Kind Regards, John