CHESTNUT

[ban-all-sheds]

BAS, you appear to be trying to invoke 433.2.2 in the manner I mentioned last night. However, how would that work if you potentailly had 2x13A fused plugs at the socket unless the Iz of the cable was >26A (which would only be the case if clipped direct) - 433.2.2 is taking about downstream overcurrent protection, and would probably not be interested in a (controversial!) argument that the double socket was only rated to take 12A or 20A total.

Controversial or not, I imagine that a BS 7671 compliant load represented by a DSO is a maximum of 20A.

 

[JohnW2]

Controversial or not, I imagine that a BS 7671 compliant load represented by a DSO is a maximum of 20A.

That might be true, but I'm not sure that's relevant to what we're talking about - which is cable protection by OPDs, and the positioning of those OPDs. Are you suggesting that the regs are happy with In > Iz if Iz > Ib ?

Kind Regards, John.

 

[ban-all-sheds]

Which In are you talking about?

 

[JohnW2]

Which In are you talking about?

That's the point. In terms of the regs in general, the In of the 32A MCB is obviously not satisfactory for protecting a 2.5mm² cable. You are trying to invoke 433.2.2 to say that you can, under some circumstances, rely on overcurrent protection at the downstream end of the cable - which in this case would (at worst) consist of 2 x 13A fuses - i.e. a worst-case In of 26A. Your argument (which I guess is similar to the thinking which resulted in the regs allowing 2.5mm² unfused spurs on 32A circuits) seems to be assuming that, if one doesn't like that In, one can substitute Ib - but I'm not sure where you're going to find that one in the regs!!

Kind Regards, John.

 

[ban-all-sheds]

Ib ≤ In ≤ Iz is about overload protection.

In the case of a spur from a ring final, Ib & In are at most 13A or 20A. They cannot, in a compliant scenario, be otherwise because that is what BS 1363 limits them to, and the spur, or radial as described above, is supplying a BS 1363 accessory.

So yes, at some point downstream of the OPD the cable's capacity becomes reduced to <32A, but it is protected from overload by a device downstream of that point with an In of 13 or 20, and is protected from fault currents by the upstream device. Subject, of course, to PFC, but then the regulations say that.

 

[ban-all-sheds]

1/ Not necessarily & not necessarily.
2/ Are any of the spur cables >3m in length?
3/ Ditto.
4/ Ditto.
5/ Ditto.
6/ Is the cable >3m in length?
7/ Are any of the cables >3m in length?

I'd like to add a further request for clarification.

Does the determination of "safe?" have to consider potential misuse by the ignorant?

 

[JohnW2]

Ib &#8804; In &#8804; Iz is about overload protection. In the case of a spur from a ring final, Ib & In are at most 13A or 20A. They cannot, in a compliant scenario, be otherwise because that is what BS 1363 limits them to, and the spur, or radial as described above, is supplying a BS 1363 accessory.

As always, who knows what was in the mind of those who wrote the regs, but I'm not finding it very easy to buy into this argument, particularly the reliance on socket 'ratings' to establish Ib or In. For a start, are you sure that BS1363 forbids the manufacture of a double socket rated at 2 x 13A? - I thought that, although it's probably true that no such animals are currently manufactured, BS1363 would actually allow them if they did exist. Maybe I'm wrong (and I don't have easy access to BS1363 - what about you?).

Perhaps more to the point, BS7671 represent 'The Wiring Regulations', about which (along with the ratings of sockets) consumers will generally have no knowlege. That being the case, I would have thought that the regs would have to accept that two 13A loads (Ib=26A) might be plugged into a double socket, each with 13A fused plugs (In=26A), the installation itself being fully compliant with BS7671.

Kind Regards, John.

 

[ban-all-sheds]

For a start, are you sure that BS1363 forbids the manufacture of a double socket rated at 2 x 13A?

It doesn't forbid it but it doesn't require it.

There is no BS 1363 compliant test to determine if it can take more than 20A.

I don't have easy access to BS1363 - what about you?).

I have an old version, but AFAIK the update I applied to the part which covers the load test is the latest.

Perhaps more to the point, BS7671 represent 'The Wiring Regulations', about which (along with the ratings of sockets) consumers will generally have no knowlege.

BS 7671 is choc-full-o-stuff that about which consumers will generally have no knowledge.

Where would you like to start constraining what those who do know may do out of concern for potential misuse by the ignorant?

IMO a good place might be to answer all 7 questions above with "not safe".

That being the case, I would have thought that the regs would have to accept that two 13A loads (Ib=26A) might be plugged into a double socket, each with 13A fused plugs (In=26A)

My position is that they cannot.

 

[JohnW2]

For a start, are you sure that BS1363 forbids the manufacture of a double socket rated at 2 x 13A?

It doesn't forbid it but it doesn't require it. There is no BS 1363 compliant test to determine if it can take more than 20A.

That's the BSI's problem isn't it - if they permit a 2 x 13A rating but do not specify a test for more than 20A? In any event, if you agree that a double socket rated at 2 x 13A could be BS1363-compliant, then it surely puts paid to your argument that a double socket can be assumed to never represent more than a 20A load?

That being the case, I would have thought that the regs would have to accept that two 13A loads (Ib=26A) might be plugged into a double socket, each with 13A fused plugs (In=26A)

My position is that they cannot.

That seems like an unrealitic assumption, and would become even more so if a 2 x 13A rated (and BS1363-compliant) socket were to appear.

Kind Regards, John.

 

[ban-all-sheds]

BS 1363 requires that a DSO be able to handle a load of 20A.

Whatever extra engineering Brand X put into theirs, any installed socket could at any time be replaced by one which complies with BS 1363 and no more.

General ignorance notwithstanding, circuits must be designed and loads arranged so that any make of BS 1363 accessory can be used. It must never be assumed that any socket can handle more than the 20A which BS 1363 requires of it.

There would be no reason for BS 7671 to assume anything other than the proper use of BS 1363 accessories.

 

[JohnW2]

BS 1363 requires that a DSO be able to handle a load of 20A. Whatever extra engineering Brand X put into theirs, any installed socket could at any time be replaced by one which complies with BS 1363 and no more. General ignorance notwithstanding, circuits must be designed and loads arranged so that any make of BS 1363 accessory can be used. It must never be assumed that any socket can handle more than the 20A which BS 1363 requires of it.

Agreed, that must never be assumed, but that's not the point in question. You have agreed that a Brand X BS1363-compliant socket could be rated to handle 2 x 13A (and we know that any BS1363 socket will accept two plugs with 13A fuses in them, connected to 13A loads) - so, to adapt your words, it must never be assumed that any socket cannot handle more than the 20A minimum which BS1363 requires of it.

As you rightly say "circuits must be designed and loads arranged so that any make of BS 1363 accessory can be used", but, to use your language, the conclusions you've drawn from that are 'AAF'. If the circuit has to be designed to be safe with any BS1363 accessory. and since you agree that a double socket rated at 2x13A could be BS1363-compliant, then one would expect BS7671 to require the design to be based on that (BS1363-compliant) possibility.

IMO, this whole mess exists because, contrary to common sense and what was always going to be the beliefs of most consumers/users, the BSI allowed themselves to be persuaded to permit manufacture and sale of a "double 13A socket" which could not handle 2 X 13A loads.

Kind Regards, John.

 

[ban-all-sheds]

Agreed, that must never be assumed, but that's not the point in question.

That is precisely the point in question.

You have agreed that a Brand X BS1363-compliant socket could be rated to handle 2 x 13A (and we know that any BS1363 socket will accept two plugs with 13A fuses in them, connected to 13A loads) - so, to adapt your words, it must never be assumed that any socket cannot handle more than the 20A minimum which BS1363 requires of it.

That adaptation is pointless - it no longer makes the point.

It must never be assumed that any socket can handle more than the 20A which BS 1363 requires of it.

Therefore you must never design a use of more than 20A from it.

Therefore you never need a properly designed circuit to be able to support more than 20A from it.

Therefore your Ib & In are 20A, not 26.

As you rightly say "circuits must be designed and loads arranged so that any make of BS 1363 accessory can be used", but, to use your language, the conclusions you've drawn from that are 'AAF'. If the circuit has to be designed to be safe with any BS1363 accessory. and since you agree that a double socket rated at 2x13A could be BS1363-compliant, then one would expect BS7671 to require the design to be based on that (BS1363-compliant) possibility.

Plenty of people have cars which can go at speeds considerably in excess of the national limit. 50% more is far from unusual.

That does not make it compliant to use it at that speed, nor does it place any imposition on road designers to make their products capable of safely supporting the use of a vehicle at that speed.

IMO, this whole mess exists because, contrary to common sense and what was always going to be the beliefs of most consumers/users, the BSI allowed themselves to be persuaded to permit manufacture and sale of a "double 13A socket" which could not handle 2 X 13A loads.

Indeed, but they did.

 

[JohnW2]

It must never be assumed that any socket can handle more than the 20A which BS 1363 requires of it.
Therefore you must never design a use of more than 20A from it.
Therefore you never need a properly designed circuit to be able to support more than 20A from it.

We're clearly never going to agree. I obviously do agree that one should never 'design' a circuit with the intention (or knowledge) that >20A load would be drawn through one double socket. However, since the designer has absolutely no control over what unskilled users may plug into that socket, the only safe design assumption is that two 13A loads (containing fuses with total In of 26A) might be plugged in.

It's very different from your speed limit analogy. Virtually all drivers know what the speed limits are, and if they choose to travel at 1.5 times that speed, it's their problem, and there is no obligation on road designers/builders to produce roads which are safe for such excessive speeds. In total contrast, very few members of the general public know that a double socket cannot safely handle 2 x 13A loads, so responsible/safe design should assume that such loads are far from impossible.

Kind Regards, John.

 

[bernardgreen]

very few members of the general public know that a double socket cannot safely handle 2 x 13A loads, so responsible/safe design should assume that such loads are far from impossible.

Simple solution.....Do not install double sockets. Install only singles in areas where over loading may be possible.

 

[ban-all-sheds]

We're clearly never going to agree.

I'm not the only one who disagrees with you.

To the list you can add the members of JPEL/64 and its predecessors, and every single electrician who has signed an EIC/MWC/EIC/EICR since 1946....