Installing extra appliance, electric supply advice needed

I'm sorry to hear that you and BAS find it hard to understand.If they were not intended to carry 13A, why would they be marked 13A?
For a start, it's only a few days since you reminded me that a manufacturer's 'rating' means nothing unless qualified - e.g. in relation to the duration of load to which it refers, ambient conditions, mounting method etc.
Does a 32A MCB have a different rating when installed next to another? or, indeed, when it is fitted with a double or triple toggle as part of a two-pole or three-pole MCB?
Well, at least in some senses (and for at least some manufacturers) the short answer appears to be 'yes' ....
Mr Wylex said:
Adjacent thermal-magnetic MCBs should not be continuously loaded at or approaching their nominal rated currents when mounted in enclosures. It is good engineering practice to apply generous derating factors or make provision for adequate free air between devices. In these situations, and in common with other manufacturers, we recommend a 66% diversity factor is applied to the MCB nominal rated current where it is intended to load the MCBs continuously (in excess of 1 hour).

Kind Regards, John
Yes, I did remind you of that - so what? 13A is a rating that is not qualified by a descriptor such as "short-term", "single-outlet only", etc.

The Wylex quote refers to mounting in enclosures. In engineering terms, it is saying that the Ithe rating is less than the Ith rating.

Sorry about that lousy formatting, I'm busy backing-up the laptop before I hand it back tomorrow - I'm retiring, as of 31 Dec! :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL: :LOL:

Would that be Major Recall Wylex ? We know him well :LOL:
 
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But it's not a matter of safety versus commercial interest. There is no real safety issue at stake here. Perhaps I'd given the wrong impression - there are others involved in the drafting of most product standards, including HSE and various consumer protection groups.
Yes, I understand all that, so maybe you did 'give the wrong impression', since it was you who wrote:
However, given that the manufacturers have no great incentive to give themselves more onerous tests to perform, the standard has not been updated in that respect.
...which seems to imply that the interests of the manufacturers resulted in the Standard not being updated, whatever other members of the relevant committees may have felt.
BSI, like nearly all other publishers, do not have technical staff to review the content of standards. That is done by the members of the committee concerned.
Indeed, but I don't think the general public would distinguish between the BSI (the 'publisher') and its committees. What matters to them is that whoever writes the Standard (the committees) are appropriately constituted so that commercial interests are not able to 'overcome' considerations of 'public interest' (e.g. 'safety') - which I imagine (hope) actually is the case..

Kind Regards, John
John,

Back in the real world, the balance of representation on committees varies. BSI have an obligation to publish most European standards without changes, but they can implement a "safeguard action" to prevent publication is they are alerted to a problem by e.g. a committee member. This would usually result in a pretty quick (in standards terms!) amendment. This happens several times per year. Although in this case BS1363 is entirely 'home'grown', the same principle could apply. This implies that no-one has accused BS1363 of leading to the placing on the market of unsafe products, and we don't hear of many instances when a fully loaded dual outlet has overheated due to simultaneous use of two 3kW loads - when they do overheat, it is due to a faulty plug, or a loose connection.

I have been involved over the last couple of years in a case where a piece of safety equipment on board a ship failed, leading to a fatal accident. In my opinion the failure was due to a faulty ISO standard, so I proposed an amendment. The BSI committee agreed, but the chairman of the ISO committee did not accept the proposal. Later on we had a Coroner's Report recommending that BSI propose the amendment I had drafted, as a result of which the ISO committee chairman will soon be an ex-chairman.
 
Would that be Major Recall Wylex ? We know him well :LOL:
We do - but, unlike Mr MK, he does seem to advise de-rating MCBs (maximum current load) when they are installed adjacent (without any 'free air gaps') in 'enclosures' (which, as I've said, I take to include CUs/DBs).

Kind Regards, John
 
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... and we don't hear of many instances when a fully loaded dual outlet has overheated due to simultaneous use of two 3kW loads - when they do overheat, it is due to a faulty plug, or a loose connection.
As I've said in my (very limited) experience, I've never encountered such a problem myself - but, as I also keep saying, I don't think I should totally ignore what (some) electricians tell me (here and elsewhere).

As eric often points out, I suspect that the greatest source of heat is actually the fuse in the plug. If a 13A BS1362 fuse is going to melt within 400 seconds (per the standard) at 30A, it must get pretty hot with a continuous current of 13A.

Kind Regards, John
 
Would that be Major Recall Wylex ? We know him well :LOL:
Yes, the one who speaks of diversity when he means derating!
Indeed. When I first saw that, I actually 'wondered' - but I eventually decided that it would make no sense for him to be talking about any sort of diversity that I understand! However, I did (and still do) worry a little about whether I am properly understanding what they mean, since the phrases "derating factor" and "diversity factor" appear in adjacent sentences, seemingly implying that someone must perceive a difference!

Kind Regards, John
 
Would that be Major Recall Wylex ? We know him well :LOL:
We do - but, unlike Mr MK, he does seem to advise de-rating MCBs (maximum current load) when they are installed adjacent (without any 'free air gaps') in 'enclosures' (which, as I've said, I take to include CUs/DBs).

Kind Regards, John
"He" is talking about derating MCBs when they are installed in an enclosure, which we agree would include use in a CU or MCB, not about derating them when they are adjacent to each other.
 
"He" is talking about derating MCBs when they are installed in an enclosure, which we agree would include use in a CU or MCB, not about derating them when they are adjacent to each other.
"He" is surely talking about both those things (simultaneously) - i.e. adjacent MCBs in an enclosure (such as a CU)? ...
Mr Wylex said:
Adjacent thermal-magnetic MCBs should not be continuously loaded at or approaching their nominal rated currents when mounted in enclosures. It is good engineering practice to apply generous derating factors or make provision for adequate free air between devices.

Kind Regards, John
 
If as is common you use two adjacent B32 MCBs in a CU, to serve 2 separate ring finals, would you derate the ring finals to avoid tripping the MCBs?

No, you (or most people) wouldn't.

That Wylex statement seems to me to be saying that they need derating because of the enclosure, but it's such a vague statement that you could be right. I'll have a look at the product standard tomorrow, if I have time - I have a lot of expenses to claim before I leave!
 
If as is common you use two adjacent B32 MCBs in a CU, to serve 2 separate ring finals, would you derate the ring finals to avoid tripping the MCBs? No, you (or most people) wouldn't.
No, most people wouldn't (but nor would they usually be expecting the circuit to be carrying a current 'at or approaching the current rating of the MCB', at least, for appreciable periods of time). As for "...to avoid tripping the MCBs", the MK literature gives no insight into the reason for the de-rating they advocate. You could be right about the 'reason', but it might also just be a question of potential thermal damage to the component (which may or may not result in tripping).
That Wylex statement seems to me to be saying that they need derating because of the enclosure, but it's such a vague statement that you could be right. I'll have a look at the product standard tomorrow, if I have time - I have a lot of expenses to claim before I leave!
Thanks. As you say, their (vague) statement seems to rely on the MCBs being in an enclosure (as well as adjacent) - but, of course, it would be totally unacceptable to use the sort of MCBs they are talking about if they were not in some sort of enclosure, so it's almost a redundant 'condition'!

Kind Regards, John
 

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