Thanks - but, as we've agreed, we wouldn't expect end users to have to do that delving!
Kind Regards, John
Current ratings of accessories
- Thread starter JohnW2
- Start date
Kind Regards, John
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Right, at a quick glance through the 190 pages, and without going into the amendments, here are a few comments.
Surprisingly (at least to me) there is no requirement to specify an OCPD.
There is no requirement for an instruction sheet, except for "8.8 If it is necessary to take special precautions when installing the switch, details of these
shall be given in an instruction sheet which accompanies the switch.
Instruction sheets shall be written in the official language(s) of the country in which the switch
is to be sold.
Compliance with the requirements of 8.7 and 8.8 is checked by inspection.
NOTE 1 Special precautions may, for example, be necessary for unenclosed switches and for switches for panel
mounting.
NOTE 2 In order to ensure that, after installation, the conditions necessary to meet the requirements of this
standard are achieved, the instruction sheet should include clear information with regard to the following:
– dimensions of the space to be provided for each switch;
– dimensions and position of the means for supporting and fixing the switch within this space;
– minimum clearance between the various parts of the switch and the surrounding parts where fitted;
– minimum dimensions of ventilating openings, if needed, and their correct arrangement.
– details of lamps to be used in cases where switches have replaceable pilot lamps."
The ratings for current and voltage, as well as for current for fluorescent loads, if different, are the ratings at which the switch can pass the tests. For example, the making and breaking capacity is tested at 1,1 time rated voltage and 1,25 tmes the rated current, using AC at a power factor of 0,3. Switches rated 10A are tested for 200 operations at 30 per minute.
So the ratings have no real meaning in themselves (unlike industrial switchgear and controlgear) but are simply used to determine the test conditions.
The nearest I can find to an answer to John's question is the temperature rise test. For a switch rated 10A, it is mounted 'as in normal use' and subjected to a current of 13,5 A for 1 hour. The permissible temperature rise "shall not be excessive". Interestingly the terminals are connected to a 1 m length of 2,5 mm2 conductor.
What's the 1 hr tripping current for a B10 MCB?
Surprisingly (at least to me) there is no requirement to specify an OCPD.
There is no requirement for an instruction sheet, except for "8.8 If it is necessary to take special precautions when installing the switch, details of these
shall be given in an instruction sheet which accompanies the switch.
Instruction sheets shall be written in the official language(s) of the country in which the switch
is to be sold.
Compliance with the requirements of 8.7 and 8.8 is checked by inspection.
NOTE 1 Special precautions may, for example, be necessary for unenclosed switches and for switches for panel
mounting.
NOTE 2 In order to ensure that, after installation, the conditions necessary to meet the requirements of this
standard are achieved, the instruction sheet should include clear information with regard to the following:
– dimensions of the space to be provided for each switch;
– dimensions and position of the means for supporting and fixing the switch within this space;
– minimum clearance between the various parts of the switch and the surrounding parts where fitted;
– minimum dimensions of ventilating openings, if needed, and their correct arrangement.
– details of lamps to be used in cases where switches have replaceable pilot lamps."
The ratings for current and voltage, as well as for current for fluorescent loads, if different, are the ratings at which the switch can pass the tests. For example, the making and breaking capacity is tested at 1,1 time rated voltage and 1,25 tmes the rated current, using AC at a power factor of 0,3. Switches rated 10A are tested for 200 operations at 30 per minute.
So the ratings have no real meaning in themselves (unlike industrial switchgear and controlgear) but are simply used to determine the test conditions.
The nearest I can find to an answer to John's question is the temperature rise test. For a switch rated 10A, it is mounted 'as in normal use' and subjected to a current of 13,5 A for 1 hour. The permissible temperature rise "shall not be excessive". Interestingly the terminals are connected to a 1 m length of 2,5 mm2 conductor.
What's the 1 hr tripping current for a B10 MCB?
Many thanks. I'm not sure I'm all that surprised. I doubt you'd find anything about protective devices in BS1363, either. I suppose it could be argued that how a user chose to protect (or not protect) the product is not their concern!
Right - so they're not really 'ratings' at all, merely pass criteria for tests - which are presumably quite likely to differ from 'recommendations for use' (aka 'ratings') if they gave them.
"Shall not be excessive"?!
Are you used to seeing language that vague in a test specified in a Standard? 14.5A - so 13.5A is really 'neither one thing nor the other'!
Kind Regards, John
BS1363 certainly refers to BS1362 fuses. Whether it mentions OCPD for the ring final I can't check, since I'm working from home today and my 1363 is in the office.
The ratings aren't pass criteria, but values from which the test parameters are derived.
There is some guidance on what is an excessive temperature rise, but it isn't clear or concise enough to quote. In any case, I would have described a 1 hour current rating as a short-term rating. Without having the C-B tripping curves to hand, I would guess that a B10 could pass 13,5 A for several hours, so we seem to have reached a conclusion that a 10A switch to BS EN 60669-1 will not be protected against small (<45%) overloads by a B10 circuit-breaker, which I think answers your original question.
The ratings aren't pass criteria, but values from which the test parameters are derived.
There is some guidance on what is an excessive temperature rise, but it isn't clear or concise enough to quote. In any case, I would have described a 1 hour current rating as a short-term rating. Without having the C-B tripping curves to hand, I would guess that a B10 could pass 13,5 A for several hours, so we seem to have reached a conclusion that a 10A switch to BS EN 60669-1 will not be protected against small (<45%) overloads by a B10 circuit-breaker, which I think answers your original question.
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Indeed, and I'm not sure you'd be able to quantify it even if you did have the curves in front of you, since the curve is almost vertical at that point.
If it does answer my original question, I think its only a partial answer, and only in relation one one specific accessory.
If the approach to accessories were the same as for cables, the situation would presumably be that a '10A' accessory was considered able to safely carry 14.5A (or, of course, any lower current) for an hour, and was therefore adequately protected by a B10 MCB. If a switch only just passed the BS EN 60669-1 test you have described, it would presumably follow that 14.5A for one hour would result in it failing that test, but does that necessarily mean that, in service (rather than in terms of passing the test), 14.5A for an hour would be unacceptable or 'unsafe'?
Kind Regards, John
Well, the criterion for passing the test is that no excessive temperature is reached, so under your more arduous test current of 14,5 A presumably the temperature reached would become excessive. These could mean a risk of burning your fingers if you touched it, or it could mean the terminals overheat thus damaging the cable insulation, or... whatever. I would say that an 'excessive' temperature is both unacceptable and likely to be unsafe.
That really depends upon exactly what the pass criteria for the test are, doesn't it? (i.e. what "excessive" means in that context). It surely would not be at all unusual (probably the converse) for a test's pass/fail borderline to be on the 'safe' side of the point at which a product would be deemed unsatisfactory/unsafe in service, would it?
Kind Regards, John
I can't see how it could. We know from past discussions that the temperature rise test for a double socket is done at 20A, and that currents above that can result in unacceptable temperature rises and damage, so no 32A (or even 20A) CPD is, in itself, going to be able to provide adequate protection.
Kind Regards, John
Simple logic John. If it doesn't meet the pass criteria then it has failed. If one of those criteria is that the temperature is not excessive, and that is failed, then it follows that the temperature is excessive. Perhaps not to the point of creating an immediate hazard, but nonetheless unacceptable.
I have a vague feeling that it refers to "intended for use in a RFC protected by XXXXX". There is certainly a refernce in the heat rise test to the RFC being loaded, i.e. the conductors will be at a higher than ambient temperature and hence will not conduct away as much heat as they would if cooler. I'll check on Friday, I'm out at a meeting tomorrow.
As I said, I don't think it is necessarily that simple - the pass/fail criteria of an acceptance test and the level at which a 'hazard in service' would exist can be very different. One sees this dramatically in many safety-critical areas - e.g. where health hazards are involved (drugs, enivornmental hazards) or in areas such as the aerospace and nuclear industries. In all such situations there are usually 'miles and miles' between the situation in which something would just fail an acceptance test and the situation in which it would be start to be regarded as a hazard 'in service'. For example, if the lowest harmful level of a contaminant in a drug or foodstuff was considered to be, say, 100 parts per million, an acceptance test may well have a fail criterion of >5 or >10 ppm.
In any event, I don't really want or need to argue with you about this, and am probably only playing Devil's Advocate at the moment. The fact is that you have already thrown a cat in amongst a good few people's pigeons by suggesting that a 10A switch is probably not 'adequately protected' by a B10 MCB - which probably means that the equivalent would probably also be true of, say, 20A and 45A switches, and maybe plenty of accessories other than switches. As you will understand, that is what I rather suspected when I started this thread - although I strongly suspect that most people will nevertheless carry on believing that (as is the case with cable, because of the 'adjustments' to the CCC tables) adequate protection is afforded so long as the In of the CPD is not greater than the 'rating' of the accessory!
Kind Regards, John
You might recall that you used the term "unsatisfactory/unsafe in service". Anything that fails the test in its standard is unsatisfactory. It might be unsafe, or maybe not.
Remember that we are not talking about pharmaceutical products, or aerospace/nuclear controls, but low-cost items that are all too often built down to a price by underpaid workers in developing countries. As a result some can be unsafe even though they scrape through the standard's tests, let alone when they fail those tests. The standards themselves recognise that; to return to the oft-discussed dual 13A socket-outlet, they are not tested at the full 26A, probably because there is no point in introducing a test that 90%+ of existing products would fail.
Remember that we are not talking about pharmaceutical products, or aerospace/nuclear controls, but low-cost items that are all too often built down to a price by underpaid workers in developing countries. As a result some can be unsafe even though they scrape through the standard's tests, let alone when they fail those tests. The standards themselves recognise that; to return to the oft-discussed dual 13A socket-outlet, they are not tested at the full 26A, probably because there is no point in introducing a test that 90%+ of existing products would fail.
I would have said that failing a test in a Standard indicated that something was "potentially unsatisfactory/unsafe in service", but that something which only just failed the test was not necessarily anywhere near the level that would actually be "unsaisfactory/unsafe in practice" - the difference being a 'safety margin', likely to be very wide in the sort of safety-critical industries mentioned above, but hopefully never zero in any situation.
If one were being opragmatic (I'm not sure whether writers of Standards do that!), I would have thought that would be a good reason for the test specified in the Standard to have a significant built-in safety margin.
However, as I wrote yesterday, this is Devil's Advocate stuff. I essentially agree with you, and hence that an accessory which may not necessarily be able to cope with 14.5A for an hour (because the test in the Standard only requires 13.5A) probably cannot reasonably be regarded as having a high enough guaranteed tolerance to current to be 'adequately protected' by a B10 MCB. That's the conclusion which interests me.
Kind Regards, John
Ah, I see. You are linking both "unsatisfactory" and "unsafe" to "in service". I was reading that as "unsatisfactory or unsafe in service", and stating that if a switch fails the test then it hasn't satisfied the requirement and hence is unsatisfactory. I agree that it could then be potentially unsafe, but it is already unsatisfactory.
Yes, I agree that this is all rather academic, and also that there is no evidence to show that a '10A switch' controlling a load that could give rise to overcurrent will be adequately protected by a B10 mcb.
Yes, I agree that this is all rather academic, and also that there is no evidence to show that a '10A switch' controlling a load that could give rise to overcurrent will be adequately protected by a B10 mcb.
Yes, you've worked out what I was trying to say, even if what I wrote was a bit ambiguous. Even your initial reading as "unsatisfactory or unsafe in service" shares the same ambiguity. To be totally clear, what I meant was "unsatisfactory in service and/or unsafe in service"!
Exactly and, as I wrote yesterday, I suspect that if we went delving further into the Standards, we would find corresponding situations in relation to switches of other 'ratings' and also accessories of other types. Of course, some may argue that the loads (e.g. light fittings) 'could not give rise to' an overload situation, and therefore that overload protection is not required.
Kind Regards, John
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