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13A supply to 16A (3.2kW) machine. It works fine, but is it illegal?

Dena Thompson

Hi,

I'm working with a machine that has a data plate for 3.2kW but this is peak, when all elements are running.  I have it running on a 13A RCD protected supply with no problems, but it has been suggested this is illegal.  I could understand a small machine running on a large supply, but the fact that it draws less current than the data plate surely means it is safe, although maybe running closer to the current limit. 

In service testing regs talk about fusing of circuit to protect, but never the other way round.

Can anyone quote me a reg saying either way?

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  • 0 in reply to gkenyon
    gkenyon said:
    Are we sure about that?

    I do not think that there is anything intrinsically unlawful about drawing 3.2 kW peak through a 13 A plug (and socket). After all, BS1363 (Parts 1 and 2) specifies a test current of 14 A for temperature rise tests.

    That said, there is insufficient information to decide how safe the arrangement is.

  • 0 in reply to Chris Pearson
    Chris Pearson said:
    After all, BS1363 (Parts 1 and 2) specifies a test current of 14 A for temperature rise tests.

    Sadly, the 14 A is a type test, and is for specified conditions for the temperature rise test only.

    The actual rating of the plug, fuse and socket-outlet is 13 A, NOT 14 A.

    What's worse, is, yes there's is actually some tolerance built into the assumptions about the 13 A rating ... BUT product standards (e.g. BS EN 60335 series) permit the actual rating of a product at nominal voltage to have some tolerance ... in the case of BS EN 60335 series, this can be up to 10 % at nominal voltage (and in fact for immersion heaters it actually is 10 %).

    Chris Pearson said:
    3.2 kW peak

    I think we mean '3.2 kW maximum' rather than 'peak' ... power, currents etc. are typically quoted rms according to the product and installation safety standards.

    When you consider that the supply has a 10 % tolerance too, with linear loads you can have 10 % on top of 10 % ... which is actually 1.21 % more current/power.

    So:

    1. Perhaps in reality the 13 A socket-outlet might be OK with more than 13 A, perhaps creeping higher by over an Ampere for very short periods ... but I wouldn't calculate that current at 230 V, it's natural tolerance built into the standards; and

    2. with a plate rating of 3.2 kW at 230 V, expect up to 16.8 A in use at 253 V supply, or a plate rating of 3.2 kW at 240 V, expect up to 15.5 A (linear load) at 253 V supply. This is a lot higher !


    In my opinion, to try and use these tolerances to justify 'overloading' is not responsible, and quite possibly leads to the sorts of overload and equipment damage we see in the real world, as Mike alluded to earlier with some great illustrative pics.

    Remember ... you might just be overloading, on a high supply voltage, with a positive tolerance on the power/load current also!

  • 0 in reply to gkenyon


    to try and use these tolerances to justify 'overloading' is not responsible, and quite possibly leads to the sorts of overload and equipment damage

    Agree totally, and in many ways the plug and socket regulations do us no favours by encouraging the use of 13A connectors in many cases when from a load perspective something bigger would be far more sense.
     
    I appreciate that BS 4343 style 16 and 32A sockets are not shuttered, but they could be - other circular socket designs exist have disks that spin to open the holes when the pins are put in , or we could use the old round pin 15As that certainly are, or Schucko if we could stomach line neutral reversal not being a fault.

    13A sockets are world leadingly good in many ways, but actually carrying 13A in adverse conditions is not one of them,


    Mike

  • 0 in reply to mapj1
    mapj1 said:
    I appreciate that BS 4343 style 16 and 32A sockets are not shuttered, but they could be

    Or, at least, the EN IEC 60309-4 products with integral interlocked isolator are used ... these are now required by BS 7671 for caravan site outlets, for example, in lieu of shuttered outlets.

  • 0 in reply to gkenyon


     Further to the earlier musingsas to  if Shuckos a better choice of 16A socket stuff,  some German EV owners have discovered, they are not that great at 16A for long periods - there are thermal images here that indicate 80C at the exposed socket face immediately after the plug is withdrawn - Ouch!! )


    Fundamentally I suspect all common domestic plugs are something of  a compromise, and the maximum rating should be interpreted as short duration. 


    Mike

  • 0 in reply to gkenyon
    gkenyon said:
    Sadly, the 14 A is a type test, and is for specified conditions for the temperature rise test only.

    If the owner of this machine were to cause some form of disaster, you can bet your bottom dollar that his or her legal representative would ask why a BS 1363 plug is not safe (i.e. should not melt like Mike's examples) at 14 A when the type testing has demonstrated that it is.

    gkenyon said:
    In my opinion, to try and use these tolerances to justify 'overloading' is not responsible

    I was not using the tolerances at all. The 14 A test current is subject to a tolerance of ±0.4 A (Table 2 of BS 1363-1:2016+A1:2018)

    gkenyon said:
    3.2 kW peak

    I think we mean '3.2 kW maximum' rather than 'peak'

    I was simply quoting the OP.

    Clearly, the higher the overload, the greater the risk, but for any legal action to succeed (i.e. to demonstrate that running the machine on a 13 A plug is, "illegal") any evidence that the situation was dangerous would have to outweigh the evidence of the type-test, which I think would be a tall order.

    Please note that if the machine really is run at a steady 3.2 kW for many hours, I do not condone that at all, but that still does not make the act unlawful.

  • 0 in reply to Chris Pearson
    Chris Pearson said:
    I was not using the tolerances at all. The 14 A test current is subject to a tolerance of ±0.4 A (Table 2 of BS 1363-1:2016+A1:2018)

    Agreed ... but:

    (a) 14.4 A only covers some 'leeway', which can, quite simply, be demonstrated not to be the whole picture, even for ratings below 3.2 kW; and

    (b) Only applies to one of the type tests in the standard, for the purpose of type-testing, NOT verifying that a 13 A product can really carry 13.6 to 14.4 A (give or teak a small percentage of test lab equipment measurement uncertainty) indefinitely.; and

    Chris Pearson said:
    If the owner of this machine were to cause some form of disaster, you can bet your bottom dollar that his or her legal representative would ask why a BS 1363 plug is not safe

    They could ask ...  The 'other side' will refute that, and might ask who decided to fit a 13 A plug (or connect via a 13 A connection unit), why they selected that approach, and who thought that person was competent?

    And questions for the person making the selection (if they are interviewed or asked to give evidence: 'Tell us, why did you think that a product rated  by both the manufacturer and the product standard at nominally 13 A can carry more than that for long periods?' (the best answer for which is probably not 'Because a test in the product standard is carried out at a higher current'?)

    Chris Pearson said:
    I was simply quoting the OP.

    I'm not disputing that, but I anticipated a response that might lead us further into semantics, and wanted to provide my basis in this regard.

    Chris Pearson said:
    but that still does not make the act unlawful.

    unless it leads to danger (as defined in the Electricity at Work Regulations) ... which is where I have been all along with this: the propensity to cause a danger ...

    But also, consider that earlier in this post, I mentioned 'competent' ... which may be another aspect that is explored (or, if the equipment really did run at 3.2 kW for long periods, might become an important consideration) ... EAWR Regulation 14.

    The likelihood of danger arising, agreed, might depend on how long the 3.2 kW is drawn, or, over what period (with or without inspections by users and competent persons, along with, where appropriate, tests) the equipment is used ... but if you look at my initial reply, I'm sure this aspect was also covered with the following:

    gkenyon said:

    So, what to do?

    If there is no evidence of overheating at the moment, recommend any 13 A equipment is checked regularly (if possible, by users) for signs of overheating.

    Recommend, if possible, connection by an appropriate-rated isolator, connection unit, or socket-outlet ... if a workplace, for example, BS EN 60309-2 or BS EN 60309-4 socket-outlet ('commando socket') could be used. Even if this requires a new circuit, it's probably still going to be in the ballpark of 'reasonably practicable' ?

    I suppose finally, though, I'd have to point out that, if the equipment never reaches 3.2 kW, and it's something 'erring on the side of caution', or to cover an option not included in the particular 'build' of the product that is being discussed, or, as some say, to cover 'cold element' ... well, I wouldn't condone doing extra work for no benefit !

  • 0 in reply to gkenyon
    gkenyon said:
    I suppose finally, though, I'd have to point out that, if the equipment never reaches 3.2 kW, and it's something 'erring on the side of caution', or to cover an option not included in the particular 'build' of the product that is being discussed, or, as some say, to cover 'cold element' ... well, I wouldn't condone doing extra work for no benefit !

    There we are in agreement. :-)

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