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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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  • +1
    Chris Pearson said:
    Not "illegal",

    Are we sure about that? It does depend on whether the machinery actually takes that much power, but if it does and something happens ... see above, Electricity at Work Regulations.

  • 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.

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  • 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.

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  • 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

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