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80% loading in Small power / Lighting Circuit breakers

Nick Parker
Is the 80% loading rule apply on lighting / socket outlet loads on a circuit breaker?, for example, if the circuit breaker rating is of 15A, the maximum load on that breaker would be 12A and you cant load more than that.

I think this rule is more common in Americas. How about this rule in Europe? Why 80% loading and not to the maximum capacity?
  • 0
    There is no rule/law/Regulation with such a requirement in the UK.

    The UK even allow some controlled overload of circuits for short periods - cooker circuits for example, a cooker with a total loading of 40 amps can be fed from a 32 amp circuit breaker, as it is known that the 'overload' will only be for a short period, and irregularly.
  • 0
    Nick Parker:

    Is the 80% loading rule apply on lighting / socket outlet loads on a circuit breaker?, for example, if the circuit breaker rating is of 15A, the maximum load on that breaker would be 12A and you cant load more than that.

    I think this rule is more common in Americas. How about this rule in Europe? Why 80% loading and not to the maximum capacity? 


    There has been talk of spacing M.C.B.s in consumer units, leaving a blank space between them if they are running near to full capacity, to prevent heating up adjacent M.C.B.s and making them more prone to nuisance trip. But that is just personal preference as far as I know.


    Z. 


  • 0
    Just wild speculation here, as I know almost nothing about US circuit breakers; but maybe in the US, CBs are labelled with the current they will eventually trip at, as opposed to here in 60898 land, where they are labelled with the current they can continuously handle .
  • 0
    wallywombat:

    Just wild speculation here, as I know almost nothing about US circuit breakers; but maybe in the US, CBs are labelled with the current they will eventually trip at, as opposed to here in 60898 land, where they are labelled with the current they can continuously handle .


    My head has the same idea in it. BS EN MCBs are guaranteed not to trip at below 113% of their rating (at least for 'conventional time ' - usually an hour) - I suspect the Americans don't have a similar margin.


    That said, some manufacturers do recommend de-rating MCBs when they're next to other heavily loaded MCBs - due to them heating each other.


      - Andy.


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