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Current carrying of plugs AC versus DC

Kelly Marie Angel

In a group discussion on Facebook it was stated that 5 amp and 15 amp plugs were designed to carry more than the stated limit because they had to work on DC as well as AC mains whereas 13 amp plug were only ever meant for AC. I cannot see how the current type would make that much difference as I type this it does occur to me that maybe skin effect comes into play but does that really make that much odds? The original discussion was about a 2 bar fire fitted with what looks like a 5 amp plug. And the fact that 2 kilowatts at 240 volts is about 8.4 amps. I was told that at one time it was permitted to run 3 5 amp sockets off one 15 amp fuse 

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    broadgage said:
    Amps are amps, and AC or DC makes no difference to the current rating. The skin effect is minute at power line frequences and at the modest currents handled by plugs and sockets.

    Agreed for practical purposes with the relatively small currents found in consumer circuits, but for future readers I'd want to emphasize that for bigger conductors skin effect is significant even at 50Hz, hence switchboard busbar shapes being material considerations, decreasing return in ampacity/mm² for larger conductors, significantly different current ratings (e.g. table 4E3) and the use of ACSR, hollow and Milliken conductors on power systems. Etc.

    Also, as Graham has pointed out, switch/disconnector ratings can be markedly different.

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    broadgage said:
    Amps are amps, and AC or DC makes no difference to the current rating. The skin effect is minute at power line frequences and at the modest currents handled by plugs and sockets.

    Agreed for practical purposes with the relatively small currents found in consumer circuits, but for future readers I'd want to emphasize that for bigger conductors skin effect is significant even at 50Hz, hence switchboard busbar shapes being material considerations, decreasing return in ampacity/mm² for larger conductors, significantly different current ratings (e.g. table 4E3) and the use of ACSR, hollow and Milliken conductors on power systems. Etc.

    Also, as Graham has pointed out, switch/disconnector ratings can be markedly different.

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