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Maximum sustained current perrmitted from 13 amp plug ?

This sounds an overly simplistic question, and the obvious answer is of course 13 amps. There is a clue in the name you know.

However in the case of a simple resistive load, the current will increase at a higher supply voltage. So at what voltage is the current measured for approval purposes ?

At 230 volts, the nominal or declared voltage ?

At 240 volts, the average voltage actually supplied most of the time in most places ?

Or at 253 volts, the maximum permitted. Or even at 256 volts the maximum achieved in an outbuilding with a bit of voltage rise due to grid tied PV on the roof.

The question has arisen due to a number of brand new "fast boiling" domestic electric kettles of reputable make failing a third party PAT test due to "excessive current"

I repeated the test with my PAT tester and achieved a similar result, FAIL in the premises in which they are to be used, but "pass" if tested elsewhere.

Tests with a variac and calibrated ammeter showed that a cold kettle on a 250 volt supply uses nearly 14 amps. just under 13 amps at 230 volts, both figures declining a little as the water starts to heat.

Had I done the original testing, I would have been inclined to use a little common sense and discretion and to pass an appliance that uses less than 10% overcurrent for a few minutes.

I would not pass an appliance such as a space heater that used even a slight overcurrent for hours at a time.

Wondered what others think.

And whilst we are on the subject, what about large portable air conditioners ? Available to hire fitted with 13 amp plugs, they appear to be a constant wattage load and use nearly 15 amps if the supply voltage is very low, and almost exactly 13 amps at 240 volts.

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0 David Stone over 4 years ago

I don't think that the test which was carried out is in any way a PAT fail. It is ridiculous to worry that a kettle takes slightly more than 13A at something above nominal voltage, and if the volts were low at 208V a 3kW appliance could quite reasonably take about 14.5A. A 13A plug will carry about 20A for short periods, and this does not cause serious overheating, because of the usual reason forgotten by electricians of thermal inertia and thermal capacity. These items will have passed the manufacturers test, be CE marked etc, and if you want to complain it would be very difficult as you would be claiming the CE mark was invalid, probably from a British manufacturer (wherever it was made) for a British brand. I suggest your PAT contractor is an Id**t and requires re-education and should not be employed again. As the PAT tester does not know what kind of appliance is connected, how does it set the maximum current anyway? It is normally a user setting, so perhaps it is incorrectly set at 13A -+ no tolerance at all as it is accurate to 0.000001%? The whole basis of this current test is nonsense.

For the other comments BG, you are making the same mistake yourself. A heater which takes slightly over 13A (say 14A) is in no way dangerous to plug or anything else. The whole 13A fuse system uses a 13A fuse to prevent overload, The fuse blows at about 17A after about an hour, and this is the safety valve for everything. If I wanted to make it fuse quickly at about 14A, I would have to use a fuse with a continuous rating of about 9A, which you will notice we do not. Why is it that almost no one here seems to understand temperatures, overload currents, fuse characteristics, and thermal capacities here, they are an important fundamental piece of electrical engineering!

Items with a negative input impedance (switch mode power supplies) take more current at lower voltages, but again are adequately protected by fuses of 13A for appliances. This may be plug in induction hobs, chargers, vfd motors etc. Forget the working current, 3 kW maximum is the expected power, a much better indicator of proper operation than the current. Remember the test instrument accuracy (probably no better than 3%) and probably more like 5 or 10% for indicated power, and remember the power factor may not be 1.
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0 David Stone over 4 years ago

I don't think that the test which was carried out is in any way a PAT fail. It is ridiculous to worry that a kettle takes slightly more than 13A at something above nominal voltage, and if the volts were low at 208V a 3kW appliance could quite reasonably take about 14.5A. A 13A plug will carry about 20A for short periods, and this does not cause serious overheating, because of the usual reason forgotten by electricians of thermal inertia and thermal capacity. These items will have passed the manufacturers test, be CE marked etc, and if you want to complain it would be very difficult as you would be claiming the CE mark was invalid, probably from a British manufacturer (wherever it was made) for a British brand. I suggest your PAT contractor is an Id**t and requires re-education and should not be employed again. As the PAT tester does not know what kind of appliance is connected, how does it set the maximum current anyway? It is normally a user setting, so perhaps it is incorrectly set at 13A -+ no tolerance at all as it is accurate to 0.000001%? The whole basis of this current test is nonsense.

For the other comments BG, you are making the same mistake yourself. A heater which takes slightly over 13A (say 14A) is in no way dangerous to plug or anything else. The whole 13A fuse system uses a 13A fuse to prevent overload, The fuse blows at about 17A after about an hour, and this is the safety valve for everything. If I wanted to make it fuse quickly at about 14A, I would have to use a fuse with a continuous rating of about 9A, which you will notice we do not. Why is it that almost no one here seems to understand temperatures, overload currents, fuse characteristics, and thermal capacities here, they are an important fundamental piece of electrical engineering!

Items with a negative input impedance (switch mode power supplies) take more current at lower voltages, but again are adequately protected by fuses of 13A for appliances. This may be plug in induction hobs, chargers, vfd motors etc. Forget the working current, 3 kW maximum is the expected power, a much better indicator of proper operation than the current. Remember the test instrument accuracy (probably no better than 3%) and probably more like 5 or 10% for indicated power, and remember the power factor may not be 1.
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Maximum sustained current perrmitted from 13 amp plug ?

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