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Old 22.09.2015, 16:21
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I don't understand why my kettle works

I have a 13a kettle, which on it says it uses 2500-3000w

2500/230 =10.8a
3000/230 = 13a

My whole kitchen, definitely including this socket (but excl cooker, dishwasher) is on a 10a circuit.

How is this possible? It never trips....


Andy
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Old 22.09.2015, 16:33
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Re: I don't understand why my kettle works

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I have a 13a kettle, which on it says it uses 2500-3000w

2500/230 =10.8a
3000/230 = 13a

My whole kitchen, definitely including this socket (but excl cooker, dishwasher) is on a 10a circuit.

How is this possible? It never trips....
The nominal power is calculated based on the resistance, and it could well be that it was assuming a 230/240V supply. If we assumed that the 2500w was based on 230V then the power draw on 240V would be 2722W. The nominal figures quoted are estimates only, so that fits.

But the AC supply these days is 220V, so recalculating based on that (i.e. working out the resistance from 2500W on 230V == 21 ohms, and putting that back into the V=IR equation) would give a current draw of 10.4A.

So given a variance in the manufacture of both the kettle element ( whose resistance will anyway vary with temperature) and the fuse/circuit breaker, it's entirely conceivable that the current is never quite getting high enough to trip the circuit.

You're quite lucky - we had one in our Basel flat, which just has the old-style ceramic-mounted fuses, and it would blow the circuit about every second or third time it was used.

Last edited by Guest; 22.09.2015 at 16:47.
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Old 22.09.2015, 16:47
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Re: I don't understand why my kettle works

The lower power rating is for use in CH, whereas if you were to use said kettle in the UK, which tends to work on 13A, it would boil quicker by using full power.

P=IR

In this case, it is the current, that determines the power.







[I think I got away with that one]
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Old 22.09.2015, 16:48
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Re: I don't understand why my kettle works

Hmm ... Strange. Are you sure that the wiring to the kettle is professionally done?
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Old 22.09.2015, 16:50
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Re: I don't understand why my kettle works

also bear in mind that the greater the power uptake, the greater the current in the cable and hence the greater the voltage drop at the socket.


The 230V nominal is actually the no-load indication, and the 3000W is a best effort indication, i.e., assuming you have the full 230V.
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Old 22.09.2015, 16:53
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Re: I don't understand why my kettle works

Quote:
the AC supply these days is 220V
No, it used to be nominally 220VAC, now it's nominally 230VAC (though actually voltage is probably still 220VAC).

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P=IR

In this case, it is the current, that determines the power.
Except that the current draw is determined by the V and the R, NOT what the circuit is fused for.

However, a 10A breaker probably really trips at 13A, so that's why it doesn't trip.

Tom
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Old 22.09.2015, 16:55
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Re: I don't understand why my kettle works

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No, it used to be nominally 220VAC, now it's nominally 230VAC (though actually voltage is probably still 220VAC).



Except that the current draw is determined by the V and the R, NOT what the circuit is fused for.

However, a 10A breaker probably really trips at 13A, so that's why it doesn't trip.

Tom
There's a way to find out ... (practice vs theory).

Edit: I can understand the OP. Debugging one's own kettle in the kitchen is more challenging than boredom related to any engineering office job in CH
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Last edited by jacek; 22.09.2015 at 17:31.
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