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PostPosted: Thu Oct 11, 2018 6:18 pm 
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wine~o wrote:
les1 wrote:
Interesting, possibly 30 amp at the use box. I have done the swop & fitted a 13 amp plug to the immersion cable it so we shall see. However thanks for the thought.


There is a very good reason that it was wired via a switch (20 Amp) rather than a 13 Amp plug.

Immersion heating elements are normally 3 Kw (3000 Watts) Now at 230 Volts (Nominal supply) that equates to 3000 divide 230 = 13.04 Amps, so not an issue, however that nominal voltage could be + 10% or - 6% at - 6% you are looking at 216 V, 3000 divide 216 = 13.87 Amps which means that the fuse will give out over time/repeated use.

Personally I'd have left it as it was originally installed or put in a dedicated immersion heater time switch (about £70 last time I checked)

I'm sure only me will put me right if I'm wrong



That is not the correct answer.

A 3kW element at 240V should be treated as a resistive load for this calculation. The resistance of the element is the only constant.

P = VI
3000 = 240 x I
I = 3000/240
I = 12.5A

R = V/I
R= 240/12.5 = 19.2 ohms

So the element has a resistance of 19.2 ohms. That is your constant for all calculations with different voltages.

Put 216V across the element and the current is

216/19.2 = 11.25A

As the voltage only changed on paper and most of the UK is still running at 240V all that has happened is that the 240V 3kW element has been rebadged as a 230V 2.7kW element.


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For this message the author OnlyMe has received gratitude : wine~o
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PostPosted: Thu Oct 11, 2018 6:30 pm 
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Thanks for correcting me OnlyMe, do you think it is a sensible idea to change the 20A switch for a socket and plug arrangement though ?

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PostPosted: Thu Oct 11, 2018 8:25 pm 
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wine~o wrote:
Thanks for correcting me OnlyMe, do you think it is a sensible idea to change the 20A switch for a socket and plug arrangement though ?

No


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