On 29/09/2020 20:58, No Name wrote:
On 29/09/2020 19:14, Harry Bloomfield wrote:
John Rumm explained :
While normally placed on their own circuit, sharing with the heating
controls sounds fine as well since they are unlikely to be more than
a couple of amp at most.

3kw immersion heater = 12.5amps !

As a very temporary solution, it will be just acceptable to connect it
via a 13amp plug, into a socket. Your heating control circuit will
likely be only 3 or 5amp amp fused.


you are using 240 V in your I = P/V calculation.

Due to EU hamronisation, system voltage is now closer to 220 V so that
makes I = 13.63A......

A couple of points to keep in mind. The EU wide voltage spec is 230V
+10%/-6% a loose spec that includes all the common generation voltages
used in the EU states.

However our generation voltage has *not actually changed*, and is still
240V. But 240V is within the allowable spec of 216V - 253V

For design purposes however we use 230V

Lastly for a resistive load, lowering the voltage does not result in it
drawing more current to compensate for the lower voltage to maintain a
given power output. If its actual power output at 240V is 3kW, reducing
the voltage to 216V will drop the power output to ~2.4kW, at 253V it
would rise to ~3.3kW.

(the heaters documentation will normally specify at what voltage the
output was calculated)


--
Cheers,

John.

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