@240v the 3kW load (e.g. immersion heater) calc comes in at 12.5 amps.
When calculating with 230v what is the current?
When calculating with 230v what is the current?
3kW load. What do you regard as the design current?
- Thread starter SgtTrojan
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H
holmslaw
..
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No way to calculate it unless you know the linearity of the power consumption against voltage. Might be a bit less than the current at 240V, could be a bit more.
In any case, although the nominal voltage in the UK is now 230V, the actual voltage is, and is likely to remain, something around 240V.
In any case, although the nominal voltage in the UK is now 230V, the actual voltage is, and is likely to remain, something around 240V.
The resistance is 19.2 Ω
The current will be 13.17 amps at the worst case highest non fault supply voltage of 253 volts (230+10% ).
Not a problem as the cable calculations will ( I assume ) have taken that into account.
The current will be 13.17 amps at the worst case highest non fault supply voltage of 253 volts (230+10% ).
Not a problem as the cable calculations will ( I assume ) have taken that into account.
Well without trying to sound like a numpty.... 
When dividing 3000 by 230v and getting a current of 13.04 amps, I would say that this 0.4 amps has been widely ignored since the "harmonisation" and accepted as the standard means when calculating the design current for 3kW loads, hence, keeping the BS1362 fuse to 13 amps.
So.. what does this mean for our trusty 100w lamp?
Worse still what does this mean for inductive loads?
How is one supposed to correctly calculate design current? This could be a mine field!!
When dividing 3000 by 230v and getting a current of 13.04 amps, I would say that this 0.4 amps has been widely ignored since the "harmonisation" and accepted as the standard means when calculating the design current for 3kW loads, hence, keeping the BS1362 fuse to 13 amps.
So.. what does this mean for our trusty 100w lamp?
Worse still what does this mean for inductive loads?
How is one supposed to correctly calculate design current? This could be a mine field!!
That's 13.04 A, so the "widely ignored" current is only 40-ish mA, or, rounded to one place of decimals, 3kW = 13A.
But that's my point. It is not true. Many design calcs are being done incorrectly. The current is 11.98 amps @230v.
How do you know? You don't know what the power is at any voltage other than the voltage the manufacturer designed for.
As far as I understand, 13A is the design load for an FCU cartridge fuse. Cartridge fuses have to carry about 1.6 x design current for 30 minutes without melting and should melt within 30 minutes at 1.9 x design current. (I might have the figures for the wrong cartridge fuse standard.)
Given that you probably have a 16A CB or 15A semi-enclosed fuse on the immersion heater supply circuit, why introduce another fuse?
Given that you probably have a 16A CB or 15A semi-enclosed fuse on the immersion heater supply circuit, why introduce another fuse?
H
holmslaw
..
Take a 240V incandescent light bulb. (Don't worry, I wont tell the EU!)
Measure the current at the rated voltage and again at a lower voltage. What happens?
Logically, yes, that was what I meant, but then I remembered that the lunatics have taken over the asylum and it's anybody's guess what the reality will be after a few years of electric vehicles, micro-generation, and smart grid.
It's very simple people - just look at the element in question. Does it say 3kW @ 240v or 3kW @ 230v and go from there !
Ricicle, 512.1.1 requires every item of equipment to be suitable for the nominal voltage, while taking into account the highest and/or lowest voltage likely to occur in normal service, so it's a fair question to which I don't know the answer.
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