Power=Voltage x Ampage that doesnt add up!

[Gus]

I’ve just started the C&G2330 course at college part time as I want a career instead of been stuck in dead end jobs like the one I’m in now, having just started learning about the industry I’m very inquisitive about everything and was wondering if some could explain to me why these figure on the card and plastic bailing machine a work don’t add up! Power 6300watts, 400volts and 6.3amps. If Power is Volts x Amps why isn’t the wattage of the bailer 2520watts or the amps 15.75? If it 3 phase 400v then surely the voltage isnt wrong.

I know this may seem like a waste of time to an experienced sparky but this is just 1 of those small things that’s bugging me!

Muchos Gracisas

 

[pushrod]

I’ve just started the C&G2330 course at college part time as I want a career instead of been stuck in dead end jobs like the one I’m in now, having just started learning about the industry I’m very inquisitive about everything and was wondering if some could explain to me why these figure on the card and plastic bailing machine a work don’t add up! Power 6300watts, 400volts and 6.3amps. If Power is Volts x Amps why isn’t the wattage of the bailer 2520watts or the amps 15.75? If it 3 phase 400v then surely the voltage isnt wrong.

I know this may seem like a waste of time to an experienced sparky but this is just 1 of those small things that’s bugging me!

Muchos Gracisas

the volts and amps figures are probably the apparent power in each phase and the 6300 watts the total real power. Because it is a motor? (an inductive load) there will be a power factor associated with it and as a result it will have to have larger cables supplying it than you would expect from a simple power = volts X amps calculation.

Your 400 x 6.3 would give you apparent power in voltamps, not the true power - (the watts figure) to get true power you multiply your voltamps by the power factor - maybe 0.8 ish in this case.

Hope this helps.

edit : if you have just started your 2330 you probs won't cover this til about half way through. It could be further complicated by the output power taking account of efficiency.

 

[Gus]

thanks for that pushrod

 

[electro]

Hi Gus

use 692.8 volts instead of 400 then try it

regards

 

[Guest123]

Hi.

3 phase Ib (design current) is worked out differently to single phase Ib as you need to include the "root 3" calculation of 1.732 in the equation.

For instance I have a 6000W 3P 400V Motor,

P/V x (root 3) x power factor - 6000/(400 x 1.732 x 0.8) = 6000/588.8 = 10.12A.

Hope this works as an example for you.