Working Out Amps For A 3-Phase Machine
- Thread starter bhamoggy
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Doesn't the machine give you a kW or KVA figure on the info plate or in the manual?
there you go then,
simply look in the BGB for an appropriate cable size,
BTW
I had a moment of blankness yesterday when I started to work out the rating of a 12v DC 10amp load ,
talk about feeling like a pillock when I got the paper out and done the sums headbang
:coat
bhamoggy
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What I was looking at was one of the online calculators like below to calculate Kva to amps.
1) enter phase (one or 3)
2) enter Kva
3) select voltage type (line to line or line to neutral)
4) enter volts
what I wasn't sure of what one to select for number 3 and why
1) enter phase (one or 3)
2) enter Kva
3) select voltage type (line to line or line to neutral)
4) enter volts
what I wasn't sure of what one to select for number 3 and why
does the machine even have a neutral?
if it does, what is it for, a few contactors or neon indicators?
why do you need to work anything out anyway?
its 37Kva, thats 12.33333333 per phase, thats all you need really, for a basic size, everything else is in the book.
if it does, what is it for, a few contactors or neon indicators?
why do you need to work anything out anyway?
its 37Kva, thats 12.33333333 per phase, thats all you need really, for a basic size, everything else is in the book.
It's 37kVA actually, & I've not done the sums!
However 12.3r A seems small for basically a 37kW load, even totally balanced across 3 phases, that would be 12.3r kW per phase if a fully balanced resistive load, which would taking a single phase calculation and ignoring pf, be about 53A per phase, if I understand the question correctly.
However 12.3r A seems small for basically a 37kW load, even totally balanced across 3 phases, that would be 12.3r kW per phase if a fully balanced resistive load, which would taking a single phase calculation and ignoring pf, be about 53A per phase, if I understand the question correctly.
I did mean 12.333333 kVA [corrected ] per phase, then do the amps, then pick the cable,
obviously, as you say, depending on the loading type,
] per phase, then do the amps, then pick the cable,obviously, as you say, depending on the loading type,
Ahh, OK sorry, as I said, the way I read it and all that!
or just divide kW by 0.692
Why would you assume a 37kW load?It's 37kVA actually, & I've not done the sums!
However 12.3r A seems small for basically a 37kW load, even totally balanced across 3 phases, that would be 12.3r kW per phase if a fully balanced resistive load, which would taking a single phase calculation and ignoring pf, be about 53A per phase, if I understand the question correctly.
Since when has kVA ignored p.f?
How on earth have you arrived at 53 amp per phase?
Regards
I've ignored pf as we don't have it, it was a simplification, as was my calculation, a simplification with certain things taken into account, and certain things ignored, to keep things simple.
If you have a purely resistive load, what would the pf be, as you are so smart?
I arrived at 53A/phase by a simplification, taking the 37kVA as 37kW, with a unity power factor as 3x single phase loads adding up to 37kVA (kW), and totally balanced.
Thus, 37,000/3 = 12.33r kW per phase.
@ 230V this is 12333.333/230 = 53.6A per phase.
A VALID, if somewhat DELIBERATELY simplified calculation given the simplifications applied due to the LACK of detail in the question.
So, what are your issues?
If you have a purely resistive load, what would the pf be, as you are so smart?
I arrived at 53A/phase by a simplification, taking the 37kVA as 37kW, with a unity power factor as 3x single phase loads adding up to 37kVA (kW), and totally balanced.
Thus, 37,000/3 = 12.33r kW per phase.
@ 230V this is 12333.333/230 = 53.6A per phase.
A VALID, if somewhat DELIBERATELY simplified calculation given the simplifications applied due to the LACK of detail in the question.
So, what are your issues?
So Chr!s it seems that you are stating that a 37kVA/kW load takes 12.33A per phase regardless of pf.
I would LOVE to see how you get to that.
Please explain in detail.
I would LOVE to see how you get to that.
Please explain in detail.
Dear me......
If the load is given as kVa then power factor has already been accounted for... If it was a purely resistive load, such as a heater, then it would have been given as 37kW....
Anyway, to go back to the original question; The relationship between No1 and 3 is fairly obvious, think about it....
So, power is 400 x current x 1.732 = well, power in kVa so swap things round a bit and we have 37000 divided by 400 = 92.5 divided by 1.732 = 53.404 Amps per phase.
If you know it is a balanced load you could do it the other way, that is 37000 divided 3 = 12333.3333 divided by 230 = 53.623 Amps per phase
So, there we are 53 amps....
john
Two further points,
1, Anyone that wants to take on Sidewinder or Steps in a debate on electrical matters is going to lose big style.
2, If you need to use an online calculator to work out that sort of thing you should not be playing around with electrical installations in the first place......
john.....
If the load is given as kVa then power factor has already been accounted for... If it was a purely resistive load, such as a heater, then it would have been given as 37kW....
Anyway, to go back to the original question; The relationship between No1 and 3 is fairly obvious, think about it....
So, power is 400 x current x 1.732 = well, power in kVa so swap things round a bit and we have 37000 divided by 400 = 92.5 divided by 1.732 = 53.404 Amps per phase.
If you know it is a balanced load you could do it the other way, that is 37000 divided 3 = 12333.3333 divided by 230 = 53.623 Amps per phase
So, there we are 53 amps....
john
Two further points,
1, Anyone that wants to take on Sidewinder or Steps in a debate on electrical matters is going to lose big style.
2, If you need to use an online calculator to work out that sort of thing you should not be playing around with electrical installations in the first place......
john.....
john,
That is not strictly true, as there are many out there, & I don't mean bhamoggy, that don't know the difference, hence why I worded my posts the way I did.
Until we have the whole picture then, certain simplifications must be made.
I still can't see how Chr!s made 37kVA or even 37kW 12. something amps per phase!
That is not strictly true, as there are many out there, & I don't mean bhamoggy, that don't know the difference, hence why I worded my posts the way I did.
Until we have the whole picture then, certain simplifications must be made.
I still can't see how Chr!s made 37kVA or even 37kW 12. something amps per phase!
Neither can I !!!
john....
john....
sidey,
I think you are mixing it up with me posting it at 12.3 per phase, when I omitted to put in kVA after it,
I was doing the simply method of 37 / 3 to get it to per phase loading to try and make it simple for bha if he didnt know how to calc the 3ph into amps.
:|
I think you are mixing it up with me posting it at 12.3 per phase, when I omitted to put in kVA after it,
I was doing the simply method of 37 / 3 to get it to per phase loading to try and make it simple for bha if he didnt know how to calc the 3ph into amps.
sorted that slightly.
:|
I do tend to agree somewhat with that statement.
Steps,
I got your point after my post as you explained it, it was as I said earlier just a bit of clarification that was required, hence why as I said, I worded my posts the way I did, & as you said the load is about 12. something kW/kVA depending on how you look at things as long as you take a unity power factor.
Also, Chr!s has queried why I did not equate kVA & kW when using a unity pf, it was because many don't know the difference, and have no clue about pf, & again I'm not including bhamoggy in this, but we don't know the accuracy of the information that he has been given, so we need to give him the benefit of the doubt if there are any errors in his information, that are not of his fault.
However, from the posts by Chr!s, it seems that he things that it is still 12. something A per phase.
I got your point after my post as you explained it, it was as I said earlier just a bit of clarification that was required, hence why as I said, I worded my posts the way I did, & as you said the load is about 12. something kW/kVA depending on how you look at things as long as you take a unity power factor.
Also, Chr!s has queried why I did not equate kVA & kW when using a unity pf, it was because many don't know the difference, and have no clue about pf, & again I'm not including bhamoggy in this, but we don't know the accuracy of the information that he has been given, so we need to give him the benefit of the doubt if there are any errors in his information, that are not of his fault.
However, from the posts by Chr!s, it seems that he things that it is still 12. something A per phase.
