Oregon requires a KVA to amp calculation for a single phase load on a 3ph 208/120Y system to be calculated using the formula of amps=kva/208x1.154. I have no doubt that this is a valid formula, but I really need to understand the vector diagramming of this. Can anyone please enlighten me on this? Can anyone help me out with the vector math? I cannot find this in any book.
Single phase load on 208/120Y calculation req'd by Oreg
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bphgravity
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Re: Single phase load on 208/120Y calculation req'd by Oreg
I don't think that formula is correct?
Wouldn't it be I = kva/1000/208 x 1.732
I don't think that formula is correct?
Wouldn't it be I = kva/1000/208 x 1.732
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Re: Single phase load on 208/120Y calculation req'd by Oreg
That is the same thing as saying Amps = KVA / 240. The number 1.154 is half of the square root of three. It is the formula you would use to convert KVA to amps for a single 120/240 volt system. But I do not understand why this would apply to a 120/208 volt system.
What do you mean when you say that ?Oregon requires. . . ?? Is there a state administrative rule or local code? Can you give me a web site or other source of information? I would like to see this rule in context.
That is the same thing as saying Amps = KVA / 240. The number 1.154 is half of the square root of three. It is the formula you would use to convert KVA to amps for a single 120/240 volt system. But I do not understand why this would apply to a 120/208 volt system.
What do you mean when you say that ?Oregon requires. . . ?? Is there a state administrative rule or local code? Can you give me a web site or other source of information? I would like to see this rule in context.
Re: Single phase load on 208/120Y calculation req'd by Oreg
Rattus
That appears to be correct. If so, then the formula given is amps = kva/208x1.154 or
amps = kva/(208 x 240/208)= kva/240 as Charlie said. What does this have to do with 208 volt single phase load?
Rattus
That appears to be correct. If so, then the formula given is amps = kva/208x1.154 or
amps = kva/(208 x 240/208)= kva/240 as Charlie said. What does this have to do with 208 volt single phase load?
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Re: Single phase load on 208/120Y calculation req'd by Oreg
Rattus: Yes, I misspoke. 1.154 is the reciprocal of half the square root of three. Thanks.
Please note that:
</font>
Rattus: Yes, I misspoke. 1.154 is the reciprocal of half the square root of three. Thanks.
Please note that:
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">208 is equal to 120 times the square root of three.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">1.154 is equal to 2 divided by the square root of three, as I mention above.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Therefore, the product of ?208 times 1.154? is the same thing as ?120 times 2 times the square root of three divided by the square root of three.</font>
Re: Single phase load on 208/120Y calculation req'd by Oreg
I don't get it. Seems that the current would be simply the apparent power, Pa, divided by the line voltage, that is:
I = Pa/Vline = Pa(VA)/208V = Iphase = Iline
Now is the 1.154 fudge factor in the numerator or the denominator?
Seems to be some fudge factor related to 240V. What say the rest of you?
[ February 15, 2005, 06:55 PM: Message edited by: rattus ]
I don't get it. Seems that the current would be simply the apparent power, Pa, divided by the line voltage, that is:
I = Pa/Vline = Pa(VA)/208V = Iphase = Iline
Now is the 1.154 fudge factor in the numerator or the denominator?
Seems to be some fudge factor related to 240V. What say the rest of you?
[ February 15, 2005, 06:55 PM: Message edited by: rattus ]
Re: Single phase load on 208/120Y calculation req'd by Oreg
I appreciate your response. The State of Oregon expects all electricians who are taking the Electrical Supervisor's test (equivalent to Master Electrician)to use this formula on any calculations in the test. If this formula is not used, the one taking the test will be docked points. I am trying to understand this from a mathematical/theory standpoint. I draw out the vectors for a 3ph 208/120Y and apply a single phase 208 load and come up with a formula of 2tan(30). I have read all the above responses and they all make sense, I wonder if this can be totally understood of drawn out with vector diagramming and math?
I appreciate your response. The State of Oregon expects all electricians who are taking the Electrical Supervisor's test (equivalent to Master Electrician)to use this formula on any calculations in the test. If this formula is not used, the one taking the test will be docked points. I am trying to understand this from a mathematical/theory standpoint. I draw out the vectors for a 3ph 208/120Y and apply a single phase 208 load and come up with a formula of 2tan(30). I have read all the above responses and they all make sense, I wonder if this can be totally understood of drawn out with vector diagramming and math?
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Single phase load on 208/120Y calculation req'd by Oreg
I can?t give you any help, unless I see this requirement in the context in which it was published.
I ask again: Can you give me a document that says this? Can you refer me to a web site at which this requirement is stated? Put it another way, how did you come to be aware of this ?requirement?? Is this just what someone told you, or did Oregon publish a study guide that includes this formula?
I can?t give you any help, unless I see this requirement in the context in which it was published.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Single phase load on 208/120Y calculation req'd by Oreg
Let me add that I am moving from Washington to Oregon. Therefore, I have a definite interest in learning about this "requirement," and about its source authority.
Let me add that I am moving from Washington to Oregon. Therefore, I have a definite interest in learning about this "requirement," and about its source authority.
Re: Single phase load on 208/120Y calculation req'd by Oreg
I wish I could supply a document. The instructors that are teaching various Supervisor exam prep classes are stating that this formula must be used when taking the Supervisor Electrician test. I have been in the electrical trade for 27years most of which is industrial/technical and have never seen this before. I have searched high and low in various technical books and also the internet and cannot find any reference to this. I am thinking of setting up an actual test to see what the results are. It just doesn't really add up.
I wish I could supply a document. The instructors that are teaching various Supervisor exam prep classes are stating that this formula must be used when taking the Supervisor Electrician test. I have been in the electrical trade for 27years most of which is industrial/technical and have never seen this before. I have searched high and low in various technical books and also the internet and cannot find any reference to this. I am thinking of setting up an actual test to see what the results are. It just doesn't really add up.
Ed MacLaren
Senior Member
Re: Single phase load on 208/120Y calculation req'd by Oreg
Ed
Sounds like the instructors got together and said - "we're not sure how to do this, but let's stick together and we'll be OK"
Ed
Re: Single phase load on 208/120Y calculation req'd by Oreg
I know I'm always missing something and a lot on here think its my brain, but who cares?
But I don't see where 1.73 would even be used on a single phase computation?
for a single phase load
I see it like this amps.=kw/208
Edited to change KVA to KW thats what I meant to say and to turn it around.
Ronald
[ February 17, 2005, 07:49 PM: Message edited by: ronaldrc ]
I know I'm always missing something and a lot on here think its my brain, but who cares?
But I don't see where 1.73 would even be used on a single phase computation?
for a single phase load
I see it like this amps.=kw/208
Edited to change KVA to KW thats what I meant to say and to turn it around.
Ronald
[ February 17, 2005, 07:49 PM: Message edited by: ronaldrc ]
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Single phase load on 208/120Y calculation req'd by Oreg
But I do not know how you drew your vector diagram, and no longer recall how to ?apply a single phase 208 load? to such a diagram. So I can?t do anything with that clue.
</font>
</font>
I hadn?t picked up on this before. Twice the tangent of a 30 degree angle gives you 1.154, the very ?fudge factor? you mention in your first post. There?s a clue!
But I do not know how you drew your vector diagram, and no longer recall how to ?apply a single phase 208 load? to such a diagram. So I can?t do anything with that clue.
That?s another clue that I missed the first time through. It?s a good question. So back to you, Specs. Is the formula,
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Amps = KVA divided by (the product of 208 times 1.154),</font>
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- <font size="2" face="Verdana, Helvetica, sans-serif">Amps = KVA divided by 208, and then you multiply the result by 1.154?</font>
Re: Single phase load on 208/120Y calculation req'd by Oreg
Accepted formula is amps=kva/208*1.154. I have been told this was taken out a electrical book that was a few years old. I would throw the formula out except that I cannot ignore it since the State of Oregon puts a lot of attention on it.
Accepted formula is amps=kva/208*1.154. I have been told this was taken out a electrical book that was a few years old. I would throw the formula out except that I cannot ignore it since the State of Oregon puts a lot of attention on it.
Re: Single phase load on 208/120Y calculation req'd by Oreg
I have checked a couple of websites with tables of formulas, and I find no factor "1.154" in any of them.
This factor is the ratio 240/208 which is related to Sqrt(3), but I have never seen such a formula. Looks like a bureaucratic foulup or maybe just a typo.
I have checked a couple of websites with tables of formulas, and I find no factor "1.154" in any of them.
This factor is the ratio 240/208 which is related to Sqrt(3), but I have never seen such a formula. Looks like a bureaucratic foulup or maybe just a typo.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Single phase load on 208/120Y calculation req'd by Oreg
Let me put on my best ?I?m a mathematician and nothing short of perfect precision is acceptable? hat , and ask again. Do you mean:
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</font>
I?m sorry to be a pain on this one, but you did not answer my question (actually, the question was from Rattus).
Let me put on my best ?I?m a mathematician and nothing short of perfect precision is acceptable? hat
, and ask again. Do you mean:</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">amps = kva / (208*1.154)</font>
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">amps = (kva/208) * 1.154?</font>
Re: Single phase load on 208/120Y calculation req'd by Oreg
Thanks for asking...
amps=kva/(208*1.154)
Any enlightenment would be appreciated. I am one that just has to understand. The gentleman at the State of Oregon is well knowledged and I have no doubt that he is correct. I just cannot figure out how.
Thanks for asking...
amps=kva/(208*1.154)
Any enlightenment would be appreciated. I am one that just has to understand. The gentleman at the State of Oregon is well knowledged and I have no doubt that he is correct. I just cannot figure out how.
Ed MacLaren
Senior Member
Re: Single phase load on 208/120Y calculation req'd by Oreg
There are very few of us that don't make an occasional mistake.
Ed
If the calculation is for the current drawn by a 208 volt single phase load supplied from a three phase 208/120Y system, the learned gentleman is wrong.
There are very few of us that don't make an occasional mistake.
Ed
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