load calcs
- Thread starter badjeepr
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- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
In three phase calculations, you will always see the square root of three pop up someplace.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
OK. Yes, you use the 1.732, in the manner shown in post #1.
continuing on....NEC tells us to calculate continuous lighting load for service conductors @ 125%. But only to calculate fixed electric space heating @ 125% for branch circuit and not for service load. Am i following along accurately? 424.3 (B) states continuous. 220.51 states 100 %
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I don't see any conflict. Those are different articles with different purposes. If you wish to add 25% to the service load calculation for the space heating, you are welcome to do so.
thank you for your responses charlie. I am not claiming there to be a conflict...just want to be sure i am interpreting correctly. i personally dont see the logic behind a double standard. why calc some of the contiinuous loads @ 125% and not all? I am currently cramming for my admin test and have no intentions of having to re-test.
It would be I = P ? E.
In calculating the neutral load, you are only concerned with 1? L-N loads. Add up the 1? L-N loads on each phase and the one with the highest total is the maximum unbalanced neutral load.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
That's my point: it's not a double standard. Calculating and designing are two separate purposes.
If I am choosing a wire size for a space heater, I will pick one with an ampacity at least 125% of the heater rating. That is not because I expect the heater to actually draw 125% of its rated current, but rather a precautionare measure to ensure the wire and the terminations do not get overheated.
But if I am deciding on the minimum service size, I do not need to add the 25% for the heater being a continuous load, because it will not really be running, without a break, for 3 hours and beyond. It turns on and off, under instructions from the thermostat. Lights, on the other hand, are often turned on and left on all day. That is why they are calculated as a continuous load.
glene77is
Senior Member
- Location
- Memphis, TN
That might ONLY mean that they had to go to work.
There was a thread recently on Calculating Neutral Load when UnBalanced.
This was a long thread.
There is an Excel calculation spreadsheet available.
Here is the link, from Search "Neutral Current Calculation"
and the Excel download is on the first Page.
http://forums.mikeholt.com/showthread.php?t=109146&highlight=Neutral+current+Calculation
Smart$ was a contributor.
Check it out, there are phase and power factor considerations.
Keep Reading.
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Ummm... the calculation badjeepr is looking at is different than calculating neutral current. He's wanting the maximum unbalanced current for a Feeder or Service Neutral.
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