Load calcs and Continuous/Non Continuous loads

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johnson151

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I'm having a difficult time understanding when to factor in continuous and non continuous loads. In most of the examples in the back of the code book, they separate the loads accordingly and a few they don't. I'm also using Mike Holly's study guide and so far it doesn't show any use of cont/non cont loads in their calcs. I've tied my brain in a knot trying to figure this out.
 
david luchini

david luchini

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Continuous/non-continuous doesn't factor into Load Calculations at all.

The 125% for continuous loads factors into conductor and ocpd sizing for branch circuits, feeders, and service conductors.
 
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johnson151

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Ok, thanks. I think I get it now (I think). I'm looking at example D4(a) in the back of the 2020 NEC and I don't understand why they didn't apply the cont/non continuous when sizing the feeders. Is it because demand factors were applied to the ranges?
 
david luchini

david luchini

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johnson151 said:
Ok, thanks. I think I get it now (I think). I'm looking at example D4(a) in the back of the 2020 NEC and I don't understand why they didn't apply the cont/non continuous when sizing the feeders. Is it because demand factors were applied to the ranges?
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The reason there is no continuous load factor applied when sizing the feeders in Example D4(A) is that there are no continuous loads in that example.
 
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johnson151

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People bake for hours! I guess that was part of my hang up. I would have thought for sure a load like that was continuous. But I guess, like many other occasions, I'm wrong. Thanks everyone for your help!
 
W

wwhitney

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So to follow up on the question in the OP, take the Annex D2(a) example, an optional calculation for a single family dwelling. The calculated service load is 90A, of which none is continuous.

Say we add a 48A (output) EVSE on a 60A branch circuit to the load calculation. An EVSE is a real continuous load, mine often runs for more than 3 hours at maximum current. Adding it to the optional calculation in D2(a), we get a new service load that is 40%*48A = 19.2A higher, or 109A.

What portion of that 109A load is continuous? Is it 48A, irrespective of the "first 10 kVA @ 100%, rest at 40%" part of the optional calculation? Or is it 41.7A (10 kVA/240V) + (48-41.7)*40% = 44A? Or is it just 19A, amount the service load increased?

Per 230.42(A)(1), the minimum ampacity for the service entrance conductors would be 121A, 120A, or 114A, respectively, depending on the answer to that question.

Cheers, Wayne
 
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Russell39

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wwhitney said:
So to follow up on the question in the OP, take the Annex D2(a) example, an optional calculation for a single family dwelling. The calculated service load is 90A, of which none is continuous.

Say we add a 48A (output) EVSE on a 60A branch circuit to the load calculation. An EVSE is a real continuous load, mine often runs for more than 3 hours at maximum current. Adding it to the optional calculation in D2(a), we get a new service load that is 40%*48A = 19.2A higher, or 109A.

What portion of that 109A load is continuous? Is it 48A, irrespective of the "first 10 kVA @ 100%, rest at 40%" part of the optional calculation? Or is it 41.7A (10 kVA/240V) + (48-41.7)*40% = 44A? Or is it just 19A, amount the service load increased?

Per 230.42(A)(1), the minimum ampacity for the service entrance conductors would be 121A, 120A, or 114A, respectively, depending on the answer to that question.

Cheers, Wayne
Click to expand...
Just ran into that scenario with an EVSE at a dwelling. Since none of the optional calculations account for continuous loads, I could have added it to the 220.82 (B) General Loads and took the demands...but I didn't. I figured the EVSE at 100% and added it to my 220.82 Optional calc total.
EVSE's are something the NEC is gonna need to address in Art. 220 to clear up the confusion of what to do with these loads.
Now, what test-takers should do, I am not sure.
 
Dennis Alwon

Dennis Alwon

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johnson151 said:
People bake for hours! I guess that was part of my hang up. I would have thought for sure a load like that was continuous. But I guess, like many other occasions, I'm wrong. Thanks everyone for your help!
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Continuous means on for 3 hours or more. A range cycles on and off so it cannot be continuous.

Look at Table 220.55--- a 12kw range calculates as 8kw in the standard calculation. In optional it is the nameplate- 12kw.
 
C

Carultch

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Massachusetts
johnson151 said:
People bake for hours! I guess that was part of my hang up. I would have thought for sure a load like that was continuous. But I guess, like many other occasions, I'm wrong. Thanks everyone for your help!
Click to expand...
Ovens are theromstatically controlled, and cycle the heating element on and off. Unless you were broiling for hours, it wouldn't count as a continuous load. Broiling doesn't last nearly as long as baking.
 
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retirede

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Illinois
Carultch said:
Ovens are theromstatically controlled, and cycle the heating element on and off. Unless you were broiling for hours, it wouldn't count as a continuous load. Broiling doesn't last nearly as long as baking.
Click to expand...

Even if the broiler was on for 3 hours straight, the range won’t be drawing full power unless all of the cooktop burners are also full on. Never happens.
 
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