overcurrent device
- Thread starter kimrichi
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jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
An adjustable trip breaker could be used, but you cannot use the "next size up" rule for OCPD selection for sizing the conductors.
IOW, if you use a 1000A breaker, your conductors must have an ampacity of 1000A.
IOW, if you use a 1000A breaker, your conductors must have an ampacity of 1000A.
iceworm
Curmudgeon still using printed IEEE Color Books
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- EE (Field - as little design as possible)
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- New Jersey
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- Journeyman Electrician
840 amps would be the minimum required. You could install a 4000 amp service if you so choose.
- Location
- Connecticut
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- Engineer
You would need to know how much of the load is continuous and how much is non-continuous to answer that question.
- Location
- Massachusetts
He said 'the calculated load' if that was done using article 220 that is already taken care of.
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- Connecticut
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- Engineer
Yes, he said 'the calculated load.' There is NOTHING in Article 220 about continuous vs. non-continuous load. It is not part of calculating the load.
should not we go down when ampacity over 800
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- New Jersey
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- Journeyman Electrician
So you're saying that whether it's continuous or non-continuous is irrelevant to this thread.
- Location
- Connecticut
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- Engineer
- Location
- New Jersey
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- Journeyman Electrician
If the load calculation said that the calculated load is 840 amps isn't that good enough to answer the question in the OP?
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- Connecticut
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- Engineer
No, the calculated load doesn't indicate whether the load is continuous or not.
As an example, lets say you had an 28,760 sf armory with a total connected lighting load of 20,000 va, and 264 general purpose duplex receptacles. You plan to supply all the lighting with one feeder and all the receptacles with another feeder. You go to Art 220 to do load calculations for each feeder (assume 208V, 3 ph.)
For the lighting feeder, 220.12 tells you you need a minimum lighting load of 1va/sf, or 1va/sf * 28,760sf = 28,760va. From T220.42, you apply a 100% demand factor, so you calculated load for the lighting feeder is 28,760va.
For the receptacle feeder, 220.14(I) tells us to include not less than 180va for each duplex receptacle, 180va * 264 = 47,520 va. From T220.44, you apply a 50% demand factor after 100% of the first 10kva, or 10,000 + 37,520*0.5 = 28,760va.
Each feeder has a calculated load of 28,760va, but per Art 215, wouldn't the non-continuous receptacle load require a min. 80A feeder, and the continuous lighting load require a min. 100A feeder?
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- Location
- New Jersey
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- Journeyman Electrician
But again the OP stated: "the calculated service load is 840 amp" why would you need any more information to answer the question? If this were a test question are you saying that it would be unanswerable?
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- Connecticut
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- Engineer
I don't know another way to say it...a calculated service load per Art. 220 would not indicate what portion of the load was continuous and what portion was non-continuous. If the calculated load was all continuous load, wouldn't you need a 1200A ocpd? And if the load was all non-continuous wouldn't you only require a 1000A ocpd?
In my example, isn't the calculated load for both feeders 80A, but wouldn't they require different min. ocpd sizes?
The question doesn't give you enough information to provide a correct anwer from a Code perspective.
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- Massachusetts
This is odd to me as we were taught in trade school that doing a 'load calculation' would include the continuous and non-continuous loads. Examples D3 and D3a both seem to bear that out. Or in other words if you havent included both types of loads you have not done a 'service calculation'.
Perhaps the place we went off the track was my saying 'per Article 220' when it is per Article 220 and other code sections.
Please take a look at the examples in annex D.
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- Engineer
The load calculations include ALL the loads, continuous and non-continuous. What is NOT included in the load calculation is a 125% factor for continuous loads. The Annex examples bear this out.
Take a look at Example D3. The first step in the example is the "Calculated Load." The calculation includes 12,200VA on non-continuous load and 16,200VA of continuous load, for a total Calculated Load of 28,400VA. The service voltage is listed as 120/240, so the calculated load amperage is 28,400VA/240V = 118.3A (Note that 125A is the next higher standard OCPD size.)
Now skip down to the bottom of the example and find "Minimum Size Feeder (or Service) Overcurrent Protection." At this point, they take the non-continuous load (from the Calculated Load in the first step) and add it to 125% of the continuous load (from the first step) giving us 12,200VA + (16,200VA * 1.25) = 32,450VA, or 135A.
So for the calculated load of 118.3A (28,400VA) you would need a conductor no smaller than 135A (before any adjustment factors) and an OCPD no smaller than 150A
If the example in D3 had only told us that the calculated load was 28,400VA, without telling us how much of the load was continuous and how much was non-continuous, it would have been impossible to find the minimum size feeder and OCPD in the last step. In the same way, it is impossible to tell the minimum size OCPD in the OP, because we don't know what portion of the load is continuous vs. non-continuous.
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- Massachusetts
David, it seems you are proving my point for me. A 'service calculation' as the op mentions includes both continuous and non-continuous loads.
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- Connecticut
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- Engineer
Let me try this...
The Calculated Service Load in Annex Example D3 is 118.3A (28,400VA @ 120/240V.)
What is the minimum size OCPD required?
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- Location
- Massachusetts
Are you in the 2011?
- Location
- Connecticut
- Occupation
- Engineer
Yes, I'm reading the online 2011.
Example D3 says...
Calculated Load (see 220.40) {Section 220.40 is the first section of Part III. Feeder and Service Load Calculations}
Non-continuous Loads: 12,200VA
Continuous Loads: 16,200VA
Total non-continuous loads + continuous loads = 12,200VA + 16,200VA = 28,400VA {which equals 118.3A @ 120/240V}
So for a calculated service load of 118.3A, what min. size OCPD would be required?
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