hhsting
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Nec 2014 Table 310.15(B)(16) has two stars next to #10 awg. #10 AWG copper conductor THHW or THWN minimum ampacity is it 30A or 35A?
Ampacity of conductor
- Thread starter hhsting
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The ampacity is 35. It can't be protected at more than 30A, except where permitted in 240.4(E) & (G).
hhsting
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Ok. So lets say I have 12 current carrying conductors sized #10 AWG THHW or THWN in one conduit. Lowest ampacity you say is 35A. Per Table 310.15(B)(3)(a):
35A*0.5 = 17.5A
so I can use 20A breaker or 15A breaker to protect the cables?
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Actually you can use the 90C rating since the wire is 90C and derate from there
40 * .5 = 20 amps
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Could be a 20A breaker per 240.4(B),
Unless its a branch circuit supplying more than one receptacle. Then it would have to be a 15A breaker per 240.4(B)(1).
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Good point. That would work for the THHW in dry locations, but not wet locations. Wouldn't work for the THWN.
hhsting
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I do have branch circuits. Each branch circuit has 2 current carrying conductors and their are 6 total branch circuits in one conduit upto power pole. Each branch circuit is going to supply two L5-15 receptacles. Each branch circuit has max load of 10 amps. The receptacles are use for plugging in spot merchandiser.
240.4(B) it would have to be 15A I guess. However, Nec 2014 210.21(B)(2) says to use Table 210.21(B)(2) and for max load 10 I can use 15A or 20A circuit rating. Meaning breaker can be 15A or 20A.
Is their a discrepancy between 210.21(B)(2) and 240.4(B) or am I missing something?
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With locking receptacles, you could maybe argue that you don't have cord-and-plug-connected portable loads, so 240.4(B)(1) doesn't apply. But with 10A loads, why not just go with the 15A circuit.
I'm not quite following you, but I don't see any discrepancy between 210.21(B)(2) and 240.4(B). They are talking about different things.
hhsting
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Went back and looked. It is locking type so i guess cord and plug does not apply.
However if it were cord and plug then Table 210.21(B)(2) says max load of 12 circuit rating can be 20A or 15A so I am assuming breaker can be 15A or 20A while 240.4(B)(1) says it would have to be 15A.
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Table 210.21(B)(2) says that the maximum load connected to any 15A receptacle is 12A. It doesn't say anything about protecting the conductor at its ampacity, like 240.4(B)(1) does.
210.21(B)(2) and 240.4(B) talk about completely separate matters. There is no discrepancy between them.
As far as 240.4(B) and locking receptacles, you would have to check with the AHJ to see how they feel about it.
hhsting
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What does Table 210.21(B)(2) mean by Circuit Rating? I thought for branch circuits, circuit rating is determine by branch overcurrent protection size. The table says for max 12A load circuit rating can be 15 or 20A.
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Let me try it this way....
210.21(B)(2) says the maximum load on any 15A receptacle of a multi-receptacle circuit is 12A.
210.21(B)(2) also says that the multiple 15A receptacles can be on a 15A branch circuit or a 20A branch circuit.
240.4(B)(1) says that the conductor ampacity on the 15A multi-receptacle branch circuit must be at least 15A, and that the conductor ampacity on the 20A multi-receptacle branch circuit must be at least 20A.
In other words, no "next higher standard overcurrent device rating" allowed for the multi-receptacle circuits.
hhsting
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I guess question boils down to lets say I have 15 amp rated multi-receptacles with max loading of 12A branch circuit and look at Table 210.21(B)(2) then I can have circuit rating of 15A or 20A. Correct.
How does NEC define circuit rating for branch circuit? Is it just branch conductor ampacity or is it overcurrent protection size? And if it is overcurrent protection device then I can use 20A but 240.4(B)(1) says to use 15A. Would that not be two different directions?
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Its the overcurrent protection size, if your on the 2017 NEC see 210.18. As Dennis pointed out in post #4 you can use the 90C column for derating your #10 THHN's.
lordofthisworld
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U R derating, so u can use the 90 degree column which is #10 is rated for 40A
hhsting
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I have 75 degree termination and insulation.
lets say I have 15 amp rated multi-receptacles with max loading of 12A branch circuit and look at Table 210.21(B)(2) then I can have circuit rating of 15A or 20A. Correct.
I can use 20A but 240.4(B)(1) says to use 15A. The two NEC 2014 articles their is discrpenancy one is saying only 15A other says I can use 20A?? Am I missong something?
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Step 1 determine the rating of your OCPD; you stated you have 10AWG THWN rated 75C not THWN-2 or something?
So you derated to 17.5A
240.4(B)(1) is telling you you cant round up when you are working with a circuit with more than one receptacle supplying cord and plug connected portable loads. And thats what you have so your OCPD is 15A.
Step 2 Pick your receptacle
2014 NEC 210.21(B)(2) Is saying a 15A receptacle shall not supply a load more than 12 Amps, and that 15A receptacle is permitted to be connected to a 15 or 20 amp branch circuit.
hhsting
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Thats the thing 210.21(B)(2) is telling me circuit rating is permitted to be 15A or 20A but that contradicts what 240.4(B)(1) is telling me that circuit rating needs to be 15A not permitted to be round up to 20A.
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That's not what 240.4(B)(1) says.
hhsting
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- Glen bunie, md, us
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See post #14. Branch ckt rating is ocpd size. Branch circuit rating 210.21(B)(2) says can be 15A or 20A while 240.4(B)(1) has to be 15A for cord and plug multi receptacles. What am I missing?
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