Branch circuits?

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Brandon Loyd

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When I find a 30 amp, 3 pole breaker in a MCC bucket with #12 wire on the load side. Am I looking at a code violation based on table 210.24 where I believe it says #12 wire will have 20 amp overcurrent protection? Or does this only apply to lighting and receptacle loads?
 
210.2 and its associated table have the abillity to amend the other requirements within article 210. You are dealing with an MCC, so the load was likely a motor, and thus the rules in 430 come into play. I believe you can have a 30 amp breaker and #12 wire serving motor loads, provided overload protection is available. This is not my strong suit, so someone else will have to complete the answer to your question.
 
I agree with Charlie that if you are dealing with an MCC you are most likely dealing with motor loads and the rules in Article 430 which would in most cases permit a 30 amp circuit breaker to provide short circuit and ground fault protection for #12 THHN branch circuit conductors provided that overload protection is provided in accordance with Part III of Article 430.

Chris
 
Look at 240.4(D) which allows us an exception for Applications under 240.4(G). The reason is that the motors will have overload protection and thus the circuit breaker is for short circuit and ground fault protection only.
 
I understand using the 30 amp breaker for Short circuit protection, but would I be correct in saying that #12 should have overload protection not exceeding 20 amps, not 25, even though the wire is rated for 25 amps? And that #10 should have overload protection of 30 amps, not 35, even though the wire is rated for 35 amps?
 
Brandon Loyd said:
I understand using the 30 amp breaker for Short circuit protection, but would I be correct in saying that #12 should have overload protection not exceeding 20 amps, not 25, even though the wire is rated for 25 amps? And that #10 should have overload protection of 30 amps, not 35, even though the wire is rated for 35 amps?
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You would be incorrect.

The small conductor rules in 240.4(D) do not apply to motor branch circuits and the ampacities listed in Table 310.15(B)(16) are permitted to be used.

Chris
 
Do you mean Table 310.16? I dont see a 310.15(B)(16) in the 2008 code book. So if I am understanding you right, for motor loads, #12 THHN Cu can be protected 25 amp overcurrent protection, #10 with 35 amp?
 
If the circuit feeds a 3 phase receptacle which is used for the connection of motorized tools, does this still hold true?
 
If you are talking grinders and other power tools then I would not think it would be permitted. If the tools you are talking about actually have an electric motor(not a power tool motor) then yes it would be permitted. The trail to get you to the proper overcurrent protection is a bit convoluted but it starts with 240.4 that states that equipment"shall" be protected in accordance with the article that covers the specific type of equipment in 240.3.
note the word"shall". 240.4 D says specifically permitted by 240.4G which says "shall" be permitted and guides you to table 240.G which again lists the equipment specifically allowed. When you peruse the 430 section on motors section 430.52(C)(1) it says a device selected for protection based on values calculted per the tables "shall" be used. Not only does the code allow us to exceed the small wire values it says we "shall" do it.
 
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