Jouneymans exam question

[gregorsc]

I am trying to prepare my class for their journeyman's exam and we had this question on a practice exam.What size THWN copper conductors and OCPD are required for an individual branch-circuit to a small processing machine with a nameplate current rating of 38 amps(continuous load)? The answer given was #8THWN and 50 amp breaker. My question is would 110.14.C.1 factor into this answer?

 

[iwire]

My question is would 110.14.C.1 factor into this answer?

Sure.

I would assume 60 C terminals unless the question made clear that the equipment had 75 C terminals.

With a load of 38 amps, I don't see it making any difference.

8 THWN is rated 40 amps @ 60 C and 50 amps @ 75 C so either way 8AWG works.

On the other hand 10 AWG is rated 30 @ 60 C and 35 @ 75 C so it can not be used for the 38 amp load.

By the way this '38 amps' was that the minimum circuit ampacity of this machine?

 

[gregorsc]

I think you still need to take into account it is a continuous load.38x1.25=47.5 amps.I agree that if the question does not give the terminal rating you apply the 60c column.Should I tell my guys that on any question asking to size a conductor to a certain ampacity unless terminal ratings are given to apply the rules of 114.C.1?

 

[infinity]

Since we're assuming, why do we assume that this is a continuous load?

 

[gregorsc]

it is stated in the question as a continuous load.

 

[cripple]

Jouneymans exam question

If the question does not stated the terminal rating you would the to assume the terminal rating to be 60 degree C. Since the name plate states 38 amps continuous load the 38 would have be increased by 1.25%. 38 X 1.25 = 47.5 Amps. The conductor would now has have a rating not less then 47.5 amps. The next size up conductor would be 6 AWG with ampacity 55 amps in the 60 degree C column. The circuit breaker would 50A next up form 47.5A per 240.4.

 

[flash hazard]

If the question does not stated the terminal rating you would the to assume the terminal rating to be 60 degree C. Since the name plate states 38 amps continuous load the 38 would have be increased by 1.25%. 38 X 1.25 = 47.5 Amps. The conductor would now has have a rating not less then 47.5 amps. The next size up conductor would be 6 AWG with ampacity 55 amps in the 60 degree C column. The circuit breaker would 50A next up form 47.5A per 240.4.

No.
if a test question gives you a type of wire like thwn or any wire rated at 75 degrees c then you go off of the 75 degree chart. when they want you to use the 60 degree chart they will specify either 60 degree or by wire type.
the correct calc. for this would be 38amp con. load x 1.25% = 47.5. off of the 75 degree chart that would be a #8 rated at 50 amps. OCPD would be 50 amp. 240.4 (B)

 

[FrancisDoody]

#8 THWN/50 amp breaker

#8 THWN/50 amp breaker

I would agree since the question stated the type of wire installed was THWN. You should assume nothing else. Use the 75 degree column.

(A small processing machine brings to mind a run of conduit and stranded wire.)

However, that in its self is an assumtion of detail.

 

[svthard]

Huh

Huh

If this calculation is correct then what good is 110.14 C. They tell you can use any wire rated above 60 deg as long as you use the 60 deg column to find amps. It is also my understanding that if equipment term ratings are not listed assume 60deg. Just tryng to understand using 110.14.c

 

[flash hazard]

If this calculation is correct then what good is 110.14 C. They tell you can use any wire rated above 60 deg as long as you use the 60 deg column to find amps. It is also my understanding that if equipment term ratings are not listed assume 60deg. Just tryng to understand using 110.14.c

Here's an example when I feel 110-14C would come into play on an exam.
What size would you need for a 50amp continuous load? Notice in the question a wire type wasn't given and a degree wasn't given. In this question you would refer to 110-14C. Since 50x1.25 is less than 100 amps and the wire size is smaller than a 1 awg you would use the 60 degree chart.

 

[cripple]

Jouneymans exam question

Section 110.14(C)(1)(a) is very clear and states conductors 14 through 1 AWG will be sized off the 600 F Colum and you may use a deferent insulation rating, provided the ampacity of such conductors is determined based on the 60?C (140?F) ampacity of the conductor size used.
Table 310.16 ampacity are based on the terminal rating. Regardless ampacity rating based the insulation type of the conductor; the ampacity of the conductor is solely based on the terminal rating, so with out the terminal rating we will need to assume the terminal rating to be 600. The question does not gave the terminal rating even if the NEC does permit the use of higher ampacity rated conductor it is clear that the terminal is what the ampacity of the conductor will be based on.

110.14(C) Temperature Limitations The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

(1) Equipment Provisions The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).

(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60?C (140?F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60?C (140?F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75?C (167?F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity.

 

[ryan_618]

I agree with those using 110.14(C) and the 60 degree column.

This is a pretty straight forward question though, so I would do it based on both and see if there are both answers. If both answers are there, mark the 110.14(C) answer, and then challenge the question. Explain in your challenge why you are right. There is alwasys a chance that the person who wrote the exam doesn't know as much as you do!

I challenged a question on an exam one time that asked me about a "service feeder". I challenged due to the fact that there is no such animal, and ending up getting the question awarded to me, regardless of my answer.

 

[haskindm]

I also agree that the 60 degree column must be used unless you are specifically told that ALL terminations are rated at a higher temperature. Often, to avoid confusion these questions will specify TW wire so there is no question about what column to use, but that is only when the test maker is in a good mood. 110.14(C) is very clear that unless you KNOW the terminations are rated higher you will always use the 60 degree column for the smaller conductors (less than 1/0).

 

[dab]

i think flash had the last word on this...