Here's a question that was on an electrician's test. The student answered (d) as the correct one. He was told he was incorrect?

What is the correct answer?

Note: See 110-5, and that no insulation, or conductor material was given?

Question No. 9: Which of the following statements about the general requirements for number 6 conductors is true?

(a) It is required to be terminated at 75 degree C ampacity.

(b) It is required to be terminated at 60 degree C ampacity.

(c) It must have insulation rated 60 degree C ampacity.

(d) It must have insulation rated 75 degree C ampacity.

I will invite the student to join this board so he can add more on this subject.

The general rule would apply and the only possible answer with what is given is that it needs to be terminated at 60 degrees.

I tend to agree, with no further info I would have to apply 110-14 C and assume (dangerous, huh ? especially on a test) that it would be terminated in unknown terminations, which would mean you have to assume under 100 amps and terminate it at it's 60 deg. C ampacity. If that was the wording with no further explanation, it was broad based, KINDA vague.

I tend to agree with the other two posts.

Since there is no Insulation type given, this could be anything from TW [60 degree C], to THHN [90 degree C].

Since we can use Conductors with THHN Insulation and rate them at 60 degrees C for wet locations, or 90 degrees C for dry locations [for ampacity adjustments], this would exclude (c) and (d).

Since we are to use the 60 degree ampacity column in 310-16 for conductors sized #14 through #1, this would eliminate (a).

By default, the only remaining answer would be (b).

Scott SET

Joe,

I think it's a poorly worded question and could be viewed different ways.

I think that it would be (b) or (c) depending on what they were looking for.
I would lean torward (c) with 60C as a Minimum rating.

Question:

Is 75C wiring also rated 60C ?


Bill

Bill:

I agree that the question may be poorly worded. Seems like we all agree on the correct answer.

Joe,

I'm not sure which answer we're all agreeing on. I see (b)s and my (c)answer. (Or, do you mean that we all agree it is poorly worded)

Does the NEC consider a 75C conductor as also being rated 60C ? like dual-rated?

Bill

Bill,
I understand that the temp. rating is the MAXIMUM temp. that the insulation can withstand without beginning to physically degrade. Therefore, if it is rated for 75 deg., any temp below is acceptable.

Redsy,

Yes, I understand. I was just wondering if that would be proper terminology to state that 75C wire is also rated 60C. I'm just asking for the purposes of this test Question but I guess that it doesn't really matter.

Joe,

You didn't tell us what was considered to be the correct answer??

Bill

Bill,
The answer is "C" !!!

I'll throw in with the others and call it "B", for the exact reasons stated (could be TW, and it's #1 or smaller, either of which qualify)
60°C

B., should be considered as the correct answer, see Section 110-14(c)(1) in the 1999 NEC.

[This message has been edited by Joe Tedesco (edited 11-21-2001).]

When I first read the question I choose B as the answer. I think that 110-14 (c)(1)(b)would confirm this answer as the correct one. I also read 110-14 after the apparant confusion in some of the posts on this one. While I still think B is the answer to the test question, I am really confused by this sentence in 110-14(c). Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both. What's up with this? This seems to be totally opposite of the termination rules. I thought ampacity adjustments were made by increasing conductor size not temperature ratings of the conductor. Could some of you sparkys shed some light on this.
(pun intended)

watthead

I will agree with the (b) answer.
To answer WattHead's question. As I understand the NEC, there are two derating applications for a conductor. The first is for temperature. Lets assume you have a 75 deg. THHN #6 conductor that passes through a higher than normal temperature area, say 60 Degree C ambient (140F), the typical attic temperature in the summer time. You have to derate the ampacity from the 75 amps by using the multiplier at bottom of Table 310-16. That is 75 X 0.71=53.25Amps. Secondly, lets say you have 4 of those conductors in a conduit. According to Table 310-15(b), the adjustment factor is 80%. That is 53.25 X .8= 42.6 Amps. The termination temperature is still a 60 degree termination.
If you start with a different conductor insulation, such as TW or UF, then the beginning ampacity is at 55 amps for the same #6 conductor. Therefore, if we apply the same multipliers, the final conductor ampacity will be: 55 X .71 X .8= 31.24 amps.
That's how I understand it.

atran,

Looks like it's just me 'n you on the "C" answer. Even though we're in the minority here I still think we got the 'right' one!

Let me take one more stab at my justification here ..

(b) It is required to be terminated at 60 degree C ampacity - not necessarily, .. right?

(c) It must have insulation rated 60 degree C ampacity. - yes, it must have insulation rated for at least 60C. (nothing lower in the table)

I'm done.

Bill

Bill, I chose "C" as well for the same reason, if it was rated less than 60ºC you couldn't terminate it at all could you? I considered "B" as a trick answer.

Whenever I have come across a question of this type in the past, I would use the basic rule and make a note at the end of the exam. In this note, you would explain that you feel the question is misleading or lacking information and explain why you gave the answer that you did. It is possible that you could still earn some credit if the answer is wrong.

"C" is more correct than "b" also in our State Journeymans/Masters tests we have an option to review our test. This means we may setup a time with the state inspection dept. to go over our answers to the questions. According to most state inspectors here there may be a few questions on the test with a.wrong, b.mostly wrong, c.partly wrong, d.right. If in a review an applicant can give a good argument as to why he or she answered a c.partly wrong question the board would give the question approval. These are only on an individual bases so 10 people could choose this anwer and only one get it correct due to their reply on the answer.