metol pole lights at traffic intersection

[geraldkinen]

Here's another question, I think I got it right.
the 20 I 240 volt copper conductor branch ckt. installed to control metal pole lights at a traffic intersection shall be permitted to contain:
A) 2#8 awg thwn & 1 # 8 thwn equipment ground
B) 2#10 awg thwn & 1 #12 awg thwn equipment ground
C) 2#10 awg thwn, when the polebase rebar cage provides the ground means.
D) 2#12 awg thwn, when a ground rod is driven at the pole base.

Answer: B . 20 I ckt I went with the #10
because the 80% Still not shure and didn't see in 250 anything else?

 

[M. D.]

I'm thinking (A)

 

[raider1]

I would say (A) as well.

250.122(B) would require that the EGC be the same size as the ungrounded conductors for a 20 amp circuit.

Chris

 

[geraldkinen]

yep

yep

I would say (A) as well.

250.122(B) would require that the EGC be the same size as the ungrounded conductors for a 20 amp circuit.

Chris

Yeah You guys are right about that. but Why #8 if it's only 20/240 volt?

 

[jumper]

Yeah You guys are right about that. but Why #8 if it's only 20/240 volt?

The answer is not why A ,#8,, but rather why not B,C, or D. #8 in answer A is the only legal one, overkill yes but legal, so it is correct. B,C, and D are violations. Celtic explained this one to me.

 

[Smart $]

The answer is not why A ,#8,, but rather why not B,C, or D. #8 in answer A is the only legal one, overkill yes but legal, so it is correct. B,C, and D are violations. Celtic explained this one to me.

Not overkill if voltage drop is being taken into consideration... but that's for a different question

 

[patsfan51]

hello,
i'm poking around here as i prepare for my exam... i've read the article(250.122b) and i thought this was for increase in size? the question doesnt mention that so I cant seem to understand why not answer B. Could someone help me understand what I dont.
thank you and this forum has been very very helpful in my prep.

 

[jumper]

Not overkill if voltage drop is being taken into consideration... but that's for a different question

Yeah,but...:grin:You like torturing us little guys, and all I can say is:
Keep it up, how else are we going to learn. I appreciate it.

 

[raider1]

hello,
i'm poking around here as i prepare for my exam... i've read the article(250.122b) and i thought this was for increase in size? the question doesnt mention that so I cant seem to understand why not answer B. Could someone help me understand what I dont.
thank you and this forum has been very very helpful in my prep.

OK, let me try to explain.

A 20 amp circuit would require #12 copper THHN conductors according to Table 310.16 and 240.4(D) (Small conductor rule).

In the answers to the question the first answer had #8 ungrounded conductors. So because a 20 amp circuit only requires #12 conductors and the installer choose (Most likely to compensate for voltage drop) to upsize the conductors to #8's then the EGC must also be increased proportional to the increase in the ungrounded conductors. So in this example a 20 amp circuit requires a #12 EGC with the #12 ungrounded conductors the EGC must be the same size as the ungrounded conductors.

Hope this makes sense.

Answer (B) was incorrect because the EGC was not the same size as the ungrounded conductors.

Chris

 

[Smart $]

Yeah,but...:grin:You like torturing us little guys, and all I can say is:
Keep it up, how else are we going to learn. I appreciate it.

Your welcome!!!

...and this is one of the few places I can depart with some of my knowledge and have it appreciated.

 

[patsfan51]

understood. thank you. about 2 min. after i posted the question and left the computer, it finally hit home. Couple of lessons i've learned. try eliminating answers to get an answer and there are a million ways to ask a question re: a certain article.