Thought Process on an NEC Question

[Abraham V]

While studying the NEC (2020), I came across the following question on a website:

Which one of the following conditions apply where Type NM cables are permitted to enter a panelboard through a nonflexible raceway without the cables being secured to the panelboard?

The following are the possible answers:

1. The raceway extends directly above the enclosure without penetrating the structural ceiling.
2. Because the cables are not secured to the enclosure with a fitting, they shall be strapped within 24-inches, measured along the cable sheath, of the outer end of the raceway.
3. The raceway shall be at least 18-inches, but not more than 130-inches long.
4. The number of cables installed in the raceway is not limited where the raceway length is not more than 24-inches.

I would appreciate an explanation of the process someone might use to answer this question, rather than simply knowing the answer by memory. Is there a keyword or an idea that directs you to a particular section in the NEC? How do you narrow that section down to a particular subsection?

Thank you.

 

[augie47]

In most cases the clue can be found through the "keyword" as you mentioned.
This one does not lend itself to that procedure very well partly because the word "panelboard" is used and the answer is in 312, "Cabinets".
In this case the question relies on your knowing the cables would actually enter the cabinet and not the panelboard (interior).
I have found that this Section is unknown to a lot of experienced electricians.

 

[Dsg319]

 

[infinity]

So what's the answer?

 

[hbiss]

So what's the answer?

#3

-Hal

 

[LarryFine]

I would say "all of the above" if the 130" is a typo that should be 120".

 

[augie47]

1. The raceway extends directly above the enclosure without penetrating the structural ceiling. Correct
2. Because the cables are not secured to the enclosure with a fitting, they shall be strapped within 24-inches, measured along the cable sheath, of the outer end of the raceway. Wrong it's 12"
3. The raceway shall be at least 18-inches, but not more than 130-inches long. Wrong..not more than 120"
4. The number of cables installed in the raceway is not limited where the raceway length is not more than 24-inches. Wrong

 

[LarryFine]

Ah, intentional errors.

 

[Abraham V]

This and several other questions are provided in a document called "Electrical License Examination Guide" on the MN Department of Labor website. Like augie47 said, the answer is A.

 

[Abraham V]

In most cases the clue can be found through the "keyword" as you mentioned.
This one does not lend itself to that procedure very well partly because the word "panelboard" is used and the answer is in 312, "Cabinets".
In this case the question relies on your knowing the cables would actually enter the cabinet and not the panelboard (interior).
I have found that this Section is unknown to a lot of experienced electricians.

I was hoping that there was something I was missing besides prerequisite knowledge, but I appreciate your response. It's comforting to know that most cases include a keyword.

 

[don_resqcapt19]

The real issue is where you find the rule. Not a place most would think to look for a question like this.

312.5(C) Cables.
Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.

Exception No. 1:
Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length, provided all of the following conditions are met:

• (1)Each cable is fastened within 300 mm (12 in.), measured along the sheath, of the outer end of the raceway.
• (2)The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
• (3)A fitting is provided on each end of the raceway to protect the cable(s) from abrasion and the fittings remain accessible after installation.
• (4)The raceway is sealed or plugged at the outer end using approved means so as to prevent access to the enclosure through the raceway.
• (5)The cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6 mm (1⁄4 in.).
• (6)The raceway is fastened at its outer end and at other points in accordance with the applicable article.
• (7)Where installed as conduit or tubing, the cable fill does not exceed the amount that would be permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all applicable notes thereto. Note 2 to the tables in Chapter 9 does not apply to this condition.

 

[Abraham V]

Thank you, don_reqcapt19. I certainly wouldn't have thought about it. Your answer prompted me to search the index under "Cables", and even there I was unable to find a reference to 312.5. I probably searched it before, but this probably brings me back to augie47's answer about there not being a good keyword for that method in this question.

 

[don_resqcapt19]

Thank you, don_reqcapt19. I certainly wouldn't have thought about it. Your answer prompted me to search the index under "Cables", and even there I was unable to find a reference to 312.5. I probably searched it before, but this probably brings me back to augie47's answer about there not being a good keyword for that method in this question.

Even though we install a lot of things covered by Article 312, many have never looked at it.