NEC Questions and Answers based on 2020 NEC^® - June 2021

Figure 01

For EC&M Magazine
By Mike Holt, NEC^® Consultant
Here's the follow-up to yesterday's newsletter. This includes the answers to the questions sent, so you can see how you did.

Note: The answers to these questions are based on the 2020 NEC.

Q1. What does the Code require when multiple Type MC cables are installed in contact with thermal insulation?
A1. Thermal Insulation. Where more than two Type MC cables are installed in contact with thermal insulation or pass through the same wood framing opening that is to be sealed with thermal insulation, caulking, or sealing foam, the ampacity of each conductor must be adjusted in accordance with Table 310.15(C)(1) [330.80(C)]. Figure 01

Q2. What is the maximum cable length allowed by the NEC between the cable entry of Type NM cable into cabinets and enclosures, and the closest cable support?
A2. Type NM cable must be supported and secured by staples or straps; cable ties listed and identified for securing and supporting; hangers, or similar fittings, at intervals not exceeding 4½ ft and within 12 in. of every cable entry termination. The cable length between the cable entry termination and the closest cable support must not exceed 18 in. [334.30]  

Author’s Comment:
►Many times, there is a tendency to leave a length of sheathed NM cable in a box or enclosure, (such as a panelboard), just to have “extra” cable. While this practice is not prohibited, the length of such sheathed cable cannot exceed 18 in. as measured in a straight line.

Q3. In one-and two-family dwellings, Type TC-ER-JP Cable is permitted by the Code for what type of use?
A3. Uses Permitted [336.10]
Type TC cable is permitted to be used: 

(9) In one- and two-family dwellings, Type TC-ER-JP cable is permitted for branch circuit and feeders where installed in accordance with Part II of Article 334 for interior wiring and Part II of Article 340 for exterior wiring . 

Author’s Comment:
►The “ER” marking on Type TC-ER cable identifies it as suitable for exposed run use in accordance with UL 1277 and the suffix “-JP” identifies it as being suitable for pulling through framing members.

Ex: Where Type TC cable is used to connect a generator and its associated equipment, the cable ampacity limitations of 334.80 and 340.80 do not apply. 

Q4. What are the uses permitted by the NEC for Type UF cable?
A4. Type UF cable is permitted [340.10]:
(1) Underground in accordance with 300.5.
(2) As a single conductor in a trench or raceway with circuit conductors.
(3) For wiring in wet, dry, or corrosive locations.
(4) Where installed as nonmetallic-sheathed cable, the installation must comply with Parts II and III of Article 334. 

Q5. What are the uses permitted by the NEC for Type LFMC?
A5. Uses Permitted [350.10]
Listed LFMC is permitted, either exposed or concealed, at any of the following locations:

(1) If flexibility or protection from machine oils, liquids, vapors, or solids is required.
(2) In hazardous locations as permitted in Chapter 5.
(3) For direct burial, if listed and marked for this purpose.

(4) Conductors or cables rated at a temperature higher than the listed temperature rating of LFMC may be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14(C).