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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.
Figure 01
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Figure 01
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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 are the Rules related to installing raceways and cables underground?
A1. 300.5 Underground Installations
(A) Minimum Cover Requirements. When cables or raceways are installed underground, they must have a minimum cover in accordance with Table 300.5. Figure 01
(B) Wet Locations. Cables and insulated conductors installed in underground enclosures or raceways must be listed as suitable for a wet location [310.10(C)].
(C) Cables and Conductors Under Buildings. Cables and conductors installed under a building must be installed within a raceway that extends past the outside walls of the building.
(D) Protecting Underground Cables and Conductors. Direct-buried conductors and cables such as Types MC, UF, and USE installed underground must be protected from damage in accordance with (1) through (4).
(1) Emerging from Grade. Direct-buried cables and conductors that emerge from grade must be protected against physical damage. Protection is not required to extend more than 18 in. below grade, and protection above ground must extend to a height of not less than 8 ft.
(2) Conductors Entering Buildings. Underground conductors and cables that enter a building must be protected to the point of entrance.
(3) Underground Service Conductors. Underground service conductors must have their location identified by a warning ribbon placed in the trench at least 12 in. above the underground conductor installation.
(4) Raceway Damage. Where a raceway is subject to physical damage, the conductors must be installed in EMT, RMC, IMC, RTRC-XW, or Schedule 80 PVC conduit.
(E) Underground Splices and Taps. Direct-buried conductors or cables can be spliced or tapped underground without a splice box [300.15(G)] if the splice or tap is made in accordance with 110.14(B).
(F) Backfill. Backfill material for underground wiring is not permitted to damage underground raceways, cables, or conductors.
Q2. What are the requirements for raceways exposed to different temperatures?
A2. 300.7 Raceways Exposed to Different Temperatures
(A) Sealing. If a raceway is subjected to different temperatures, and where condensation is known to be a problem, the raceway must be filled with a material approved by the authority having jurisdiction that will prevent the circulation of warm air to a colder section of the raceway. Sealants must be identified for use with cable insulation, conductor insulation, a bare conductor, a shield, or other components.
(B) Expansion, Expansion-Deflection, and Deflection Fittings. Raceways must be provided with expansion, expansion-deflection, or deflection fittings where necessary to compensate for thermal expansion, deflection, and contraction.
Q3. What are the rules related to electrical continuity of metal raceways and metal parts?
A3. 300.10 Electrical Continuity
Metal raceways, cable armor, and other metal enclosures must be metallically joined into a continuous electrical conductor to provide effective electrical continuity [110.10 and 250.4(A)].
Ex 1: Short lengths of metal raceways used for the support or protection of cables are not required to be electrically continuous, nor are they required to be connected to an equipment grounding conductor [250.86 Ex 2 and 300.12 Ex 1].
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