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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 paralleling of conductors?
A1. 310.10 Uses Permitted
(G) Conductors Connected in Parallel.
(1) 1/0 AWG and Larger. Phase, neutral, and equipment grounding conductors are permitted to be connected in parallel (electrically joined at both ends). When paralleling phase and neutral conductors, they must be sized 1/0 AWG and larger. Figure 01
Authors Comment:
â–ºWhen conductors are installed in parallel (electrically joined at both ends), the current flow will be evenly distributed between the individual parallel conductors.
(2) Conductor and Installation Characteristics. All parallel phase conductors, neutral conductors, equipment grounding conductors, and supply-side bonding jumpers must comply with the following:‚
(1) Be the same length.
(2) Be the same conductor material (copper, aluminum, or copper-clad aluminum).
(3) Be the same size in circular mil area (minimum 1/0 AWG).
(4) Have the same type of insulation.
(5) Terminate in the same manner (set screw versus compression fitting).
Author's Comment:
â–ºRaceways or cables containing parallel conductors for Phase A, Phase B, Phase C, neutral, and the equipment grounding conductor must have the phase, neutral, and equipment grounding conductors (or supply-side bonding jumpers) in each raceway [300.3(B)(1)].‚Conductors that comprise one paralleled set are not required to have the same physical characteristics as another paralleled set.‚
(5) Equipment Grounding Conductors. Equipment grounding conductors must be sized in accordance with 250.122(F), but they are not required to be 1/0 AWG and larger.
(6) Bonding Jumpers. Supply-side bonding jumpers must be sized in accordance with 250.102(C) and load-side bonding jumpers must be sized in accordance with 250.102(D), but they are not required to be 1/0 AWG and larger.
Q2. How do you size dwelling unit service and feeder conductors?
A2. 310.12 Dwelling Services and Feeders
Dwelling unit services and feeders can be sized in accordance with the following:
(A) Services. Service conductors supplying the entire load associated with a one-family dwelling unit can be sized in accordance with Table 310.12(A) where there is no conductor ampacity adjustment or correction as required by 310.15.
Example:
Question: What size service conductors are required if the calculated load for a single-family dwelling unit requires a service disconnect rated 200A?
(a) 1/0 AWG (b) 2/0 AWG (c) 3/0 AWG (d) 4/0 AWG
Answer: (b) 2/0 AWG [Table 310.12(A)]
Author's Comment:
â–ºTable 310.12(A) cannot be used to size service conductors for two-family or multifamily dwelling buildings.
(B) Feeders. Feeder conductors supplying the entire load associated with an individual dwelling unit can be sized in accordance with Table 310.12(A).Example
Question: What size feeder conductors are required if the calculated load for a single-family dwelling unit requires a service disconnect rated 200A, and the feeder conductors carry the entire load of the dwelling unit?
(a) 1/0 AWG (b) 2/0 AWG (c) 3/0 AWG (d) 4/0 AWG
Answer: (b) 2/0 AWG [Table 310.12(A)]
(C) Feeder Conductors Not Greater Than Service Conductors. The feeder conductor ampacity for an individual dwelling unit is not required to be larger than the service conductor.‚
(D) Neutral Conductors. Neutral conductors are permitted to be sized smaller than the phase conductors if the requirements of 220.61 and 230.42(C) for service conductors, or the requirements of 215.2(A)(2) and 220.61 for feeder conductors are met.
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