Several rules must be followed when installing conductors in parallel. Most of the rules for parallel conductors are found in 310.10(H) and additional rules pertaining to installing equipment grounding conductors in parallel are located in 250.122(F).

The rules for parallel equipment grounding conductors in multiconductor cables are kept separate from individual parallel equipment grounding conductor installations in raceways or cable trays.

If a sheet metal auxiliary gutter is installed and supplied by multiconductor cables in parallel, the gutter is required to be connected to the equipment grounding conductors in each parallel cable. These equipment grounding conductors must be sized from Table 250.122 based on the size of the overcurrent device protecting the multiconductor cables.

Section 250.122(F)(2)(c) allows a single equipment grounding conductor, sized in accordance with 250.122, in combination with the equipment grounding conductors provided within the multiconductor cables. This allowance recognizes that situations can occur where the equipment grounding conductor in each parallel multiconductor cable may not be sufficient in size for larger feeders or branch circuits in the same auxiliary gutter. In this case, an individual equipment grounding conductor is permitted to be installed in addition to the equipment grounding conductors provided within the multiconductor cables as long as all equipment grounding conductors are connected together.

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2020 Code Language:

250.122(F) Conductors in Parallel. For circuits of parallel conductors as permitted in 310.10(H), the equipment grounding conductor shall be installed in accordance with (1) or (2).

(1) Conductor Installations in Raceways, Auxiliary Gutters, or Cable Trays.

(a) Single Raceway or Cable Tray, Auxiliary Gutter, or Cable Tray. If circuit conductors are connected in parallel in the same raceway, auxiliary gutter, or cable tray, a single wire-type conductor shall be permitted as the equipment grounding conductor. The wire-type equipment grounding conductor shall be sized in accordance with 250.122, based on the overcurrent protective device for the feeder or branch circuit.

(b) Multiple Raceways. If conductors are installed in multiple raceways and are connected in parallel, a wire-type equipment grounding conductor, if used, shall be installed in each raceway and shall be connected in parallel. The equipment grounding conductor installed in each raceway shall be sized in accordance with 250.122 based on the rating of the overcurrent protective device for the feeder or branch circuit.

(c) Wire-Type Equipment Grounding Conductors in Cable Trays. Wire-type equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)⁠(1)(c).

(d) Metal Raceways, Auxiliary Gutters, or Cable Trays. Metal raceways or auxiliary gutters in accordance with 250.118 or cable trays complying with 392.60(B) shall be permitted as the equipment grounding conductor.

(2) Multiconductor Cables.

(a) Except as provided in 250.122(F)(2)(c) for raceway or cable tray installations, the equipment grounding conductor in each multiconductor cable shall be sized in accordance with 250.122 based on the overcurrent protective device for the feeder or branch circuit.

(b) If circuit conductors of multiconductor cables are connected in parallel, the equipment grounding conductor(s) in each cable shall be connected in parallel.

(c) If multiconductor cables are paralleled in the same raceway, auxiliary gutter, or cable tray, a single equipment grounding conductor that is sized in accordance with 250.122 shall be permitted in combination with the equipment grounding conductors provided within the multiconductor cables and shall all be connected together.

(d) Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)⁠(1)⁠(c). Cable trays complying with 392.60(B), metal raceways in accordance with 250.118, or auxiliary gutters shall be permitted as the equipment grounding conductor.