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Thread: Grounds in parallel circuits, cable tray vs. raceway

  1. #1
    Join Date
    Nov 2017
    Location
    Denver, CO, USA
    Posts
    10

    Grounds in parallel circuits, cable tray vs. raceway

    First some background, per 2017 NEC 250.122 (F) (1),

    Conductor Installations in Raceways, Auxiliary Gutters, or
    Cable Trays.


    (a) Single Raceway or Cable Tray. If conductors are installed
    in parallel in the same raceway or cable tray, a single wiretype
    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. Wiretype
    equipment grounding conductors installed in cable trays
    shall meet the minimum requirements of 392.10(B)(1)(c).
    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.

    This appears to allow a single EGC for the whole parallel circuit, sized per Tbl 250.122

    The other case, just below the above:

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

    Requires a full-sized EGC in each raceway, and some discussion in the NEC handbook confirms this and explains why.

    Here's my question: when using cable tray to connect a Main Dist swgr or panel to feed, say an MCC, even though most of the wiring is in cable tray, at each end, the parallel groups commonly leave the cable tray and enter the gear thru conduit nipples stubbed up out of the gear, one group per nipple. Does this conversion into conduit force you to install a full sized EGC with each parallel group?

  2. #2
    Join Date
    Jul 2005
    Location
    Tennessee
    Posts
    15,973
    That's an interesting question.
    My first thought would be that the conduits were being used more as sleeves and not a conduit system bujt it does lead one to wonder how you route the individual conductor when you leave the tray and enter the utilization equipment. Perhaps in an individual non metallic conduit ?
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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