parallel supplemental grounding

[rayertz]

We have 2 sets of 3C # 4/0 parallel feeders with a # 4 ground, This is tray rated cable with a 400 amp fused OCPD. This feeds a 150 hp exhaust fan. Typical for 3 fans.

The cable is standard built with the # 4 ground, to get a larger ground would require a special ordered cable. Per code it should be a # 3 ground in each cable.

is there a way to add supplemental grounding. I.E., pulling another cable in the tray to each fan or can the tray be calculated and considered supplemental.

Thanks in advance for your help.

 

[jumper]

I know of no alternative method.

This has always been a problem with paralleling standard cables, SER cables suffer the same problem.

 

[raider1]

The 2017 NEC has a change to address this exact situation. Take a look at 250.122(F)(2)(b)&(c)

(2) Multiconductor Cables.
(a) If multiconductor cables are installed in parallel, the
equipment grounding conductor(s) in each cable shall be
connected in parallel.
(b) If multiconductor cables are installed in parallel 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.
(c) 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.
(d) Except as provided in 250.122(F)(2)(b) 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.

Chris