parallel feeder EGC

Status
Not open for further replies.
R

Rich Elec.

Senior Member
Location
Pennsylvania
Here is the installation: 480v 8000 amp service. Draw-out breakers.
Breaker 1 2000 amp, feeds MCC Main Breaker 2000amp. 5 parallel sets of 500 MCM, run with 5 parallel sets of 4/0 EGC. All run in a cable tray.

The EGC raised a red flag to me, so I checked on it when I got home and I believe that this is an undersized EGC.
250.122(F)(1) Each parallel EGC shall be sized on the basis of the ampere rating of the overcurrent device protecting the conductors...
I think that table 250.122 says EGC 2000amp 250kcmil.

Now we also pulled a 4/0 EGC for the 800amp main breaker which is oversized:confused:

I mentioned this to the foreman and I was told that I was wrong.

Am I interpreting this wrong?
 
Rich Elec. said:
The EGC raised a red flag to me, so I checked on it when I got home and I believe that this is an undersized EGC.
250.122(F)(1) Each parallel EGC shall be sized on the basis of the ampere rating of the overcurrent device protecting the conductors...
Click to expand...

250.122(F) does not apply to cable tray installations.
 
Check the trip setting on 2000A CB.If it is set 0n 1600A then the foreman is right.But in General 250-122 requires 250MCM on 2000A CB.
 
I am a licensed contractor in nj and I agree with you. Table 250.122 says you can use a 250mcm copper EGC run with each set of parrallel feeds. The 800 amp breaker would need a 1/0 copper EGC. In my interpretation 250.122 applies to conductors used for equipment ground wether they are in cable tray or not. Using the cable tray as your equipment ground is legal but a whole other issue that doesn't apply here.
 
Bob, how did you determine that 250.122(F) does not apply to cable trays?

If it does not apply to cable trays, then how is the EGC sized? Is it sized as a single run of feeders? 500mcm, 400amp OCPD, #3 EGC?

I also wonder why the NEC would determine that 250.122(F) would not apply. They are parallel feeders.


vicdelta, I will check the ampere setting.

dbnj49, it seems to me that it applies, and yes, the tray is not being used as the ground.

Thanks guys,
Rich.
 
250.122(F) is for raceways, cable tray is not a raceway. IMO one EGC sized according to 250.122 for the OCPD ahead of the conductors will satisfy the grounding requirement.
 
infinity said:
IMO one EGC sized according to 250.122 for the OCPD ahead of the conductors will satisfy the grounding requirement.
Click to expand...

Are you saying to run only one EGC with the 5 paralleled bundles in the tray?

I had considered that cable tray is not a raceway. I checked the definition and you have a point.
 
Rich Elec. said:
Are you saying to run only one EGC with the 5 paralleled bundles in the tray?

I had considered that cable tray is not a raceway. I checked the definition and you have a point.
Click to expand...


Is there a requirement to run more than one in a cable tray. I may be incorrect but I don't know of one. If you used one trough would you still run 5 EGC's or only one?
 
Hey, you have a good point. Maybe I am hung up on pulling feeders in conduit.

So, one EGC sized for the OCPD ahead of it.

I think that I agree.
Thanks for the help.
Rich.
 
Rich Elec. said:
Hey, you have a good point. Maybe I am hung up on pulling feeders in conduit.

So, one EGC sized for the OCPD ahead of it.

I think that I agree.
Thanks for the help.
Rich.
Click to expand...

Again I can't seem to find a requirement for more than one EGC for a cable tray. Inside of parallel conduits is a different animal since 250.122(F) specifically addresses that type of installation.
 
Status
Not open for further replies.
Top