Grounding Conductor in PVC

[dduffee260]

Say there are 4 A/C units on a building. 2 will have #8 3 phase 208 units and 2 will have #10 3 phase 208 units. There is also a 120 volt GFI outlet for maintenence. Both are going in 1" conduits. One conduit will have 3-#8's, 3- #10's and a #10 green. The other conduit will have 3-#8's, 3-#10's and 2-#12's. The conduits both terminate in the same enclosure.

Can you pull a single green ground wire for both conduits and ground the enclosure or does it take a ground wire for each conduit? Conduits are PVC sch 40 with GRC 90's. Set aside the derating factor because the wire is oversized per unit anyways. Again, one ground wire for both pipes or two, one for each pipe?

 

[tom baker]

No. Each raceway must have its own EGC. See 300.5(I)

Heres why. All the circuit conductors must be in the same raceway cable or trench, or the circuit impedance will increase as the magnetic fields don't cancel. This is especially important on a ground fault as the currents can be 10X the normal. You could possibly have a ground fault and the circuit OCD not trip.

The code has a lot of rules with the assumption that you understand electrical principles. Thats the advantage of the forum we can help explain the what and why. Thanks for using the forum.

 

[pete m.]

One other consideration would be how is the bonding of the GRC 90's being accomplished?

Pete

 

[dduffee260]

No. Each raceway must have its own EGC. See 300.5(I)

Heres why. All the circuit conductors must be in the same raceway cable or trench, or the circuit impedance will increase as the magnetic fields don't cancel. This is especially important on a ground fault as the currents can be 10X the normal. You could possibly have a ground fault and the circuit OCD not trip.

Tom, what if the two conduits are in a 6" trench? Would this qualify as being in the same trench? Would this be the same condition as running a direct burial underground service with a seperate ground wire in the trench. The only thing between the ground wire and the conductors would be the pvc itself.

I understand about the impedance with the grounding. Same as when alot of electricians install a 1/2" emt from the meter to the ground rod and do not bond the end of the conduit. We install pvc for our service ground.

 

[charlie b]

Tom, what if the two conduits are in a 6" trench? Would this qualify as being in the same trench? Would this be the same condition as running a direct burial underground service with a separate ground wire in the trench. The only thing between the ground wire and the conductors would be the pvc itself.

Not allowed. You will need two ground wires.

To make sure we are using the same terms, the rules for a “ground wire” associated with a service are talking about the “grounding electrode conductor,” not the “equipment grounding conductor.” 300.5(I) is talking about EGCs, not GECs.

Also, when 300.5(I) mentions “in close proximity in the same trench,” it means direct buried conductors that are not also enclosed in conduit.

So there are two things that have to be done, if you are using two conduits for this application. One is that the conductors associated with any particular load, including the phase, neutral, and EGC conductors, must be in the same conduit. You can’t, for example, put the phase conductors in one conduit and the neutrals in another. The other is that each conduit must include the EGC that is associated with the circuits in the same conduit.