Grounding question

[adavey]

A distribution panel (208/ 3 Phase) is being fed from the MDP, via 2-sets of 500MCM in 2-4" galvanized conduits (6 conductor - NO Nuetral or grounding conductor). The panel is feeding misc. 3 phase loads.

Question: This is an existing installation and was wondering if the 4" galvanized conduit is sufficient as the "equipment grounding conductor" ????????

 

[LarryFine]

A distribution panel (208/ 3 Phase) is being fed from the MDP, via 2-sets of 500MCM in 2-4" galvanized conduits (6 conductor - NO Nuetral or grounding conductor). The panel is feeding misc. 3 phase loads.

Question: This is an existing installation and was wondering if the 4" galvanized conduit is sufficient as the "equipment grounding conductor" ????????

I can't see any reason why not, as long as proper bonding is seen to at each end.

 

[bphgravity]

Do you have any doubts of the continuity of the raceway?

 

[adavey]

The continuity of the conduit, I'm assuming, is fine. How would I ckeck ??????

Also, would a "bonding bushing" w/ the properly sized "bonding jumper" suffice ?????????

 

[bphgravity]

A simple continuity test would indicate the raceway is intact and not completely separated at a coupling/connector, and a megger test would identify the resistance of the raceway as a circuit conductor which should be near zero.

 

[bob]

A distribution panel (208/ 3 Phase) is being fed from the MDP, via 2-sets of 500MCM in 2-4" galvanized conduits (6 conductor - NO Nuetral or grounding conductor). The panel is feeding misc. 3 phase loads.

Question: This is an existing installation and was wondering if the 4" galvanized conduit is sufficient as the "equipment grounding conductor" ????????

Tests have shown that the conduit is superior to a conductor as a low impedance path for ground faults.

 

[thinfool]

Grounding bushings are necessary if you enter an enclosure thru an 'open bottom'.

If the conduits enter a metal enclosure thru knockouts then double locknuts and any bushing (plastic, fiber) are acceptable as long as the knockouts do not have concentric rings larger than the conduit you are using. (I can't say that I have ever seen concentrics larger than 4")

 

[infinity]

Bonding bushings aren't neccessary for your installation.

 

[adavey]

Now I'm getting confused.

Any code references to help me understand ??????????

 

[infinity]

Now I'm getting confused.

Any code references to help me understand ??????????

Rigid metallic conduit may be used as an equipment grounding conductor as long as it's terminate with two locknuts or one locknut and a metal bushing. A separate copper of Aluminum EGC is not required.

 

[ramsy]

..500MCM in 4" galvanized conduits (6 conductor - NO Nuetral or grounding conductor).

Hope they didn't use RHW or RHH, since 500kcmil x6, insulation class RHx, will not fit in 4" GRC. NEC Appendix C, Tbl.C8.

 

[infinity]

Hope they didn't use RHW or RHH, since 500kcmil x6, insulation class RHx, will not fit in 4" GRC. NEC Appendix C, Tbl.C8.

I thought the same thing too. But after reading the OP again I realized that it said:

2-sets of 500MCM in 2-4" galvanized conduits

Sounds like a lot more conduit than he really needed.

 

[adavey]

thanks infinity

 

[adavey]

Ramsy

The 500 MCM feeders are original from 1953 " WireTYPE RW" and in suprisingly good condition; even at the terminations.

 

[ramsy]

The 500 MCM feeders are original from 1953 " WireTYPE RW" and in suprisingly good condition; even at the terminations.

That was about half a generation before I was born.

53 years seems a long time for undergound GRC. Maybe PVC is currently favored for cost, but I've heard of alkaline soils destroying GRC in a few months. Even if terminated by well presereved Myers hubs, excellent bonds won't slow normal corrosion.

I would not be surprised if that GRC failed a megger test, as bphgravity suggested, which means faulting bewtween phases is more likely with a conduit breached by corossive elements.

If you only have 3 #500's per pipe (is that right?), there's lots of room to check for a breach (using a vacuum, etc.), or perhaps talk the customer into pulling new EGC's to preserve system integrety in the future, or even explain the reasons to repair the run if EGC's won't pull through.

 

[RUWired]

Now I'm getting confused.

Any code references to help me understand ??????????

Try article 250.118(2) (2005)

 

[don_resqcapt19]

Bryan,

and a megger test would identify the resistance of the raceway as a circuit conductor which should be near zero.

A megger would not be a good tool for this type of testing. You need a meter designed to measure very low resistance...a megger is for high resistance. I am using the them megger in its generic meaning...the Megger company does make instruments suitable for low resistance testing.
Don

 

[hillbilly]

That was about half a generation before I was born.

Ahhhh...you young kids. I was but a wee lad on me mama's knee in 53.
Don't close your eyes for too long or 20 years will jump by. You'll see.
steve

 

[ramsy]

Don't close your eyes for too long or 20 years will jump by.

As long as good company or family can be found nearby, I don't mind closing my eyes for a while.