Grounding Electrode Conductor (GEC) Conduit Pullbox Bonding

[W6SJK]

(2008 NEC) I know that the GEC must be bonded to a ferrous raceway at both "ends" but what about intermediate pullboxes in the conduit run where say #1/0 bare copper GEC in threaded rigid conduit and double locknuts are used in punched holes (not eccentric/concentric) of a UL listed pullbox? Seems to me that the conduit attachment qualifies as a continuous ground path so bonding fittings are not needed. Do you agree? (Seems like this would have been covered ad nausium but couldn't find the pullbox question anywhere.) TNX

 

[kwired]

(2008 NEC) I know that the GEC must be bonded to a ferrous raceway at both "ends" but what about intermediate pullboxes in the conduit run where say #1/0 bare copper GEC in threaded rigid conduit and double locknuts are used in punched holes (not eccentric/concentric) of a UL listed pullbox? Seems to me that the conduit attachment qualifies as a continuous ground path so bonding fittings are not needed. Do you agree? (Seems like this would have been covered ad nausium but couldn't find the pullbox question anywhere.) TNX

I don't think they are required but not completely certain either. The bonding at both ends is not for purpose of insuring the raceway is bonded - a connection at just one point will do that, it is done because of inductive effects from only having one conductor in the raceway, and is required any time only a single conductor is installed in a metal raceway - thing is a GEC is about the only time you are permitted to put a single conductor in a metal raceway.

 

[jwelectric]

In high frequency current there is something that eddy does that causes the current to leave the wire and go to the metal. Can?t explain how eddy gets into the raceway but because he does we need to keep both ends of the raceway and enclosures bonded so he won?t put then in jail.

I did a Google search about eddy but got to reading about Eddy Arnold and forgot what I was looking for because the world went away.

http://www.youtube.com/watch?v=hTKeo4w7npA

 

[W6SJK]

The ferrous conduit interferes with the electromagnetic field around the wire caused by the current flow in the wire (right hand rule), becoming a 'choke,' increasing the impedance, unless it is part of the circuit. But, staying on topic - I'm mainly interested in what bonding is required ALONG the conduit route?

 

[jaggedben]

(2008 NEC) Seems to me that the conduit attachment qualifies as a continuous ground path so bonding fittings are not needed. Do you agree?

I think the code is a bit messed up on this. The 2011 NEC attempted to clarify but perhaps made it worse...

New in 250.64(E) (in part)

Bonding methods in compliance with 250.92(B) for installations at service equipment locations and with 250.92(B)(2) through (B)(4) for other than service equipment locations ...

250.92(B)
This part is also new in 2011.

... Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section ...

(And then it goes on to list other acceptable methods.)

Now it seems to me one could focus on the second sentence and say that your method requires additional bonding means. Or one can focus on the first sentence and say that it isn't required in the case of a correctly sized punched hole. I've gone back and fourth five times as I've typed this. :?

One thing I know is that in solar we always just use threaded boxes or bonding bushings so we don't have to argue with inspectors. We also have to comply with 250.97 half the time as well, so we just get used to bonding bushings.

 

[BCSVirginia]

Grounding Electrode Conductor Raceway and pullbox - Bonding

Grounding Electrode Conductor Raceway and pullbox - Bonding

after several days of research via code and online - I have yet to find a definitive answer to the following applications:

1. Multiple Grounding Electrode Conductors (GEC) raceways per design are routed through GRSC conduits into pullbox's (multiple boxes in route to the grounding electrode/grid). The pullboxes are UL listed however the pullbox weremodified by field personnel (cut out bottom where conduits enter into box and reconnected with nuts, bolts screws as needed). All the GEC raceways have bond bushings.
   1. The question is what size bonding jumper is required for each raceway to bond the raceways and box?
   2. Can a singular bonding jumper interconnect all the bonding bushings provided that its rated properly and bonded to the pullbox?
2. Per design their is a Grounding Buss bar installed in the main Electrical room (2" x 1/4" copper) that is run around the entire room continuous. All the Grounding electrode conductors from seperately derived systems are routed to this grounding buss bar. Each GRSC conduit is connected at their respective sources with either rated grounding locknuts or with bonding bushings. the GRSC conduits are stopped approximately 18" short of the 2" x 1/4" ground bars and have bond bushings. The raceways are for protection of the GEC only however the NEC requires that the conduit be bonded on both ends. What size bonding jumper is required? I believe that the bonding jumper is required to be the same size as the GEC.

 

[Dennis Alwon]

1. Multiple Grounding Electrode Conductors (GEC) raceways per design are routed through GRSC conduits into pullbox's (multiple boxes in route to the grounding electrode/grid). The pullboxes are UL listed however the pullbox weremodified by field personnel (cut out bottom where conduits enter into box and reconnected with nuts, bolts screws as needed). All the GEC raceways have bond bushings.
   1. The question is what size bonding jumper is required for each raceway to bond the raceways and box?

1. 1. The size of the bonding jumper should be based on T250.66 same as for the GEC.

      [*]Can a singular bonding jumper interconnect all the bonding bushings provided that its rated properly and bonded to the pullbox?

I don't see why not as long as it is size to the largest jumper required.

What size bonding jumper is required? I believe that the bonding jumper is required to be the same size as the GEC.

I agree