Ground wire in each duct bank envelope

[Mike Weinberg]

How do you size a "ground wire (as stated in the specifications)" that is encased in the concrete envelope of a duct bank? I am installing various sizes of PVC in a steel reinforced concrete duct bank and required to connect to switchgear and MCC ground buses and assume to all steel racks and hardware inside manholes. The PVC contains everything from 2000amp service feeders to 4-20ma signal wiring.

 

[don_resqcapt19]

Re: Ground wire in each duct bank envelope

The code requires that an EGC be installed in each raceway or cable. The installation of an external grounding conductor for the duct bank does not satisfy the code rule.
Don

 

[tom baker]

Re: Ground wire in each duct bank envelope

All circuit conductors must be grouped together, in this case inside the racewa. By separating the conductors, including the EGC, the impedance is increased, this is due to the physics of alternating current. It would be a violation of 250.4 A 5 and 300.5 I

 

[Mike Weinberg]

Re: Ground wire in each duct bank envelope

Originally posted by don_resqcapt19:
The code requires that an EGC be installed in each raceway or cable. The installation of an external grounding conductor for the duct bank does not satisfy the code rule.
Don

The "external grounding conductor" is over and above the EGC that is installed in each raceway. This encased ground wire is supplimental to the installation. The installation is required by the specifications but is not designated with a size.
Mike

 

[Mike Weinberg]

Re: Ground wire in each duct bank envelope

Originally posted by tom baker:
All circuit conductors must be grouped together, in this case inside the racewa. By separating the conductors, including the EGC, the impedance is increased, this is due to the physics of alternating current. It would be a violation of 250.4 A 5 and 300.5 I

The external grounding conductor is over and above the EGC that is installed in each raceway. This encased ground wire is supplimental to the installation. The installation is required by the specifications but is not designated with a size.
Mike

[ February 01, 2006, 12:32 PM: Message edited by: Mike Weinberg ]

 

[charlie b]

Re: Ground wire in each duct bank envelope

Mike: There is no need to say the same thing twice, to two different members. We all see the same posts.

 

[charlie b]

Re: Ground wire in each duct bank envelope

What you are describing is not an "Equipment Grounding Conductor." It might be something along the lines of a "Grounding Electrode," but I'm not sure they can be built in the manner you describe.

But to directly answer your question, the NEC does not have any requirements related to sizing the thing you are describing. Size it with 2000 MCM wire, or with #22 AWG wire: the NEC doesn't care because the NEC does not recognize its existence. It would be like looking in the NEC for rules about what kind of trees or shrubs are allowed to be outside the substation's fence. Plant whatever you want; the NEC doesn't care.

And now to be more practical: I suggest you contact the engineer or other owner's representative, and get a clarification on this "spec requirement."

 

[don_resqcapt19]

Re: Ground wire in each duct bank envelope

Mike,

I am installing various sizes of PVC in a steel reinforced concrete duct bank and required to connect to switchgear and MCC ground buses and assume to all steel racks and hardware inside manholes.

I don't see where the code permits the us of this conductor to bond the manhole hardware. That should be connected to the EGC of the circuit that is likely to energize the hardware.
Don

 

[tkb]

Re: Ground wire in each duct bank envelope

Originally posted by Mike Weinberg:
I am installing various sizes of PVC in a steel reinforced concrete duct bank and required to connect to switchgear and MCC ground buses and assume to all steel racks and hardware inside manholes.

I have done projects like this before. Our bare cooper wire in the concrete was connected to the ground rings of the buildings that the duct banks connected.
The wire size was the same as the ground rings. In my cases it was a 4/0 ring and a 4/0 ground cable in the duct bank. The sizes were by the EE for the project. I don't know why or where he got his sizes though.