250.64(E) Bonding Raceway Enclosing Grounding Electrode

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ed downey

ed downey

Senior Member
Location
Missouri
I was out looking at a project and the Electrician installed a 10' stick of EMT conduit from the Ground bar in the main electrical room to the building steel overhead (for the grounding electrode conductor). The EMT is not connected to anything on either end. He installed a Ground bushing on the bottom end but not on the top. Per 250.64(E) (Ferrous metal enclosures that are not physically continuous from cabinets or equipment to the grounding electrode shall be made electrically continuous by bonding each end of the raceway or enclosure to the grounding electrode conductor).

I think he needs a ground bushing on the top end of the conduit in addition to the one he has already installed.

Let me know your thoughts about this.

Thanks
Ed
 
A picture ,... pvc would have been a better choice.

507ecm1704.jpg
 
Most of the time, the NEC does not give a reason for some requirements. Failure to bond the GEC at each end in a metallic raceway will only allow 1/40 or 3% of the fault current thru. The raceway creates an impedance "choke". Remember lighting is high frequency and high current and does not follow the rules of 60hz power. By bonding it, you acutally allow more current to flow as you decrease the resistance and increase the surface area.
 
Take note that the bond jumper shall be no smaller than the enclosed GEC. Too many times that I've seen it in a 1" or 1-1/4" with a 4/0, and than run a little #6 to bond it. It has to be the same size to counter the "choke" affect.
 
tom baker said:
Most of the time, the NEC does not give a reason for some requirements. Failure to bond the GEC at each end in a metallic raceway will only allow 1/40 or 3% of the fault current thru. The raceway creates an impedance "choke". Remember lighting is high frequency and high current and does not follow the rules of 60hz power. By bonding it, you acutally allow more current to flow as you decrease the resistance and increase the surface area.
Click to expand...

Won't the fault current travel mostly on the system bonding jumper?
 
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