Grounding Bushing Required

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zcanyonboltz

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I'm doing a service change where from main panel a 2" EMT will carry branch circuits and a feeder and the cold water GEC into a gutter then transition to romex (not GEC) into house. My question is do I need a bonding bushing on 2" connector? Looking at 250.92 I believe I don't as this raceway will contain no service conductors. However, looking at 250.64 (E) (1) reads the metal raceway or enclosure for GEC must be electrically continuous from point of attachment to cabinets or equipment. I am thinking this only applies to raceway that carries GEC the entire length of run correct? 250.64 (E) (4) refers to raceway article if raceway is only used for protection. This raceway could be considered protection and I install EMT in accordance with 358. Thanks I could always run the GEC outside of raceway but I'd like to understand my question better.
 

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Thank you. By both sides I need a bonding bushing in main panel and gutter? I was hoping I could not use bonding bushing since GEC was not in EMT all the way to cold water source. I will use bonding bushing (s), or I will run GEC into house not via raceway and gutter.
 
So I'm thinking just one bonding bushing on side of my choice?
This is bit technical but probably not too uncommon.... Say 2" schedule 80 PVC runs from main panel to metal gutter then a lug containng GEC is required in gutter?
 
I re-read 250.64 and the answer to my question above would be yes, metal raceway or enclosure for GEC shall be electrically continuous.
What is the reasoning behind this rule? What difference does it make that the GEC passes through a raceway that may or may not contain other conductors as long as the raceway and or enclosure are bonded by their connection to a grounded panel whats the need for a bonding bushing?
 
You need to bond the GEC at both ends. Some inspectors might insist on bonding bushings, while others may be fine with having the GEC bonded to both the main and the gutter and proper bonding fittings in between.

Some inspectors might prohibit running the GEC with other conductors at all per 250.6 (objectionable current). For at least one inspector I worked with, that could have been a judgement call depending on how long your 2" EMT was and whether you had a feasible option to route your GEC differently.

A GEC (unlike other green wires) is expected under normal circumstances to carry some amount of current. In general that's the reason it's treated differently.
 
jaggedben said:
You need to bond the GEC at both ends. Some inspectors might insist on bonding bushings, while others may be fine with having the GEC bonded to both the main and the gutter and proper bonding fittings in between.

Some inspectors might prohibit running the GEC with other conductors at all per 250.6 (objectionable current). For at least one inspector I worked with, that could have been a judgement call depending on how long your 2" EMT was and whether you had a feasible option to route your GEC differently.

A GEC (unlike other green wires) is expected under normal circumstances to carry some amount of current. In general that's the reason it's treated differently.
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Thanks for reply. Just some thoughts, I'm thinking about what would be different as far as bonding if ran in PVC vs Metal. Maybe the thought is that in metal and not bonded some ground current is lost to the metal raceway but not so if raceway is bonded. If GEC is insulated objectional current would not transfer though right?
 
Yes if you have changing current flows in a single conductor inside a ferrous raceway, the magnetic field heats up the raceway. It's a similar principle to what's at work in a transformer, but not useful. It's also why we have 300.20. Bonding the raceway means that current flows on it and neutralizes the heating effect.
 
zcanyonboltz said:
I re-read 250.64 and the answer to my question above would be yes, metal raceway or enclosure for GEC shall be electrically continuous.
What is the reasoning behind this rule? What difference does it make that the GEC passes through a raceway that may or may not contain other conductors as long as the raceway and or enclosure are bonded by their connection to a grounded panel whats the need for a bonding bushing?
Click to expand...
Having only one conductor of an AC circuit running through a ferrous metal raceway creates an inductive choke and limits the amount of current that can flow on the conductor. Bonding that conductor to the ferrous raceway at both ends eliminates the inductive choke. This inductive choke is not created where you install all of the conductors of the AC circuit within the same ferrous raceway. A GEC that is carrying current is one conductor of an AC circuit and this rule is to prevent the installation of the GEC in a ferrous metal raceway from impeding the flow of current on the GEC.
 
Thanks for the replies! Is it then legal to run a bonding jumper of the same size as the GEC from the ground bar in main panel to the bonding bushings (one bonding bushing in main panel one in gutter)? If not I will strip the sheathing from the #4 stranded GEC and attach GEC conductor itself to the bonding bushings. I'm thinking yes, here's why. 250.64 (E) (2) refers me to 250.92 (B) (2) through (B) (4). 250.92 (B) (4) reads "bushings with bonding jumpers"
 
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It is legal to run a bonding jumper to a bonding bushing if for some reason it is too difficult to land one of the green wires going through the raceway. The latter would always be my first choice though.
 
What code article refers to sizing a bonding jumper to the bonding bushing? Does the jumper need to be same size as the grounding electrode conductor? I know when doing meter stacks the 3/0 cold water GEC had to be bonded with bonding bushings at all gutters and cabinets, I was thinking a smaller jumper to bushing would be nice. My foreman had no clue why we were even using bonding bushings. Now I can refer him to 250.64 (E) since the GEC was passing through other enclosures.
 
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