Transformers conduit bonding

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Dexie123

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When grounding a transformer to building steel does the conduit need a bonding locknut or bushing on either end? This is a ceiling transformer with emt out of it, changing to flex for 12'' and to building steel.
 
Yes the GEC's conduit needs to bond at both ends, 250.64(E)
Also notice 250.92(A)(3) & picture:
1113920864_8.jpg

Mike Holt has a good comment about bonding the conduit of a GEC,
"CAUTION: The effectiveness of the grounding electrode can be significantly reduced if a ferromagnetic raceway containing a grounding electrode conductor isn’t bonded to the grounding electrode conductor at both ends. This is because a single conductor carrying high-frequency lightning current in a ferrous raceway causes the raceway to act as an inductor, which severely limits (chokes) the current flow through the grounding electrode conductor. ANSI/IEEE 142, Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) states, “An inductive choke can reduce the current flow by 97 percent.”

Author’s Comment: To save a lot of time and effort, simply run the grounding electrode conductor exposed if not subject to physical damage [250.64(B)], or enclose it in a nonmetallic conduit that is suitable for the application."
 
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The drawing brings up a question from me. At the panel where the GEC raceway attaches to the panel, say the raceway is EMT with a connector to the panel. Do we actually need a bonding bushing and bonding jumper at the connector, or can we rely on the fitting/panel enclosure/main bonding jumper to serve as the connection to the GEC which is terminated at the neutral bar?

I think we can.
 
crossman said:
The drawing brings up a question from me. At the panel where the GEC raceway attaches to the panel, say the raceway is EMT with a connector to the panel. Do we actually need a bonding bushing and bonding jumper at the connector, or can we rely on the fitting/panel enclosure/main bonding jumper to serve as the connection to the GEC which is terminated at the neutral bar?

I think we can.
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I have mentioned this before. The bonding jumper in Mike's graphic from the bonding bushing within the disco to the neutral bar is redundant since the conduit is bonded to the disco and the neutral is also bonded to the disco. The NEC says bonded at both ends, IMO without the bonding jumper in the disco the GEC raceway is still bonded at both ends.
 
crossman said:
...Do we actually need a bonding bushing and bonding jumper at the connector,...?
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Yes I think so, to help example this as well see "Physical protection" .100(A)(6) or Articles 800, 820, & 830, these are installed for the same purpose.

The best installation probably does include an open conductor but I think it would need a plastic bushing at the entrance to any ferrous metallic enclosure. We certainly don't want to eliminate the GEC's purpose and if installed wrong ?An inductive choke can reduce the current flow by 97 percent.?
 
tryinghard said:
Yes I think so, to help example this as well see "Physical protection" .100(A)(6) or Articles 800, 820, & 830, these are installed for the same purpose.

The best installation probably does include an open conductor but I think it would need a plastic bushing at the entrance to any ferrous metallic enclosure. We certainly don't want to eliminate the GEC's purpose and if installed wrong ?An inductive choke can reduce the current flow by 97 percent.?
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But take a look at Mike's graphic again. The jumper within the disco is in parallel with the disco enclosure. IMO the jumper won't do much of anything.
 
True except it is ensuring the correct sized effective path rather than just mechanical connections. Wouldn't this be the same as a feeder that has EGC with a bond bushing?
 
that graphic doesn't meet the OP, unless I am mistaken. With the flex, you will need a bonding wire and bonding bushings, no ? 348.60 (2005)
 
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nakulak said:
that graphic doesn't meet the OP, unless I am mistaken. With the flex, you will need a bonding wire and bonding bushings, no ? 348.60 (2005)
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Yes, I think this is more for a circuit but all the more reason to bond the GEC if in flex.
 
tryinghard said:
True except it is ensuring the correct sized effective path rather than just mechanical connections. Wouldn't this be the same as a feeder that has EGC with a bond bushing?
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But, by NEC, we could run a 200 amp feeder in EMT and use the listed EMT/connectors as the equipment ground. We wouldn't even need an actual EGC wire in the EMT. And if the connector/panel enclosure is okay for that, then why wouldn't it be okay for the connection to the GEC conduit at a relatively small transformer i.e. the OP said it was a xfmr mounted in the ceiling.

I still say no bonding bushing and jumper needed.
 
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