Grounding Locknut on Transformer Secondary

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CCallahan

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Wichita, KS, Sedgwick Cnty
I've read a lot of posts about bonding in the transformer but mostly about whether grounding bushings are required or not. Our local inspector is asking for a grounding locknut on the flexible conduit coming into the secondary side of the transformer.

To give more detail, we have a transformer being fed from a breaker in a large panelboard. Transformer drops the voltage and the secondary out feeds another panelboard. EMT conduit being used on the primary and flexible metal conduit on the secondary with listed fittings (standard locknuts/lockrings). We punch our own holes for these, no concentric. Everything bonded to XO in the transformer including an EGC to primary and secondary panels, GEC, bonding jumper and frame bond. Basically wired up with the steps outlined by Mike Holt and EC&M.

Is a grounding locknut required on the secondary conduit connection in the transformer? If so, where can I find it referenced in the NEC? If not, what can I use to defend my position?


Thanks.
 
I don't think you will find that requirement. Taking into account the restrictions on flexible conduits of any type as a grounding conductor a grounding locknut would be of little value.
 
As Augie stated the bonding locknut is not required in your installation. You said that the inspector is asking for it, ask him for a code reference.
 
Well....usually getting an explanation from them is next to impossible but I did get one that I agree with. They are going off of 250.96(A) because there was a job previous to this one where someone used a die cast fitting with the flat locknut that, in their opinion, does not penetrate through the paint. The inspector said if a steel locknut with the angled teeth is used then the grounding locknut is not required. Personally, I don't like any of the die cast fittings but a lot of guys still will use them on the smaller flex connections.

Thanks for everyone's input.
 
CCallahan said:
Well....usually getting an explanation from them is next to impossible but I did get one that I agree with. They are going off of 250.96(A) because there was a job previous to this one where someone used a die cast fitting with the flat locknut that, in their opinion, does not penetrate through the paint. The inspector said if a steel locknut with the angled teeth is used then the grounding locknut is not required. Personally, I don't like any of the die cast fittings but a lot of guys still will use them on the smaller flex connections.

Thanks for everyone's input.
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Removal of said paint would be another option. Still somewhat pointless on flexible conduit that has limitations on use as an EGC, IMO.
 
CCallahan said:
Well....usually getting an explanation from them is next to impossible but I did get one that I agree with. They are going off of 250.96(A) because there was a job previous to this one where someone used a die cast fitting with the flat locknut that, in their opinion, does not penetrate through the paint. The inspector said if a steel locknut with the angled teeth is used then the grounding locknut is not required. Personally, I don't like any of the die cast fittings but a lot of guys still will use them on the smaller flex connections.

Thanks for everyone's input.
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Aren't all locknuts listed to cut into the paint on an enclosure? And this is on FMC? IMO the inspector is wrong.
 
infinity said:
Aren't all locknuts listed to cut into the paint on an enclosure? And this is on FMC? IMO the inspector is wrong.
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Maybe, there are definitely some out there (and they are more common on die cast EMT fittings) that are questionable as to how well they may cut into paint of an enclosure.
 
kwired said:
Maybe, there are definitely some out there (and they are more common on die cast EMT fittings) that are questionable as to how well they may cut into paint of an enclosure.
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I've never seen a manufacturers instructions with any fittings that come with locknuts that say that the paint must be removed. I'm too lazy to look but I would bet that it's part of the listing of the fitting that the locknut provides sufficient bonding of the raceway without removing that paint first.
 
infinity said:
I've never seen a manufacturers instructions with any fittings that come with locknuts that say that the paint must be removed. I'm too lazy to look but I would bet that it's part of the listing of the fitting that the locknut provides sufficient bonding of the raceway without removing that paint first.
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I don't know if I ever have looked at instructions for such fittings. That said is the locknut part of the fitting or is it an additional fitting? You can purchase locknuts without a fitting to go with them.

Like I said some (especially the now gone Regal company) had some very flat and not too obvious to have ability to pierce into paint locknuts, don't know what they had to say about grounding continuity - though we never removed any paint with them, and used a lot of raceway as the EGC and have seen such installations carry fault current - enough to trip overcurrent protection.
 
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