Bonding

[Djelite]

on service conductors and service equipment a bonding lock nut bonding bushing is required. Is this because these conductors arent protected by a ocpd? Lock nuts are still required for tightening purposes with a bonding bushing, jumper. Is there a bonding bushing, jumper combo where you dont need a regular lock nut?

 

[infinity]

If there are no concentric or eccentric KO's you can just use a bonding locknut on one end of the raceway and no bonding bushings would be required. I've only seen bonding bushings that work in conjunction with a locknut for service raceways.

 

[texie]

For the first question, yes. All metallic items on the line side must be bonded per 250.92.

 

[electrofelon]

. I've only seen bonding bushings that work in conjunction with a locknut for service raceways.

Rob, I had never even considered it, but are you saying you can't use a lock nut on the outside and then a metal bonding bushing on the inside with no lock nut? I thought I remember that being discussed and that we can do it generally but not with service raceways?

 

[infinity]

Rob, I had never even considered it, but are you saying you can't use a lock nut on the outside and then a metal bonding bushing on the inside with no lock nut? I thought I remember that being discussed and that we can do it generally but not with service raceways?

I don't think that I stated it very clearly, I'm saying that you would need at least one standard locknut and the bonding bushing if you had RMC. An EMT connector would also require a locknut with the bonding bushing.

 

[Djelite]

I don't think that I stated it very clearly, I'm saying that you would need at least one standard locknut and the bonding bushing if you had RMC. An EMT connector would also require a locknut with the bonding bushing.

Good because even the way its worded in the code book might lead people to think a lock nut is nut needed where a bonding bushing/jumper combo is installed. Forther more the fact that they dont explain why atleast in the hand book is disappointing and thats why we have people doing things but dont know why

 

[Djelite]

Good because even the way its worded in the code book might lead people to think a lock nut is nut needed where a bonding bushing/jumper combo is installed. Forther more the fact that they dont explain why atleast in the hand book is disappointing and thats why we have people doing things but dont know why

 

[Fred B]

If there are no concentric or eccentric KO's you can just use a bonding locknut on one end of the raceway and no bonding bushings would be required. I've only seen bonding bushings that work in conjunction with a locknut for service raceways.

What about

BRIDGEPORT 2 in. Grounding Locknuts with 14-1/0 AWG Lug (10-Pack) 166-G - The Home Depot

Refine your electric circuit with BRIDGEPORT Grounding Locknuts with Lug.

www.homedepot.com

 

[infinity]

What about

BRIDGEPORT 2 in. Grounding Locknuts with 14-1/0 AWG Lug (10-Pack) 166-G - The Home Depot

Refine your electric circuit with BRIDGEPORT Grounding Locknuts with Lug.

www.homedepot.com

Where's the bushing?

 

[Djelite]

Where's the bushing?

Lol thats a grounding lock nut nothing new. We were talking about grounding lock nuts AND bushing needing to work in conjunction with a standard lock nut

 

[Dennis Alwon]

I have always had questions on this issue. Here is an explanation from Bridgeport which is actually in the NFPA Link enhanced content

ENHANCED CONTENT
Collapse
Standard locknuts, sealing locknuts, and metal bushings are not acceptable as the sole means for bonding a raceway or cable to an enclosure on the line side of the service disconnecting means. For concentric, eccentric, or oversized knockouts, electrical continuity must be ensured through the use of a supply-side bonding jumper that connects the raceway to the enclosure. If these knockouts were in service enclosures, they would impede the bonding connections. Bonding jumpers are required in those situations. They would also be required if reducing washers are used to provide a suitable path for the high level of ground-fault current that is available on the line side of the service disconnecting means.

(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
The following exhibit illustrates an acceptable grounding and bonding arrangement at a service that has one disconnecting means.

The next exhibit illustrates an acceptable grounding and bonding arrangement for a service that has three disconnecting means as permitted by 230.71(A).

See also 250.24(C), which specifies that the grounded service conductor must be run to each service disconnecting means and be bonded to the disconnecting means enclosure.

(4) Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers
Bonding-type locknuts and grounding and bonding bushings for use with rigid or intermediate metal conduit are provided with means (usually one or more set screws that make positive contact with the conduit) for reliably bonding the bushing and the conduit on which it is threaded to the metal equipment enclosure or box.
Grounding bushings used with fittings for rigid or intermediate metal conduit or with electrical metallic tubing (EMT) have means for connecting a bonding jumper or have means provided by the manufacturer to attach a wire connector. This type of bushing may also have one or more set screws to reliably bond the bushing to the conduit.
Threaded hubs used to connect rigid metal and intermediate metal conduits to service equipment and other line-side enclosures are suitable for bonding the conduit only if they have been listed as grounding and bonding equipment per UL 467, Standard for Grounding and Bonding Equipment. Such hubs are available with gaskets and are suitable for use in wet locations so that a conduit connection can be to an enclosure above the live parts. Grounding and bonding hubs are provided with a grounding and bonding locknut to ensure that the connection between the hub and the conduit is suitable for the higher levels of fault current available at the service location. Although many threaded hubs are listed as conduit fittings, not all threaded hubs have additionally been listed as grounding and bonding equipment. Conduit hubs listed as grounding and bonding equipment are also required (see 250.97) where the conduit contains feeders or branch circuits rated above 250 volts to ground.
The exhibit below shows a listed bonding-type conduit bushing used to connect a threaded conduit to an enclosure and provide the bonding connection required by 250.92(B).

 

[Djelite]

Very nice

 

[Grouch1980]

I have a question on Dennis Alwon's post #11 above, with the 2 pictures. The first pic is from 250.92(B)(1) and the second pic is from 250.92(B)(4).

(B)(1) is strictly bonding to the grounded conductor. The use of bonding bushings are allowed?
(B)(4) is using bonding bushings, but in this case you bond the bushing to the metal box / enclosure using a bonding jumper; no connection to the grounded conductor correct?

 

[Carultch]

I have a question on Dennis Alwon's post #11 above, with the 2 pictures. The first pic is from 250.92(B)(1) and the second pic is from 250.92(B)(4).

(B)(1) is strictly bonding to the grounded conductor. The use of bonding bushings are allowed?
(B)(4) is using bonding bushings, but in this case you bond the bushing to the metal box / enclosure using a bonding jumper; no connection to the grounded conductor correct?

In the case that the enclosure does NOT host the service disconnect, or other equipment where the NEC requires bonding the grounded conductor to the EGC, the bonding bushings or other bonding jumper fittings will exclusively apply to the EGC (green or bare wire). The grounded conductor (white or gray wire) remains isolated from the enclosure, the conduits, and any other piece of metal that is not intended to carry current under normal circumstances. (White or gray) remains isolated from (green or bare), and only (green or bare) is involved in bonding the raceways and enclosures.

It is only when it is a location where the NEC requires bonding the grounding and grounded conductors (e.g. the service disconnect), that you would be allowed to run a bonding jumper from the bonding bushing to a busbar that contains grounded conductor terminations. Everywhere else, only the green/bare wires connect to the bonding bushings and enclosure.

 

[Grouch1980]

In the case that the enclosure does NOT host the service disconnect, or other equipment where the NEC requires bonding the grounded conductor to the EGC, the bonding bushings or other bonding jumper fittings will exclusively apply to the EGC (green or bare wire). The grounded conductor (white or gray wire) remains isolated from the enclosure, the conduits, and any other piece of metal that is not intended to carry current under normal circumstances. (White or gray) remains isolated from (green or bare), and only (green or bare) is involved in bonding the raceways and enclosures.

It is only when it is a location where the NEC requires bonding the grounding and grounded conductors (e.g. the service disconnect), that you would be allowed to run a bonding jumper from the bonding bushing to a busbar that contains grounded conductor terminations. Everywhere else, only the green/bare wires connect to the bonding bushings and enclosure.

I follow. So it's not that you have a choice between (B)(1) or (B)(4). It depends on what's inside the enclosure, whether or not you have a service disconnect inside or not, that dictates if you use (B)(1) or (B)(4). I wish the code was a little clearer.

Another question: in post #11, the 2nd picture with the enclosure that has the neutral terminal block before the 3 service switches... that enclosure with the neutral terminal block is considered as part of the service equipment 'assembly'? I'm assuming that would explain bonding the conduit and enclosure to the neutral block... thereby following (B)(1).

 

[Carultch]

I follow. So it's not that you have a choice between (B)(1) or (B)(4). It depends on what's inside the enclosure, whether or not you have a service disconnect inside or not, that dictates if you use (B)(1) or (B)(4). I wish the code was a little clearer.

IMO, the neutral-to-ground bonding really belongs in the transformer, rather than the service disconnect, as that is where it makes the most sense based on the physics of grounding. I.e. you establish the voltage-to-ground of the neutral point, where you first derive the system. The neutral-to-ground bond is supposed to be just one path, so that the EGC is a dead-end path that won't carry current under normal circumstances, and doing it in the transformer would eliminate redundant bonding jumpers between N*G, when there are multiple disconnects on its secondary. But given the fact that service transformers are usually utility-owned, and the utility isn't governed by the NEC, the service disconnect ends up being the de-facto place that the NEC has settled upon for accomplishing this bond, so that it happens in customer-owned equipment.

For customer-owned transformers, you have a choice of either doing it in the transformer, or in the 240.21(C) disconnect, and I would recommend opting for the transformer secondary as the place to do this.

Another question: in post #11, the 2nd picture with the enclosure that has the neutral terminal block before the 3 service switches... that enclosure with the neutral terminal block is considered as part of the service equipment 'assembly'? I'm assuming that would explain bonding the conduit and enclosure to the neutral block... thereby following (B)(1).

That's correct. There is no distinction of ground and neutral on the supply side of the service disconnects, hence why you connect the bonding bushings to it. The bonding bushing jumpers are SSBJ's instead of EGC's based on the context, but it is still the same principle as if they were EGC's. The sizing algorithm is slightly different, as it follows the SSBJ table instead of the EGC table, but the end result is still that you still install them to establish proper continuity of the raceways to the system's grounding.

 

[Grouch1980]

IMO, the neutral-to-ground bonding really belongs in the transformer, rather than the service disconnect, as that is where it makes the most sense based on the physics of grounding. I.e. you establish the voltage-to-ground of the neutral point, where you first derive the system. The neutral-to-ground bond is supposed to be just one path, so that the EGC is a dead-end path that won't carry current under normal circumstances, and doing it in the transformer would eliminate redundant bonding jumpers between N*G, when there are multiple disconnects on its secondary. But given the fact that service transformers are usually utility-owned, and the utility isn't governed by the NEC, the service disconnect ends up being the de-facto place that the NEC has settled upon for accomplishing this bond, so that it happens in customer-owned equipment.

For customer-owned transformers, you have a choice of either doing it in the transformer, or in the 240.21(C) disconnect, and I would recommend opting for the transformer secondary as the place to do this.



That's correct. There is no distinction of ground and neutral on the supply side of the service disconnects, hence why you connect the bonding bushings to it. The bonding bushing jumpers are SSBJ's instead of EGC's based on the context, but it is still the same principle as if they were EGC's. The sizing algorithm is slightly different, as it follows the SSBJ table instead of the EGC table, but the end result is still that you still install them to establish proper continuity of the raceways to the system's grounding.

Good stuff, got it. .... what about sections (B)(2) and (B)(3)? do they follow (B)(4) and are only done where the service disconnect is not inside the enclosure?

 

[texie]

IMO, the neutral-to-ground bonding really belongs in the transformer, rather than the service disconnect, as that is where it makes the most sense based on the physics of grounding. I.e. you establish the voltage-to-ground of the neutral point, where you first derive the system. The neutral-to-ground bond is supposed to be just one path, so that the EGC is a dead-end path that won't carry current under normal circumstances, and doing it in the transformer would eliminate redundant bonding jumpers between N*G, when there are multiple disconnects on its secondary. But given the fact that service transformers are usually utility-owned, and the utility isn't governed by the NEC, the service disconnect ends up being the de-facto place that the NEC has settled upon for accomplishing this bond, so that it happens in customer-owned equipment.

For customer-owned transformers, you have a choice of either doing it in the transformer, or in the 240.21(C) disconnect, and I would recommend opting for the transformer secondary as the place to do this.



That's correct. There is no distinction of ground and neutral on the supply side of the service disconnects, hence why you connect the bonding bushings to it. The bonding bushing jumpers are SSBJ's instead of EGC's based on the context, but it is still the same principle as if they were EGC's. The sizing algorithm is slightly different, as it follows the SSBJ table instead of the EGC table, but the end result is still that you still install them to establish proper continuity of the raceways to the system's grounding.

Just for the record, the POCO transformer will ALWAYS have the neutral bonded at the transformer when supplying a grounded system.