Thread: When is IGB required?

I may have asked this before, but I couldn't find the answer. When you have two panels connected with metal conduit, is an IGB ever required in residential? I am finding some information regarding when there are concentric knockouts in the panel. But then I also see some information that only pertains to systems over 250 volts, which takes most residential systems out of the equation.

Here was another example that the owner is trying to get corrected, but only lock nuts and bushings were installed, not the IGB fitting. Anyone have a good answer as to when an IGB should be used? I can't see how it would hurt to put one on, but the electricians sure don't seem to want to do it for some reason.

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Is that just flex pushed up near a nipple,

Originally Posted by Jim Robinson

I may have asked this before, but I couldn't find the answer. When you have two panels connected with metal conduit, is an IGB ever required in residential? I am finding some information regarding when there are concentric knockouts in the panel. But then I also see some information that only pertains to systems over 250 volts, which takes most residential systems out of the equation.

Here was another example that the owner is trying to get corrected, but only lock nuts and bushings were installed, not the IGB fitting. Anyone have a good answer as to when an IGB should be used? I can't see how it would hurt to put one on, but the electricians sure don't seem to want to do it for some reason.

Jim,

I guess I am not up on my TLAs. What is an IGB?

You mention conduit, but what kind? Some conduits may be used as an equipment ground and some may not. I only see three conductors. Assuming a 240 volt feed, there should be two ungrounded (hot), one grounded (neutral) and an equipment grounding conductor. One conductor is connected to a circuit breaker, but I cannot tell what the other two do. There should be some provision made for an equipment ground. Rigid, intermediate and EMT can be used as equipment grounds. Flex cannot. In this particular case, the conduit is not an effective equipment ground.

As a home inspector, I would probably note the problems (all red insulated conductors, no effective equipment ground) and recommend appropriate corrections by a licensed electrical contractor. I would be reluctant to design a specific repair.

Originally Posted by Jim Robinson

I may have asked this before, but I couldn't find the answer. When you have two panels connected with metal conduit, is an IGB ever required in residential? I am finding some information regarding when there are concentric knockouts in the panel. But then I also see some information that only pertains to systems over 250 volts, which takes most residential systems out of the equation.

Here was another example that the owner is trying to get corrected, but only lock nuts and bushings were installed, not the IGB fitting. Anyone have a good answer as to when an IGB should be used? I can't see how it would hurt to put one on, but the electricians sure don't seem to want to do it for some reason.

250.92 (2008) addresss bonding and mentions that bonding jumpers "shall be used around concentric knockouts or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for bonding required by this section."

I have always used grounding bushings any time that any portion of a concentric ring remained at a point where conduit entered. We stopped using prepunched cans while I was doing industrial so that this would no longer be an issue.

This was called an IGB when I was younger. I think they just call it a grounding bushing now.
It was EMT, with a bushing on each end. Two conductors and a neutral, no EGC present.

I'll stay with my original thoughts about needing an IGB when the concentric knockouts are in use. I was curious about the 250 volt aspect that popped up.

This was just corrected by a licensed electrician (in the first photo). I know he is going to tell the owner that I don't know what I am talking about. I talked to a friend who is an electrical contractor, and he felt the same way I did, that an IGB should be used in this situation.

Originally Posted by Jim Robinson

This was called an IGB when I was younger. I think they just call it a grounding bushing now.
It was EMT, with a bushing on each end. Two conductors and a neutral, no EGC present.

I'll stay with my original thoughts about needing an IGB when the concentric knockouts are in use. I was curious about the 250 volt aspect that popped up.

This was just corrected by a licensed electrician (in the first photo). I know he is going to tell the owner that I don't know what I am talking about. I talked to a friend who is an electrical contractor, and he felt the same way I did, that an IGB should be used in this situation.

Jim what section lists the 250 volt mention? When I did industrial work we always used grounding bushings on concentrics, even on the 110V branch circuits, nearly all of the three phase we punched our own holes in the panels and did not need ground bushings, but we used grounding locknuts on those.

Typically, when the NEC mentions voltage it is referring to "voltage to ground", not voltage between conductors.

Zooming in on the photo (on my phone), it looks like a concentric KO, thus a grounding bushing should be installed if ... (I am sure it is) ... if the EMT is being used as the equipment ground path.

There is also the lack of proper conductor color identification.

Originally Posted by Alton Darty

Jim what section lists the 250 volt mention? When I did industrial work we always used grounding bushings on concentrics, even on the 110V branch circuits, nearly all of the three phase we punched our own holes in the panels and did not need ground bushings, but we used grounding locknuts on those.

It popped up on Mike Holt's site a few times. I don't think it applies to the stuff I am looking at since I am only doing residential. I'm not sure if this has changed later in the code cycles.

Article 250.97 (NEC 2005) states the following: For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in250.92(B), except for (1).Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed for the purpose, the following methods shall be permitted:
(a) Threadless couplings and connectors for cables withmetal sheaths
(b) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(c) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(d) Listed fittings that are identified for the purpose

(underlining is mine, I also removed the bold)

Originally Posted by Jim Robinson

Article 250.97 (NEC 2005) states the following: For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (1).Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed for the purpose, the following methods shall be permitted:
(a) Threadless couplings and connectors for cables with metal sheaths
(b) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(c) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(d) Listed fittings that are identified for the purpose

Looks like a chase nipple to me. Even so, not a good installation.

Originally Posted by Brad Richter

Looks like a chase nipple to me. Even so, not a good installation.

That's what it looks like to me to - a chase nipple.

Originally Posted by Jerry Peck

... it looks like a concentric KO, thus a grounding bushing should be installed if ... (I am sure it is) ... if the EMT is being used as the equipment ground path.

Jerry,

I had thought that conduit connections at concentric knockouts required a grounding bushing, and have been trying to find that requirement in the NEC, but have been unsuccessful. I found the requirement for a grounding bushing on the line side (250.92(B) in the 2011 NEC), but would like to know where the load side requirement is. Should I be looking under raceways?

I don't have access to my codes now, but grounding doesn't have a line/load side ... so I'm not following you.

Originally Posted by Jerry Peck

I don't have access to my codes now, but grounding doesn't have a line/load side ... so I'm not following you.

Yeah, I was unclear. Sorry about that. When I referred to the conduit bushing on the line side, I was referring to the conduit before the main service disconnect. I suppose I should have stated that.

In a previous post, you stated:

Originally Posted by Jerry Peck

Zooming in on the photo (on my phone), it looks like a concentric KO, thus a grounding bushing should be installed if ... (I am sure it is) ... if the EMT is being used as the equipment ground path.

The way I read 250.92 is that it is specific to the service entrance, not for conduits in general. I was looking for the requirement to provide a grounding bushing for metal conduits (EMT, rigid, intermediate) that serve as the equipment grounding conductor that are not part of the service entrance.

250.96 requires bonding of raceways, where necessary, but does not specifically refer to concentric knockouts.

2013 California Electric Code (based on the 2011 NEC)
250.92
(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections. such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means tor the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).

250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non-current-carrying parts that are to serve as equipment grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary.

Originally Posted by Gunnar Alquist

2013 California Electric Code (based on the 2011 NEC)
.
.
250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non-current-carrying parts that are to serve as equipment grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them.

...

Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary.

I broke the section at the applicable location showing a requirement for (basically speaking) 'whatever is required ... I.e., grounding bushings.

Originally Posted by Jerry Peck

I broke the section at the applicable location showing a requirement for (basically speaking) 'whatever is required ... I.e., grounding bushings.

UGH! 250.92 is very clear and 250.96 is pretty darned vague (at least to me). I tell you what... It sure would be nice if the code could be more consistent and less vague.

I would have a hard time saying that 250.96 call for grounding bushing over a standard locknut. They would be bonded simply by landing on the metal enclosure.

Originally Posted by Jim Port

I would have a hard time saying that 250.96 call for grounding bushing over a standard locknut. They would be bonded simply by landing on the metal enclosure.

Jim,

I agree, that is really vague. Is there a clearer section that requires a grounding bushing at concentric knockouts? Or do you feel that a grounding bushing is not required in this case?

Originally Posted by Jim Port

I would have a hard time saying that 250.96 call for grounding bushing over a standard locknut. They would be bonded simply by landing on the metal enclosure.

I would have a hard time saying that 250.96 eliminates grounding bushing being required at concentric and eccentric KOs.

Jim, you were vague in what you are referring to '"a standard locknut" ... over what type of opening?

None of this shown is over 250 volts i to ground so I don't see it as applicable

Originally Posted by Gunnar Alquist

UGH! 250.92 is very clear and 250.96 is pretty darned vague (at least to me). I tell you what... It sure would be nice if the code could be more consistent and less vague.

Public input is about to be accepted for useful changes to the 2020 NEC (the 2019 cycle). If you have ideas, great! Visit www.nfpa.org/70 and click "Next Edition"; I'd start trying in a week.