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| Subject - Conduit as Ground | |
| David Hyatt | When using EMT, what do you have to do to make it the ground instead of pulling a ground. Fittings, bushing ECT.... I usually always pull an equipment ground because conduit can come apart, but I would like to know this procedure. |
| Ryan_J | Nothing special...but if I'm the AHJ you will have to prove to me that the length of pipe will create the "effective ground-fault current path" as defined in 250.2 and discussed in 250.4(A)(5). |
| cs409 | the more connection you make the more chance for a problem,,,pull a ground with your runs ...this way you know it is grounded. |
| David Hyatt | Yea, I always do, just checking. Wasn't sure about grounding bushings and such as that. |
| JimmyDee | Back toward the beginning of my apprenticeship, in a local industry, a person was killed because a EMT connector came apart in a wood building and lost its ground. From that point on, that industry required rigid conduit. They would have saved a bundle if they would have pulled a ground wire. Although not always necessary, a ground wire is a good idea. Jim |
| Ryan_J | In another thread I gave a link to a nice software that talks about this very thing :) |
| euharlee457 | This is for whom it concerns,this is in reply to a subject in this post,about when using bonding bushing's.I use them whenever there eccentric or concentric knockouts that have not been knocked out to their largest conduit application.I use them on all service entrance equipment or when using reducing bushings.Can anyone add or take away from this?Any infomation would be most helpful. Thanks! |
| euharlee457 | Using your conduit as a equipment grounding conductor.I am against the use of just using conduit as a ground because the conduit is like a chain,it is only as strong as it's weakest link.If a loose connection whether it be a loose coupling,locknut,connector,etc....This causes a high impedance and it may not be an effective enough ground to clear a ground fault which in turn could lead to more problems,such as short circuit's or insulation damage. Of course when using your conduit as the ground it's best to have a good connection cause any loose connection can cause high resistance.We as electrician's know that electricity follows the path of least resistance.But using bonding pigtails on all outlets' and jbox's we can hope to ensure a low impedance ground.Obviously impedance being the total opposition to the flow of current. Thus me personally if when my supervisor suggest's conduit grounding I just still pull a grounding conductor for safety.You can never be safe enough,and we are harnessing one of the most powerful form of energy. "We don't creat electricity,we simply create electron movement." Tom Henry |
| cs409 | any time i find the conduit as the ground, it usually gets fixed with a new wire run,,,,just dont like to use emt as a ground! in my opinion,,,,what good would a grounding bushing really do!! my point, all connections with a set screw etc and you then go to all the problem of a grounding bushing, it just doesnt make good work IMO..... |
| SteveMc | Along the same lines, but a different question. When runnning a ground wire in EMT is it necessary to install a ground pigtail in every device box? I always do, but isn't the device to box connection enough to meet Code? |
| JimmyDee | Without the pigtail and the bonding of the box, I would think the use of the ground wire would be made useless. Bonding is important for the insurance of a good ground/electrical connection. Jim |
| cs409 | 1000percent agree with jimmy |
| SteveMc | But, what about 250.146(B)? Does 250.148 contradict 250.146(B). Just something I've always wondered about because I've seen a lot of devices wired this way. |
| JimmyDee | quote: quote: What I see here is that within the box, if it has splices or a device of any kind associated with the conductors, the grounding conductor will be spliced with all associated grounding conductors. 250.146 (B) has nothing to do with this. It is allowing for conditions that a bonding jumper does not have to be attached to the grounding wire. If a bonding jumper is installed, it would have to be spliced to the grounding conductor. Jim |
| David Hyatt | So let me understand here, any device or junction box needs to have ground wire bonded to box. Machine screw in back of box, right? I know this is a good idea but is it required? Or will conduit serve as the ground and the ground wire connects to the device? |
| David Hyatt | The more I think about this, I don't see where grounding the box on a device is necessary because the device screws will do the same, if the device is grounded. Now in junction boxes I see grounding to the box. What do you all think? |
| David Hyatt | Ryan, I guess I should have read further, I see what you are talking about. If the conduit broke and you removed the receptacle then the ground would be lost. I did ask the inspector today the same question and he told me I did not have to that the receptacle would work for the ground. Maybe its because the box is mounted to metal studs which are bonded to the building frame. What do you think about that? |
| Ryan_J | 250.148 says that if there is a ground wire and you have a splice or termination in the box you must bond the box the way you described. If you don't have an EGC, you don't need to bond the box unless you are installing a cover mounted receptacle, in which case 250.146(A) applies, unless you have a listed combination of recpetacle+cover that is listed for grounding. |
| lctrc789 | We always use green pigtails in all steel boxes, with a green grounding screw, we all no that you cannot use tec screws etc. Every junction box every device box is grounded and bonded. I know what you are saying the device is really gorunded thru the 6/32 screws but not really, all mettalic parts must be bonded to each other for bonding and grounding. |
| Ryan_J | Hi David. What I am refering to is a "raised steel" or "industrial" cover. A cover where, in order to take off the cover you must isolate the receptacle from the box as well. Picture yourself with a 4 sqaure box and an industrial cover. You open the box to get to the wiring and you now have an ungrounded receptacle in your hand. Does that make sense? |
| David Hyatt | Yep, I have been using plaster rings, so the receptacle is still intact when removing face plate. I have a EGC on the receptacle, and the box is mounted to the metal stud, so I guess I am ok without the bonding screw. |
| Ryan_J | Anytime you have an EGC in the raceway, and you splice or terminated in a box, the box must get bonded. The rule I was talking about above is used when you don't have an EGC but you have a faceplate mounted receptacle, which would require you to use a bonding jumper (pigtail) from the box to the device. I guess really the bottom line is that if you have an EGC, and you have a box with a splice or termination, you must bond the box with it. :) |
| SteveMc | quote: Thanks Ryan, that makes it simple. |
| David Hyatt | Thanks, Ryan it took a while but I guess you got through to my thick scull. |
| Ryan_J | No problem David :) |
| Pierre Belarge | When using metal boxes in a grounded system, it is not always required to have a bonding conductor from the metal box to the receptacle - using a 'self grounding device is permitted as per 250.146(B). So the requirement does permit the removal of the device from the box and not have a bonding conductor - definitely a potential problem in the wrong hands. |
| jagerbombme | i am local 176 in joliet illinois and work residential, unless the ahj requires we never pull grounding conductor for branch circuits, rarely do we even jump from the recep to the box. we all rely on EMT, i was just wondering how the gentleman died when the EMT came apart and if anyone else knows of specific things that have happened or things to watch out for when relying on emt as a ground. I guess if there was current on the emt and you went to service it and pulled apart two peices at a coupling you could become a load. doesn't sound appealing to me, never would've thought of that though. |
| Wirenutz | interesting Jag i understand your locality dictates all emt , no romex residentially so how do you verify continuity? do you meg out long runs  ~W~ |
| lucky1122 | My input to your posting is simply this . You are on the right track by including an equipment ground with the conduit run.though the NEC recognizes certain raceways such as rigid and Emt as an equipment ground ,under certain conditions the effectiveness can be breached. It is always good practice to include a separate equipment ground with the raceway and to exceed the NEC requirement ,which is a minimum safety requirement.The important thing having done that ,is to effectively bond the box and raceway to the equipment grounding conductor by an approved means such as a bonding screw.This must be drilled and taped.( Self drilling screws won't do ,nor will wires wrapped around screws supporting the box). If there is metal to metal contact such as a surface box (handy box) the code recognizes that as grounding the yoke when a washer is pulled. situations involving raised covers require a bonding jumper .Any raceway relied upon as an equipment ground connected using reducing washers or concentric ko's must be bonded around using grounding bushings. |
| JimmyDee | quote: The EMT was surface mounted in an industrial setting. The building was an all wood type of building. Not sure how the conduit came apart but it did and the ground part of the receptacle became hot. That about all I know about it. We spent the next year or so replacing all the exposed EMT in the factory with rigid. Over kill? Maybe but I'm just reporting the facts. Jim |