250-64(B) Grounding electrode conductor raceway

Status
Not open for further replies.
W

Wedge

Member
Why is liquid-tite flexible metal conduit or steel flexible metal conduit not an approved raceway for GEC and bag wire is?
Example: Indoor installation, 75KVA transformer mounted on tilt-up concrete wall @ 10ft A.F.F with approved wall bracket & isolation pads to reduce noise.
3/4" Rigid conduit to building steel & cold water with uninsulated #2 GEC and
30" of liquid-tite flexible metal conduit only at transformer connection with ground bushing.

Question clarification.
The building electrical specifications require rigid conduit and transformers to be installed on isolation pads to decrease noise.
Primary and secondary feeders to transformers require 30" liquid-tite flex for final connection at transformers to aid in decrease of noise travel. The GEC conduit can not meet building spec and satisfy the code.
Oviously the NEC is the final authority and flex is not an approved conduit for grounding electrode conductor.
Unfortunately the code does not allow exceptions or provide alternatives for this application.
My question is why liquid-tite flex or steel flex is not an approved conduit per 250-64(B)
Other than PVC, the conduit is bonded to limit difference of potential between the GEC and conduit. The grounding electrode conductor is the low impedence path and if uninsulated when installed, where is the hazard? If the liquid-tite flex connector or steel flex connector is insufficient why wouldn't an external bond jumper satisfy.
It seems a loose set screw EMT fitting would pose a greater threat in difference of potential for the GEC installation.
 
Last edited:
Why ask why? It is not, end of story. It may be because the manufacturer did not go to the expense of having it tested and listed as a grounding conductor. It may be because it failed the testing required to be listed as a grounding conductor. The bottom line is that it is not listed as being suitable for a grounding conductor, so don't try to use it as one. Would it work 99% of the time? Probably. Would you be liable if you used it as a grounding conductor and someone got hurt or there was a fire? Definitely.
Don't take the risk. Install it as it was intended and CYA.
 
Bob,
I don't know what you mean by "no current flow in a fault condition". The whole purpose of the grounding conductor is to provide a "low impedence path" so that in the event of a fault there will be high current flow (often hundreds of amps) through the grounding conductor which will cause the overcurrent device to operate quickly. The confusion may be because the OP used the shorthand "GEC" when he really means (I think) grounding conductor. The GEC is the conductor to the Grounding Electrode, which would rarely if ever be a conduit or metallic casing. The grounding conductor will often be conduit or the casing of type AC cable, etc.
Now that I re-read the original post, I am not really sure what he is asking. I thought he was asking about the the casing of flexible metal conduit being used as a grounding conductor, but now it looks like he is asking about using flex conduit as a raceway for the GEC. The systems that may be used to protect the GEC are spelled out in 250.64(B). If it is not listed there, it can't be used. That is even simpler.
As usual, I got off on the wrong tack, sorry for the confusion.
I also do not know what "bag wire" is.
 
Last edited:
Bag Wire is a trade term for manufactured armored cable with (1) #6 or #8 bare solid conductor used for connection to grounding electrode, typically for residential services or temp power applications. Its also considered suitable protection agaist physical damage.
 
It would appear he is talking about a GEC.

I don't know that there is any special requirement for what is used to pretect a wire from damage. I am not even sure it has to be inside anything if the wire is not liekly to be damaged.

Approval comes from the AHJ.
 
infinity said:
What is bag wire?
Click to expand...
Bare Armored Ground (BAG) wire. A bare copper conductor #8 #6 #4 solid or stranded with steel or aluminum armor. I'ts a good product used by the mile out here in the wild west as a GEC etc.

Bob on the left coast.
 
See 250.64(B) for sysems that are acceptible to protect the GEC. They are only required when GEC is subject to physical damage as determined by the AHJ. The simple fact is that Flexible conduit is not included as one of the acceptable methods and "cable armor" is.
 
haskindm,
I don't know what you mean by "no current flow in a fault condition". The whole purpose of the grounding conductor is to provide a "low impedence path" so that in the event of a fault there will be high current flow (often hundreds of amps) through the grounding conductor which will cause the overcurrent device to operate quickly. The confusion may be because the OP used the shorthand "GEC" when he really means (I think) grounding conductor.
Click to expand...
I don't agree that the original question is about the equipment grounding conductor. It is about protection for the grounding electrode conductor.
Based on that, I agree with Bob, there should be very little current on the grounding electrode conductor even under fault conditions.
Don
 
Don,
If the OP is talking about a conduit for the GEC, I agree with you. The explanation he has added to the original post has confused me even more.

Wedge,
Are you asking about protection for the GEC or using conduit or flexible metal conduit as an equipment grounding conductor? There is a big difference between the GEC and an equipment grounding conductor.
 
Wedge,
Other than PVC, the conduit is bonded to limit difference of potential between the GEC and conduit.
Click to expand...
No, the conduit is required to be bonded at both ends to prevent the "choke" effect that will act to limit the current flow on the grounding electrode conductor. The choke effect occurs anytime that you have a single AC current carrying conductor within a ferrous raceway. As to why the raceway that you want to use is not permitted by the code, I have no idea.
Don
 
Wedge,

In OP it says ,specs. say 30" of flex for pri. and sec. feeders, The GES

raceway is neither of them!! Pipe it right to transformer.
 
Don,
Yes I am talking about protection. The only approved conduits for GEC are RMC, IMC, RNC, EMT, or cable armor per 250-64(B).
I wanted to know the reason liquid-tite flexible metal conduit or steel flex are not also approved conduits.
 
Wedge said:
Don,
Yes I am talking about protection. The only approved conduits for GEC are RMC, IMC, RNC, EMT, or cable armor per 250-64(B).
I wanted to know the reason liquid-tite flexible metal conduit or steel flex are not also approved conduits.
Click to expand...

They don't provide suitable protection .
 
Brian,
Flexible metal conduit and liquidtight flexible metal conduit will provice as much protection as RNC. In areas like mine, where we have cold weather, those two items will provide more protection than RNC as it is easily broken when cold. I expect that no one has ever submitted a proposal to permit the use. Both are permitted to be used to protect service condutors in lengths not over 6'. If they can protect service conductors they should be able to protect the GEC.
Don
 
Its funny, I was talking to a member of Panel 5 about this section just yesterday. He and I are both of the opinion that it needs better language. For example, why do I need a raceway or cable armor for a solid 8 AWG conductor that is concealed in a sheetrocked wall?
 
Either the code panel foresees some problem with the use of these materials or the manufacturers have not submitted them for testing and listing as suitable for this application. The bottom line is that they are not one of the recognized methods that we are allowed to use. If it is a problem for you, you could submit a proposal for the 2011 code (I believe it is too late for 2008) that this section be changed to include this method along with those that are already accepted.
 
normally we run a copper wire to subpanel from main panel to bond it to grounding bar in subpanel, then from it run several wires to different equipments, so i am not sure the wire from main panel to subpanel is GEC or EGC.
 
zyhml said:
normally we run a copper wire to subpanel from main panel to bond it to grounding bar in subpanel, then from it run several wires to different equipments, so i am not sure the wire from main panel to subpanel is GEC or EGC.
Click to expand...

GEC....Grounding Electrode Conductor
EGC... Equipment Grounding Conductor
The GEC is bonded to and runs from the main service panel to the first grounding electrode (ground rod, ufer, water line, etc.). There is only one GEC.
Any conductors used to connect additional grounding electrodes together and to the GEC are called Bonding Jumpers.
The connection in the main panel between the Grounded conductor and the Grounding conductor is called the Main Bonding Jumper (It's usually a green screw although it can be a wire or strap).
The Equipment Grounding Conductor is the green or bare grounding wire that you run with all of your circuits. The wire from the main panel to the sub-panel that you describe is a EGC. The grounding wire from the sub-panel to any equipment is a EGC.
I agree that the terminology is hard to remember....grounded conductor, equipment grounding conductor, grounding electrode conductor, etc. That's why some people (me included) still (improperly?) say neutral and ground.
I almost got confused while typing this.
If I got anything wrong, I'm sure somebody will tell me.
steve
 
Status
Not open for further replies.
Top