Unique solution to an expensive situation.

[iwire]

We all have seen pipes that came apart.

And I am sure we have all seen badly made EGC splices so obviously the only safe and practical solution is to pull the service off the building doing away with this dangerous electricity.

 

[SAC]

Highlighted in red is a stretch. As mentioned before, you have to [megger?] test the wire for isolation from the emt by unlanding both ends. This test has to be donw to assure the wire was not bonded somewhere along the way.

As for the one ohm (or less), that is not an assurance either. If the EMT run used conductive supports to a steel structural members, there are multiple paths to the MBJ/SBJ. So a conductive break in the EMT may still test as low ohmage to ground.

I agree. I'm not proposing or approving any test methodology here - I'm just trying to lay some interpretation as to what I think that the OP meant about the "less than one ohm" comment - in particular, to explain why I don't think there is enough information to assess that "With that high a resistance, the original plan is dead in the water".

 

[SAC]

If the GEC was grounded on one end the reading should be "0"

That depends on what function of what device was being used to measure the resistance. For example, if the meter had a lower scale of .01 ohm, just the resistance of the 200 ft of wire would be unlikely to read "0".

 

[kwired]

All true but we do not need to take extra risks....quote]


We take a risk everytime we energize something, plug something in, drill or cut something, use tools or equipment, sometimes when turning something off it is a higher risk than leaving it on.

I feel safer doing most of my work than I do driving with all the other idiots that are on the road.

Your post almost seems contradictory to the point I tried to make. I agree these additional paths provide a lower resistance grounding. That in itself is great.

But as you said, the NEC does not recognize these extra paths as an equipment grounding conductor. Therefore, simply testing with an ohmeter will not verify the continuity of the EMT run.

The run, short of physically testing the mechanical integrity at each joint, would have to be at least visually confirmed for continuity... and I'm not saying one has to inspect every single inch, but at least to a degree of reasonable certainty for the issue at hand.

Here is what could happen in a situation like this. The panel has many runs of emt and it is possable one of them runs is making connection to build steel. That now gives you a path to ground so you get 0 ohms. Now the problem, remodeling for some reason removes that run of emt. Now your run that you thought was grounded just lost its ground.
An ohm meter will not prove you have the ground you think you have. It can prove you do not have connection

And I am sure we have all seen badly made EGC splices so obviously the only safe and practical solution is to pull the service off the building doing away with this dangerous electricity.

I am with iwire on this, if you want to ensure it is safe from all possible electrical hazards turn it off.

There are many other things that can come apart, or otherwise fail, there are users that modify or abuse things and who knows what may happen from this.

My point was that if you have a structure or equipment with a lot of bonded metal paths I don't really care what NEC recognized equipment grounding method you use - from a safety point of view that equipment is inherently grounded very well and it is difficult to make it not grounded.

I pull more equipment grounding conductors through metal raceways than I used to but still feel for the most part is unnecessary. There are times when I have had something like a gas furnace having problems and the heating guy says I need to have a ground wire in the supply conduit to solve this problem. I install the ground wire and his problem does not go away. I understand why he needs a low resistance ground but apparently my raceway was not the problem. I now install the ground to this type of equipment regardless so they do not have to call me back on that.

Most pulled apart fittings I have seen whether the set screw or compression nut was tight or not could have been prevented by properly securing and supporting of the raceway which we all are supposed to do anyhow.

IMO the only good test the ability of a raceway to carry a fault current is to impose fault level current on it. Or at very least any type of load with current levels above the normal current in the contained conductors. The most expensive ohm meter will not tell you what the effects of the high level current will have on a loose fitting. A megohmeter is a high voltage but low current and will pass through this fitting and maybe even give you a good reading if the contact pressure it tight at time of reading. Heating within the loose fitting during a high current event is what is going to change the impedance of this connection.

 

[mcclary's electrical]

I am with iwire on this, if you want to ensure it is safe from all possible electrical hazards turn it off.

There are many other things that can come apart, or otherwise fail, there are users that modify or abuse things and who knows what may happen from this.

My point was that if you have a structure or equipment with a lot of bonded metal paths I don't really care what NEC recognized equipment grounding method you use - from a safety point of view that equipment is inherently grounded very well and it is difficult to make it not grounded.
I pull more equipment grounding conductors through metal raceways than I used to but still feel for the most part is unnecessary. There are times when I have had something like a gas furnace having problems and the heating guy says I need to have a ground wire in the supply conduit to solve this problem. I install the ground wire and his problem does not go away. I understand why he needs a low resistance ground but apparently my raceway was not the problem. I now install the ground to this type of equipment regardless so they do not have to call me back on that.

Most pulled apart fittings I have seen whether the set screw or compression nut was tight or not could have been prevented by properly securing and supporting of the raceway which we all are supposed to do anyhow.

IMO the only good test the ability of a raceway to carry a fault current is to impose fault level current on it. Or at very least any type of load with current levels above the normal current in the contained conductors. The most expensive ohm meter will not tell you what the effects of the high level current will have on a loose fitting. A megohmeter is a high voltage but low current and will pass through this fitting and maybe even give you a good reading if the contact pressure it tight at time of reading. Heating within the loose fitting during a high current event is what is going to change the impedance of this connection.

MSHA has the same outlook on it. When they test for an EGC at a piece of equipment, they simply test for continuity between the service and the equipment. They DO NOT isolate the EGC for the test, IMO, they don't care what path it's taking, as long as it gets there

 

[brian john]

That depends on what function of what device was being used to measure the resistance. For example, if the meter had a lower scale of .01 ohm, just the resistance of the 200 ft of wire would be unlikely to read "0".

Did I misread what the OP said? I could have swore he said megger typically one ohm resolution is not viable with a megger when insulation resistance testing.




http://www.aemc.com/techinfo/techworkbooks/megohmmeters/tech_megohm.pdf

 

[Jim W in Tampa]

And we all see installs that were miss used with result of coming apart. If emt alone was 100% safe nobody would run a ground wire. This is not about the safety of a properly installed and maintained system, those are safe without the added ground. We only run the extra wire to add to the safety.
What i see here in the OP is he removed the added safety. Nothing bad SHOULD happen but if it does then what ?

Seems we are all divided on this post. Seeing it might change my mind. Could very well be dozens of paths back to ground thru building steel but could they carry fault current ?

I worked for the type of guy that never allowed me to do what the op did. His reputation and name was for quality not min. code.

 

[Volta]

Did I misread what the OP said? I could have swore he said megger typically one ohm resolution is not viable with a megger when insulation resistance testing...

I think you read it correctly, I assumed (I know :roll that 'megohmmeter' as used by the OP was either a digital megger with a regular scale setting or just a simple DMM being called megohm.

 

[iwire]

I think you read it correctly, I assumed (I know :roll that 'megohmmeter' as used by the OP was either a digital megger with a regular scale setting or just a simple DMM being called megohm.

That is how I took it as well.

 

[kwired]

Did I misread what the OP said? I could have swore he said megger typically one ohm resolution is not viable with a megger when insulation resistance testing.




http://www.aemc.com/techinfo/techworkbooks/megohmmeters/tech_megohm.pdf

from post #8 by OP

I already disconnected the ground, put a clamp on the EMT and tested it with a megohmeter. I got less than one ohm between the ground wire and the EMT.

I took this as being testing continuity between the raceway and grounding conductor. Less than 1 ohm would be a pretty good reading with couple hundred feet of conductor being tested. He did not state exactly what he disconnected but would not matter much at this point yet.

What he did not mention and has been brought up is that after doing this he needed to disconnect the grounding conductor on the other end and check continuity again to verify that it is not bonded someplace else in the run and there you should expect a high resistance there for the result that is desired - that would be the place to possibly use a megohmeter.

 

[growler]

Nothing bad SHOULD happen but if it does, then what ?

An investigation would happen. And no matter who conducts said investigation they will be looking for the least possible reason to point the finger at someone and guess who is now the center of attention.

Jim, I agree that this is a big risk for very little reward.

This guy is getting $300-$400 for a dedicated circuit but he really isn't getting anything to assume liability for the possible poor ground.

 

[Strife]

You are missing something: #4 resistance is .24 ohms/M. So on that run of 200-300 feet, the resistance is .06-.08 ohms. So it would be quite impossible to reach a dead 0, or even .01.
And yes, I tested it as you describe it.

The statement that I quoted seemed to be expressing concern that "less than one ohm" was "too high" to be used as an EGC. Since the test was not adequately described by the OP, almost any conclusion can be drawn about what the test actually was. However, the intent of the test was described as being to determine if the EMT was continuous for use as the EGC. In order to do this, one would disconnect the EGC wire at the load end, leaving it connected at the panel. At the load end, measure the resistance between the EGC wire and the EMT. If the resistance is sufficiently low, then one can conclude that the EMT is continuous from the load end to the panel (where the EGC and EMT are bonded) and can be used as the EGC once the EGC wire is repurposed for the neutral. However, "less than one ohm" could be as high as .99 ohm, which really isn't low enough for a good fault current path - though .01 ohm is plenty low enough.

 

[mivey]

You are missing something: #4 resistance is .24 ohms/M. So on that run of 200-300 feet, the resistance is .06-.08 ohms. So it would be quite impossible to reach a dead 0, or even .01.
And yes, I tested it as you describe it.

Are there any junction boxes within the 200-300 feet where the wire might be bonded to the conduit?

 

[acrwc10]

Are there any junction boxes within the 200-300 feet where the wire might be bonded to the conduit?

Don't for get the tone has been " but it saved money" what more could you want?

How about being focused on the 1 ohm issue, as if this is going to show that the conduit is capable of carrying the currant imposed on it in a fault. I can get 1 ohm or less on a phone cable, it doesn't mean it can handle a 200 + amp fault. The EMT may be just touching at a separated coupling, or be connected to a concentric knock out that is ready to fall out,or a hundred other conditions, that could give a low ohms reading. Once a load is imposed on it it could fail. With out inspecting every inch of the conduit and every connector and coupling in it, you can not say it is an acceptable ground path.
I love how I have read hundreds of times on this forum "if you wire a job to the code minimum it will be the last job you get from that customer" and those same people are arguing here that this method is "acceptable" and the reason they are quoting "because it meets the code minimum". PICK A LANE:roll:

 

[brian john]

Don't for get the tone has been " but it saved money" what more could you want?

How about being focused on the 1 ohm issue, as if this is going to show that the conduit is capable of carrying the currant imposed on it in a fault. I can get 1 ohm or less on a phone cable, it doesn't mean it can handle a 200 + amp fault. The EMT may be just touching at a separated coupling, or be connected to a concentric knock out that is ready to fall out,or a hundred other conditions, that could give a low ohms reading. Once a load is imposed on it it could fail. With out inspecting every inch of the conduit and every connector and coupling in it, you can not say it is an acceptable ground path.
I love how I have read hundreds of times on this forum "if you wire a job to the code minimum it will be the last job you get from that customer" and those same people are arguing here that this method is "acceptable" and the reason they are quoting "because it meets the code minimum". PICK A LANE:roll:

THE ONE OHM was his megger reading between the COPPER EGC and the EMT.

Personally I do what I said (transformer and panel for the load) and leave the copper EGC intact. And generally we install copper EGC with all conduit runs, BUT.

Remember that the copper EGC, EMT ECG and all the metallic components in a facility make up the grounding path.

 

[Jim W in Tampa]

There simply are some here that can not or will not see all the problems associated with EMT systems being used as the ground. They are the ones that can bid lower because they offer less. EMT is the min. and is legal. It is the EC responsibility to install it to code. I will agree that if installed correctly it makes a good ground. If your useing old conduit not installed by yourself how can you be sure all the fittings were put all the way on and screwed tight. Even if it is a short run you can't be sure that the installer didn't cheat at a spot where he cut it bit short.
OP has already done the job so now not much he can do even if he wants to. I personally will run a ground wire but do respect it was his call, let's hope it works.

 

[mivey]

How about being focused on the 1 ohm issue, as if this is going to show that the conduit is capable of carrying the currant imposed on it in a fault.

I may have skimmed over the thread too fast but I thought that was showing that the wire could not be used as the ungrounded conductor because it was obviously in contact with the conduit and would create a parallel neutral current path.

The EMT may be just touching at a separated coupling, or be connected to a concentric knock out that is ready to fall out,or a hundred other conditions, that could give a low ohms reading. Once a load is imposed on it it could fail. With out inspecting every inch of the conduit and every connector and coupling in it, you can not say it is an acceptable ground path.

Then just dump some fault current on it and see if the breaker trips. :grin: (don't really do that).

I love how I have read hundreds of times on this forum "if you wire a job to the code minimum it will be the last job you get from that customer" and those same people are arguing here that this method is "acceptable" and the reason they are quoting "because it meets the code minimum".

Got to thin out the problem customers somehow.

PICK A LANE:roll:

Same way I feel. Until I want to change lanes.:grin:

 

[mivey]

I will agree that if installed correctly it makes a good ground. If your useing old conduit not installed by yourself how can you be sure all the fittings were put all the way on and screwed tight. Even if it is a short run you can't be sure that the installer didn't cheat at a spot where he cut it bit short.

The same can be said for a ground wire. How many do we run across that have sub-standard connections? How do you check pre-existing ground wires?

For the record, I prefer a ground wire.

 

[Jim W in Tampa]

The same can be said for a ground wire. How many do we run across that have sub-standard connections? How do you check pre-existing ground wires?

For the record, I prefer a ground wire.

Differance here is if i tie into existing ground wire that is green (or bare) i am not taking on as much liability because it was existing. Removing a ground wire that was there now places liability on you to be sure the EMT is doing its job. Yes you will find some that made bad connections. They will be connected to the box or panel at both ends so chances are better that you still have a ground thru the emt. Your brakes in your car should stop you but it's nice having the emergancy break as back up.

 

[acrwc10]

I may have skimmed over the thread too fast but I thought that was showing that the wire could not be used as the ungrounded conductor because it was obviously in contact with the conduit and would create a parallel neutral current path.
Then just dump some fault current on it and see if the breaker trips. :grin: (don't really do that).
Got to thin out the problem customers somehow.
Same way I feel. Until I want to change lanes.:grin:

I hope you don't think I was picking on you. ( I was not ) you are one of the few that pointed out one of the "short" comings of an using this, uh, "solution" as the OP called it.:roll:
like Brian John said , a transformer and a new panel would be the best way to do the job in lack of running a neutral/ grounded conductor. Every one else is getting their panties in a wad that this would cost to much. And running a neutral is to expensive due to the length of the run, but the longer the run the more chance for failure of the EMT ground path due to the increase of connections.