What Would You Do?

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A/A Fuel GTX

Senior Member
Location
WI & AZ
You are replacing an old sub panel in a residence that has a three wire feeder contained in a severly rusted underground rigid conduit. The replacement requires the installation of a metallic junction box in place of the old panel and a new panel about 6' away. The question: do you bond the new junction box and panel to the grounded conductor or rely on the rusted rigid conduit as the grounding path and keep the grounded conductor isolated? 250.24(A) (5) seems to prohibit this but given the condition of the raceway, I would not feel comfortable relying on it to clear any faults.
 

Strathead

Senior Member
You are replacing an old sub panel in a residence that has a three wire feeder contained in a severly rusted underground rigid conduit. The replacement requires the installation of a metallic junction box in place of the old panel and a new panel about 6' away. The question: do you bond the new junction box and panel to the grounded conductor or rely on the rusted rigid conduit as the grounding path and keep the grounded conductor isolated? 250.24(A) (5) seems to prohibit this but given the condition of the raceway, I would not feel comfortable relying on it to clear any faults.
First thing I notice, is if you are using your teminology correctly a "subpanel" implies a disconnecting means ahead of it. That means that you can, under no circumstances bond your neutral to your ground in this panel. So that one is out. If you are not comfortable with the integrity of the raceway, you have only three choices, pull a ground in the existing conduit, run new conduit, or run away and let a hack do the job!
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
I was thinking that 250.32(B)(1) Exception might allow the bonding to the grounded conductor. I would not consider the rusted rigid to be a continuous metallic path.
 

kwired

Electron manager
Location
NE Nebraska
Did you dig it up to see how rusted it really is?

The portion near the surface of the soil is most subject to corrosion, the deeper portions don't get much oxygen that is needed to rust and may be in better condition than you think.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Did you dig it up to see how rusted it really is?

The portion near the surface of the soil is most subject to corrosion, the deeper portions don't get much oxygen that is needed to rust and may be in better condition than you think.
Not completely but the conduit has been in the ground for 40+ years. It's kind of a catch 22, do you use the conduit as a grounding path that quite possibly will not clear a fault or use the grounded conductor that definately will but is not the accepted method?
 

kwired

Electron manager
Location
NE Nebraska
Not completely but the conduit has been in the ground for 40+ years. It's kind of a catch 22, do you use the conduit as a grounding path that quite possibly will not clear a fault or use the grounded conductor that definately will but is not the accepted method?
If the raceway is intact it will be parallel to the grounded conductor and carry current during normal operation if you bond it to the grounded conductor, and can create stray voltage issues, just to add more to your catch 22 situation. The problem can be compounded even more if there are any conductive paths between the supply and load end. I guess it wasn't clarified if this was a feed to a separate building or structure or not. If not a separate structure I think that bonding the grounded conductor at the load end is not even an option.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
If the raceway is intact it will be parallel to the grounded conductor and carry current during normal operation if you bond it to the grounded conductor, and can create stray voltage issues, just to add more to your catch 22 situation. The problem can be compounded even more if there are any conductive paths between the supply and load end. I guess it wasn't clarified if this was a feed to a separate building or structure or not. If not a separate structure I think that bonding the grounded conductor at the load end is not even an option.
No, It's not a separate structure. So you are saying that I'd be better off keeping the grounded conductor isolated and possibly not having an equipment ground that is functional?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
No, It's not a separate structure. So you are saying that I'd be better off keeping the grounded conductor isolated and possibly not having an equipment ground that is functional?
You need an effective EGC no matter what. If that requires putting in a new piece of conduit, that is what you will need to do.

You do not get to opt out of having an effective EGC just because it is inconvenient or costly.

Can you pull out the existing conductors and run new ones that include an EGC?
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Can you pull out the existing conductors and run new ones that include an EGC?
Not an option here due to the integrity of the original raceway. So, in a situation like this, the main issue is the parallel path? Three wire feeders were allowed until recently if memory serves me correctly.
 

kwired

Electron manager
Location
NE Nebraska
Not an option here due to the integrity of the original raceway. So, in a situation like this, the main issue is the parallel path? Three wire feeders were allowed until recently if memory serves me correctly.
And existing ones still are allowed. The fact that you were going to extend it some makes it more questionable as to whether or not it can be left as a three wire feeder. But bonding the grounded conductor to equipment grounding was not allowed (in more recent editions of NEC anyway) if there was other metallic pathways between the two structures, and probably still is not allowed in the case where an existing feeder is involved.

Can you isolate the metal conduit and maybe emerge from grade with PVC? Then you will not have a 2nd current path for neutral current and can bond the neutral at the second building. Might want to talk about it with AHJ first.
 

jumper

Senior Member
Not an option here due to the integrity of the original raceway. So, in a situation like this, the main issue is the parallel path? Three wire feeders were allowed until recently if memory serves me correctly.
AFAIK 3 wire feeds were for other buildings, 2005, not a sub in the same one. Ranges and dryers were allowed as 3 wire branch circuits, but that stopped in 1993.
 

Strathead

Senior Member
I was thinking that 250.32(B)(1) Exception might allow the bonding to the grounded conductor. I would not consider the rusted rigid to be a continuous metallic path.
IF the original installation had a bonded neutral then you may have an argument. The Rigid was a continuous path given your description, and this code section was put there to allow old buildings to grandfather in, since the code has changed in this area.

The thing you need to ask yourself is, "If the electrical system fails and there is significant damage to equipment or personnel, are you willing to trust the court not to find you liable and also will you not find yourself liable?" My answer would be no for me!
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
So the greatest " Sin " here appears to be the possible parallel path on the rigid and if someone got in series with the conduit, they will be potentially shocked. So what is worse, the above scenario or the possibilty of a marginal or non existant equipment ground? FWIW, the only exposed part of the conduit run is about 3' coming up from the concrete floor where the main service equipment is located.
 

Strathead

Senior Member
So the greatest " Sin " here appears to be the possible parallel path on the rigid and if someone got in series with the conduit, they will be potentially shocked. So what is worse, the above scenario or the possibilty of a marginal or non existant equipment ground? FWIW, the only exposed part of the conduit run is about 3' coming up from the concrete floor where the main service equipment is located.
I am going to get on my high horse once and then bow out of this discussion. There are so many things that can happen. What if the neutral opens up at the main service, You now have 240 volts on the conduit, panel shell etc. trying to find a path. If the conduit is as bad as you think this would probably result in death! Regardless of how unlikely that is, it is really possible. When the neutral and ground are bonded at least a ground rod is driven, but that is sometimes not enough, which is likely why the code was changed in the first place. I have not been here as long as you, but if you are looking for a place to validate substandard work, this is probably not the best place. Tell the customer to install a new conduit run or walk away from it. The greatest sin here would be someone trying to circumvent the code and getting someone else killed. That is a VERY REAL albeit unlikely result.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
You are better off isolating the rigid pipe and bond the neutral to the can. You could also test the rigid to see if there is enough of it together that the impedance is not to high. Personally I would try and run a new run with PVC and 4 wires. If the conduit is that bad then the wires are probable sitting in the soil in places. I wonder whether the insulation is rated for wet location.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
I am going to get on my high horse once and then bow out of this discussion. There are so many things that can happen. What if the neutral opens up at the main service, You now have 240 volts on the conduit, panel shell etc. trying to find a path. If the conduit is as bad as you think this would probably result in death! Regardless of how unlikely that is, it is really possible. When the neutral and ground are bonded at least a ground rod is driven, but that is sometimes not enough, which is likely why the code was changed in the first place. I have not been here as long as you, but if you are looking for a place to validate substandard work, this is probably not the best place. Tell the customer to install a new conduit run or walk away from it. The greatest sin here would be someone trying to circumvent the code and getting someone else killed. That is a VERY REAL albeit unlikely result.
I truly appreciate your candor here and respect your opinion. I'm one of those guys that likes to try and understand why something is fine in one situation and not fine in another ie, like I mentioned regarding a service. A parallel path is fine there but not in this situation. Believe me, I'm the last one that wants to do anything illegal and some of these older electrical installations make it real difficult to comply with todays' requirements. On the rare occasion I run rigid underground, I wrap it so this kind of a problem may be avoided in 40 years.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
You are better off isolating the rigid pipe and bond the neutral to the can. You could also test the rigid to see if there is enough of it together that the impedance is not to high. Personally I would try and run a new run with PVC and 4 wires. If the conduit is that bad then the wires are probable sitting in the soil in places. I wonder whether the insulation is rated for wet location.
I agree Dennis but unfortunately, the vast majority of this run is under a concrete floor and there is really no way to install a new raceway without busting up the concrete.
 

Strathead

Senior Member
I agree Dennis but unfortunately, the vast majority of this run is under a concrete floor and there is really no way to install a new raceway without busting up the concrete.
Apparently overhead is not an option. I have no idea what the situation is. How far, etc, but there is always an option. What about a directional bore? If you can't get the equipment inside, then start outside and just cross a hole cut in each location? Just one idea, but it seems to me that a building where you can't runa new feeder is about as likely an open neutral killing someone. :?
 

north star

Senior Member
Location
inside Area 51
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IMO, the greatest "sin", in this case, is to not inform the
property owners of your concerns and let them decide
what to do.......Of course this will probably mean that
you will have to type a legible statement of the conditions,
...in an easily understandable manner, and present it
to them......This is one of those situations that requires
you to go beyond the normal duties of the job.

Do you have immediate access to the property owner?


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