Current on Service Raceway

Merry Christmas

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
So, being a 95% residential/service guy, I'm coming to my first service with a GRC enclosed service entrance conductors (between the meter base and the service disconnect). If I understand it correctly, the GRC needs to be bonded with a supply-side bonding jumper; this is easy enough. My question is, since the GRC is connected to the meter can and the meter can is bonded to the grounded conductor, there will be current normally flowing on the GRC in parallel with the grounded conductor. I can't see that this hurts anything, but it seems odd. Do I have this correct?

As always, thanks.

Mark
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes, this is one of the few times that objectionable current is permitted by the NEC because there is no way to eliminate it when using a metal raceway.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Install PVC and there isn't an issue but I presume that pvc will not stand up as well as emt or rigid conduit. You don't see commercial jobs with Pvc very often
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Install PVC and there isn't an issue but I presume that pvc will not stand up as well as emt or rigid conduit. You don't see commercial jobs with Pvc very often
I think he is talking about the conduit between the meter and service panel. That most likely is in the wall and PVC would be fine for this and hold up as well as GRC as it's not exposed to the weather.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
There are areas, like mine, that only permit rigid or IMC for service conductors. I have never seen this cause any real world issue as a result of the current on the metal service raceways.
Much the same as the current on our metal underground water piping systems. In older areas of many cities, the water service pipes are all metal and so are the water mains. In areas like that is common for 20% or more of the neutral current to be on the water lines.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree that PVC would solve the objectionable current problem but there are many reasons why metal service raceways are still used. Don provided one.
 
While I agree that the word "objectionable current" is vague and undefined and this parallel path being discussed is generally accepted as being okay,. Most commercial meter sockets have a removable N-G bonding jumper, so one could remove it and install an ssbj to bond the meter socket. IMO an inspector would be within his rights to require this.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
On the line side of the main disconnect, there is no EGC. The neutral and any metallic raceway or enclosure are considered to be the same conductor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
While I agree that the word "objectionable current" is vague and undefined and this parallel path being discussed is generally accepted as being okay,. Most commercial meter sockets have a removable N-G bonding jumper, so one could remove it and install an ssbj to bond the meter socket. IMO an inspector would be within his rights to require this.
There would be any number of utilities that would not permit that extra wire in their cash register.
 

jap

Senior Member
I think he is talking about the conduit between the meter and service panel. That most likely is in the wall and PVC would be fine for this and hold up as well as GRC as it's not exposed to the weather.

I may be wrong, but, I think he's talking about the thousand of rigid nipples seen between the meter and the Serviced Disconnect whether that be out on a pole or on the outside of a structure before it goes into the wall.

JAP>
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I agree. It is baffling the NEC refuses to clarify this, but then again, they are not a very competent organization.
If you see it as a problem, have you submitted a Public Input to make a code change? Other than a few inputs made by the code making panels, code changes come from code users.

I don't see any need for a code change. Can you cite cases where this current has resulted in a real world issue? Without that information the code will not get changed.
 
If you see it as a problem, have you submitted a Public Input to make a code change? Other than a few inputs made by the code making panels, code changes come from code users.

I don't see any need for a code change. Can you cite cases where this current has resulted in a real world issue? Without that information the code will not get changed.
Don, no I have not submitted a public input. The Cmp's have demonstrated little interest in clarifying ambiguity in the code so I don't see the point. Just to be clear, I don't have an issue with the way many services are set up as a safety issue, I just hate the ambiguity of "objectionable current". Where no one seems to know what it means. They should just delete it if they are not going to define it.
 

domnic

Senior Member
Occupation
Electrical Contractor
So, being a 95% residential/service guy, I'm coming to my first service with a GRC enclosed service entrance conductors (between the meter base and the service disconnect). If I understand it correctly, the GRC needs to be bonded with a supply-side bonding jumper; this is easy enough. My question is, since the GRC is connected to the meter can and the meter can is bonded to the grounded conductor, there will be current normally flowing on the GRC in parallel with the grounded conductor. I can't see that this hurts anything, but it seems odd. Do I have this correct?

As always, thanks.

Mark
What is GRC conduit?
 

JoeStillman

Senior Member
Location
West Chester, PA
I agree that this seems like a case of objectionable neutral current, even though the code requires it. A simple solution would be to move the bonding jumper out of the meter socket and into the service disconnect.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
I agree that this seems like a case of objectionable neutral current, even though the code requires it. A simple solution would be to move the bonding jumper out of the meter socket and into the service disconnect.
No.
1st It is not objectionable current.
2nd, all the residential grade meter sockets I've seen are bonded. Not able to be isolated. POCOs require it. Many want a rod there as well.
I see no reason to fix something that isn't broken.
 

jap

Senior Member
I agree that this seems like a case of objectionable neutral current, even though the code requires it. A simple solution would be to move the bonding jumper out of the meter socket and into the service disconnect.

The current is still going to flow through a galvanized rigid nipple back to the Utility Transformer, and, the true bonding jumper is already in the Service Disconnect.

JAP>
 

JoeStillman

Senior Member
Location
West Chester, PA
...I see no reason to fix something that isn't broken.
Just revisited article 250 and I have to admit you are right, according to the letter of the law. But I also can't shake all the other things I've read, like this passage from the handbook, in 250.30 on separately derived systems;

Common Misconception
Does installing a system bonding jumper at both the source of a sepa-

rately derived system and the first system disconnecting means provide
a better connection to ground for a separately derived system?
Installing a system bonding jumper at both the source and the first
disconnecting means can result in establishing an unintended paral-
lel path for current that would otherwise utilize the grounded con-
ductor. exposed normally non–current-carrying metal components
are often included as part of this parallel path and can present an
unintentional safety hazard. this type of installation is prohibited
with the exception of a building or structure supplied by an outdoor
separately derived system, provided that such a connection does not
create a parallel path for the grounded conductor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Just revisited article 250 and I have to admit you are right, according to the letter of the law. But I also can't shake all the other things I've read, like this passage from the handbook, in 250.30 on separately derived systems;
What is the source of that comment? The code clearly permits the use of the neutral for all required bonding and grounding within and on the line side of the service equipment enclosure and that will always result in a parallel path for neutral current where the service conductors are in a metal raceway.
 
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