Current on Service Raceway

[busman]

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]

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]

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]

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]

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]

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.

 

[electrofelon]

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]

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]

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.

 

[electrofelon]

There would be any number of utilities that would not permit that extra wire in their cash register.

I agree. It is baffling the NEC refuses to clarify this, but then again, they are not a very competent organization.

 

[jap]

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]

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.

 

[electrofelon]

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]

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?

 

[electrofelon]

What is GRC conduit?

Galvanized Rigid conduit.

 

[JoeStillman]

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]

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]

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]

...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]

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.