ser vs seu?

[infinity]

Yes, objectionable current yet the NEC allows emt or metal conduit between the meter and the first panel along with a neutral conductor. Is that not parallel and objectionable when it is all bonded together? I never understood that.

That two of us.

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

 

[jxofaltrds]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

No.

We (I) do not understand how this is different.

 

[infinity]

No.

We (I) do not understand how this is different.

I'm guessing that it's allowed because there are installations where it cannot be eliminated. Metallic service raceways is one such installation.

 

[jxofaltrds]

I'm guessing that it's allowed because there are installations where it cannot be eliminated. Metallic service raceways is one such installation.

I can live with that answer.

 

[don_resqcapt19]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

Either the parallel path for grounded conductor current is a hazard or it is not a hazard. It can't be a hazard on one side of the service disconnect and safe on the other side.
The code needs to be changed to either permit this path on both sides of the service disconnect or prohibit it on both sides.
It can be eliminated on the line side if the utilities were required to run an ECG in with the grounded and ungrounded conductors and the only point of bonding was at the utility transformer.

 

[brian john]

Yes, objectionable current yet the NEC allows emt or metal conduit between the meter and the first panel along with a neutral conductor. Is that not parallel and objectionable when it is all bonded together? I never understood that.

Agree 110%. Especially when PVC is a simple option. Had a job with almost 400 amps on a trough between the utility XMFR and Main Service.

There are several simple options.

There are several sources for non-metallic conduit PVC and others.

There could be isolation couplings installed.

But even this will not resolve all issues, in particular where a utility transformer is on the same structure and the concrete has rebar. We have seen current on the rebar, all thread, cable tray.

 

[reddy kw]

Not so sure about that,

From here:

http://forums.mikeholt.com/showthread.php?t=95495

"Electricity does not seek the path of least resistance to the earth. It seeks all available paths back to it’s source, in proportion to their resistance... "
I believe "...in propoirtion to their resistance...", is saying the same thing in different way. Of course resistance affects ground fault path.

"Driving a ground rod to ‘ground’ any electrical equipment does not provide the low-resistance path required..."
Isn't that the reason for different methods of creating a grounding electrode?

What works depends on local conditions, soil porosity, etc. You may need metal underground water pipes, multiple ground rods, ground rings or plates, to get lowest resisatance. NEC requires we find path of lowest possible resistance for ground fault current.

Where there's non-metalic water pipes run from well to basement, and metal water pipes run throughout house, people can get zapped by stray current over water pipes (like old homes that lack proper grounding/bonding). This is electrician's fault when adequate measures weren't taken to prevent such accidents.
IMHO, it's my job to prevent those accidents.

 

[reddy kw]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

Let's not confuse objectionable current vs. normal current, re: pupose of grounded metalic conduit and enclosures.
Metal enclosures and conduits at SE are bonded from ground lugs to grounding bushings to allow temporary flow of accidental fault current.
Downstream, metalic enclosures and wiring methods are used as ground paths for small ground currents created by motors, transformers, etc, which the Code doesn't consider "objectionable".
Under emergency conditions (fault current to ground), the metal raceway and enclosures are used as temporary paths to allow dangerous fault currents to flow back to SE, where they're routed out of system and into GEC, to GE.
In some jurisdictions all wiring is encased in steel or aluminum (conduit, cable, boxes, etc). Plastic pipe, boxes and cable are verbotten. Then, EGC is deriveded from GEC at service entrance. EGCs (metal cables, conduits, enclosures) are connected through the bonding at SE. No separate EGC is run with phase conductors.

 

[iwire]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

Let's not confuse objectionable current vs. normal current, re: pupose of grounded metalic conduit and enclosures.
Metal enclosures and conduits at SE are bonded from ground lugs to grounding bushings to allow temporary flow of accidental fault current.
Downstream, metalic enclosures and wiring methods are used as ground paths for small ground currents created by motors, transformers, etc, which the Code doesn't consider "objectionable".
Under emergency conditions (fault current to ground), the metal raceway and enclosures are used as temporary paths to allow dangerous fault currents to flow back to SE, where they're routed out of system and into GEC, to GE.
In some jurisdictions all wiring is encased in steel or aluminum (conduit, cable, boxes, etc). Plastic pipe, boxes and cable are verbotten. Then, EGC is deriveded from GEC at service entrance. EGCs (metal cables, conduits, enclosures) are connected through the bonding at SE. No separate EGC is run with phase conductors.

ready kw, the current infinity is talking about is not 'temporary fault current' it is continuous current flowing on the metal raceways between the service disconnecting means and a meter socket because both of those enclosures are bonded to the neutral.

 

[jumper]

NEC requires we find path of lowest possible resistance for ground fault current.

It does?:-? Where?

GECs do not clear ground faults, they are for lightning strikes.

 

[infinity]

ready kw, the current infinity is talking about is not 'temporary fault current' it is continuous current flowing on the metal raceways between the service disconnecting means and a meter socket because both of those enclosures are bonded to the neutral.

Thanks Bob, that is what I meant. I was speaking of the normal neutral current flowing on the metallic raceway because it's in parallel with the service neutral.

 

[LEO2854]

It does?:-? Where?

GECs do not clear ground faults, they are for lightning strikes.

250.56 /on page 70-106/NEC2008 Talks about 25 ohms or less.

 

[Dennis Alwon]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

That is exactly what I would do.

 

[jumper]

250.56 /on page 70-106/NEC2008 Talks about 25 ohms or less.

Do the math, 25 ohms will not clear a fault.

 

[Dennis Alwon]

Do the math, 25 ohms will not clear a fault.

I agree....Go further and you see that you need 6 ohms to get to 20 amps. 120V/6ohms= 20 amps. Do people really think that is a realistic number. Heck 25 ohms is impossible around here with standard rods.

 

[reddy kw]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

IMO, I don't think using plastic instead is the answer. Many installations need better protection then Schedule 80.
The NEC should require separate ground wires be run with phase conductors when using metal conduit and enclosures, and not permit metal conduit as EGC/GEC.

 

[infinity]

So what would you change in the NEC to eleiminate this objectionable current? Ban metallic raceways on services between the meter and service disconnect?

IMO, I don't think using plastic instead is the answer. Many installations need better protection then Schedule 80.
The NEC should require separate ground wires be run with phase conductors when using metal conduit and enclosures, and not permit metal conduit as EGC/GEC.

I agree with you on the metallic service raceway but I'm confused about the need for requiring separate ground wires. How would this change objectionable current one a metallic service raceway?

 

[don_resqcapt19]

IMO, I don't think using plastic instead is the answer. Many installations need better protection then Schedule 80.
The NEC should require separate ground wires be run with phase conductors when using metal conduit and enclosures, and not permit metal conduit as EGC/GEC.

That won't really change anything without a redesign of the meter can or the use of some type of isolating connection on one end of the raceway. The grounded conductor is almost always bonded to the can and you are required to bond the service equipment enclosure to the grounded conductor. The addition of an EGC just adds a third parallel path.

 

[don_resqcapt19]

Has anyone seen a real world hazard that was caused by the conduit being in parallel with the grounded conductor on the line side of the service disconnect?

 

[iwire]

Has anyone seen a real world hazard that was caused by the conduit being in parallel with the grounded conductor on the line side of the service disconnect?

I have not.