NEC Handbook Diagram - Uneven Parallel Feeders ?

[schneiderjm]

Hello Forum Members;
Attached is a diagram from the NEC Handbook identifying Bonding for Service Raceways.
It appears to me this is shown incorrectly, as there would be parallel paths for the neutral current on both the grounded conductor and the bonding jumpers (via raceway) from the disconnect enclosure to the neutral bar??
Violation of 250.24A5 ??
Can someone clarify this for me?

 

[Dennis Alwon]

Unfortunately there is always a parallel path on a service as long as metal conduit is used. I guess it has never been an issue but the neutral being bonded to the can and the metal conduit create those pathways.

 

[infinity]

As Dennis stated this is one of the times (metallic service raceways) when parallel paths cannot be avoided and are therefore permitted.

 

[ronaldrc]

Its just another code book mistake.

I understand we do this all the time and it is accepted.
I don't see a problem with it.

And like everyone else on here since there is a bonding bushing on
the feeder conduit it must be metal.


But if the meterbase neutral is bonded it is a NEC. violation unless
the bonding code has changed since 2002.

I'm retired and my latest NEC hand book is a 2002 and on page 186

Section250.30 (A)(1) Exception No 1. makes it a violation.

Ronald

 

[don_resqcapt19]

Not only are parallel paths permitted for the grounded conductor current on the line side of the service disconnect, there are cases where they are required by the code rules.

 

[joeblurton]

don't like it

don't like it

I disagree with this set up in theory. The neutral can not be disconnected at the individual service. If it were a common enclosure there would be a one point connection, and I would probably do the same with multiple enclosures; unless I reviewed the code.

 

[jumper]

I disagree with this set up in theory. The neutral can not be disconnected at the individual service. If it were a common enclosure there would be a one point connection, and I would probably do the same with multiple enclosures; unless I reviewed the code.

I assume you are referring to 230.75. The neutral terminal buss connections in the trough and the individual connections in each disconnect fulfill this requirement.

230.75 Disconnection of Grounded Conductor. Where
the service disconnecting means does not disconnect the
grounded conductor from the premises wiring, other means
shall be provided for this purpose in the service equipment.
A terminal or bus to which all grounded conductors can be
attached by means of pressure connectors shall be permitted
for this purpose. In a multisection switchboard, disconnects
for the grounded conductor shall be permitted to be in
any section of the switchboard, provided any such switchboard
section is marked.

 

[ronaldrc]

The main fault I see in this accepted situation is that and if you ever loose
your Neutral connection the conduit and enclosures will act as your Neutral.

You probably would never know you lost your neutral untill your lights start acting funny
like dimming and brightening when you turn on certain heavy Electrical loads. This would
get worse as your connections at the locknuts and bonding hardware degrade with time.

In the worse case could cause a fire, or electrocute a trouble shooter unaware
of the situation untill it is too late.


Ronald

 

[Smart $]

Not only are parallel paths permitted for the grounded conductor current on the line side of the service disconnect, there are cases where they are required by the code rules.

I would tend to say not explicitly prohibited [250.142(A)] but quite possibly a violation, subject to interpretation of 250.6(A) & (B).

For example diagrammed in OP, invoke 250.6(B)(3) using PVC bewteen trough and disconnects.

What section requires creating a parallel grounded conductor current path via grounding? Example please...?

 

[hurk27]

I would tend to say not explicitly prohibited [250.142(A)] but quite possibly a violation, subject to interpretation of 250.6(A) & (B).

For example diagrammed in OP, invoke 250.6(B)(3) using PVC between trough and disconnects.

What section requires creating a parallel grounded conductor current path via grounding? Example please...?

Here is a couple places in the NEC where the requirement can end up in requiring a paralleled neutral:
250.24(A)(3) and 250.58 there are others as well but these are the two most common and the handbook graphic is about one such place, I have also seen other graphics that also show the same parallel path where multiple meters and disconnects are used that have the common GEC run between them that 250.58 is talking about.

I know it can and will cause problems if the neutral is ever lost at one of these disconnects but that is a "What If" and you know where that gets ya as far as enforcing a law. its been done like this for many years, I do try to use PVC between the meter and the main disconnect but that is my choice not a requirement of the NEC.

Also keep in mind that the NEC will require that we use table 250.66 for sizing any bonding conductor ahead of the service disconnect so at least in some cases it will be a larger size and can even be as large as the grounded conductor.

 

[hurk27]

I would also like to point out one of the most dangerous parallel paths that the NEC and other codes require is the bonding of a cable TV coax or the drain wire of one at the pole (to the MGN) and the house to the service grounding, Article 800 clearly requires us to bond the shield at our end and other codes require it to be bonded at the pole, I'm sure we can see that a bad neutral (grounded conductor) can and has caught the siding on fire on a few houses when the neutral connection went bad. this is one practice that if any should be eliminated, shielded Tel-co line is another one that can be a problem in a case like this.

 

[Smart $]

..
250.24(A)(3) and 250.58 there are others as well but these are the two most common...

I don't see how either of those require a grounding method which creates a parallel path for grounded conductor current...???

 

[Smart $]

.... this is one practice that if any should be eliminated, shielded Tel-co line is another one that can be a problem in a case like this.

I agree... especially when there are methods and equipment available specifically for isolating the grounding of these communications systems.

 

[ronaldrc]

Wayne

"What if"
Has nothing to do with this, If the truth was known the CMP probably
never even thought this out enough to even know what hazards
it could produce.

Ronald

 

[hurk27]

I don't see how either of those require a grounding method which creates a parallel path for grounded conductor current...???

True 250.24(A)(3) doesn't really require us to make a parallel path as PVC could be used but in 250.58 it does require us to use the same electrode system on a building and if we have separate meters and disconnects we will be required to parallel the neutral when we use a common GES and PVC pipe will not solve this.

 

[hurk27]

Ok heres one that is a requirment:

Water pipe electrode bond when the water line is common to other dwellings?

 

[hurk27]

Wayne

"What if"
Has nothing to do with this, If the truth was known the CMP probably
never even thought this out enough to even know what hazards
it could produce.

Ronald

I agree on the CMP part, but "What If's" are basically anything that happens out of the normal, wet and dry locations are based upon this in the definitions, a properly installed neutral should never fail if installed correctly if not we have problems, many years ago we had meter cans that you had to keep the neutral continuous because the lug was only made to accept one conductor we would strip enough of the neutral mid span to land in this lug, anytime I get a lay-in neutral lug I still do this even if it does have two set screws, but they are getting harder to find.

More and more the NEC is getting full of "What If's" that as many say dumb down the NEC, like the "What if" someone works on a multi-wire circuit without turning off all the breakers to it, the NEC was supposed to be written for the qualified and even says such?

But if we really want to address this problem then there are two options, we could make meter manufactures stop bonding the neutral in the meter cans or we could persuade the utilities to provide a 4 wire drop making the main bonding point at the transformer and eliminating the bond at the main service disconnect which would also require a non-bonded meter can?

 

[Smart $]

True 250.24(A)(3) doesn't really require us to make a parallel path as PVC could be used but in 250.58 it does require us to use the same electrode system on a building and if we have separate meters and disconnects we will be required to parallel the neutral when we use a common GES and PVC pipe will not solve this.

Ok heres one that is a requirment:

Water pipe electrode bond when the water line is common to other dwellings?

Okay... but I guess I wasn't thinking of wire conductors when I asked the question. I was referring to metal conduit and enclosures.

 

[don_resqcapt19]

I would also like to point out one of the most dangerous parallel paths that the NEC and other codes require is the bonding of a cable TV coax or the drain wire of one at the pole (to the MGN) and the house to the service grounding, Article 800 clearly requires us to bond the shield at our end and other codes require it to be bonded at the pole, I'm sure we can see that a bad neutral (grounded conductor) can and has caught the siding on fire on a few houses when the neutral connection went bad. this is one practice that if any should be eliminated, shielded Tel-co line is another one that can be a problem in a case like this.

Those are the paths I had in mind, along with a common metal underground water piping system.

 

[hurk27]

Okay... but I guess I wasn't thinking of wire conductors when I asked the question. I was referring to metal conduit and enclosures.

Ya Kind of thought so.

The funny thing is no one thinks about what happens when you loose a neutral connection and there is not a parallel path:huh:

Because of the main bonding jumper everything bonded to the neutral through the MBJ will be at the voltage of the neutral to earth voltage, water pipes, service equipment cases, panel cover, washing machine, which is the lessor of the two evils? being electrocuted or having parallel current on another pathway?