ser vs seu?

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don_resqcapt19 said:
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?
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I have not either however, it is odd that the nec 250.6 wants us to arrange our work to prevent objectionable current yet it allows it in this particular situation. I would assume there must be current flow, to some degree, on the metal raceway in parallel with the neutral, unless there is something I am missing.
 
Dennis Alwon said:
I have not either however, it is odd that the nec 250.6 wants us to arrange our work to prevent objectionable current yet it allows it in this particular situation. I would assume there must be current flow, to some degree, on the metal raceway in parallel with the neutral, unless there is something I am missing.
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If the current is not causing a problem, then it is not objectionable current.:D

My whole problem with this issue is that the code requires us to create parallel paths for grounded conductor current on the line side of the service disconnect, but yet says such parallel paths are a safety hazard on the load side.

I'm sorry, but it is one or the other. It it is truly a hazard, then the code should be changed to prohibit those parallel paths on the line side of the service disconnect.
 
don_resqcapt19 said:
My whole problem with this issue is that the code requires us to create parallel paths for grounded conductor current on the line side of the service disconnect, but yet says such parallel paths are a safety hazard on the load side.

I'm sorry, but it is one or the other. It it is truly a hazard, then the code should be changed to prohibit those parallel paths on the line side of the service disconnect.
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I agree whole heartedly.. Somebody ought to measure the current on a service with metal pipe. I would be curious to know how much current actual occurs. It would appear there would be alot.
 
don_resqcapt19 said:
My whole problem with this issue is that the code requires us to create parallel paths for grounded conductor current on the line side of the service disconnect, but yet says such parallel paths are a safety hazard on the load side.

I'm sorry, but it is one or the other. It it is truly a hazard, then the code should be changed to prohibit those parallel paths on the line side of the service disconnect.
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The difference, as I see it, is that the service neutral-EGC/GEC system bond point (main disco enclosure) is the grounded-conductor reference for the premises. What happens ahead of that point doesn't affect us.
 
LarryFine said:
The difference, as I see it, is that the service neutral-EGC/GEC system bond point (main disco enclosure) is the grounded-conductor reference for the premises. What happens ahead of that point doesn't affect us.
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Sure it does...an open neutral on the line side of the main bonding jumper energizes everthing connected to the electrical grounding system.
 
don_resqcapt19 said:
Sure it does...an open neutral on the line side of the main bonding jumper energizes everthing connected to the electrical grounding system.
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Yes, but at least the neutral and EGC float around together. :cool:

My bad. I should have said something more like "is none of our business." :grin:

Don, do you feel that services should be supplied using separate EGC's?
 
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LarryFine said:
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Don, do you feel that services should be supplied using separate EGC's?
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Not really as I don't see a real hazard with the current installations.

That being said I still have a problem with the code telling us that the electrons behave differently based on where they are. If the parallel paths for the grounded conductor current are as hazard, then those paths should be prohibited on both sides of the main bonding jumper....not just on our side.
 
"our" side "their" side?

"our" side "their" side?

I too have always been confused by the distinction between a service entrance panel which contains the main disconnect and a sub panel (load side) when the neutral bar is / is not bonded to the enclosure. I do what the NEC requires but like many on this post I'd prefer to understand the theory behind it. As one poster said, electrons don't behave differently depending upon which side they are on.

So I wonder - is the difference "man made" and does it arise from NEC applying to "our" side of the meter can and not the public utility and isn't a separate service disconnect on "our side" ?
 
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Maybe I'm confused, but isn't this a situation where you would use a bonding

bushing on one end of the metallic conduit connected to GEC ?

A big Thank You to all members on this forum for the wealth of knowledge.
 
don_resqcapt19 said:
If the parallel paths for the grounded conductor current are as hazard, then those paths should be prohibited on both sides of the main bonding jumper....not just on our side.
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To me, it's not the parallel path itself we're trying to avoid, it's the intentional connection of a current-carrying circuit conductor to conductive equipment housings and enclosures. The change of 3- to 4-wire major-appliance feeds is a great example.

People have said that the change wasn't necessary, with almost zero problems with the 3-wire circuits, but, I have experience to the contrary. A customer was badly shocked when caught between his range with a brokem neutral, and the sink.

We're all familiar with what happens when a normally-zero-volts-to-earth neutral conductor is broken: the EGC system becomes energized. It could be much worse when it happens to one piece of equipment, surrounded by still-grounded metal.

At least, with an intact EGC system, the various normally-grounded equipment and other conductive surfaces, both electrical and plumbing, are still bonded, acting as an equi-potential grid of sorts. Grounded or not, gradients are minimized.

The main disco enclosure, where the neutral is bonded, is the beginning of the premises EGC system. It's not earth that the EGC is solidly bonded to for fault current, it's the service grounded conductor. The goal is to make sure a breaker or fuse opens.

If one circuit's grounded conductor or its EGC opens, the immediate hazard isn't really increased. But, if a combined-purpose conductor opens, the hazard is increased. At least, because of the still-intact EGC system, all equipment is at the same potential.
 
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In my own point of view, Objectionable current on the lineside of the service equipment cannot be eliminated unless the distribution utility provide EGC coming from the transformer (like what sir Don proposed).

Meaning, if the supply is 3-phase 4-wire, then it should be 3-phase 4-wire plus the EGC (5 wires should be provided by the utility).

Bonding of the GSC, GEC and EGC at the service equipment will also provide a current flow at the earth through the grounding electrode at normal condition because of neutral loads.

Just my thoughts.
 
enteng14 said:
Meaning, if the supply is 3-phase 4-wire, then it should be 3-phase 4-wire plus the EGC (5 wires should be provided by the utility).
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It's really not necessary, though, since the neutral is the "goal" of fault current. The additional EGC's length would only serve to increase the fault-current pathway impedance.
 
LarryFine said:
It's really not necessary, though, since the neutral is the "goal" of fault current. The additional EGC's length would only serve to increase the fault-current pathway impedance.
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What i'm trying to say sir is to provide an EGC and neutral conductor at the transformer, by doing this, the neutral should not be bonded at the service equipment enclosure and it will eliminate the objectionable current flowing at the lineside of service equipment and also at the earth coming from the bonding of neutral at the service equipment. EGC and neutral should still be bonded at the transformer.

View attachment 5093

There is no additional length of EGC wire but instead an additional wire coming from the transformer that will serve as EGC. The picture above illustrates what i'm trying to suggest.

Neutral is a current carrying conductor at normal condition while the EGC will have the current flow during fault condition.

Would it be possible that the utility will provide EGC and Neutral as separate conductors but bonded at the transformer?
 
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LarryFine said:
I've never seen it.
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You're right sir Larry, i've never seen it either but i think it would eliminate the current flowing in the enclosure and raceway at the lineside of service equipment and also the current flowing in the earth through the GEC bonded at the main bonding jumper.

Utility owned transformers do not provide a separate conductor for EGC but in the case of customer owned transformer (separately derived source, SDS), EGC and Neutral are bonded only at single point, either at the SDS or at the first disconnecting means.
 
With the system we use now there is an inherent danger to it with the 3-wire system.

If the neutral is lost anywhere ahead of the main bonding jumper, it can cause two things, it will put a high voltage on anything grounded after the MBJ, and it can create a high current path on conductors not design to carry it such a cable TV bonded at the house and MGN, and I have seen a couple fires cause by that one.
While loosing the neutral is considered rare, I have seen it happen enough to know its a problem, and have even myself been shocked on a house that lost the neutral, and know of other such electrocutions. now having a house without a solid water pipe connection to the next houses service that would limit this is also rare as most houses here have this, very common here, so this problem is rare, but with the move to using more underground plastics I can see this coming to light allot more.

I would believe after a few more deaths caused by a lost service neutral we might just see 4-wire service drops sometime in the future.
 
I think that it is a must that 4-wire be provided for safety and neutral conductor should not be bonded at the service equipment, only the EGC. Would we wait for many electrical accidents to come before adopting the 4-wire method?

I will also suggest this 4-wire here in our country for safety. I don't want that the next victim of electricution would be my relatives or friends.
 
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