No equipment ground pulled to sub-panel

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JoeNorm said:
I still want to know if this is a "safe" set-up. What are the potential hazards here and why did they change the code?
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As it is, yes, it's safe. As has been said, it's the same as every residential service.

If the neutrals and grounds are bonded, essentially the neutral is used as the EGC? Correct?
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Correctamundo.

If the neutrals and grounds were separated in sub and still had no equip ground, this poses danger? Correct?
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Yes, because (presuming the neutral is what you leave connected) a short from a hot to what should be grounded will energize what would otherwise be bonded and trip a breaker

I am pretty sure pulling the EGC won't be that bad, we will do this at no charge. But I want to understand electrically what is going on, and why some situations are safe and some not, and why the code would change.
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As I mentioned earlier, it's like the past allowance for 3-wire major appliance circuits that may remain, while new installations require the 4-wire circuit. Many code rules evolve because of events that occur over time that cause reconsideration of past rules.

I had a customer whose son was severely shocked because the neutral of their 3-wire-supplied range became disconnected in the range's wiring compartment, and he contacted the range and the sink simultaneously. They had noticed that the clock and light stopped working, but those still energized the range cabinet.
 
lordofthisworld said:
I would have to say if u are working on/in this panel, you would have to bring it up to standard codes.
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Where do you draw the line?

Adding a simple circuit in the panel, with a just a new breaker, and you are going to insist on a new 4-wire feeder to it first?

What if a home inspector flagged two wires landed on a breaker, and all you have to do is join them to a tail in a wirenut? New 4-wire feeder first? Oh, and all arc-fault breakers, too?

My only question is if the PV install works just fine backfeeding to main meter through the 3-wire feeder through another panel. I don't do PV (even though I got state certified because I thought the test was easy) and have no idea about that part.
 
MAC702 said:
...

My only question is if the PV install works just fine backfeeding to main meter through the 3-wire feeder through another panel. I don't do PV (even though I got state certified because I thought the test was easy) and have no idea about that part.
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Assuming amp ratings are sufficient all the way through ... Yes, it works just fine.
 
JoeNorm said:
Thanks,

So with the neutrals and grounds bonded together, this was compliant years ago?

Why was the rule changed?
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Off top of my head, I think the rules changed on feeders to separate structures in 2005. Definitely was no later than 2008.

Why? well I think many have took a shot at that, I think biggest reason is potential voltage on non current carrying but bonded to the grounded conductor metal items. Though we still have somewhat same issue at service equipment. Kind of can ask why did it take so long to make this change?

Exceptions were added and still exist to let those existing installations remain as is, provided the install was proper at the time - if there is other metallic paths between the structures it may not be allowed to remain.
 
kwired said:
... I think biggest reason is potential voltage on non current carrying but bonded to the grounded conductor metal items.
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Put another way, the neutral is a current carrying conductor and will have a voltage drop from one end to the other. If you bond to the neutral for your equipment grounds you are putting the exposed metal of that equipment at the same potential as the neutral, which can be at a voltage different than ground. So contact with that electrical equipment and a water faucet or a cable or phone line could be a shock hazard.

-Hal
 
Understood,
so why the poco is allowed to do exactly that, while we are no longer (old 250.32b) begs the rationale and underlying theory to back it up ~RJ~
 
Because the bonding at the service entrance creates a "zero reference point" for the POCO neutral and the EGC. Maintaining separate neutrals and EGCs after that point ensures that whatever the EGC is connected to is at the same potential as any grounded object within the building. This is why the EGC is prohibited from carrying any current (except fault current).

-Hal
 
hbiss said:
Because the bonding at the service entrance creates a "zero reference point" for the POCO neutral and the EGC. Maintaining separate neutrals and EGCs after that point ensures that whatever the EGC is connected to is at the same potential as any grounded object within the building. This is why the EGC is prohibited from carrying any current (except fault current).

-Hal
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or an MBJ Hal

So we can have multiple MBJ's (also called an earthed neutral) w/in the same structure , but not in a detatched garage....

~RJ~
 
The change in the code isn't about voltage drop differential between neutral and ground, as it makes that situation worse. I believe it was motivated by a wish to avoid objectionable current on other metal systems connecting buildings. Hence the way the exception is written. It would also help somewhat, shock hazard wise, in an open-neutral situation.
 
romex jockey said:
or an MBJ Hal

So we can have multiple MBJ's (also called an earthed neutral) w/in the same structure , but not in a detatched garage....

~RJ~
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Unless I'm confused by what you are saying, there can only be one MBJ, that being at the service disconnect or main panel.


jaggedben said:
The change in the code isn't about voltage drop differential between neutral and ground, as it makes that situation worse. I believe it was motivated by a wish to avoid objectionable current on other metal systems connecting buildings. Hence the way the exception is written. It would also help somewhat, shock hazard wise, in an open-neutral situation.​
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I don't see how it makes the situation worse. Certainly there could be objectionable current on metallic paths such as a water line or other wiring that link the two buildings if they were to be connected to the neutral/ground at the detached structure.

-Hal
 
hbiss said:
Unless I'm confused by what you are saying, there can only be one MBJ, that being at the service disconnect or main panel.




-Hal
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Then what would you call earthing a neutral for multiple SDS's w/in the same structure , using the same building steel Hal?

~RJ~
 
hbiss said:
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I don't see how it makes the situation worse. Certainly there could be objectionable current on metallic paths such as a water line or other wiring that link the two buildings if they were to be connected to the neutral/ground at the detached structure.

-Hal
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What I meant was that the code change increases the voltage-drop differential between neutral and ground at the detached building, because that differential now occurs along the entire wiring length from the service and not just along the wiring length in the detached building. I shouldn't have called that a 'problem', because it isn't one. But it isn't the reason the code was changed.

romex jockey said:
Then what would you call earthing a neutral for multiple SDS's w/in the same structure , using the same building steel Hal?

~RJ~
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Those are called System Bonding Jumpers. Actually, it's the GEC that earths the neutral, but I think you meant the item that bonds the EGC?

The definition of MBJ ends with '...at the service.' Under the old rules for a detached building, there definitely needs to be a bonding jumper between neutral and EGCs at the detached building. But it doesn't meet the definition for either of those special names. It's just a Bonding Jumper.
 
romex jockey said:
Understood,
so why the poco is allowed to do exactly that, while we are no longer (old 250.32b) begs the rationale and underlying theory to back it up ~RJ~
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POCO uses a MGN network (in many cases), the reasons are more associated with their primary distribution system than they are for the derived secondary systems scattered throughout their network. But grounding a primary and a secondary conductor and bonding them together at each transformer, kind of makes one common grounded conductor throughout the entire network.
 
hbiss said:
I don't see how it makes the situation worse. Certainly there could be objectionable current on metallic paths such as a water line or other wiring that link the two buildings if they were to be connected to the neutral/ground at the detached structure.

-Hal
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or ph, cable line, or even the earth itself....all revelant to it's impedance

jaggedben said:
Those are called System Bonding Jumpers. Actually, it's the GEC that earths the neutral, but I think you meant the item that bonds the EGC?

The definition of MBJ ends with '...at the service.' Under the old rules for a detached building, there definitely needs to be a bonding jumper between neutral and EGCs at the detached building. But it doesn't meet the definition for either of those special names. It's just a Bonding Jumper.
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The NEC is tad semantical juxtaposed to the inherent theory Jag.....

methinks you'll find other countries addresing the same application differently.

think xformers scattered over 1/4 mile of industrial electrical infastructure

the only dif betwix a bonding jumper-main, and a bonding jumper-system (or our detatched 3wire garage for that matter) is it's proximity to the incoming service

They all 'earth' a neutral .ergo, they all have potentials between each other relevant to their impedance (cue Mr Kirchoff)



kwired said:
POCO uses a MGN network (in many cases), the reasons are more associated with their primary distribution system than they are for the derived secondary systems scattered throughout their network. But grounding a primary and a secondary conductor and bonding them together at each transformer, kind of makes one common grounded conductor throughout the entire network.
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as well as a common return to them. in fact, the closer one gets to substations, the less earth worms one will find....:p

~RJ~
 
mjf said:
Since you stated the homeowner did the sub panel years ago my first question is did HO get a permit and inspection at the time of installation.

If no permit/inspection then I'd say everything must be up to present day code.
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Kind of depends on rules in the particular jurisdiction though.

If that HO's previous work did not require permit yet was not done to code at that time, can get a little more complicated on how to deal with it.

Here I can completely rewire a single family dwelling and even wire a new addition to it with no permit required, as long as I haven't changed the service.
 
romex jockey said:
...The NEC is tad semantical juxtaposed to the inherent theory Jag.....
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Yes, it sure is. But if one wants to be clear about what one is saying it's our main reference for agreeing on the meaning of terms. Thus...

the only dif betwix a bonding jumper-main, and a bonding jumper-system (or our detatched 3wire garage for that matter) is it's proximity to the incoming service
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It's not the proximity, it's whether you are bonding the neutral connected directly to the utility (MBJ) or some other, separately-derived neutral.

They all 'earth' a neutral .ergo, they all have potentials between each other relevant to their impedance (cue Mr Kirchoff)
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No, bonding and earthing are not the same. I can earth all the EGCs on a site and not bond the neutral. I can bond all the EGCs to the neutral and not earth them (except through assuming the utility earthed the neutral on its side). In fact, 'earthing' is a less ambiguous word in this respect than 'grounding'.

...

Just trying to avoid confusion. :lol:
 
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