Need opinions on sub-panel wiring.

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  #1  
Old 09-05-14, 08:44 AM
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Need opinions on sub-panel wiring.

Hello. I live in the USA in Nevada. My question is about sub panels and separating the neutral/equipment ground.
My house was built in the mid 1980's. It is all brick and the wiring is basically in accessible from above or below.

My service entrance/meter is located about 150' from my home on a pedestal. From there I have a sub panel on a pedestal about 10' from my house that serves as my main distribution point to my house feeding several other sub panels in my house. This panel near my house has the neutral and equipment grounds on the same bus bar. It also has a grounding rod that is buried and attached to the the sub panel pedestal. From there, two additional sub panels are fed that are located in my house. One in the garage, and one in the kitchen. All of these panels are fed with 3 wires only. 2 hots and a neutral. All equipment grounds are attached to the neutral bus bar. All circuits in the house utilize a EGC which return to the sub panel in the kitchen which has a shared neutral/EGC bus bar. In the garage, no EGC exists at all in any circuit.

Due to the size of the wire/conduit coming from my service entrance, it does not seem feasible to pull a 4th wire to the service enterance panel, or any of the other sub panels for that matter.

I discovered this while trying to see if I could separate the neutrals and EGC in my sub panels, only to realize it appears that it would make no difference because they is no EGC provided in any of my panels.


My questions are:
1. Was this NEC compliant back then?
2. Is this dangerous?
3. Would I benefit from driving a grounding rod for each of these sub panels and installing an EGC bus bar and switching all of my EGC to this bus bar?

Any input appreciated!

Thanks
Rob
 
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  #2  
Old 09-05-14, 08:57 AM
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I think you mean that it's fed with 2 hot leads & a ground. I haven't looked at the Code but I doubt that much has changed since the house was built. I don't think that it's dangerous either. What makes you think that there is a problem, all of a sudden?
 
  #3  
Old 09-05-14, 09:24 AM
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Thanks for your reply!
The three wires are color coded as Red(Hot), Black(Hot), White(Neutral). After much reading, I do believe that having the equipment ground and neutral on the same bus bar in a sub panel is against NEC code except at the main service entrance. The sub panel in my garage actually had a wire that went from the neutral bar and was screwed to the sub panel itself. I do not know if this was the code in force back in the 80's when this house was built or not, but my main concern is my familys safety. I've had one electrician tell me it is unsafe as is and that if something was to go wrong with the white neutral wire it opens the possibility for my appliances and such to become energized as the electricity tries to find a path back to the source. Much of the house is wired with MC and metal boxes so the potential for it to carry current is certainly there.
Thanks again,
Rob
 
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Old 09-05-14, 09:39 AM
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Wait for someone who knows that code better than I do.
 
  #5  
Old 09-05-14, 09:51 AM
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He is correct. Once upon a time all subpanels were 3-wire, hot-hot-neutral-no ground*. Yours are probably grandfathered. Not dangerous, just less safe.
Would I benefit from driving a grounding rod for each of these sub panels and installing an EGC bus bar and switching all of my EGC to this bus bar?
No. A GEC (Ground Electrode Conductor) is not a substitute for an EGC. An EGC is a low resistance path through a wire to clear faults, dirt isn't.

Edit: I failed to mention if the two panels are connected by metal conduit that can serve as your EGC. A 3-wire bonded neutral subpanel can be converted to isolated neutral bar using the conduit as your EGC and adding a ground bar. Sub panels not in the same structure also need a GEC and ground rod.

*There was an exception to the old 3-wire code. If the subpanel was in a detached structure and there were additional metallic paths such as water pipes or phone lines then it had to be 4-wire.
 

Last edited by ray2047; 09-05-14 at 03:26 PM.
  #6  
Old 09-05-14, 01:36 PM
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Is the panel that is 10' from the house the first overcurrent device? If so, that is your main panel. All the others are sub panels.

Is there a metallic path back to the main panel? (You mentioned conduit) That might be your grounding path. Otherwise, as others have mentioned, in the past it was allowed to run 2 hots and 1 neutral to a subpanel and then install a ground rod. This was mostly done for detached buildings.

An EGC does not have to be installed in the same conduit as the other conductors. It can be run outside the pipe.
 
  #7  
Old 09-05-14, 06:22 PM
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Thanks for all the replies. The first overcurrent device is located in the panel 150' from my house near the meter. The conduit is PVC. It appears then that it was built to code in force at that time. An EGC in a separate conduit, although a lot of work, might be doable. Thanks for the idea! And thanks to all who replied!
Rob
 
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Old 09-06-14, 12:43 AM
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What size is the circuit breaker at the meter? What size is the conduit and what size are the conductors? Since an equipment grounding conductor is usually significantly smaller than the current carrying conductors pulling an EGC may not be as hard as you think.
 
  #9  
Old 09-06-14, 05:58 AM
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Most likely you can still add branch circuits but you would not be able to add or replace or upgrade any of the panels unless the complete path upstream from it were brought current including single cable or conduit containing separate equipment grounding conductor to all supra-panels in line if any.

As a point of information, a correct and up to date installation has just one point where neutral and ground are bonded (together). Should a problem occur in a neutral path, the presence of the EGC network will not protect against abnormal voltages associated with open neutrals in branch circuits or between panels in the building.

There are three categories of home equipment grounding:
1. From load or utilization point to panel with that circuit's breaker,
2. From subpanel to supra-panel.
3. From first main disconnect to utility lines.

If the branch circuit has a proper equipment grounding conductor then protecting from open combined neutral/ground in #2 or #3 does not require corrective action in #1.

Nothring forbids the addition of separately run equipment grounding conductors between subpanels and their supra-panels. (Run separately they're called bonding jumpers.) Should the panels not have separated neutrals and EGCs then these separately run conductors will share the carrying of return current. This redundancy is only coincidental; a correct system with separate neutral and EGC does not use EGC as a redundant #1 or #2 neutral return. Better would be to (piecemeal if convenient) replace or upgrade any 3 conductor groundless connection between subpanel and its supra-panel with a connection with 3 conductors plus EGC and separate neutral and EGCs at the subpanel.
 

Last edited by AllanJ; 09-06-14 at 06:50 AM.
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