I am a local building inspector working in an area with mostly older homes using 3 wire service entrance to the house. I am conflicted on how to handle the bonding when adding a transfer switch for a generator. These existing services consist of meter box, service disconnect panel and then breaker box inside house. Since they are 3 wire service entrances, these panels are generally bonded to the cabinet and earth in the outside service disconnect. The inside breaker box generally has neutrals and grounds( if present) landed on the neutral bar together. My conflict is with the addition of the transfer switch, that now becomes the service disconnect which should be the first point of bonding. Obviously in a perfect world I would like to see a 4 wire service entrance installed with grounds and neutrals isolated from each other, but I don't live in that world and in most cases it is not practical to make those upgrades. I would love to hear some of your thoughts on this scenario. Thanks.
How to handle bonding with an existing 3 wire service when adding a transfer switch and generator?
- Thread starter Matt@GB
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Certainly not following Code but our inspectors pretty much look at it on a case by case basis. When practical, the feeder is changed to 4 wire, N & G separated inside and GEC to the service disconnect. When doing so requires tearing out a significant portion of wall/ceiling cover the old 3 wiore entrance is often left to suffice.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Welcome to the forum.
It sounds like these installations have been non-compliant since before you got there.
That part is correct, with or without a transfer switch.
That part is not correct, with or without a transfer switch.
With the disconnect outside, the feeder and panel should be 4-wire with or without a transfer switch.
It sounds like these installations have been non-compliant since before you got there.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Granted these were installed well before, but couldn't they now be considered compliant under 2020 with the outside disconnect being the emergency disconnect? The interior panel would have to be nearest the point of entrance of course.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Don't you mean the LAST point of bonding?
These houses were built in the 50's and 60's mostly and are grandfathered in based on 250.32 B(1) exception 1 where it says buildings supplied by 3 wire feeder are permitted to have the grounded conductor serve as the ground fault return path. That is the reason the N's and G's are together in the subpanel. We are on the 2017 NEC currently.
A lot of the time, the addition of the generator and transfer switch occurs with no other updates being made to either service disconnect or sub panel inside the house. My question is what to do with grounding and bonding on the outside of the house, knowing in most cases, G's and N's are together throughout the system. The GEC is in the service disconnect panel landed with N and bonded to cabinet. The electricians will want to bond to cabinet in new transfer switch since it is now the first point of disconnect but this creates side by side cabinets with a main bonding jumper. Should I make them move the GEC over to new transfer switch and remove bonding jumper in service disconnect or leave existing install as is and just run equipment ground to transfer switch? I hate this situation but I want to make a bad situation as safe as possible. Thank you all for the feedback. It is making for great discussion in my department.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
So what is the piece of equipment on the outside of the house that the transfer switch is replacing? I guess that would be what you referred to in the op as "service disconnect panel". Is that a main breaker load center? Are there any circuits in it? Or is it a fused or non-fused safety switch?
The transfer switch doesn't replace anything. It is being added to the existing install. In most cases the "service disconnect" panel is a loadcenter with a main breaker and also serving some, not all, of the branch circuits in the house.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Is the service disconnect panel outside? Then the inside panel that is also bonded, how far inside the house is that typically?
Yes, it is outside. Yes, in most cases the inside panel is federal pacific panel with N's and G's together and bonded to cabinet. These are generally smaller houses so I would say anywhere from 5-20' away.
brantmacga
Señor Member
- Location
- Georgia
- Occupation
- Former Child
Locally, the inspectors require us to upgrade to a 4-wire service per code. Only once that I can remember was I allowed to leave a 3-wire feeder, and it was a home in the historical district, and replacing the feeder would've required removing a 100/yr+ old vaulted ceiling.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
I am curious. I know there are people here with old codes, and I wonder if your statement is correct. I am aware that pre 2000 codes allowed feeders to a separate building to have the neutral ground bond in the panel (no grounding wire) but I don't believe that would have ever been allowed with a feeder that stays in the same building. Anyone that has that old code? It sounds like it was never code compliant.
In my area, it was typical to install just the meter outside and then run a three wire through the attic to the panel with the main disconnect. Using the "nearest the point of entrance" clause Improperly in my opinion. Later, someone comes along and puts a disconnect outside and fails to upgrade the feeder.
In my opinion, it needs to be upgraded in your scenario, unless your interpretation of the previous feeder code is right.
Choice_Gorilla
Member
- Location
- New England
- Occupation
- Journeyman Electrician
I’ve installed quite a few home standbys mostly generac. Typically if we were installing a service rated transfer switch we would bring bring the 3 wire SEU cable into the ATS from the load side of the meter socket. From the load side of the ATS we would run a 4 wire SER cable to the load center inside. The Neutral and ground would be bonded in the ATS, and then we would go into the load center, add a ground bar, separate the grounds and the neutrals, and then remove the main bonding jumper (green screw).
If you are adding a transfer switch ahead of the existing service disconnect I don't see how there is any exception to rewiring it as a 4 wire from the new service disconnect in the transfer switch to the existing disconnect/panel.
What difference does it make if it's 2' away or 50' away through drywall?
What difference does it make if it's 2' away or 50' away through drywall?
I agree with the install of the service rated transfer switch on the load side of the meter, where I run into issues is from the load side of the ATS to the load center inside the house. That is in almost every case a 3 wire cable (no ground) and to upgrade would require major renovation and tear out inside the house. Obviously where feasible we require them to do that, but I have a hard time requiring that when it leads to major expenses to the homeowner.
But the NEC doesnt have any exceptions when it comes to major expenses to the homeowner.
It's code or it's not code
Or they can submit a modification to the state and let the state electrical inspector make the call
Choice_Gorilla
Member
- Location
- New England
- Occupation
- Journeyman Electrician
Should be a 4 wire cable leaving the ATS. The issue to me seems like the original installation was incorrect. If there’s already a service disconnect on the outside of the house, ground and neutral should be bonded there and it should have had a 4 wire SER coming off the load side. Around me, we would be required to fix that. The electrical contractor should have done their due diligence and quoted the job appropriately to the home owner to correct the issue. If they keep the original service disconnect switch and install a non service rated transfer switch, they should leave the neutral ground bond in the disconnect but everything after it should be 4 wire. So you would have 3 wire leave the meter into the service disconnect, then 4 wire from the service disconnect to the ATS, and then another 4 wire from the ATS to the panel, and you remove the neutral ground bond from the ATS.
In this area (and I'm sure many others) service installations were allowed with an unlimited length of SE cable from the meter to the service disconnect. Often this cable was routed behind finished surfaces.
Our AHJ often tales the approach that adding the ATS provides OCP to the exiting cable (previously there was none) and it has been serviceable for decades. If the homeowner wants to add a generator it's hard to justify $ 10k in structural repair to accomplish a grounding rule.
Our AHJ often tales the approach that adding the ATS provides OCP to the exiting cable (previously there was none) and it has been serviceable for decades. If the homeowner wants to add a generator it's hard to justify $ 10k in structural repair to accomplish a grounding rule.
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