Subpanel fed by 3 wire without EGC

[Jarnipman]

Hi everyone,

This forum is great and I have been looking at it for years, until today (I just joined, thank you for the great forum) to get some help with the following situation:

I have a sub-panel in a detached garage with 3 feeds and no fourth ground running back to the main panelboard. The feeds are aluminum direct burial. There are grounding rods installed at the detached building. The subpanel is bonded to neutral in the detached garage (definitely a no-no with a 4 wire feed, but this was built in 1988 with no dedicated EGC). As I understand it, NEC allows an exception for the 3 wire system as being grandfather in, providing there are no other metallic connection between the two buildings? First am I correct on this? Now my next question. A gas line was just installed to the detached garage and bonded to the subpanel - I don't know if the gas line is also bonded inside the house, I assume it is, but can't see the line in the walls to verify this, maybe someone did not bond it, which makes two scenarios here. I was ok with the 3 wire bonded electrical sub in the garage until the new metallic gas line was installed. Now that the two buildings are now also bonded through the gas pipe with no dedicated ECG between the sub and main panelboard, what do I do? Do I keep the grounds in the garage that are currently bonded to neutral as they are, or do I separate the ground from neutral at the sub or do I now need to run a ground wire from the sub to the main panelboard? What kind of electrical monkey wrench, if any, has this new gas line introduced? All of this bonding business has always driven me mad. I wish the previous electrician ran a fourth wire in 1988 so I do not have to think about this. I am not 100% comfortable with the old 3 wire feeds without a dedicated ground anyway, so now I am uneasy about this situation.

So leave the subpanel bonded as it is now, do not bond the subpanel, or install a 4th wire (keeping in mind that the ground is frozen solid and it is impossible right now to do any digging and besides digging sucks anyway and I would like to avoid digging anything).


Thanks!

 

[Smart $]

Hi everyone,

Hello, and welcome. :thumbsup:

This forum is great and I have been looking at it for years, until today (I just joined, thank you for the great forum) to get some help with the following situation:

I have a sub-panel in a detached garage with 3 feeds and no fourth ground running back to the main panelboard. The feeds are aluminum direct burial. There are grounding rods installed at the detached building. The subpanel is bonded to neutral in the detached garage (definitely a no-no with a 4 wire feed, but this was built in 1988 with no dedicated EGC). As I understand it, NEC allows an exception for the 3 wire system as being grandfather in, providing there are no other metallic connection between the two buildings? First am I correct on this?

Yes

Now my next question. A gas line was just installed to the detached garage and bonded to the subpanel - I don't know if the gas line is also bonded inside the house, I assume it is, but can't see the line in the walls to verify this, maybe someone did not bond it, which makes two scenarios here. I was ok with the 3 wire bonded electrical sub in the garage until the new metallic gas line was installed. Now that the two buildings are now also bonded through the gas pipe with no dedicated ECG between the sub and main panelboard, what do I do? Do I keep the grounds in the garage that are currently bonded to neutral as they are, or do I separate the ground from neutral at the sub or do I now need to run a ground wire from the sub to the main panelboard? What kind of electrical monkey wrench, if any, has this new gas line introduced? All of this bonding business has always driven me mad. I wish the previous electrician ran a fourth wire in 1988 so I do not have to think about this. I am not 100% comfortable with the old 3 wire feeds without a dedicated ground anyway, so now I am uneasy about this situation.

So leave the subpanel bonded as it is now, do not bond the subpanel, or install a 4th wire (keeping in mind that the ground is frozen solid and it is impossible right now to do any digging and besides digging sucks anyway and I would like to avoid digging anything).


Thanks!

I would look into whether the gas line actually has continuity back to the house (turn on one-side of panel's 120V loads, other side off; clamp garage gas line bonding jumper).

If no current is indicated, gas line may be plastic at some point. If current is indicated, consider putting in a dielectric fitting (i.e. plastic) to isolate the house from the garage.

 

[ptonsparky]

Welcome to the Forum.

Sounds like you have your ducks in a row.

Have you explained to the owner your dilemma?

The ground should be fairly easy to dig next to the gas line once things thaw. Most AHJs are understanding. Don't forget the GES at the garage when you put the new 4 wire feeder out there. Conduit is always better IMO.

Tile spades work pretty well if it isn't too far. That and an apprentice are even better.

 

[winnie]

If the gas line is metallic underground, then you now have a 'parallel path' situation; any current that would otherwise be flowing on the neutral will now be split between the neutral and the gas pipe. Avoiding these parallel paths while at the same time insuring proper bonding for fault current is what makes this complex.

IMHO your first step is to figure out if the gas line is continuously metallic between the two buildings.

-Jon

 

[Jarnipman]

Thank you everyone for the warm welcome and the advice. The gas line is metallic, there is a T on the meter where it branches to both buildings in full non-isolated copper, so the buildings are definitely bonded very well through the copper gas line and I did test and verify this. So it seems that there are two solutions possibly? It seems the best solution would be to install a dedicated ground wire from sub to main panelboard and then isolate the ground from neutral at the sub panel once that is done - this has the bonus of being up to 2014 code (actually this was changed in 2008 right?)- the inspector did not require me to do this when I did major work on the garage because the feeds were already in place since 1988 - I actually replaced the subpanel and it was not an issue, maybe it should have been? This will cost the homeowner more money, by virtue of trenching and I would like to avoid trenching because of the possibility of hitting something else underground, which I will of course be responsible for breaking. I will never forget when I broke someone's water main and had to pay $1200 to repair it!!!! Ouch, I wasn't doing the digging, but it was my job, my guy, my responsibility. What if I left the subpanel bonded and then asked the gas fitter to isolate the gas line with a delectric union - I am no expert in gas lines, but this should be quick work for the gas fitter right? Would that solve the problem? The gas fitter might take 1 hour to isolate the line, I might take a whole day at least to trench 150 feet with a couple of guys digging. There is also no room for digging, so all digging is going to be done right on top of the garage service feeds, gas line as well as the utility gas line, electrical utility service feeds and the bonus of a sprinkler system. In the future any water lines would also need isolated if I isolated the gas line, but that is easy. I guess this is an example of how different trades need to communicate together, had I not known a gas line was going in, then I would not have thought about this. Now that I think about it, there are tons of 3 wire feeds without a ground and gas, water and comm lines go in constantly after the fact. This must be a very common problem? Many plumber don't even call an electrician to bond their pipes if they tie into the bare copper grounding system when they are digging, so this must happen all the time. Any votes on option A, isolate the gas line, leave the subpanel bonded, or option B, dig and install a new ground - the homeowner does not have a lot of money to spend on this at this point, and I have always found it near impossible to explain bonding and grounding to anyone that is not an electrician.

 

[Fitzdrew516]

Sounds to me like isolating the gas line would be easiest, but I, like you am not a pipe fitter so I'm not sure the complexity of the task. I can't imagine it's more work than trenching all the way to the sub panel. Look at the bright side - You act as a GC in this circumstance and sub the gas work out to a plumber and charge an extra % for your GC fee. FREE MONEY :thumbsup:

 

[Smart $]

IMO, with current ground freeze condition, there is no choice... at present.

 

[Jarnipman]

Problem solved and thanks to everyone! The gas fitter is going to install a $5 dielectric gas union and it will take him 30 minutes. For now with the frozen world, this is the best solution and the homeowner is happy with it, but I told them to call me for a quick inspection if they put in a water or comm line to make sure it's not a repeat issue.

 

[iwire]

Awesome!

 

[ptonsparky]

That was too easy! Do you have a picture or a catalogue number of that device?

I know we have customers with that problem although those date back to the time propane & power were installed from the '40s and since then.

Kind of makes you wonder just how bad the problem actually is.

 

[Jarnipman]

Yes it was to easy, but I'll take the win. I think the problem must be huge out there because most homeowners and other trades might not think about this after the 3 wire feeds are installed without a ground. Also consider that I ran 2000 feet of cable and replaced the subpanel in the garage (big shop really) and the electrical AHJ passed my work with no comments and the mechanical AHJ passed the gas line with no comments. Nobody noticed it, and even I thought initially thought the sub was grounded back to the main (I did install the electrical originally), it was not until I tested it as a measure of good practice that I found out it was not. I think it's very easy to miss on an inspection or future work because someone sees a 4-6 AWG bare copper wire going somewhere underground and assumes that it runs back to the main panel, when it likely in these older installs runs to a GES only. I wonder how many accidents have occurred from this. It's pretty innocuous to install a water or gas line or phone line and not consider this.

I think a much bigger safety problem is not bonding the panel and not knowing that your over current devices are worthless because you assume you are working with a 4 wire system vs an older 3 wires system. There is a huge belief by a lot of people that don't have the experience we do that subpanels should NEVER be bonded (based on the assumption that detached buildings have 4 feeds and 2008 NEC changes), but that's not always true as in this case and seeing the GES one might even remove the bonding screw accidentally thinking it was a mistake to bond it initially. The problem is compounded by many incorrectly believing that a GES is sufficient to operate over current devices. I wonder how many detached buildings, particularly home workshops were it is more likely that a homeowner or handyman did the electrical work vs. commercial, have no functional over current devices because of this? Every homeowner with a detached building that is older should perhaps buy one of those $10 testers that tests GFCI, polarity and high ground impedance to check their buildings.

Well that's enough of my philosophy, in my case the dielectric union is going on black pipe and this is what the gas fitter is using, after he installs it I will test the line to make sure it really is isolated. A similar cheap device can be used to isolate water lines, but I don't know how to isolate communication lines, I shudder to think of 15 + amps running through a phone line. They probably make a brass dielectric union as well, but I don't know where to find it. I guess it's important to remember that the union will isolate the line, but lightning could jump the union, so I made sure both ends of the gas line are connected to GES at both buildings.

[h=1]Zurn Wilkins Dielectric Union, 3/4 In. Fip X 3/4 In. Fip, Black Iron Pipe[/h]http://www.globalsupplyoutlet.com/zurn-wilkins-dielectric-union-3-4-in-fip-x-3-4-in-fip-black-iron-pipe.html?utm_source=google&utm_medium=shopping&gclid=Cj0KEQiArou2BRDcoN_c6NDI3oMBEiQANeix5hfgLR_T_hqrfLx3NFcUJIWwSSpE_FsBeLkptmKCL4caAq6M8P8HAQ

 

[iwire]

An interesting side note is that all the possible prohibited parallel paths with a feeder to a separate building or structure are allowed, or even required, parallel paths with the service conductors.

 

[Jarnipman]

.

 

[JFletcher]

I don't know how to isolate communication lines, I shudder to think of 15 + amps running through a phone line.

Something like this for coax:

http://www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M

A while back I posted an incident (fire) report of a lost POCO neutral, it smoke the coax since it (the coax) was (by code) bonded to the main panel.

eta: here it is:

http://www.electrical-forensics.com/Open-Neutral/Open-Neutral.html

 

[ActionDave]

An interesting side note is that all the possible prohibited parallel paths with a feeder to a separate building or structure are allowed, or even required, parallel paths with the service conductors.

Yep. We do what we can though.

I think the EGC to a separate strutcure is a good rule. There should be an exception to a meter pedestal though.

 

[wrobotronic]

Tile spades work pretty well if it isn't too far. That and an apprentice are even better.

Apprentices are a fantastic resource. Although I inspect now, I have found many apprentices these day DEMAND a back hoe or ditch witch.... I am floored by this sentiment.
Sorry for the distracting post...