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It pains me to ask this question when there are so many similar ones out there - but I feel like I’ve read them all and still don’t have a satisfactory understanding of what the correct options are.

I have a house built in 1988. It has 400A service and three sub panels on the structure itself. They are all fed with 4-wire HHNG. One of those sub panels feeds a separate structure (barn) about 150’ away via underground feeder. This feed is 3-wire HHN and is on a 60A breaker at the house.

At the barn the panel has a grounding rod and that is bound to neutral from the house.

I believe this used to be to code and is grandfathered in. I also understand it isn’t great, and hence why it’s no longer to code.

I’ve read all kinds of discussion and solutions.

  1. Replace with 4-wire feeder and separate the G and N (which would be code for a new install)
  2. Put a GFCI on the feed line (at the house panel?) and split G & N
  3. Install a transformer to make it a separated service (and bond G N)
  4. Leave it as is but understand it’s potentially hazardous?

First please let me know if I’m misunderstanding those four options?

One other complication though - the two structures are connected by a conductor....they share copper water pipes. Seems like this could change the equation. Can/should those pipes be used as grounding between the structures (in which case you would separate the G&N in the panel?)

I am looking to both make sure I understand the logic and make a good interim decision - in a few years we should be able to replace the feeder with 4w and just follow the current code.

Most relevant posts I’ve read are this and this one that just kept going

Edit - the current feeder is 3x#6awg THHN in 3/4” PVC Sch40 conduit. No practical room to run a 4th in there, especially given the length (200’).

When the time comes we will eventually run 4x#2...

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    Is the 3 wire cable or conduit? – manassehkatz-Moving 2 Codidact Dec 28 '20 at 19:14
  • And if in conduit, what's the conduit? (Metal or plastic?) – Ecnerwal Dec 28 '20 at 19:31
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    Wow, in that "just kept going" thread, every post I read was wrong. That's what happens when you don't have an upvote/downvote reputation system. Forums are generally pretty toxic, but that's not even an electrical forum - it's a sound forum. You might as well ask a barber or taxi driver. Forget everything you read there, wow... – Harper - Reinstate Monica Dec 28 '20 at 19:32
  • I don’t know what it’s in the entire way, but it is in PVC Sch40 when it enters/leaves the ground....so no option to use the conduit as a conductor. – noelep Dec 28 '20 at 21:36
  • Can you post photos showing what type of wire is used for this feeder? – ThreePhaseEel Dec 29 '20 at 1:32
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You have a 5th option if no grounding path is available and you want to update. Current code allows for a separate grounding conductor to be added to be compliant with 4 wire feed (if not metal conduit approved for use as such).

And a 6th option, install a GFCI breaker or receptacle at the first device in each branch circuit. This is the same option that allows 2 wire receptacles in homes to be converted to 3 wire and a tag stating no equipment ground on the receptacle (they come with these stickers pre printed).

Your system is the same as any home built prior to 1999 is it really hazardous? Code allowed this for almost 100 years. If it was really hazardous code would have changed much earlier in my opinion. Having a separate grounding conductor makes sense even if you have a grounding electrode at the detached building. Most non electricians spout all kinds hazards but think about this the grounding conductor can be smaller and if a large current is on that conductor there will be a larger voltage drop so is it really that much safer? , how many electrocutions do you hear about? Not many to start with.

Your #1 would be just like a new install but now that you updated the panel most jurisdictions want all the receptacles to now meet code every circuit with a receptacle requires GFCI protection (yes even lighting there are no exceptions unless local).

Your #2 put a GFCI on the feed at the house panel. I hope you are trying to get in shape because not only is this expensive you will be making a lot of trips to the house to reset it (GFCI’s do not use ground, but they do use the neutral code defines them differently grounding / grounded).

Your #3 install a transformer 1:1 again an expensive task it creates a separately derived system and you can now bond the neutral and ground in the main Panel it is no longer a sub 15kva 1:1 $600+ new $400-500 with shipping eBay used (shipping hurts here).

Your #4 leave it as it is, understanding millions of homes have this same setup.

As you can tell I might suggest running a new grounding conductor at the most. Possibly GFCI breakers or receptacles but I don’t have them in my shop. I have a customer that calls me almost every other month to replace a GFCI receptacle on one of his 3 saws he is afraid of electricity even though he has never been shocked and had me add GFCI receptacles almost 10 years ago well before they were required.

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  • Running new feeder with 4w is the ultimate plan...but it’s likely a few years away. Any thoughts on whether the copper pipes will act as a common ground? My concern here is that if I keep it as-is (with bonded NG) then having a separate route to ground via the pipes is actually making it potentially worse. The code does specially call out having an existing conductive connection between the structures as being a reason you cannot bond NG... – noelep Dec 28 '20 at 21:46
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    You are correct the copper pipes create a parallel path and that would be objectionable current in code speak. To isolate them dielectric unions would be legal and then the pipe at the sub would be an approved grounding electrode as long as 10’ in ground. I do remember something about pipe and the 3 wire sub I will try to find it. – Ed Beal Dec 28 '20 at 22:27
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You'll need to pull a 4th wire or throw a transformer at this to fix this up due to the parallel path

The bad news is that this is a "fix now" situation, not a "fix eventually", because that copper water pipe creates a parallel path for neutral current to flow on, via the water pipe bonds and N-G bonds at each end. You could insert a dielectric union in the pipe, but it'd have to go underground in order for the piping at both ends to retain its status as a legal grounding electrode without defeating the union. (Code inspectors write the situation you're in up as "objectionable grounding current", which is a NEC 250.6(A) violation.)

Fortunately, though, there is enough space in the conduit to fit a grounding wire in it, although just barely, as your existing 6AWG THHNs take up 32.71 * 3 = 98.13mm2, and a bare 10AWG copper ground adds 5.261mm2 of fill, while a ¾" PVC conduit provides 105mm2 of usable area if it's Schedule 80 (the worst case) and 131mm2 of usable area if it's Schedule 40. It'd be best done as a slow, easy pull, attaching a pull string to the existing wires before pulling them out, then using that string to pull the replacement wires in, and you'll want to be generous with pulling lube as well. Obviously, if you take this route, you'll have to separate neutral and ground in the barn's panel and pull the bonding screw or strap from it, as well as moving the grounding electrode conductor connection in the barn's panel from the neutral bar to the grounding bar.

If that's off the table somehow, then your only other option to get this to comply with Code would be to fit a transformer on the outside of the barn. A standard 15kVA, 240/480x120/240 dry-type transformer in a NEMA 3R enclosure would suit the application here, and can be hung on the outside of the barn provided suitable studs are available to take the quite considerable weight involved. As to wiring it, the primary would be wired for 240V operation with the existing wiring redone as Hot/Hot/Ground (instead of Hot/Hot/Neutral), and the secondary would be wired for 120/240V center-tapped service, with Hot, Hot, Neutral, and a supply-side bonding jumper running from the transformer to the barn's panel via a suitable conduit.

Note that the supply-side bonding jumper in this situation basically looks like an equipment grounding conductor: nothing prohibits it from being green or bare, and it's running from the transformer case grounding lugs to the grounding bar in the barn panel. However, it needs to be sized according to Table 250.102, which in practice means you need an 8 AWG jumper instead of 10AWG, or to use rigid metal raceway of some flavor (EMT works) to run the wires from the transformer to the panel. The bonding jumper in the panel stays in place as well, as the transformer has effectively regenerated an isolated neutral at the barn.

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  • A few questions on this if I may? (1) the pipes are not explicitly being used as a grounding electrode at either the house or barn. There is a separate grounding rod. If, at the entrance to the barn, I transition to PEX for the entirety of the plumbing system does this problem go away? (2) Are there any benefits in going the transformer route...such that you would choose it over a 4w feeder? – noelep Dec 29 '20 at 16:45
  • @noelep -- (1) the pipes must be part of the grounding electrode system at both locations, as 250.50 quite explicitly says that ALL grounding electrodes present at a structure SHALL be bonded together to form the grounding electrode system for a structure. Note that 250.52(A)(1) says nothing about the material the interior plumbing system is made from as long as piping is electrically continuous from where it enters the structure to the bonding/grounding electrode conductor attachment point – ThreePhaseEel Dec 29 '20 at 21:32
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    @noelep -- (2) the transformer is mostly an alternative for cases where pulling that 4th wire is utterly impractical. There are situations where it can be an advantage, but they don't come up on this site. – ThreePhaseEel Dec 29 '20 at 21:35
  • Turns out the copper water pipe is not bonded to the panel, and is in fact inside PVC conduit between the house and barn. I think I’ll treat this as a standard 3w situation until I can get a new 4w feeder in. – noelep Jan 1 at 22:01
  • @noelep -- it's still a conductive parasite path between the house and the barn even if it is in that conduit – ThreePhaseEel Jan 1 at 22:03
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Ground options.

Let's take a look at NEC 1999 which provides an allowance for a no-safety-ground-wire situation.

This is NEC 1999 here. Not current Code.

250.32. Two or More Buildings or Structures Supplied from a Common Service.

(a) Grounding Electrode. [deleted: short version: you need ground rods].

(b) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either (1) or (2).

(1) Equipment Grounding Conductor. An equipment grounding conductor as described in Section 250-118 shall be run with the· supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. Any installed NEUTRAL shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

(2) NEUTRAL. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment [GFPE] has not been installed on the common ac service, the NEUTRAL conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.

This is NEC 1999 here. Not current Code. I placed the word NEUTRAL where Code refers to that (it normally uses an obtuse and very confusing phrase).

250.32(B)(2) is the interesting part. It's describing the cases where you're allowed to bootleg ground off neutral.

  • Obviously it's not allowed if you have a ground wire
  • It's not allowed if there's another "metallic path" available
  • It's not even possible if the feeder has GFPE (GFCI) protection.

That seems like it gives you a pretty good roadmap.

If you're willing to install a GFCI, that'd do the trick. Note that the 1999 Code calls for a "30ma" GFPE, which is actually a weaker version of a GFCI designed only to protect equipment not humans. It's the same thing as a "whole house RCD" found on most of the houses in the UK and Europe. When you're doing a whole building, the "5ma" human-protection GFCIs are just too sensitive and will have nuisance trips. You'll need to call a real electrical supply to find a GFPE breaker. It's not adequate for human safety, so you still need GFCI receps at relevant places.

However, xHHN means conduit.

It's not legal to direct-bury xHHN wire, which strongly suggests you have a continuous conduit between A and B.

If that's true, see if the conduit is not collapsed (i.e. see if the wire is pullable). If the wires are able to move, then add a ground wire and be done with it. Because of the age of the conduit and the risk of collapse somewhere, I would start by trying to fish in just a ground wire. But the normal way is to pull all the wires out, add the extra wire, and pull them back in.

Meanwhile, address what's the deal with a 60A breaker on THHN wire.

  • #8 Cu or #6 Al THHN is good for 50A and takes a 50A breaker. Ground is 10Cu/8Al.
  • #6 Cu or #4 Al THHN is good for 65A and takes a 70A breaker. Ground is 8Cu/6Al.

You can put a 60A breaker instead of the 70A if you really want to, but that doesn't get you off the hook for using the larger ground wire.

If conduit fill is at a premium, a copper ground can be bare.

If you find aluminum wire and it's AA-1350 alloy, you should probably change that to AA-8000 alloy, but I'd stick with aluminum. I generally prefer aluminum for large or long feeders like this, unless conduit fill forces my hand into copper. (I had to do that once with 1000 kcmil - $1000 for a 15' run of wire.)

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  • The HHNG usually means hot,hot,neutral,ground as the op stated this is how all the other subs are fed. Please read 110.14.C.1.A . You would not pass a journeyman test in my state with that advice. But common mistake. – Ed Beal Dec 28 '20 at 20:35

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