To bond or not to bond neutral and ground in new electric service panel?

[JPRambo]

There is no problems with a multi-wire branch circuit that is wired correctly. I wired homes for 18 years using many of these. No problem with any of them. If they are wired correctly.

 

[STx]

The ground/neutral bond should only happen at the main service entrance. Everywhere downstream of that, ie, sub-panels, neutral and ground are to be kept separate.

Code calls for ground rods at outbuildings. That only applies to a feeder, where there is a panel and multiple circuits in the outbuilding. If it's a branch (ie, single circuit hanging off your main panel) then ground rods are not required.

This is correct but, code also requires 4 wires run to the sub-panel, 2 hots, 1 neutral and 1 ground. If you've only run 3 wires, 2 hots and a neutral, run a 4th wire if you can easily. If you can't, bond the panel.

Here's the risk/issue that you're dealing with, the ground wire is for fault current. We always say that electricity want's to find the quickest path to ground but, it's really trying to find the quickest path to it's source. If you don't have the 4th wire or the bonding screw installed, you're relying on the conductivity of the Earth as your fault current carrier back to the ground rod at the meter pole, and that's not a good bet. More likely, you're going to become the fault current carrier in some way.

The code does allow 3 wire service to an outbuilding if you run the wire in metallic conduit that is connected to both panels and acting as the ground carrier.

 

[STx]

I don't see a ground wire from the house out to the barn sub-panel. Just two hot one neutral for 100 amp 240 service. Does that change anything?

I know the barn was wired by amateurs some 55 years ago, and I think electricity was added to the existing house in the 1920's. An outlet tester at some locations shows combinations of lights that aren't on the list of good/bad responses.

I had to remedy something that made the chrome-plated kitchen percolator tingle when touched. That could have been deadly if someone added a longer cord and filled it at the faucet while plugged in. I suspect electricity bleeding to ground somewhere was the cause of major pipe corrosion, galvanic action, that seems to have ended after I got a few things wired like they should be.

This farmhouse is out in the country, never had a building inspector sign off anything. Dad's advice was just bulldoze the place when he was gone, too much was beyond repair. Now I'm getting old and telling the same thing to my kids. It's a cute little farmhouse (and outbuildings) but everything needs attention continually to stay functional.

Unless they ran it in metallic conduit that is bonded to both panels and acting as the ground conductor, you need to either run a 4th conductor (the correct fix) or install the bonding screw. While not compliant withe newer versions of the code, installing the bonding screw will eliminate the risk.

 

[STx]

Shared neutrals can be real fun when a 2 or 3 pole breaker isn't used when trouble shooting, till you figure it out. Yes, way back on commercial work a shared neutral was allowed on 3 phase. Tied handle breakers were also not required. I believe the current code requires separate neutrals on all circuits. When computers started to proliferate in the working world those shared neutrals ruined a lot of computers. We then started specifying separate neutrals even though code allowed. Shortly it became a trade practice.

Ron

You can share a neutral with current code but, it has to be on a single handle or connected breaker. Still not a good idea in most cases.

 

[s219]

This is correct but, code also requires 4 wires run to the sub-panel, 2 hots, 1 neutral and 1 ground. If you've only run 3 wires, 2 hots and a neutral, run a 4th wire if you can easily. If you can't, bond the panel.

Here's the risk/issue that you're dealing with, the ground wire is for fault current. We always say that electricity want's to find the quickest path to ground but, it's really trying to find the quickest path to it's source. If you don't have the 4th wire or the bonding screw installed, you're relying on the conductivity of the Earth as your fault current carrier back to the ground rod at the meter pole, and that's not a good bet. More likely, you're going to become the fault current carrier in some way.

The code does allow 3 wire service to an outbuilding if you run the wire in metallic conduit that is connected to both panels and acting as the ground carrier.

Yep, agree with all of that. I have had some interesting conversations with our inspector about this, having run power to a pier, from a generator shed, and to a barn. For my pier, which has 220V service, I ran 4-wire and drove ground rods in at the top of the stairs, about 20' from the waterline. Generator has four wire but no ground rods. When running power to my barn, which is only used for lights and a 110V GFI outlet, I ran 3-wire using #6 aluminum service wire to minimize voltage drop. Had some interesting conversations with the inspector since he had never run 110V "service" to an outbuilding, but we agreed 3-wire for hot, neutral, and ground was correct, with ground rods at the barn.

 

[Jcoon]

I just put in a new home this past summer, 2017, service goes to meter out front and 200 amp breaker with small panel, then to house 200 amp panel box 320 feet away, then another 100 feet to 100 amp panel for garage. 3 wire to everything, two 8’ ground rods at each panel, and every panel is neutral ground bonded.

 

[ultrarunner]

I love threads like this because they make for interesting discussion of the hows and whys of things.

I managed one 1920 3-unit apartment building and the entire building was served with a single 30 amp Edison Fuse Main with knife disconnect and from there to 3 sub-panels each with a single 15 amp Edison fuse... ninety five years in service!

The property was sold and the new owner took it to the studs and also raising the building... the downstair's unit only had 7' ceilings... now it is getting 4 meters... 3 for the units and 1 House Meter...

So one single Electric Meter and three Gas Meters...

Still lots of 1200 square foot homes with 30 amp electrical service dating from 1920's around...

Also, Federal Pacific is in everything "Modern"... these panels are split disconnect so no single breaker will kill everything... it does cause confusion for Do it Yourself weekends warriors... not being sure the power is off.

Pulled a lot of permits for Service upgrades... found the Electric Inspectors professional and engaged... typical is going from 30 amp 120v service to 100 amp 240v service.

Few older homes have any grounding... and this includes the overhead feed to the detached 1920 garages out back.

 

[grsthegreat]

I just put in a new home this past summer, 2017, service goes to meter out front and 200 amp breaker with small panel, then to house 200 amp panel box 320 feet away, then another 100 feet to 100 amp panel for garage. 3 wire to everything, two 8’ ground rods at each panel, and every panel is neutral ground bonded.

Thats odd. I guess they dont enforce national electric code in your neck of the woods. Technically its ok as thats how it was done for years, but this has not been a legal way to do it for quite awhile.

 

[Jcoon]

Thats odd. I guess they dont enforce national electric code in your neck of the woods. Technically its ok as thats how it was done for years, but this has not been a legal way to do it for quite awhile.

They enforce all codes to a T, and I’m also in probably one of the worst towns for building codes also, what the local electrical store that I bought all my supplies from told me was that if I was putting in a double wide or any type of trailer, it needs a 4 wire, but because it’s a modular on a foundation I can do the 3 wire, the front main panel and the house panel where both inspected by different electrical inspectors also.

 

[California]

[responding to this prior post]

Unless they ran it in metallic conduit that is bonded to both panels and acting as the ground conductor, you need to either run a 4th conductor (the correct fix) or install the bonding screw. While not compliant withe newer versions of the code, installing the bonding screw will eliminate the risk.

Bonding screw? I don't think I have one. This Federal Pacific 100 amp sub-panel in the barn was installed about 1966 but it might have been a used salvage panel at that time, Dad was 'frugal'.

As I noted in the prior post the panel is fed by two hots and a neutral, no ground wire, then has its own good (recently replaced) grounding rod. All the neutral wires within go to the same neutral bussbar as does the grounding rod - and also a couple of green wires from circuits added later. (nearly all the sub-circuits are two-wire).

I assume this shared neutral/ground bussbar has the same effect as a bonding screw between neutral and ground in newer construction.

Is this scheme merely obsolete or a real immediate problem?