Strang electrical issue.

[chrisrosenb]

I had a pole barn built about 3 years ago. The only electrical in the building since that time has been the main panels with a 110 & 220 outlets below the panel. I ran extension cords to 2 door openers. The barn is unfinished inside with an open 14 foot high ceiling.

I needed to build a loft, shelving & lumber racks before doing lights & outlets. All of that is now in place, so this week I have been doing the electrical work. The wiring for the lights in the main part of the barn & all outlets are run in EMT conduit.
The wiring for the loft was run with Romex.

The feed wire for the loft lights was run in EMT conduit to the switch & first light, then romex to all of the lights. The lights are porcelain lamp holders with led bulbs mounted on steel octagon boxes.

I did all of the lighting in the loft first. I tested the lights & they all worked.

I then started installing conduit for the over head lighting in the main area of the barn. I was working on of roll around scaffolding. As I was working around one of the steel overhead doors that has an opener, I thought I got shocked. I touched things again, but felt nothing. I went on working.

As I was working around another overhead door with an opener, I know I go shocked. I knew I had power through the ground. The openers had been used since the barn was built, so I ruled them out. The only other thing powered on was the loft lights.

I checked the voltages at the panel between both bars, the neutral & ground. I had 120  volts between each bar & the neutral. I had 237 volts between one bar & ground & 7 volts between the other. When I turned off the breaker for the loft lights, all voltages read normal.

I unhooked the wiring at the first loft light & rechecked the voltages at the panel. All were normal.
I took all of the lamp holders loose from the boxes to check connections. Everything looked fine except for a couple of ground wires being a little low in the ceiling boxes. I put everything back together, turned on the breaker & rechecked the voltages. Now all was normal.

The only thing I can come up with is that one of the low ground wires was touching the hot screw on a lamp holder.

How could the ground make contact with the hot & not trip the breaker?

 

 

 

[tjbnwi]

Your calling this a main panel, is this a sub panel feed from another panel that is elsewhere?

Was a ground rod installed and connected on this panel?

Tom

 

[chrisrosenb]

Thanks Tom,

I thought of the sub panel on my way to the big box this morning after I posted the question.
It is a sub panel off of my shop main panel. Being that it is an unattached building, the ground wire does not go back to the main panel. The ground rod is at the pole barn. The ground & neutral wires are isolated in the sub panel.

 

[Rick Christopherson]

Thanks Tom,

I thought of the sub panel on my way to the big box this morning after I posted the question.
It is a sub panel off of my shop main panel. Being that it is an unattached building, the ground wire does not go back to the main panel. The ground rod is at the pole barn. The ground & neutral wires are isolated in the sub panel.

If the ground is not coming from your main panel, then this is NOT a subpanel. It is actually classified as a "separately Derived System". It's a code violation to set up an outbuilding like this under current code, unless the building was wired under previous code (at least before 2008, maybe 2005).

You need to confirm where the end of your ground is located. Just because you have a ground rod at the building (2 are required), does not mean that the ground still isn't originating from the main panel (but then you DO have a subpanel). If you can confirm that the ground is isolated and exist only at the outbuilding, then you need to bond the neutral and ground at the outbuilding.

By pole barn, I assume this is a metal shelled building. If so, the building itself must be grounded. From the description in your first post, I concluded that your building likely wasn't grounded, and that is why you felt the shock in the first place.

 

[Brent Taylor]

I had a site with a similar problem,  first have it checked out properly. If the feeds to the barns panel are reversed and you try to ground it you will be in for a hell of a shock. I was a Building  Inspector  for 15 years and saw more than a few wire backwards and nearly lost my brother to this very same issue. Be safe and get it checked out by a professional. 

 

[Kev]

Just curious ... with you average outlets typically being a less lethal 110V ... do you make common use of earth leakage detectors in the US ?

 

[tjbnwi]

Just curious ... with you average outlets typically being a less lethal 110V ... do you make common use of earth leakage detectors in the US ?

It is current that matters far more than voltage.

https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

Tom

 

[Kev]

Just curious ... with you average outlets typically being a less lethal 110V ... do you make common use of earth leakage detectors in the US ?

It is current that matters far more than voltage.

https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

Tom

Agreed, regardless ... do you guys use ELDs?

 

[tjbnwi]

Just curious ... with you average outlets typically being a less lethal 110V ... do you make common use of earth leakage detectors in the US ?

It is current that matters far more than voltage.

https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

Tom

Agreed, regardless ... do you guys use ELDs?

Not a common practice.

Tom

 

[Rick Christopherson]

Agreed, regardless ... do you guys use ELDs?

Not a common practice.

Tom

Yes they are. But you call them GFCI.  [big grin]

 

[Holmz]

Just curious ... with you average outlets typically being a less lethal 110V ... do you make common use of earth leakage detectors in the US ?

I had a friend killed with 110, so less lethal is somewhat relative.

But your subtle suggestion is good.
I would be putting a GFI on that and then one at least understands which circuit is the issue.
It is possible that one could probably figure it out with an ohm meter, but some intermittent issue is difficult.

The worst are roofs. The sheeting can be screwed down and go through a wire. The whole roof is then live. The fellow or lady on the latter completes the circuit.

 

[Holmz]

Thanks Tom,

I thought of the sub panel on my way to the big box this morning after I posted the question.
It is a sub panel off of my shop main panel. Being that it is an unattached building, the ground wire does not go back to the main panel. The ground rod is at the pole barn. The ground & neutral wires are isolated in the sub panel.

If the ground is not coming from your main panel, then this is NOT a subpanel. It is actually classified as a "separately Derived System". It's a code violation to set up an outbuilding like this under current code, unless the building was wired under previous code (at least before 2008, maybe 2005).

You need to confirm where the end of your ground is located. Just because you have a ground rod at the building (2 are required), does not mean that the ground still isn't originating from the main panel (but then you DO have a subpanel). If you can confirm that the ground is isolated and exist only at the outbuilding, then you need to bond the neutral and ground at the outbuilding.

By pole barn, I assume this is a metal shelled building. If so, the building itself must be grounded. From the description in your first post, I concluded that your building likely wasn't grounded, and that is why you felt the shock in the first place.

Whether ^that^ is code or not, the idea of bonding the ground to the neutral is somewhat akin to the idea of a "True ground". There is not anything existing as a "true ground" or infinite sink. Airplanes do not have ground rods.
Therefore any voltage on the neutral will then be present on the ground.

So adding more grounding only helps if the voltage is entering at the bonding point, and to keep the neutral from floating away in general. If the voltage is entering from the circuit then more grounds are less elegant than an RCD/GFI.

So one should use a GFI/RCD to detect a current leak "in the circuit".

Once the circuit is confirmed to NOT be leaking current, then the issue could be easier traced to mechanisms of a ground loop or the bad grounds.

----
Another way of saying it is that the building being energized is either coming from;
1) the lire wire being in contact with the building (Say via a nail or screw)
2) from the neutral being in contact.
3) Or from induced current such as from ground loops.

To address #1; use an RCD
To address #2; the neutral can be tied directly to the ground as a separate and dedicated ground.

The building itself can be tied to a separate ground.

Envision the box's neutral is tied to a "ground terminal", and the building it tied to that same "ground terminal". Now cut that wire runs to the ground, and you will see that the entire building is tied to the neutral.
That is something you do not want.