The service comes down to the pole into a box. That box has a 100A
breaker that runs to the shop, and a 200A breaker that runs to the
house. The pole to shop is about 200 yards and there are 3 large
The meter and service are at the pole. The house and shop are subpanels.
The shop and house panels could have hot-hot-neutral-ground feeds and be
wired with a separate ground bar and no N-G bond. Grounding electrode(s)
required (also required in the other method).
Your description is hot-hot-neutral feed. The shop and house panels are
wired the same as a service panel. Neutral-ground bond required (neutral
and ground bars are effectively the same).
[This method is not allowed in the 2008 NEC for new installations. Seems
like what you have is common and safe.]
With a separate ground bar I suspect your panel doesn't have a
neutral-ground bond. If missing it could be a mistake or a local wiring
practice or inspection authority quirk. IMHO it is not safe. The NEC
does not allow the earth to be used as a return. That is because the
earth does not provide an effective return. The need for a metal (not
earth) path for ground fault current back to the transformer is not
understood as well as it should be.
Bud -- thanks for all the info! You a a bit over my head, but I'll
try to figure this out.
I'm looking into my shop panel now:
There a 3 large wires - 4 ga. aluminum - coming up from the bottom
(from the pole). One goes to the left and is fixed to the neutral
bar, the other two go to the bars where the breakers attach (one on
the left side, the other to the right).
The neutral bar has a place to afix white wires on both the left side
and the right side (the panel hardware attaches the right bar to the
left bar, so neutral whites could be brought in to either side -- in
my case all are on the left side where the big wire from the poles is
There is a ground bar attached to the grey metal box.
All circuits coming in connect bare ground to the ground bar, 110v
whites to the neutral bar, 110v blacks to the breaker, and black and
white wires to the 220v breakers.
From what I see, ground is not tied to the neutral in any way.
The ground bar has a larger wire running out the bottom of the box
(but not with the 3 other large wires) and I see that wire ouside the
shop going into the ground.
I don't quite understand your discussion about the ground and neutral
being connected in the box.
Resorting to my old analog multitester (bec. the battery in the cheap
digital one is dead...)
breaker bar L to neu bar - 120v
breaker bar R to neu bar - 120v
breaker bar L to breaker bar R - 240v
breaker bar L to grd - 120v
breaker bar R to grd - 120v
neu bar to grd - 1v (a trace of voltage, but not 0)
resistance between grd and neu - 20 ohms (that's 2-0, and not K, etc,
I was on the meter 1x setting)
I did some reading tonight in some 'code' book at Lowes. I now see
what you mean by neu-to-grn "bond". There is suppose to be this
"bond" in the service panel, and then any sub panels should be fed by
4 wires - hot1, hot2, neutral, ground.
But my shop panel is fed by 3 wires - hot1, hot2, neutral. There is
only an earth ground in the panel.
I guess I should go pull the cover off the panel on the pole (which
feeds the shop on a 100A breaker and the house on a 200A breaker).
What should the pole panel look like?
What should my shop panel look like? (given it has 3 wires from pole
What should my house panel look like? ( I need to look at it also)
The voltage of interest is N-G.
If there is voltage from N-G you can't measure the resistance. 20 ohms
could be a reasonable measurement if the shop subpanel has no N-G bond
and the path is through the earth.
That is true for a subpanel in the same building.
It is one way to wire subpanels in a *different* building.
That was a second way of powering a *different* building. But the NEC
then requires a N-G bonding jumper. Without the jumper there is no metal
path back to the transformer, and a short-to-ground will not reliably
cause a breaker to trip (and can make the "grounds" hot).
You still don't know where the grounding problem is. From what I
remember it could possibly be one circuit (but probably not).
Connect a light bulb, 100W or larger would be nice, from a hot to
ground. Is the light fully bright? What is the voltage between the
neutral and ground bus? Note all the grounds in the building, including
the panel, may be "hot" when you do this.
If you actually have 20 ohms N-G, a100W light bulb might give you about
15V from N-G. I would expect well under a volt if there is a N-G bond.
As I said a couple times, the N-G bond is often a screw that looks like
it could just be a mounting screw for the neutral bus. Recent ones are
probably green. If not installed there will be an empty hole in the
If the shop panel does not have the N-G bond I would certainly check the
house (or check it anyway).
You may want to call an electrician.
(There is a minute possibility local practice is to not add the N-G
bond. That would be very unwise.)
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