Bad Grounding and Good Luck

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hillbilly

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Had a call from a new customer.

"I'm getting "shocked" when I touch my A/C compressor":-?

I turn off the breaker to the unit and open the disconnect....all is well.
Turn the breaker back on and check voltage.
238V line to line, 119V line A to ground, 238V line B to ground!
What the HEY?....The ground is energized (so was the disconnect enclosure, and the A/C unit enclosure).
Good thing I was working this like it was energized (which it was).

This was on a double wide mobile home, so I start at the beginning.
Open 200A disconnect at outside pole, looks OK.
4 wire 3/0cu feeder underground to house panel....all connections tight....overhead service looks OK.

Open breaker panel inside home, and both grounded feeder conductors are landed on the (isolated) Neutral bar:-?!!.....bonding strap removed.....Equipment grounds landed on terminal strip mounted to the metal enclosure....No grounding continuity!!
The equipment grounds were not bonded to the service ground!
Actually, they weren't bonded to anything other than every grounding conductor in the home.

I start checking receptacles in the home, and some have 238V between the grounding terminal and a phase leg (Line B).
What I've got is a floating ground circuit with a short(?) somewhere that's powering up the grounding circuit.

I leave my meter on one of the receptacles with the "hot" ground and start turning off breakers.
When I get to the range breaker and turn it off, the voltage on the ground goes away.
Un-plug the range, turn on the circuit and check again, voltage gone.

I pull the range out of it's space and check for continuity at the range cord.
Sure enough, one power leg shows continuity to ground....range is shorted.
I inform homeowner that the range is defective....he needs to call repair man.
I tell him to look for shorted wire...element...etc.

To correct the house grounding, I installed a lug on the breaker panel enclosure and moved one of the grounded feeders to this lug....making continuity between the panel enclosure, circuit grounding conductors and the service ground.

When I think of this situation...and I have a lot in the last couple of days...I realize that I may have saved someones life.
It's still sinking in how dangerous this situation was for the homeowners.

I asked the homeowner who installed the electrical service to his home, and he said that he and his son did.....16 years ago:roll:.
They had tried to troubleshoot this problem but couldn't figure it out.

All that time and no equipment grounds in (or outside) the home.
The first time(?) something shorts out, the breaker doesn't trip and every ground in the house is energized :-?
It was just a matter of time until someone got shocked and maybe killed.

Sorry for the long post, but it's still on my mind.
This is one time a homeowner doing his own work put his family in real danger.
Luckily (and thanks to the good Lord), nothing bad happened.

steve

ps....The appliance repairman came and found a shorted wire on the range top.
Apparently a wire (clip) had fallen loose and created a dead short to the range chassis.
 
hillbilly said:
Open 200A disconnect at outside pole, looks OK.
4 wire 3/0cu feeder underground to house panel....all connections tight....overhead service looks OK.

Open breaker panel inside home, and both grounded feeder conductors are landed on the (isolated) Neutral bar:-?!!.....bonding strap removed.....Equipment grounds landed on terminal strip mounted to the metal enclosure....No grounding continuity!!
The equipment grounds were not bonded to the service ground!
Actually, they weren't bonded to anything other than every grounding conductor in the home.
Click to expand...

If the main disconnect is at the outside of the trailer, then you count the panel inside as a sub-panel. Sub-panels have to have an isolated neutral bar, don't they? You would remove the bonding strap, but the ECG's would still be landed on the ground bar, which should be attached/bonded to the panel enclosure... I don't see any problems there. Check article 250.24 A(5) - (at least for the 08 code).
 
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Kdawg67 said:
If the main disconnect is at the outside of the trailer, then you count the panel inside as a sub-panel. Sub-panels have to have an isolated neutral bar, don't they? You would remove the bonding strap, but the ECG's would still be landed on the ground bar, which should be attached/bonded to the panel enclosure... I don't see any problems there. Check article 250.24 A(5) - (at least for the 08 code).
Click to expand...

The way he described the problem and the way he corrected it was the correct way it should have been in the first place.
 
The main disconnect for the service is outside. You would not bond the neutral & ground together beyond the main (unless it's a separately derived system).

250.24 - Grounding service supplied AC systems
(A)5 Load-Side Grounding Connections. A grounding connection shall not be made to any grounded conductor on the LOAD side of the service disconnecting means except as otherwise permitted in this article. (which pertains to separately derived systems)

Also,
250.142 Use of Grounded Circuit Conductor for Grounding Equipment
(A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non-current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:
(1) On the supply side or within the enclosure of the ac service disconnecting means
(2) On the supply side or within the enclosure of the MAIN disconnecting means for separate buildings as provided in 250.32(B)
(3) (pertains to separately derived systems)

(B) Load Side Equipment. Except as permitted in 250.30 (A)(1) and 250.32(B) ***(again these exceptions pertain ONLY to sep.derived systems)*** , a GROUNDED CIRCUIT CONDUCTOR SHALL NOT BE USED for grounding non-current carrying metal parts of equipment on the LOAD SIDE of the service disconnecting means OR on the load side of a separately derived system disco means....

The original installation (i.e. bonding jumper removed at the trailer panel) was correct. It was also correct for there to be an isolated neutral bar, because that panel in the trailer is LOAD SIDE equipment. The installation now is in code violation, because you have tied the grounded conductor to the grounding conductor after the main.
 
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After re-rereading I do see the issue with the grounded & grounding conductors landing BOTH on the neutral bar. The grounding conductor should have been landed on the grounding bar. But those neutrals should stay isolated (i.e. no bonding jumper) at the trailer panel. And, the grounded & grounding conductor should have been bonded together at the service disconnect outside.
 
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I have a trailer that is wired the kindof the same way it has disconnect outside and the neutual is bonded at the disconncet. It had H H N pulled inside the netuatral isolated and a ground bar. When I checked it it did not have a ground in the trailer anywhere I told the owner I would have to install a ground wire to the ground bar to the ground rod. This is to code isn't it? At least 2005 code.
 
sgr1 said:
I have a trailer that is wired the kindof the same way it has disconnect outside and the neutual is bonded at the disconncet. It had H H N pulled inside the netuatral isolated and a ground bar. When I checked it it did not have a ground in the trailer anywhere I told the owner I would have to install a ground wire to the ground bar to the ground rod. This is to code isn't it? At least 2005 code.
Click to expand...

It sounds like you have a 3-wire feeder between the disco & the panel. If there are ANY ground rods (most trailer services I've seen do not) the grounding electrode conductor would go from the grounding electrode to the service disconnect, not to the panel inside the trailer. And with an isolated neutral, I can see the issue with no grounding means @ at the panel, because the neutral is isolated... How do all the EGC's find their way back to earth ground? I'll keep looking for the answer to that one. Any ideas out there?
 
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hillbilly said:
Had a call from a new customer.

"I'm getting "shocked" when I touch my A/C compressor":-?

I turn off the breaker to the unit and open the disconnect....all is well.
Turn the breaker back on and check voltage.
238V line to line, 119V line A to ground, 238V line B to ground!
What the HEY?....The ground is energized (so was the disconnect enclosure, and the A/C unit enclosure).
Good thing I was working this like it was energized (which it was)..
Click to expand...

This is one of the main reasons that I always use a 'voltage wand' or 'volt tic' that can sense the voltage without touching anything. Its good you found the problem, but after the homeowner made that comment about 'getting shocked when touching the compressor, I dont believe you took all the proper safety precautions (gloves/ volt wand etc) before starting IMHO. Im suprised no one has said this already.

Im happy to see you worked like it was hot but I would not have turned it back on right away cause after using the volt tic it wouldve picked up the inductance off the metal frame, and i would have shut the breaker off right away and warned the homeowner to not touch anything until I was done. Then checked the continuity between the ground and neutral and that wouldve showed what the problem right away. Never the less, Im glad you found the problem. Just be sure to use a volt tic next time. ;)
 
hillbilly said:
Had a call from a new customer.

To correct the house grounding, I installed a lug on the breaker panel enclosure and moved one of the grounded feeders to this lug....making continuity between the panel enclosure, circuit grounding conductors and the service ground.
Click to expand...

There should have already been a lug on the ground bar for the ground wire, trailers properly come from the factory with the neutrals and grounds isolated, no bond screw to remove. There are so many trailers out there that not properly grounded, probably a two to one ratio. At least with this one they did use a four wire feeder, most of the time it is a three wire. Yes, you probably saved a life, it was a terrible accident waiting to happen.
 
Sorry if I didn't describe the situation clearly.:smile:

The reason that I mentioned the inside bonding jumper being removed is because.....If the installer had at least left the jumper in place, the range breaker would have tripped, or at least the short circuit would have burned open. The range..and a lot of other equipment (anything with a grounding conductor attached to it) wouldn't have been at 120V potential between it and any grounded object that a person might touch.:-?
Not code, but safer that what existed....IMO.
There was a bonding jumper in the panel, and it had been disconnected.

What I found was a grounding system with no bond to the service ground...or the outside ground rod(s).....Basically just paralled grounded (neutral) service feeders from the outside disconnect to the inside breaker panel (isolated) neutral bar.

As for the comments about how I worked the problem.
I did it safely considering the circumstances....and the problem is now fixed.:)

How many of you have seen a grounding circuit with line voltage applied.
No breakers or fuses opening...no smoke....no sparks....just sitting there like a coiled snake?
Even the steel home framing was at 120V potential.
The house had a basement with a dirt floor where the homeowner had a work bench and spent a lot of time.

steve
 
hillbilly said:
Sorry if I didn't describe the situation clearly.:smile:

The reason that I mentioned the inside bonding jumper being removed is because.....If the installer had at least left the jumper in place, the range breaker would have tripped, or at least the short circuit would have burned open. The range..and a lot of other equipment (anything with a grounding conductor attached to it) wouldn't have been at 120V potential between it and any grounded object that a person might touch.:-?
Not code, but safer that what existed....IMO.
There was a bonding jumper in the panel, and it had been disconnected.

What I found was a grounding system with no bond to the service ground...or the outside ground rod(s).....Basically just paralled grounded (neutral) service feeders from the outside disconnect to the inside breaker panel (isolated) neutral bar.

As for the comments about how I worked the problem.
I did it safely considering the circumstances....and the problem is now fixed.:)

How many of you have seen a grounding circuit with line voltage applied.
No breakers or fuses opening...no smoke....no sparks....just sitting there like a coiled snake?
Even the steel home framing was at 120V potential.
The house had a basement with a dirt floor where the homeowner had a work bench and spent a lot of time.

steve
Click to expand...


Cant say Ive seen it, only heard of it from other electricians. Its scary when you think about this, and seeing how the metal skin of that mobile home was 120v to ground was there for years and not hurting anybody is just short of a Miricale!! Just emphasizes importance of using a 'volt tic' before touching anything.
 
hillbilly said:
Had a call from a new customer.

To correct the house grounding, I installed a lug on the breaker panel enclosure and moved one of the grounded feeders to this lug....making continuity between the panel enclosure, circuit grounding conductors and the service ground.

I asked the homeowner who installed the electrical service to his home, and he said that he and his son did.....16 years ago:roll:.
They had tried to troubleshoot this problem but couldn't figure it out.

steve

ps....The appliance repairman came and found a shorted wire on the range top.
Apparently a wire (clip) had fallen loose and created a dead short to the range chassis.
Click to expand...

steve. in reading this post i got to ask you a guestion. did you remove all the grounds that was on the neutral bus if not you may want to look at article 550.... 550.16- 550.16a,b,c
 
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