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Old 12-28-2018, 12:34 PM   #1
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Default Mobile Home Park Neutral to Ground Connection

Can anyone tell me how how a mobile home park in California would be laid out where a switch gear enclosure feeds dozens of pedestal meters? I need to understand where the ground to neutral connections are made. Are they in the individual pedestals? Is it in the switch gear enclosure? Has anybody ever seen rigid run under ground between switch gear and pedestals?


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I was working in a mobile home park. Each mobile home is fed by a pedestal meter panel that contains a meter, a main breaker, and a 4 prong receptacle into which the mobile home is plugged. I only worked on 1 unit in the park. The occupant was getting shocked from the metallic surface of a freezer. Ground for this and all other receptacles, in the unit, was 120V with respect to neutral. I found 3 problems:
1. A metal bracket holding the circuit breaker onto the "deadfront" was contacting the red phase bus bar so the pedestal enclosure was also 120V to neutral.
2. There was no connection between the pedestal enclosure and neutral.
3. There was no wire connected to EGC terminal on the receptacle.

To remedy these problems
1. Re-positioned the bracket so it would not contact the busbar
2. Bonded the pedestal enclosure to neutral.
3. Connected a wire from the enclosure to the EGC terminal of the receptacle.

6 Wires entered / exited the pedestal.
The wires were:
L1 enter
L1 exit
L2 enter
L2 exit
Neutral enter
Neutral exit
No ground was seen.

There was a switch gear enclosure about 100 feet from the mobile home. The switch or breaker, for the unit on which I was working, also fed 3 other units.
The only way I see that this could ever have been code compliant is if the wires between the switch gear and the pedestal were in rigid conduit and rigid conduit fittings bonded the switch box and pedestal enclosures. If this conduit completely corroded away under ground then it would cause the problem for which I was called. Otherwise if underground wires were PVC or UF then the pedestal was connected incorrectly and I solved the problem and there are no other concerns.
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Old 12-28-2018, 03:46 PM   #2
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I work in campgrounds which are similar. The feeders to the pedestals are 4 conductor (for 240 volt) and the bond between ground and neutral is made in the main panels, not in the pedestal. In your case it sounds like the rigid conduit is the 4th (ground) conductor. The ground terminal of the receptacle should be bonded to the pedestal as is the conduit. If I understand what you did, I would go back and remove the pedestal to neutral bond. The rest sounds good.
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Old 12-29-2018, 12:40 AM   #3
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550.16 (A) (1)
Connect the grounding, and grounded conductors at the service equipment. I'm assuming that means the pedestal.
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Old 12-29-2018, 10:33 AM   #4
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Quote:
Originally Posted by armsjac View Post
I work in campgrounds which are similar. The feeders to the pedestals are 4 conductor (for 240 volt) and the bond between ground and neutral is made in the main panels, not in the pedestal. In your case it sounds like the rigid conduit is the 4th (ground) conductor. The ground terminal of the receptacle should be bonded to the pedestal as is the conduit. If I understand what you did, I would go back and remove the pedestal to neutral bond. The rest sounds good.


I didn't see rigid coming into the pedestal nor did I see what raceway technique, if any, was used. But rigid underground is the only code compliant way I can think of where 3 wires can can supply the pedestal with 240V with no neutral to enclosure connection in the pedestal. So one of my questions was: "Have you ever seen rigid run underground in this application?"
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Old 12-29-2018, 10:56 AM   #5
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I didn't see rigid coming into the pedestal nor did I see what raceway technique, if any, was used. But rigid underground is the only code compliant way I can think of where 3 wires can can supply the pedestal with 240V with no neutral to enclosure connection in the pedestal. So one of my questions was: "Have you ever seen rigid run underground in this application?"

No. I see direct buried 4 wire feeders. If you have a 3 wire feeder, for 240 volts then yes, I would bond in the pedestals.
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Old 12-29-2018, 11:18 AM   #6
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Thanks armsjac. Hopefully a few more people with experience in trailer parks and campgrounds will respond. Since the pedestal was in good condition for a 1962 trailer park, there is a good chance it was installed wrong during replacement.
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Old 12-29-2018, 11:38 AM   #7
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It was common years ago to use 3 wire feeders. 1962 certainly qualifies as years ago. Was there any sign of a ground rod at the pedestal by chance?
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Old 12-29-2018, 12:03 PM   #8
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I've done a bunch of work on MH parks in Cali.

Most did have direct buried conductors from the main disconnect, with only 3 conductors being present. They would use the pedestal as the main, bonding to the water line and calling it good.

On the few that did have some GRC going out of the main, it was toast and wasn't a complete run anymore. I have worked on a few pedestals where they must have tossed out the GRC below the pedestal because it had rotted off. Just make sure to always use caution in the parks, a ton of stuff is rigged up left and right.

I have seen the state making a number of the parks upgrade the electrical infrastructure lately though, and that is a good thing.
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Old 12-29-2018, 02:09 PM   #9
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Quote:
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It was common years ago to use 3 wire feeders. 1962 certainly qualifies as years ago. Was there any sign of a ground rod at the pedestal by chance?
Yes, there was a ground rod bonded to the pedestal enclosure.
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Old 12-29-2018, 05:52 PM   #10
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Years ago trailers had there own panel and the ground was bonded there. Times changed and they stopped bonding inside the travel trailers and relied on a 4 wire feed.

On ones i have seen recently the grounds are bonded behind the meter. The idea is that no one except the power company can access this area to remove the bonding jumper.

If you power a travel trailer from a generator you are meant to use a grounded generator or a grounding plug in a unused receptacle due to your inside panel no longer being bonded.

Still have to wonder how a phase went to the pedestal and shocked a person inside a trailer. Surely there were more problems than just the shocks.
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Old 12-30-2018, 12:42 PM   #11
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Still have to wonder how a phase went to the pedestal and shocked a person inside a trailer. Surely there were more problems than just the shocks.
The Zinsco main breaker is attached to the deadfront of the pedestal with a metal bracket. The main breaker feeds a receptacle which is also mounted in the deadfront. When you pull off the deadfront, the breaker disengages from it's input busbar and you have only a neutral wire connecting the pedestal to the receptacle.. Now you have to disconnect this neutral from the receptacle to fully detach the deadfront. So now the detached deadfront holding the main breaker and the receptacle is sitting on the deck and out of the way. A neutral wire is dangling out of pedestal since it was removed from the receptacle. In this configuration, the problem vanishes The pedestal is floating but no longer at 120V. The problem was that the metal bracket, mentioned in the first sentence, was contacting the breaker's input busbar only when the deadfront was installed. This was fixed by re-positioning the bracket down about an inch.

In my experience, the only problem besides shock, would be burned up surge protectors. The guts burn for floating grounds and would surely burn for 120V between ground and neutral.
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Old 01-02-2019, 12:53 AM   #12
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Seems like this would depend on where the utility service ends and the customer wiring begins... Are the meters owned by the park or by the utility? If the switchgear is on the supply side of the utility, then the pedestals could have 3 wires with a bonded neutral. If the switchgear is customer owned, then it could be either depending on when it was installed. Prior to 2008, the NEC allowed 3 wire feeders to remote structures if no other metallic connections existed.

At any rate, there should be a 4 wire feed going to each trailer.
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