Vehicle mounted generator supplying house through inlet

sw_ross

Senior Member
Location
NoDak
This is in a rural setting where the poco commonly mounts a meter that has an integrated manual transfer switch, so you manually select between utility power and generator.

HO has a 10 kW vehicle mounted (military surplus) generator. The "vehicle" has receptacles mounted on it in the form of a construction site spider box. It appears to have "feed through" capability with a 50 amp 4-wire twist-lock feeding into it from the generator, then a 50-amp female plug (twist lock) on the opposite side.

the spider box has CB's to protect the other receptacle mounted on it.

He wants to use a 4-wire pigtail out of this spider box to feed a 50-amp inlet at the manual transfer switch in the meter box (neutral is not switched).

From the meter/manual transfer switch location service conductors (3-wire) feed to various locations on the property, including the house which has a 200-amp service panel.

The meter location is not considered the service disconnect by the poco and the electrical AHJ, it's considered a "site isolating switch". Each structure that is fed by this meter is set up as a service with neutral ground bond.

Basicly we're trying to decide whether the neutral and ground at the generator need to be bonded or not, given the situation?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I would call that a semi-automatic transfer switch. It appears the generator voltage switches it.

As the neutral-ground bond is maintained on the load side of the TS, your generator bond should be disconnected.
 

sw_ross

Senior Member
Location
NoDak
If I were to break down my question to its simplest form my question would be,

Using a breaker interlock kit and a generator inlet should the neutral be bonded to the ground at the generator?

In my mind thinking about it, it seems that would allow objectionable (neutral) current to flow on the ground path since the neutral is bonded in the house service panel? Am I thinking about that right?

Thanks
 

kwired

Electron manager
Location
NE Nebraska
IMO you are tying into service conductors, there is no EGC established yet, all non current carrying parts are bonded to the grounded conductor.

It sort of doesn't matter if you run three or four wires to the generator, but is more proper to have the separate EGC if the generator doesn't have a bonded neutral.

If you have bonded neutral in the generator then you will have a parallel grounded conductor between generator and the transfer switch, sort of wrong, yet not really going to hurt anything either, if you place generator close to the switch and have non metallic covered wiring method between them.
 

kwired

Electron manager
Location
NE Nebraska
Those combination units POCO's install that have a meter and manual transfer switch are not listed.

Nothing you connect generator wise is really NEC compliant with these.

POCO's can get away with installing something not listed, we can't. I have one serving where I live, was cheaper than any transfer switch I could have provided myself. I have a 4 wire supply from my portable generator when I use it for standby. My generator does not have a bonded neutral in it, without the 4th wire generator frame is left floating when the rest of system starting at transfer switch has a ground reference(s).

I say reference(s) because the supply side is POCO and is an MGN system and has a ground electrode at nearly every structure of the system.
 

sw_ross

Senior Member
Location
NoDak
Yes, Larry you did say that - Thanks!
I guess I didn't understand what you meant by "semi-automatic" transfer switch

Kwired- Thanks!

oh yeah, thanks to ActionDave also!
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
IMO you are tying into service conductors, there is no EGC established yet, all non current carrying parts are bonded to the grounded conductor.

It sort of doesn't matter if you run three or four wires to the generator, but is more proper to have the separate EGC if the generator doesn't have a bonded neutral.

If you have bonded neutral in the generator then you will have a parallel grounded conductor between generator and the transfer switch, sort of wrong, yet not really going to hurt anything either, if you place generator close to the switch and have non metallic covered wiring method between them.
I agree.

There is a whole lot of hand-ringing that goes on around generators, but if you understand how and why you bond a service the way you do and why you connect a sub panel the way you do, it makes hooking up a generator a whole lot easier.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Those combination units POCO's install that have a meter and manual transfer switch are not listed.
Not listed with which agency?
what kind of listing do you want?
 
Last edited by a moderator:

kwired

Electron manager
Location
NE Nebraska
The ones being installed around here are not listed AFAIK. They are Durham Manufacturing units, most common is 200 amp single phase but there are other configurations. They have meter socket, and a double pole double throw switch - no overcurrent devices. You showed a device that can be plugged into pretty much any meter socket.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Yep, that’s the unit I what I was referring to. I posted it in another thread. Got too many generator threads going on...

Durham is weird on their stuff for some reason. We use their products occasionally, but they ask for a special number for UL listing. Like the meterbases start with a “U” in the number. I guess it costs to get one listed? Looks like if they build one unit that is listed it would be good for all of the exact same units...

I don’t know the ins and out of UL listing requirements. Maybe they charge you for each units listing??
 

kwired

Electron manager
Location
NE Nebraska
Yep, that’s the unit I what I was referring to. I posted it in another thread. Got too many generator threads going on...

Durham is weird on their stuff for some reason. We use their products occasionally, but they ask for a special number for UL listing. Like the meterbases start with a “U” in the number. I guess it costs to get one listed? Looks like if they build one unit that is listed it would be good for all of the exact same units...

I don’t know the ins and out of UL listing requirements. Maybe they charge you for each units listing??
You ever compare one that is listed to one that isn't? Possible that listed unit has extra items added to it that are necessary to pass listing but don't really effect operation.

The particular model I see around here, their catalog doesn't mention listing option, does for other units
 
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