Bonded or floating neutral for load center in Trailer?

jbowman88

Member
Location
Renton, WA
Im working on an RV/trailer with a standard 120/240 V load center fed by a shore-power cord that plugs into a standard 50 Amp 120/240V receptacle. My question is whether or not the grounded conductor (neutral) should be bonded at the panel in the trailer, or be left floating?

The trailer spends half its time connected to a standard RV hookup on the side of a building. I believe it should be left floating for this situation; it’s basically just a sub-panel fed by the building’s main panel.

However, it spends the other half of its time connected to a pair of small portable generators (2 Honda EU2000s in parallel operation) which do not have a bonded neutral. So, in this case I pressume the panel inside the trailer should have a bonding jumper in place.

I can’t very well have folks taking the bonding screw in and out depending on the power source, so I have to choose between leaving it in or taking it out all together. What’s worse: having no neutral bonding point, or having 2 neutral bonding points?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Im working on an RV/trailer with a standard 120/240 V load center fed by a shore-power cord that plugs into a standard 50 Amp 120/240V receptacle. My question is whether or not the grounded conductor (neutral) should be bonded at the panel in the trailer, or be left floating?

The trailer spends half its time connected to a standard RV hookup on the side of a building. I believe it should be left floating for this situation; it’s basically just a sub-panel fed by the building’s main panel.

However, it spends the other half of its time connected to a pair of small portable generators (2 Honda EU2000s in parallel operation) which do not have a bonded neutral. So, in this case I pressume the panel inside the trailer should have a bonding jumper in place.

I can’t very well have folks taking the bonding screw in and out depending on the power source, so I have to choose between leaving it in or taking it out all together. What’s worse: having no neutral bonding point, or having 2 neutral bonding points?
Why don't you ground the neutral at the generators?
 

Adamjamma

Senior Member
Hmm, sounds like what we normally use on field days... should have a grounding screw, if I remember right, near front under the plugs and the dc output.

when we operate where we cannot put together a ground we run several milk jugs of salt water with copper pipe dropped into them, and use that as a temporary ground... bonding wire from each of them..l four of them seems to always be enough to ground our complete field day site and was all the old sergeant I dealt with ever seemed to do. Of course, have seen the guys in the Caribbean do similar, some 4 guage wire run out to the beach and toss a ground rod into the ocean.
But, sure somewhere that this is not code.
 

kwired

Electron manager
Location
NE Nebraska
I'd be more concerned about making sure things are proper when connected to a utility supplied system - whether things are bonded or not. The utility supplied system will have a ground reference (and with MGN distribution usually a very good reference) and that alone increases shock risk if exposed but not bonded metallic items become faulted to ungrounded conductors.

With the generator and no bond - you have an ungrounded system. Should a conductor (L1, L2, or N doesn't really matter) fault to exposed metallic components - you simply create a ground reference with that first fault, a second fault on another system conductor hopefully causes opening of overcurrent protection.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
...when we operate where we cannot put together a ground we run several milk jugs of salt water with copper pipe dropped into them, and use that as a temporary ground...
Which does absolutely nothing. The Caribbean guys you mention are using salt water to connect to earth and likely have a better connection to it than most ground rods, but those jugs of salt water sitting on the ground are not connected to anything. You might as well wave your "ground wires" around in the air.
 

jbowman88

Member
Location
Renton, WA
My question was not about grounding. It was about whether or not to bond the Grounded Conductor (Neutral) inside the panelboard.

I found the the correct answer in NEC 551.54(C).

The neutral is not to be bonded anywhere on the trailer, and the bonding screw is to be discarded.

I guess that means you should only use generators with a neutral-to-ground bond to power an RV. That rules out a huge number of portable generators...
 

jumper

Senior Member
My question was not about grounding. It was about whether or not to bond the Grounded Conductor (Neutral) inside the panelboard.

I found the the correct answer in NEC 551.54(C).

The neutral is not to be bonded anywhere on the trailer, and the bonding screw is to be discarded.

I guess that means you should only use generators with a neutral-to-ground bond to power an RV. That rules out a huge number of portable generators...
The problem is with the genny set up. It needs to be used as a SDS supply with neutral bonded to frame and and a GES.

http://services.brilliantelectric.biz/Brilliant_Electric/Article_250_Part_4_files/droppedImage.jpg
 

kwired

Electron manager
Location
NE Nebraska
The problem is with the genny set up. It needs to be used as a SDS supply with neutral bonded to frame and and a GES.

http://services.brilliantelectric.biz/Brilliant_Electric/Article_250_Part_4_files/droppedImage.jpg
In that image there is a GES because there is also service equipment involved. What if the generator is mounted on the vehicle/trailer? Might need to bond neutral to generator frame but pretty certain you would not be required to connect to a grounding electrode.
 
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