Whose rules do you follow when installing electrical systems in mobile vehicles and trailers?

For example I was involved in a project that was a mobile control center for a remote robotic system. The trailer was setup to connect to an outside power source, with either a generator or building feed. I assume that when we were connected to a generator, we needed to bond the neutral to the ground, but when we were fed from an existing service, we could not double bond the neutral to the ground.

What are the rules for the portable X-ray or dentistry trailers?

How about the panel truck that has a small workshop in it with lights, air compressor, and convience outlets for small power tools?

How about the portable video studios for large public entertainment events like the Superbowl or award shows?

If you can't twist these things around to be RVs I am not sure where the code would apply.

You may get some clout on the mobile medical facilities through your health department rules.

So the NEC does not directly apply to mobile trailers, trucks, etc, that are not Recreational Vehicles.

OK, that makes sense.

Now, who's rules do apply?

I think that with the possible exception of medical facilities, probably covered by the state health agencies, these are largely unregulated.

Larry...

The US Federal Government has jumped in and regulates them.

Manufactured homes are somewhere under HUD

Their site associated connection are regulated by the NEC/ States.

Because road-borne anythings cross state lines the Feds have long regulated them.

As a practical matter, the methods and fittings seen in manufactured housing are often identical to that of RVs.

Unlike stick-built homes, it would be most unusual for specific construction inspection for either manufactured housing or RVs.

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In either event, I'd run away before I ever got involved trying to correct wiring problems in manufactured housing. They're built to be built -- not repaired.

Larry:
Over the years, I worked (as EC) for a company that did 'first responder' type vehicles. A few of the larger rescue rigs had gensets & 'shore power' with 120/208 or 120/240, 3 phase QOB panels.

Doing the installs, repairs, retrofits, etc. we followed the 'plans' from an engineer. That was based on NEC, and trade practices. A manual, 4 pole transfer sw did the gen/shore power choice. Gen and shore were bonded to the truck frame. All the 120 was GFI.

Shore power was via a 100 amp (overkill) RS pin & sleeve.

If this is not a mobile dwelling I do not see how HUD can regulate it and I am not sure the "first responder" vehicle is legally required to be inspected although I can see why the government's insurance carrier might want it.

I inspected a trailer IBM set up to display a small computer system but it was acting as the IBM Installation Planning Rep, not as an electrical inspector and this thing traveled all over the country. I never heard of any problems. It was set up to plug into a garden variety 50a RV post. (actually 2 for the full boat load) Internally there were 2 50a panels, one for the house loads and one for the computer system.
This had no "living" facilities (plumbing or sleeping area) so they dodged HUD. Actually, unless the rules have recently changed, RVs are not HUD regulated either.
My son in law had a trailer that was really a house on wheels but it was titled as an RV and was not HUD certified.

These guys
http://www.nationalcabinsales.com/ but they called themselves Stewart Lodges then.

I neglected a few things. THe rigs were 'inspected' by the engineer, and a heck of a lot of firemen, EMTs & police.
I have no clue about any insurance inspections.

The 'shore power' receptacles were permitted and inspected.

As to Teslas comment regarding HUD, I believe he thinks the OP is talking mobile homes, which are HUD inspected. The 'manufactured' homes (prefab) that I have seen are inspected at the point of manufacture, by an 'in-plant' inspector that signs off on the finished product.

Sorry, if I mislead anyone.

Do not bond the neutral and ground. If the on board generator has the neutral and ground bonded then use a transfer relay that switches the neutral. I wire many of these type units. I got into battles with EMS vehicle builders who would put a panel board on the vehicle and connect the neutral and grounds together. When the EMS operator would remove the shoreline cord, they would get a shock due to the grounded conductor being lifted before the hot. This would briefly cause the chassis to become hot. If the shore power was connected to an receptacle that the neutral and hot were reversed (or a 3 to 2wire adapter was used and there was a poor or no ground, the outside of the chassis will be hot. As long as the neutral is kept isolated at least the chassis will not become energized. This is also why many older camper trailers trip a gfci (and why there are a lot of campgrounds with rigged wiring) Campers also have a small panel board and most used the neutral bar for both the grounds and neutrals. GFCI's do not like that!! Robert

Robert:
Thank you for the above. Reading back my comments, I neglected to be specific on having the neutral isolated from ground.

Your guidance will come from Article 90, the introduction to the NEC.

Look at what the NEC is intended to address- and, just as important, what it does not address. You will note that vehicles, ships, aircraft, light rail, rolling stock, and a great many other things are not addressed by the NEC.

Why, you ask, might this be? Well, here are a few reasons:

First off, any 'rule book' is based on a set of basic principles. Different folks developing something, independent of each other, will often take opposing approaches. Either approach might be excellent, but the two methods are not compatable. For example, look at the gulf between "Windows" and "Apple."

Many things - ships, trains, and mines come to mind - already had their set of principles, their 'rule book,' long before the NEC came about.

Likewise, the basic assumptions might be irrellevant to another application. For example, a ground rod is a bit impractical for the Space Station. You might even create a dangerous situation - one example is when folks apply the NEC to a mine, and wind up blowing things up or electrocuting people.

That's why a designer has to have a very clear understanding of electricity, lest bad things happen. One absolutely must understand the difference between 'grounding' and 'bonding.'

That said, we are seeing far more circumstances that challenge the traditional role of the NEC, and it's not an area that's settled at all. There's more to electricity than volts and amps - and we're only beginning to learn.

To answer your basic question, though ... If the application involved people and the usual appliances at the usual voltages, MOST NEC principles will be reasonable. Otherwise, all bets are off.

Many years ago, the fire dept I was in had a pumper with a 5K winco generator on it. All the cords had 15 amp 125/250 v 3wire (non grounding)twist lock plugs and cord caps. When ever there was a fire, if they use the generator with the lights or smoke ejector, if you touched the truck you go a tingle or even a bite. Only happen at major fires where lines (water) were laid from the pumper. After this happen at a major fire I asked the chief if I could find the problem. Two of the hand lights and one fan had the ground and hot reversed on the plug. The outside of the light was hot. The neutral and ground were bonded at the generator. Since the truck was isolated (rubber tires) most of the time no one got shocked. But on a large fire, hoses were laid and all was wet, including the light, ground and the firefighter. Since the light was now grounded to the earth (hot side) The wet earth around the truck was hot in relation to the truck chassis. They were sure glad when I fixed the problem. I replaced all the twist-locks with grounded types and made sure all polarities were correct. Robert

I find it a bit odd how the NEC doesn’t seem to include mobile vehicles and trailers, like the OP has described, yet when it comes to mobile homes, 550.4,[A] also addresses mobile homes not intended as a dwelling unit and then goes on to list some examples of these other uses, like contractor onsite offices, banks, clinics, mobile stores…etc., and how they are not required to meet the provisions of this article pertaining to number or capacity of circuits required. Aren’t these mobile homes for other than dwellings also towed or transported over public roadways as well?

I think you need to go back to the definition of "mobile Home".



If this was manufactured as a utility trailer (and titled as such where they title trailers) it is not a mobile home.
The one IBM had was a garden variety semi trailer that they made pretty. It had a New York semi trailer tag on it.
The welder that fixes my boat works out of a regular box trailer that you would expect to see hauling materials to a job site but it is outfitted as a metal shop inside, running off of a big diesel generator/welder. I am not sure if he has "shore power".
When he has worked for me he just fires up the genny.


The school board also has a "bathroom" trailer and I don't think anyone ever inspected that either but school boards are pretty autonomous anyway.

Agreed. I just see it as a little strange how the NEC decided to cover interior wiring for mobile home units when used as a dwelling, even if they are transported from place to place, but when these mobile homes used as a type of commercial space, like mobile clinics, banks, etc., the usual requirements for commercial spaces don’t seem to apply. I suppose this would maybe default back to the local building code requirements for commercial spaces?

Do local building codes only apply to "permanent" structures?

To the best of my knowledge, construction & office type trailers are not under the 'local' building, elec, fire & plumbing codes for the 'unit'. They do however here in NJ require permits. Building for anchoring, stairs/ramp; electric for power hookup, and plumbing IF there are any sanitary, or domestic water connections.

The range of 'trailers' I see varies from the 'McTrailer' to ocean cargo containers, and a lot in between.

550.4(A) does give the NEC some degree of jurisdiction over a "mobile home" used as another type of occupancy. The thing that is unregulated is a utility trailer or truck body that is used as some kind of occupancy if it is not titled as an RV.
There may be some state laws that plug this hole tho, particularly if this is open to the public.

"Do local building codes only apply to "permanent" structures?"

There was a man in Reno, Nevada named Joe Comforte. He was in the business of providing "comfort," if you know what I mean.

His business establishment was made of three mobile homes, parked right at the junction of three counties. Whenever he heard of an 'inspection' by the 'AHJ,' his girls would roll the trailers a few feet, over the county line.

This charade finally ended, when the State formally admitted that there was no state rule against his business, and one of the counties licensed his operation.

It's rather impractical for any location to attempt to regulate the moveable.