Ramifications of NOT Grounding a Vehicle

Not my field but, It is quite common to use inverter power sources in mobile equipment. The impossibility of grounding a moving or frequently moved structure essentially means that any ground used will be simply to the containing structure, vehicle body, frame etc. I worked for a geophysical company for a while and we had equipment powered by generators, battery powered inverters and even thermal generators. If the power source was grounded to anything, it was grounded to the vehicle frame. If the power was to be used outside the vehicle to provide power to other vehicles, trailers, and so on, in a fixed location, there was a ground drilled in and the equipment was grounded to a common point. We often used ground fault protection on circuits that were powering portable equipment like core drills, cooling fans and such stuff.

Having explained the practice I observed, I have no idea what the code calls for in this case.

Have FUN!
TT3

There are several different possible answers to your question. But first, some questions.

How do you switch between the sources?

Do you use a transfer switch of some kind? If so, how many poles on it?

You need to see if the neutral, or the identified conductor (using Canadian code language), from the inverter (is there more then one?) is tied to the case of the inverter. See if there is continuity between the neutral and the case and let me know.

How much power in watts are we using? Is the inverter powered by the vehicle alternator or batteries or a combination of both? What is the input voltage to the inverter(s)?

Any RF systems involved in this rig?

Interesting question... to give you proper advice, the asked for information is needed.

Switching is done automatically by the inverters. The inverter senses loss of external power and switches to inverter mode.

RF-yes; primarily receiver systems (UHF, VHF) and one microwave transceiver (25W RF power out 11 GHz).

There are 2 inverters each running in parallel to the vehicle's alternator/battery 24VDC system. Each inverter provides on-the-order of 2500W of power to separate distribution circuits (done inside of a power distribution box with current protected swithes to various branch circuits.

One inverter mode is Internal Neutral-to-Ground Switching (Battery .Inverter. Mode)-The AC output neutral is connected to the chassis ground by an internal relay when the inverter is operating from the batteries, thus creating a neutral to ground bond within the inverter.

A second inverter mode is External Neutral-to-Ground Switching (AC .Shore Power. Mode)-The inverter's internal relay opens and removes the ground from the neutral conductor when the vehicle is connected to an external AC power source. The neutral is connected directly to the output neutral thus providing the neutral bond at the external AC source.

Grounding doesn't hurt, you can't be to safe. That said, you shouldn't have any problems with the built in inverter as this is essentially a floating AC power supply with the neutral and ground circuits returning to the vehicle frame. The external power generator also needs to be grounded to the frame. The vehicle is insulated from the earth ground by its tires, so to prevent static build-up you should have at least a dragging strap or better yet. when you stop to use your equipment use an actual grounding rod. This is especially true if you're running any kind of transmitter.

Ahh, an interesting observation about ground and neutral on vehicle frame. The wiring infrastructure in this case is that neutral is isolated (with the intent that it ties together at the source when using an external source).

This begs the question; Would it be prudent to implement a method by which to tie the neutral and ground together when in the inverter or vehicle power mode?

Tony

Correction

Neutral to ground is switched-see post #5