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Doing the grounding thing.

The M934 expansible van, the equipment inside it, the 60-KW generator it is pulling and the trailer that generator is riding on are all one system.

A system requires a system ground. It's not enough to ground just one or two pieces of the system. They all need to be grounded.

Without a good system ground, there is potential damage to your equipment, your health and the health of those around you.

Here's some advice on how to ground:

The Generator and Trailer: Ground Rod

Effective grounding of the 60-KW generator starts with the ground rod.

There are two ground rods available. NSN 5975-00-224-5260 brings a single-section 6-ft rod. NSN 5975-00-878-3791 brings a 9-ft rod in three 3-foot sections.

For the 9-ft, 1-in thick ground rod, you'll need clamp, NSN 5975-01-034-8882, to hold the grounding strap to the rod.

The 6-ft rod comes with a thumb screw for holding the strap. If you need to replace it, you can use a nut, bolt and washer, or order clamp, NSN 5999-00-4965834. Since this rod is thicker than the 9-ft rod you cannot use the same clamp.

To install the 6 ft rod, use sledgehammer, NSN 5120-00-243-2957. To install the 9-ft, sectional rod, use slide hammer, NSN 512001-013-1676.

The ground rod needs to be driven down to the water table so it pierces the moisture line. The top of the ground rod should be at least an inch below the ground surface. Too many are left sticking up from ground level and become a walking hazard as well as decreasing the effectiveness of the ground.

The immediate area around the top of the ground rod should be dug out and the soil prepared with chemicals and water, as necessary.


The conductor should be at least 6 AWG copper or copper-clad aluminum. Flat straps meeting these requirements work best because they have low impedance.

The conductor should not be spliced and should go continuously from the rod to the generator trailer as straight and short as possible. It also must run downhill from the trailer to the rod. Don't loop it up and over any other equipment.


The ground connection for the trailer is a ground stud above the curbside front step. The surface immediately around the stud must be free from corrosion, paint, grease and dirt. The stud should be clean and corrosion free.

The connection at the ground rod should be tight and the conductor pressed against the ground rod by the arms of the clamp and not the tightening bolt.

Don't twist or tie the conductor to the rod. The connection is poor and it could work free entirely.

From the same connection point, run a conductor strap to the ground stud located on the circuit breaker side of the switch box.

Your generator and its trailer are now grounded.

The Van: Outside

The surface wire ground system (SWGS) kit, MK-2551A/U, NSN 5820-01-263-1760, is a good system to use for the M934 expansible van.

To set up the SWGS, lay the grounding cable on the ground around the van with one end near the power entrance panel. Connect that end to the ground stud in the power entrance panel.

Drive the grounding pegs following the route of the cable at 5-ft intervals and attach the grounding cable.

Attach the two other connector cables by running one from a ground peg to the front bumper of the vehicle and the other from a ground peg to the signal entrance panel ground stud on the van.

If the soil is dry, keep the areas around the SWGS pegs wet.


Inside the van, part of your grounding system is having each piece of communications equipment bonded to the shelf it sits on.

Check these bonds often to make sure movement hasn't loosened them and that the surface-to-surface contact is maintained.

Bonding the Van to the Generator/Trailer

If the van has a different voltage potential than the generator/trailer and you touch both at the same time, you could get seriously injured. This is especially true if you touch them with bare hands and provide a path for electricity to travel right across your chest!

To prevent this, keep their voltage potential the same by bonding them together. Run a bonding conductor (at least 6 AWG and copper) between the van and the generator/trailer.

You can make this bond at a couple of places. Connecting a grounding stud on your generator/vehicle and a grounding stud on your van is one. Connecting between the generator/vehicle ground rod and the SWGS is another.

Other Methods of Grounding

Getting a good ground depends on soil conditions. Sometimes you must prepare the soil with water and chemicals to get a good ground and keep it.

Sometimes a grounding plate instead of a ground rod or a SWGS can be used. Sometimes plumbing, buried tanks, copper grids and the metal framework of buildings can be used.

The important things are getting a good ground; grounding all your equipment to the earth; bonding your equipment to other equipment; doing it safely; and keeping it from becoming a hazard to foot traffic.
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Copyright 2003, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:M934-Series Expansible Van ...
Publication:PS, the Preventive Maintenance Monthly
Date:Dec 1, 2003
Previous Article:Battery tester a bright idea.
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