A medical trailor is going to be transported to our Firefighters Training Academy. It will be used for testing for 4 days and then taken away. It will come equipped with a 60 amp. 120/240V. 60A. 4W. power cable and attachment cap. A 4W. receptacle will be installed near a subpanel to provide power. Is a ground rod required?
Does the medical trailer have a panelboard? If it does have a panelboard then I would consider it a structure. Which would lead to Article 250-32, etc., requiring a ground rod. If it doesn't, then I would consider the trailer as portable equipment. Which wouldn't require a ground rod.
[This message has been edited by Mike (edited 06-15-2001).]
The metal shell of the trailer must throughly and solidly bonded to the EGC. You should test the resistance and find it to be low (<2 ohms). If it isn't bonded properly, then I see the need to get it correctly bonded. I don't see the need for a ground rod. A ground rod doesn't make a dangerous trailer safer.
I'm also assuming that the trailer will have a steel jack that would provide a path to earth if lightning strikes the trailer. The trailer really should have metallic contact with the earth for lightning.
I'm assuming that the trailer has a panelboard - but I still consider it portable as evidenced by the fact that it will be rolled away after only 4 days.
I would consider the trailer as portable equipment since it has a cord and attachment plug. Even though the trailer was probably manufactured to the stringent standards of MHMA and other required standards (which by the way are now a lot stricter than they were twenty and thirty years ago when I bought my first mobile home). The cord and plug have two phase conductors, a neutral and a ground. The receptacle supplying power to the unit is deemed as grounded and providing a ground return path. Having said all of that, I think I would insure the shell and frame are electrically connected to the ground in the cable. An ohmmeter check should suffice. If your meter is in the truck a couple of hundred feet away then a scrap piece of #10 connected to the frame and to the receptacle conduit should provide a suitable ground path for fault currents. A separate ground rod may set up a situation with circulating ground currents, and may cause additional problems.