Grounding electrode conductor options
Grounding electrode conductor options
(OP)
I work for an industrial equipment OEM, and in our latest project we are tasked with building portable processing equipment. Our equipment has been built into a semi-trailer. It comes with a power system and filler equipment. It has a 30KVA XFMR to step 480v 3ph down to 120/208 3ph with a neutral for single phase loads. The NEC requires this transformer to have grounding electrodes and a grounding electrode conductor. I found an odd exception in the nec, art. 250.30.a.3exc.2. that seems to be telling me the grounding electrode conductor at the building's main service may be used as the grounding electrode conductor for the seperately derived system, and is not considered a shared grounding electrode conductor (and forced up to a large 3/0 conductor).
How does this exception get applied in the real world, and would that have an application to my portable equipment?
All input is appreciated!
How does this exception get applied in the real world, and would that have an application to my portable equipment?
All input is appreciated!






RE: Grounding electrode conductor options
Rafiq Bulsara
http://www.srengineersct.com
RE: Grounding electrode conductor options
Thanks.
RE: Grounding electrode conductor options
You would be required to install a ground rod and GEC which would be a #6CU + connection to any listed electrodes.
I assume you have a breaker panel in the trailer. You have
3 phase conductors and equipment grounding conductor, EGC,
connected to the transformer per table 250.122. The size of secondary GEC is determined by 250.66. The exception you list does allow the use of the main panel grounding electrode. If the structural components of the trailer are metal and was bonded to the GEC, it could be used for this purpose just as the metal structural beam are used in a building.
RE: Grounding electrode conductor options
Is this the best way?
RE: Grounding electrode conductor options
Rafiq Bulsara
http://www.srengineersct.com