Temp Office Trailer Grounding

[boss11]

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• <font size="2" face="Verdana, Helvetica, sans-serif">We installed an overhead #2 Quadraplex to a pole set next to the Trailer ( about 175' total length). We are supplying 120/240 single phase power to the Trailer Panel. We used 2 insulated conductors for phases, 1 insulated conductor for the neutral, and the bare #2 conductor for the grounding conductor. The source is an existing outdoor weatherproof Dist. center with branch breakers up to 100A single and 3 phase. We treated the Trailer panel as a Sub-Panel, single branch circuit, with an isolated Neutral which originates in the main service Dist. Panel. We attached the Grounding Conductor to the Trailer Panel Buss with a jumper out to the Trailer Frame Ground Lug & at the Dist. Panel Ground Buss. We are now being told that we need to drive a Ground Rod at the Trailer and connect it to our Ground Buss at the Trailer. In this installation without the Ground Rod at the Trailer an NEC Code Violation. Our local inspector opined that it is not, but another local authority has asserted that it is a code violation. We believe that our installation is supported by the following sections of the NEC. 250.32 (A) exception, 500.16 Grounding (Mobil & Manufactured Homes), 500.16 (A)Insulated, 500.16 (B) Electrical System. Is it optional to install this additional Ground Rod ? We have provided a full size Grounding conductor with our feeders. Won't the addition of this Rod create a Ground Loop and an alternate path with different Impedance then the service ground ?</font>

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[eprice]

Re: Temp Office Trailer Grounding

boss11,

It's been a long time since I dealt with a mobile home, but I'll give it a shot, and maybe someone else can correct me if I get it wrong . I assume your references to 500.16 were intended to be 550.16.

If I understand the description of your situation, the service equipment is not located adjacent to the trailer as required in the first part of 550.32(A), therefore a disconnecting means suitable for service equipment must be provided as required in the last part of 550.32(A). Is the trailer panel suitable for service equipment?

550.16(A)(1) which you referenced, requires the grounded conductor to be insulated from the grounding conductors. Does the trailer panel have seperate busses for grounding and grounded conductors?

I see nothing in 550.16 that addresses the question of the ground rod, but the last part of 550.32(A) referes to 250.32 which you also referenced. I don't believe the exception to 250.32(A) applies, since you are supplying the trailer with a feeder, rather than a branch circuit. Therefore, 250.32 requires the installation of the ground rod. Furthermore, unless you can show the resistance to ground at that rod to be 25 ohms or less, 250.56 requires a second rod to be installed.

 

[hurk27]

Re: Temp Office Trailer Grounding

Boss11

Won't the addition of this Rod create a Ground Loop and an alternate path with different Impedance then the service ground ?

No as the ground to the trailer is isolated on the load end and there will be no current to loop.
and the fault current would not be concidered as to being objectional.

545.12 only requires that you need to route a GC with the feeders back to the main service GE, and not install a electrode. this GEC will also act as your EGC

545.12 Grounding Electrode Conductor.
Provisions shall be made to route a grounding electrode conductor from the service, feeder, or branch-circuit supply to the point of attachment to the grounding electrode.