Have a neighbor that bought a portable classroom and is using as supplemental space for daycare. (Main care is in home, this structure just used as play area a portion of the day.)
Wired from breaker at a pole, two hots & neutral. Main breaker in panel in portable classroom, with N-G bond. Ground rods at both structures. Inspector says separate ground is required to trailer(treating like a mobile home?)
This would fall under 550 Manufactured Buildings? Service is at the pole, this is second structure with no other common metallic paths. Does anyone see any problems with the installation?
Seems to me that if the portable structure is fed from a separate service, then ground is required, and the N-G bond is also required. On the other hand, if this unit is sub-fed from another service (ie - the home), then regrounding is OK, but the N-G bond must go.
So does the portable unit have it's own service? That would be helpful to know.
There are 10 types of people. Those who know binary, and those who don't.
Service is at the pole (meter and OCP) Trailer is fed from pole service. (House has its own service from different pole/xfmr/meter etc.)
I am looking at section 250.32.B.2 Wouldnt this be the same as feeding a garage fom a house? two ways to do it. 1) 4 wire feeder, no N-G bond at second structure. 2) 3 wire feeder, reground neutral at second structure (w/ no metallic paths between)
First check the label on the portable classroom. If it has a label it may also have instructions on the type of supply. Does it have a label on the side saying "connect 120 / 240 volt single phase four wire feeder here". ? When in doubt read the instructions or check with the manufacturer. I have not seen any portable classrooms that did not have a service located outside and a four wire feeder to the panel in the unit. Alan --Inspector.
It does appear that the "main panel" is the disconnect at the pole, and the panel in the classroom is a "sub," so the inspectors' view is reasonable. The pole is where the neutral/main are connected.
That aside, assuming PVC, USE, or other non-metallic raceway between the pole and the classroom, I don't see much cause for concern if the panel in the classroom has a "main" breaker, and is treated as the "main" panel.
THe question I would ask is at the pole is it a main breaker feeding a panel in the structure? If it is then the exception to 250.32(a) could not be used and the bonding would be required in addition to the equipment grounding conductor. If the main is at the pole then do not use the green bonding screw in the panel.