petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
I am currently working on a project that involves two trailers that have equipment installed in them and are rented to companies for extended periods of time (sometimes the equipment may run for years).
I have been asking myself some questions and am not comepletly convinced of the answers I gave myself so thought I'd ask some experts.
The first trailer is fed 480/3ph/delta. The power feeds into a Nema4 enclosure and terminates on a disconnect switch.
The incoming ground terminates on a ground bar. A #4 wire comes off the ground bar and connects to the trailer steel and some equipment skids inside the trailer.
120V control power is made by a connection on the line side of the disconenct switch through a seperate fused disconnect to a small transformer.
A second trailer is to be fed from the line side of the main 480V disconnect. The second trailer only needs 120/240 3wire service, so I am planning to feed two phases of the incoming 480V after the main disconnect through a fuse block to the second trailer.
In the second trailer I will have a transformer 480V primary, 240/120V secondary. This will feed into a 240V/120V 3 wire panelboard. Panelboard will be mounted adjacent to the transformer but maybe not physically attached to it, and the main cb of the panelboard will service as the OCPD for the transformer secondary.
My plan at present is to bring a ground from the ground bar of the first trailer to the panelboard of the second trailer and conenct it to the ground bar I am adding to panelboard in the second trailer. Then I would bring a ground from the ground bar to the centertap of the transformer and a neutral from the neutral bar of the load center and connect both at the transformer centertap. This would create the neutral at the transformer.
First question - is a bond required inside the panelboard between the neutral and the ground bus? My first thought was no, but others have suggested it does need to be in both places.
Second question - does either or both of the trailers require a driven ground rod? Its likely the electrical connection between the two trailers would be in hard conduit. Its also likely they will be located adjacent to each other, probably within a few feet, if that makes any difference. my thought is a rod for the first one but not the second.
I have been asking myself some questions and am not comepletly convinced of the answers I gave myself so thought I'd ask some experts.
The first trailer is fed 480/3ph/delta. The power feeds into a Nema4 enclosure and terminates on a disconnect switch.
The incoming ground terminates on a ground bar. A #4 wire comes off the ground bar and connects to the trailer steel and some equipment skids inside the trailer.
120V control power is made by a connection on the line side of the disconenct switch through a seperate fused disconnect to a small transformer.
A second trailer is to be fed from the line side of the main 480V disconnect. The second trailer only needs 120/240 3wire service, so I am planning to feed two phases of the incoming 480V after the main disconnect through a fuse block to the second trailer.
In the second trailer I will have a transformer 480V primary, 240/120V secondary. This will feed into a 240V/120V 3 wire panelboard. Panelboard will be mounted adjacent to the transformer but maybe not physically attached to it, and the main cb of the panelboard will service as the OCPD for the transformer secondary.
My plan at present is to bring a ground from the ground bar of the first trailer to the panelboard of the second trailer and conenct it to the ground bar I am adding to panelboard in the second trailer. Then I would bring a ground from the ground bar to the centertap of the transformer and a neutral from the neutral bar of the load center and connect both at the transformer centertap. This would create the neutral at the transformer.
First question - is a bond required inside the panelboard between the neutral and the ground bus? My first thought was no, but others have suggested it does need to be in both places.
Second question - does either or both of the trailers require a driven ground rod? Its likely the electrical connection between the two trailers would be in hard conduit. Its also likely they will be located adjacent to each other, probably within a few feet, if that makes any difference. my thought is a rod for the first one but not the second.
