Dick Perin
Member
- Location
- Atlanta, Georgia
My background is I am a EE (electronics as opposed to electrical) and have worked in engineering with 53' Mobile TV trucks for the last 11 years and I am helping a college that is putting together a "bread truck" sized unit for sports use and have questions on power distribution and grounding.
If you are curious, for large mobile units, there are two sets of 5 Cam-Loc connectors. One set is for HVAC (typically two 10 ton systems) and the other set is for video equipment. A transfer switch allows both HVAC and equipment to be powered by one set of connectors. Incoming power is 3-Phase Wye (208V). If HVAC and equipment are combined, each leg uses a little under 200A. If separate, about 95A for equipment and about 85A for HVAC (depending on outdoor temperature). Besides the 3 phases of power, there is a neutral and an earth ground. Earth ground goes to the mobile unit's chassis. If anyone is curious, I can describe what happens downstream.
For the truck I am helping the college with, they want to be able to plug the truck in at different venues. Eventually they want to tow a generator behind and have the ability to be completely stand-alone for power. The challenge is the university has standardized on a Hubbell connector for all of their venues (for other needs). It is a four pin connector, with each phase rated at 60A. It is also a low Wye system with a neutral - no earth ground. So the question becomes, do they need a Hubbell connector and a Cam-Loc connector, where the Cam-Loc connects the truck body to earth ground? If that isn't needed for code requirements, I assume the neutral should be bonded to the truck body? The load consists of two 120VAC air conditioners (roof mounted) that draw about 13A each. I would put them on one leg. The other two legs would power the equipment (120VAC) and all of the equipment together uses about 30A - 40A. The work will be done by the university electricians, but I am suspicious of their knowledge of the NEC. I attempted to research this on my own and every 'answer' led to a new question. Sure glad I don't have to deal with the NEC everyday. ; - ) Thanks.
If you are curious, for large mobile units, there are two sets of 5 Cam-Loc connectors. One set is for HVAC (typically two 10 ton systems) and the other set is for video equipment. A transfer switch allows both HVAC and equipment to be powered by one set of connectors. Incoming power is 3-Phase Wye (208V). If HVAC and equipment are combined, each leg uses a little under 200A. If separate, about 95A for equipment and about 85A for HVAC (depending on outdoor temperature). Besides the 3 phases of power, there is a neutral and an earth ground. Earth ground goes to the mobile unit's chassis. If anyone is curious, I can describe what happens downstream.
For the truck I am helping the college with, they want to be able to plug the truck in at different venues. Eventually they want to tow a generator behind and have the ability to be completely stand-alone for power. The challenge is the university has standardized on a Hubbell connector for all of their venues (for other needs). It is a four pin connector, with each phase rated at 60A. It is also a low Wye system with a neutral - no earth ground. So the question becomes, do they need a Hubbell connector and a Cam-Loc connector, where the Cam-Loc connects the truck body to earth ground? If that isn't needed for code requirements, I assume the neutral should be bonded to the truck body? The load consists of two 120VAC air conditioners (roof mounted) that draw about 13A each. I would put them on one leg. The other two legs would power the equipment (120VAC) and all of the equipment together uses about 30A - 40A. The work will be done by the university electricians, but I am suspicious of their knowledge of the NEC. I attempted to research this on my own and every 'answer' led to a new question. Sure glad I don't have to deal with the NEC everyday. ; - ) Thanks.