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Joined: Mar 2001
Posts: 2,056
Redsy Offline OP
Are the neutral & ground buss always isolated in construction trailers?


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Joined: Oct 2000
Posts: 2,749
550.4 General Requirements.
(A) Mobile Home Not Intended as a Dwelling Unit. A
mobile home not intended as a dwelling unit — for example,
those equipped for sleeping purposes only, contractor’s on-site offices, construction job dormitories, mobile
studio dressing rooms, banks, clinics, mobile stores, or intended
for the display or demonstration of merchandise or
machinery — shall not be required to meet the provisions
of this article pertaining to the number or capacity of circuits
required. It shall, however, meet all other applicable
requirements of this article if provided with an electrical
installation intended to be energized from a 120-volt or
120/240-volt ac power supply system.
Where different voltage
is required by either design or available power supply
system, adjustment shall be made in accordance with other
articles and sections for the voltage used.

550.16 Grounding. Grounding of both electrical and nonelectrical
metal parts in a mobile home shall be through connection
to a grounding bus in the mobile home distribution
panelboard. The grounding bus shall be grounded through the
green-colored insulated conductor in the supply cord or the
feeder wiring to the service ground in the service-entrance
equipment located adjacent to the mobile home location. Neither
the frame of the mobile home nor the frame of any appliance
shall be connected to the grounded circuit conductor
(neutral) in the mobile home. Where the distribution panelboard
is the service equipment as permitted by 550.32(B), the
neutral conductors and the equipment grounding bus shall be

Joe Tedesco, NEC Consultant
Joined: Dec 2004
Posts: 1,064
Redsy, I have always seen them isolated, due to the fact that there always a panel after the meter outside on the pole.


Joined: Mar 2001
Posts: 2,056
Redsy Offline OP
Thanks, guys!

I've been asked to provide power to a trailer on a customers site from an existing service in a small industrial building, and I plan to run quadruplex. I was just curious as to whether the neutral & ground werealways isolated.

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