Did you know that for the installation of a temporary job-site trailer, you need to refer to several NEC articles? Let’s see how to navigate this.

For the temporary installation of a job trailer (manufactured buildings and relocatable structures), one would think you would begin with Article 545. However, the section that should first be visited is Article 590. I know what you’re thinking… “It’s just temporary.” Nevertheless, while reviewing Article 590 we find that there are some things that are relaxed and many that have more restrictive rules.

To begin, installations must comply with ALL other applicable articles except as SPECIFICALLY modified by 590. In Colorado, there is also a relaxed requirement for the grounding electrode system. Colorado allows a single rod, pipe (which you cannot use due to lack of listing), or plate electrode to be installed for all temporary installations that require a GES.  However, 590.3 lists the time constraints for a temporary installation as “During the Period of Construction.” The temporary installation is to be removed immediately upon the completion of construction. 590.4 then tells us that the service must comply with parts I through IV of article 230. If the unit is to be provided electrical power through a feeder, it must have overcurrent protection in accordance with 240.4, 240.5, 240.100 and 240.101. The conductors used for the feeder are permitted to be within cable assemblies or multiconductor cords or cables as identified in table 400.4 for hard usage or extra hard usage (typically type S through SOOW). For flexible cords, you will need to use column A of Table 400.5(A)(1) to find the conductor sized to fit the need, up to #2 AWG at 80 amps max. For all other approved wiring methods, you will use 310.16 to find the ampacity. You are also permitted to use Type USE cable in a raceway underground for the purpose of temporary installation only.

Next, 590.4(J) requires that cable assemblies and flexible cords and cables must be supported to prevent physical damage and cannot be installed on the floor or ground (extension cords are exempt from this). Flexible cords containing fine stranded conductors like class I, K and M, may not be rated for use with the terminal lugs of the panelboards and OCPD’s installed in/on the trailer.

Additionally, we must visit Article 545, Part II, Relocatable Structures. Part II is a recent revision to the 2020 NEC that was taken from previous cycles within Article 550. Previous code text from Article 550 that applied to mobile homes used as other than dwelling units, has now been relocated to Part II of Article 545 and is titled “Relocatable Structures.” Part II of Article 545 applies to relocatable structures, like jobsite trailers.

Finally, The State of Colorado requires that all manufactured buildings that were manufactured after 1991 bear a DOLA/DOH insignia. These requirements are found in 8CCR 1302-14 4.21.2. Without the insignia, the unit will not receive power. If manufactured prior to 1991, the insignia is not required and proof of date of manufacture is to be provided. The vehicle registration will show the date of manufacture.

In conclusion, we would need to use articles 590, 545, 230, 240, 250, chapter 3, and 400 from the NEC as well as state statutes to install electrical power to a job site trailer (manufactured building/relocatable structure). What do we do with a converted semi-trailer that needs power? Hmmm… That will have to be tabled for another day.

Thank you, and I hope this is helpful!