NEC Article 550 (Classroom Building) - Plan Review

[Npstewart]

Im working on a county project for a school. Basically, the project scope is take about (4) building sections (ie. White classroom trailers) and put them together which will then collectively serve as a single classroom for K-12 kids, located on the school site.

Each trailer comes with an individual 100A single phase panel, and there are (4) trailers per group. On my drawings, I showed a feeder coming from the transformer to a disconnect near the transformer, and then im feeding (1) 400A MCB panel located on the assembled sections, and then each panel gets fed from that panel. Overall, very simple.

However, I received a plan review comment that says:
" Service Disconnect(s) nor permitted to be mounted on trailer. NEC 2017, 550.32(A) "

NEC 550.32(A)
(A) Mobile Home Service Equipment. The mobile home ser-vice equipment shall be located adjacent to the mobile home and not mounted in or on the mobile home. The service equipment shall be located in sight from and not more than 9.0 m (30 ft) from the exterior wall of the mobile home it serves. The service equipment shall be permitted to be located elsewhere on the premises, if a disconnecting means suitable for use as service equipment is located within sight from and not more than 9.0 m
(30 ft) from the exterior wall of the mobile home it serves and is rated not less than that required for service equipment in accor-dance with 550.32(C). Grounding at the disconnecting means shall be in accordance with 250.32.


My assumption is that he is referring to section 550.4 (A):

550.4 (A)
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.



The issue is that if you read the section in its entirety, theres so much within this section that clearly does not apply to a classroom, or any other non-dwelling unit type building. Infact, its pretty clear that it applies strictly to a dwelling unit. In order to cite 550.32(A) as an applicable section, you would have to ignore the other 80% of the same section.

Questions:

1. Do you consider a classroom trailer building a "Mobile Home"?
2. Would I also have to comply with non-applicable sections within 550 such as 550.10 which states only (1) 50A feeder can be used? Even though the trailers are state permitted and pre-built with multiple 100A panels and demand calcs greater than 50A per panel?
3. Why does this section allow for different voltages for design calculations, but later wihtin the same section explicitly states only a 120/240-1 service shall be provided?
4. Why is this section so convoluted?

THANKS!

 

[Charged]

Are you saying you think They referenced the wrong section ?
To me they just want it on a H-frame next to the trailer instead of on it and they have correct reference.

 

[augie47]

Questions:

1. Do you consider a classroom trailer building a "Mobile Home"? Yes per 550.4
2. Would I also have to comply with non-applicable sections within 550 such as 550.10 which states only (1) 50A feeder can be used? Even though the trailers are state permitted and pre-built with multiple 100A panels and demand calcs greater than 50A per panel? It says 50 amp cord or permanently installed feeder. I read that to mean the 50 amp restriction is for cords.
3. Why does this section allow for different voltages for design calculations, but later wihtin the same section explicitly states only a 120/240-1 service shall be provided? Last sentence 550.4
4. Why is this section so convoluted? Because it's the NEC

I agree with Post#2

 

[david]

[*]Would I also have to comply with non-applicable sections within 550 such as 550.10 which states only (1) 50A feeder can be used? Even though the trailers are state permitted and pre-built with multiple 100A panels and demand calcs greater than 50A per panel?
[
[/LIST]


THANKS!

A local project here used job trailers for temp classrooms during a school remodeling similar to what your describing

because they were temporary, there was some leeway given.

There is a section in 550 stating something like when not being used as a dwelling.

550 does not limit the supply to 50 amps when not cord and receptacle supplied

a feeder size is given on the manufacture name plate

yes the section limits the supply to a single feeder

yes the section disallows the service equipment attached to the trailer

work with your building department mount the service equipment on a pedestal

mount a distribution panel on the trailer. distribution to the individual panels from there

keep in mind you are combing four individual trailers into one buildings
there are probably no manufacturers instructions allowing that to happen

the building department allowing that to happen means the are already working with you

Sent from my SM-S901U using Tapatalk

 

[don_resqcapt19]

Even you are on the 2017 code, I would reference Article 545 in the 2020 code for this application. There were changes made in 545 because the rules in 550 do not do a good job with trailers used for other than dwelling units.

 

[Npstewart]

Even you are on the 2017 code, I would reference Article 545 in the 2020 code for this application. There were changes made in 545 because the rules in 550 do not do a good job with trailers used for other than dwelling units.

Thank You. I did look through Article 545 in 2017 but I did not think to look in 2020. I usually avoid looking in newer codes until they're adopted because I get them mixed up. However, I have done this in the past when future codes were changed for clarity.

Much appreciated!