Mobile Home Extension Cords

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Steve Merrick

Steve Merrick

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Location
Anchorage, AK
I have a question regarding a mobile emergency response trailer supplied by a 480Volt, 50 Amp, 3-phase flexible power cord. The trailer is used to respond ot toxic and radiological waste spills, and contains cleanup materials and protective clothing and equipment, and also serves as a changing room for the response crew. We need to supply the trailer with approximately 100 feet of flexible power cord. Our AHJ has determined that this is not a temporary power application, but falls under 550.4(A) and (B) Mobile Home Not Intended as a Dwelling Unit in Other Than a Mobile Home Park. That said, extension cords are apparently not allowed under NEC 550.10(B), and also the power supply cord can't be longer than 36 1/2 feet under 550.10(D). This makes our trailer virtually useless, as we will rarely have a convenient 480V, 50A receptacle within 36 feet of where we will need to locate the trailer. I am aware that 50A UL listed mobile home or RV extension cords are readily available for sale, which leads me to believe that we may be missing something in the Code. Any help that you can provide me in finding a way to get power to this trailer would be vastly appreciated.
 
Re: Mobile Home Extension Cords

How about your AHJ is just flat wrong. I cannot imagine any place were the temporary wiring rules would be more properly applied then to supply power to mobile equipment that will be at a site for less than a week.
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Tom Horne
 
Re: Mobile Home Extension Cords

Thanks, Tom.

I tend to agree with you, however the AHJ hangs his hat on two points to rule out temporary power: 1) our application is not for "construction, remodeling, maintenance, repair, or demolition..." and it's not always used for emergencies, and is therefore not covered under 590.3, and 2) he points out that all temporary wiring installations must be "approved," [590.2(B)] presumably by the AHJ, and he refuses to provide such approval except under very limited circumstances.

Q: Could the trailer simply be classified as "utilization equipment" under 400.7(A)(6) which provides a list of permissable uses for flexible cords? We would then treat the trailer the same as we would a portable arc-welder or skid-mounted pump, etc.

If not and 550 is the correct article to apply, am I misinterpreting 550.10(B) to intend that no extension cords are ever permissable on mobile homes, mobile offices, or RVs? If that is the case, then why are extension cords available that are UL listed for mobile home use?

Thanks again for your responses,
Steve Merrick, PE
Electrical Engineer
 
Re: Mobile Home Extension Cords

Steve,
I believe the solution is:
The "service" part of the installation could be covered under 590 with no problem. This would start at the source of the 480V power connection with over current protection and end at the trailer's "service disconnect" located within 30' of the trailer.
From this disconnect to the trailer, 550 would apply. Keep in mind that 5 service conductors would need to be run from the "service" all the way through to the trailer. That means with a 480V wye supply, you will need 3 phase conductors, 1 neutral or grounded conductor and 1 grounding conductor. You will also need 1 grounding electrode at the "service", 1 at the the trailer's "service disconnect" and 1 at the trailer. The grounded and grounding conductor will not be bonded except at the "service".

I would take this idea to your AHJ and ask him to consider it.
 
Re: Mobile Home Extension Cords

Is this trailer built to any Federal standard (i.e HUD) for mobile homes?
 
Re: Mobile Home Extension Cords

Now that i have my code book in front of me. 550.2 defines a mobile haome as "...connected to the required utilities..."
550.4(A) says that this section applys if "... provide with an electrical installation intended to be supplied from a 120V or 120/240V ..." system.
 
Re: Mobile Home Extension Cords

Originally posted by Steve Merrick:
Thanks, Tom.

I tend to agree with you, however the AHJ hangs his hat on two points to rule out temporary power: 1) our application is not for "construction, remodeling, maintenance, repair, or demolition..." and it's not always used for emergencies, and is therefore not covered under 590.3,
Click to expand...
Unfortunately I'm still looking at the '02 NEC. However my text states "or similar activities". That means it doesn't have to be a classic building. Golf courses refer to such work as "Ground Under Repair". Cleaning up spills inside or outside of structures is still "repair". The fact that you may not be working a classic structure doesn't change the nature of the work. Cleanup is an integral part of all repair and remodeling work.
 
Re: Mobile Home Extension Cords

Alright, found the '05 read-only link from the forum FAQ. You are in fact covered under 590.3 whether the AHJ likes it or not.

As I stated in my prior post you ARE doing repair work. Spill cleanup and activities that support that work qualify whether performed on a structure or the ground.

Cleaning up a water damaged basement requires pumping out the contaminent and hauling out contaminated material. Where does this differ from outside spills other than the specific media being handled? The work is the same.

Although "repair of ground" is not specifically stated it qualifies fully under "Similar Activities".

Tom Horne had it pegged in the first reply. Your AHJ is flat wrong. So the new question really is: How do I straighten out the AHJ or get him overruled?
 
Re: Mobile Home Extension Cords

Jim,
The last sentance 550.4(A):
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.
Click to expand...
This would allow the 480V.
 
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