Portable job trailer wiring

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Cow

Senior Member
Location
Eastern Oregon
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Electrician
I'm getting ready to quote wiring a portable job trailer like you see on any typical jobsite, in a jurisdiction known to have inspectors that are sticklers. So I want to cover my bases.

I'll admit, this is the first time I've looked up codes on job trailers for as long as I can remember.:ashamed1:

My main two questions relate to feeder size and installing a GES.

1. Reading 550.4(A) leads me to believe article 550 applies. (I've searched, it's seems this article and 545 have been debated a fair amount). To paraphrase part of 550.4(A), "shall not be required to meet the provisions of this article pertaining to the number or capacity of circuits required." Then on to 550.33(B) which mentions "feeder circuit conductors....shall be rated not less than 100 amperes."

So, am I able run #2 AL to this trailer with a 60-90 amp breaker as long as it meets the calculated load of the trailer since 550.4(A) seems to give me a pass on the 100 amp minimum?

2. When I install the rods, am I allowed to attach the GEC to the steel trailer frame which is typically bonded with a #6 green back to the panel from the factory or must I fish the GEC up into the interior panelboard?

Thanks.

It's one of those things I think, where the older I get, the less I know, or remember. Maybe I said that wrong, I don't remember how it goes...:D
 
if the distribution panel in the job trailer is 100 amp (Main) 240/120 V

coming from a pedestal 100 amp service with 100 amp main breaker 100 amp feed through lugs

drive two ground rods at the 100 amp pedestal service.
100 amp 4 conductor with insulated green equipment ground as a feeder to the job trailer
 
david said:
if the distribution panel in the job trailer is 100 amp (Main) 240/120 V

coming from a pedestal 100 amp service with 100 amp main breaker 100 amp feed through lugs

drive two ground rods at the 100 amp pedestal service.
100 amp 4 conductor with insulated green equipment ground as a feeder to the job trailer
Click to expand...

Trailor would need a GES also.
 
jumper said:
Trailor would need a GES also.
Click to expand...

Per 550.16, grounding shall be through the mobile home panelboard grounding bus, connected through the green-colored insulated feeder in the supply cord or feeder wiring to the grounding bus in the service-entrance equipment located adjacent to the mobile home location.

The GES at the adjacent service equipment/disconnect would be the only required GES.
 
david said:
if the distribution panel in the job trailer is 100 amp (Main) 240/120 V

coming from a pedestal 100 amp service with 100 amp main breaker 100 amp feed through lugs

drive two ground rods at the 100 amp pedestal service.
100 amp 4 conductor with insulated green equipment ground as a feeder to the job trailer
Click to expand...

1. 100 amp wire needed.
2. GES only at service.

jumper said:
Trailor would need a GES also.
Click to expand...

1. ?
2. Trailer GES too.

Craigv said:
Per 550.16, grounding shall be through the mobile home panelboard grounding bus, connected through the green-colored insulated feeder in the supply cord or feeder wiring to the grounding bus in the service-entrance equipment located adjacent to the mobile home location.

The GES at the adjacent service equipment/disconnect would be the only required GES.
Click to expand...

1. ?
2. GES only at the service.

So not a lot of comments on feeder size, and a toss up between the members on whether rods are required at the portable trailer or not.

At least it appears I'm not alone in trying to determine what is correct for installation like this.

Thanks for the help so far.
 
I never put that much thought into it.

I go inside the trailer and see what size main it has in the panel and size the temp service and feeder to that.

I've yet to install and additional ground rod at the job trailer on any of them I've ever hooked up, but, wouldn't be against it if I was asked to.


JAP>
 
If there are stickler inspectors in your area, call them and ask them what they expect before you ever get started and save yourself the grief if it worries you.

JAP>
 
jap said:
I never put that much thought into it.

I go inside the trailer and see what size main it has in the panel and size the temp service and feeder to that.
Click to expand...

Most every job trailer I see, big or small, has a 100 amp main breaker panel in it regardless of the actual trailer load. I'm not interested in running 100 amp cords/feeders simply because of a panel rating. I'm sure my customers would appreciate NOT spending unnecessary dollars if not required, especially something that is temporary.

jap said:
If there are stickler inspectors in your area, call them and ask them what they expect before you ever get started and save yourself the grief if it worries you.

JAP>
Click to expand...

The inspectors aren't allowed to take phone calls during the day and can only return calls in the morning. If they remember to call you back. In my very limited prior experience in this jurisdiction, a prompt call back is a rarity.
 
Cow said:
Most every job trailer I see, big or small, has a 100 amp main breaker panel in it regardless of the actual trailer load. I'm not interested in running 100 amp cords/feeders simply because of a panel rating. I'm sure my customers would appreciate NOT spending unnecessary dollars if not required, especially something that is temporary.



The inspectors aren't allowed to take phone calls during the day and can only return calls in the morning. If they remember to call you back. In my very limited prior experience in this jurisdiction, a prompt call back is a rarity.
Click to expand...

A 100 amp feeder is not that big a deal and is quite common actually.

Most job trailers are located fairly close to temporary services so it's usually not a huge cost to get the service put to it, and, I'm not interested in dealing with a general contractor's foreman whose job trailer is 130 degrees in the dead of summer or freezing in the winter because a temporary feed to his trailer wasn't adequate.

Point is, there's no one here that can answer your questions about your install better than the inspector in your area who knows what the local ordinances require.

JAP>
 
Craigv said:
Per 550.16, grounding shall be through the mobile home panelboard grounding bus, connected through the green-colored insulated feeder in the supply cord or feeder wiring to the grounding bus in the service-entrance equipment located adjacent to the mobile home location.

The GES at the adjacent service equipment/disconnect would be the only required GES.
Click to expand...

Maybe, it seems that it comes down to the bolded sentences in these sections and how they directly relate to each other.

I read this thread:

http://forums.mikeholt.com/showthread.php?t=141520

The only thing that I can say for sure is that I am sure is that it left my head spinning.:)

550.32 Service Equipment.

(A) Mobile Home Service Equipment. The mobile home service 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, provided that a dis- connecting 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 accordance with what 550.32(C). Grounding at the disconnecting means shall be in accordance with 250.32.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) sup- plied by feeder(s) or branch circuit(s) shall have a ground- ing electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing ground- ing electrode, the grounding electrode(s) required in 250.50 shall be installed.
 
jumper said:
Maybe, it seems that it comes down to the bolded sentences in these sections and how they directly relate to each other.

I read this thread:

http://forums.mikeholt.com/showthread.php?t=141520

The only thing that I can say for sure is that I am sure is that it left my head spinning.:)

550.32 Service Equipment.

(A) Mobile Home Service Equipment. The mobile home service 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, provided that a dis- connecting 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 accordance with what 550.32(C). Grounding at the disconnecting means shall be in accordance with 250.32.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) sup- plied by feeder(s) or branch circuit(s) shall have a ground- ing electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing ground- ing electrode, the grounding electrode(s) required in 250.50 shall be installed.
Click to expand...

550.16 specifically covers mobile homes and describes the means of grounding.
 
jap said:
A 100 amp feeder is not that big a deal and is quite common actually.

Most job trailers are located fairly close to temporary services so it's usually not a huge cost to get the service put to it, and, I'm not interested in dealing with a general contractor's foreman whose job trailer is 130 degrees in the dead of summer or freezing in the winter because a temporary feed to his trailer wasn't adequate.

Point is, there's no one here that can answer your questions about your install better than the inspector in your area who knows what the local ordinances require.

JAP>
Click to expand...

Let's file this under "You run 100 amp feeders every time, no matter what."

Noted.

Now for everyone else in this thread, I have already investigated any state amendments(W.A.C.) to the code in this instance and haven't found anything pertaining to the questions I'm asking. So it appears I'm only bound to the NEC.

https://www.google.com/url?sa=t&rct...-039-222.pdf&usg=AOvVaw0xmFnVgfaiZtoJKvcLAWz1

Thanks for the help.
 
Craigv said:
550.16 specifically covers mobile homes and describes the means of grounding.
Click to expand...

That is one point of view, I see another in that thread I posted.

At this point, I am just do what I have always done and not worry. Both are safe.

I do like the idea of why it may not be required because of the 30’ limitation of the disconnecting means.
 
Cow said:
Let's file this under "You run 100 amp feeders every time, no matter what..
Click to expand...

Nope

I said I size the feeder for whatever the size of the main is in the panel of the trailer, but that's just me.

If you're planning on using #2 aluminum as was mentioned in your 1st post, you're probably going to find that a 2p 60 or even a 2p 90 is going to be he same price as a 2p 100 so why choke it?

Jap>
 
if the job trailer is manufactured using article 550 as the design there should be a manufactures tag at the feeder conduit stating what the feeder size needs to be something like 240/120 V. 100 amp 4 conductor
 
Keep in mind article 550 does amend article 230 in aspect of where the service equipment is allowed to be located
(within 30 ft. without a permanent foundation)

when the subject is the buildings service the grounding electrode conductor is connected to the service conductors or service equipment in both article 250 or article 550

so connect your grounding electrode conductor to the service equipment neutral wherever the service equipment is located
in your case the service pedestal.

Check for a manufactures tag stating the required feeder conductor min ampacity
 
jumper said:
That is one point of view, I see another in that thread I posted.

At this point, I am just do what I have always done and not worry. Both are safe.

I do like the idea of why it may not be required because of the 30’ limitation of the disconnecting means.
Click to expand...

I read the linked thread. Please see page 1 and the last post. They had it right on page 1. The last post summarizes nicely, including the humor seen in the obfuscations. Some folks like to complicate the simple.

Article 90.3 establishes that the latter articles supersede the earlier articles where they apply to specific installations.

Articles 230 and 250 establish basic grounding and feeder rules.

Article 550 establishes the specifics of feeders and grounding as applied to mobile homes.
 
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