Subpanel for trailer

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  #1  
Old 04-06-05, 04:14 PM
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Subpanel for trailer

My son recently purchased a used 8’ x 28’ construction trailer that is 9 years old. It is in real good shape. My son had it hauled and placed on his undeveloped property out of state. We are going to use it as shelter during hunting season in the fall and fishing in the summer during vacations.

Over the past 10-12 years we were using a popup camper and simply plugged in an extension cord to the existing service.

The service that we had installed 12 years ago is a 100 amp Square D, rain tight, service panel on a pressure treated 4” x 4”. The trailer is located approximately 25 ft. from this panel.

The trailer has a Bryant sub panel with a double pole 50 amp back fed breaker as the main.
The trailer has:
2 – 15 A, 115 V wall AC units.
3 – 240/208 V, 1000/750 W baseboard electric heaters
3 – 40 watt fluorescent light fixtures

All of the above are working.

In addition we plan to put in a small college dorm type microwave and refrigerator, Direct TV and whatever we feel will make life comfortable while “roughing it”.

I plan to put a 50-amp double-pole Square D breaker in the existing service panel to feed the trailer’s sub panel. I am running 4 - #6 THWN for the feed to the trailer in underground PVC conduit. (2 – hot, 1-neutral and 1- equipment ground).

I have 3 questions:

1. Do I drive a ground rod at the trailer?
2. The existing panel has separate neutral and ground buses. The neutral bus is isolated from the panel enclosure. Do I leave it that way or bond it to the ground bus?
3. The trailer’s undercarriage is made of 2 steel beams running the full 28’ length with several steel beams running across the 8’ width connecting the 2 lengthwise beams. All are welded together to create the undercarriage. Do I bond this undercarriage to ground?

Hope that the above is clear. Any guidance would be genuinely appreciated.
 
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  #2  
Old 04-06-05, 04:54 PM
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1. Yes.
2. Leave it alone. But it must already be bonded somewhere. Is there a main disconnect switch and/or main breakers outside the existing panel? Or maybe it's really bonded in this panel in a way that escapes your notice.
3. Not sure if it's required, but it sounds like a good idea to me. Anybody else agree or disagree?
 
  #3  
Old 04-06-05, 05:55 PM
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Originally Posted by John Nelson
1. Yes.
2. Leave it alone. But it must already be bonded somewhere. Is there a main disconnect switch and/or main breakers outside the existing panel? Or maybe it's really bonded in this panel in a way that escapes your notice.
3. Not sure if it's required, but it sounds like a good idea to me. Anybody else agree or disagree?
Hi John,

Thank you for your prompt response.

In #2 above, you say that it "must already be bonded somewhere". I checked both the neutral & ground bus with a continuity tester. There are not bonded. There is no continuity between the neutral bus and the enclosure. The mounting screws for the neutral bus are insulated from bus by way of plastic or other dielectric material. They seem to have treated this installation as a detached garage would be wired. Why do you say it must be bonded?

There is no main disconnect or main breaker outside the main panel. The feed to the panel came through the floor from the outside in a 1-1/4” conduit stub.

Regards,
Mike
 
  #4  
Old 04-06-05, 06:25 PM
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If there is no bonding anywhere between neutral and ground, then all of your equipment grounding wires are useless. They provide no safety. If a fault to ground should occur, there would be insufficient current to trip the breaker.
 
  #5  
Old 04-06-05, 06:34 PM
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This would be treated the same as a mobile home.
The trailer frame must be bonded to the panel. I would use #8cu as this is most likely a 100 amp panel, regardless of how it is backfed. Keep the grounds and neutrals isolated in the trailer.

John saying there must be a bond somewhere means at the service. I would assume the main breaker enclosure at the post is bonded as is typical. This is appropriate.

Just run a 4-wire feeder from the main on the post to the trailer and do not sink a ground rod. Do bond the frame.

If you are just running a 50 amp feeder to the trailer I would install a 50 amp breaker at the post to feed the trailer. This is protecting the feeder conductors, not the trailer.

Have fun "roughing it".
 
  #6  
Old 04-06-05, 06:39 PM
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Originally Posted by John Nelson
If there is no bonding anywhere between neutral and ground, then all of your equipment grounding wires are useless. They provide no safety. If a fault to ground should occur, there would be insufficient current to trip the breaker.

Hi John,

There will be a bond at the existing service panel on the pole where I will get the feed for the subpanel. The ground and neutral will terminate on a common bus there. I was not aware that the neutrals & grounds must be bonded in a subpanel in the trailer.

Thank you and Regards,
Mike
 
  #7  
Old 04-07-05, 04:28 AM
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Originally Posted by Speedy Petey
This would be treated the same as a mobile home.
The trailer frame must be bonded to the panel. I would use #8cu as this is most likely a 100 amp panel, regardless of how it is backfed. Keep the grounds and neutrals isolated in the trailer.

John saying there must be a bond somewhere means at the service. I would assume the main breaker enclosure at the post is bonded as is typical. This is appropriate.

Just run a 4-wire feeder from the main on the post to the trailer and do not sink a ground rod. Do bond the frame.

If you are just running a 50 amp feeder to the trailer I would install a 50 amp breaker at the post to feed the trailer. This is protecting the feeder conductors, not the trailer.

Have fun "roughing it".

Hi Speedy Petey,

Thank you for your reply and the clarification.

When John said, <i><b>“Is there a main disconnect switch and/or main breakers outside the existing panel?”</b></i>, I thought he was asking if their was another disconnect switch and/or main breaker, <b>in or on the trailer itself</b>, in addition to the existing subpanel. I apologize for my misunderstanding of the question.

I have another question.
The bottom of the existing service panel on the pole is approximately 36” above grade. The bottom of the trailer floor is approximately 22” above grade. Is it okay to use PVC conduit and fittings for these above grade runs? or….. Do I have to use galvanized steel conduit? The reason I ask is, I do not know of any electrical suppliers that will cut & thread the (2) steel conduit lengths. Do you have any suggestions or work arounds?

Regards,
Mike
 
  #8  
Old 04-07-05, 05:23 AM
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PVC is fine for this. Use schedule 80 for the above grade sections.
 
  #9  
Old 04-07-05, 05:50 AM
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John & Speedy Petey,

Thank you both for your prompt, courteous and knowledgeable responses. It sure does make these kinds of DIY projects easier and more enjoyable when one is pointed in the right direction.

I will post an update, after this is completed, for anyone that may be interested in the results and/or problems that we encounter while trenching. We are going to rent a ditch witch.

Again, thank you. I genuinely appreciate your guidance.

Regards,
Mike
 
  #10  
Old 04-07-05, 06:07 AM
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good morning, this would be considered a mobile home service, the service pole is within 30 ft of the trailer. The ground rod should be at the pole. You may find the chassis is already bonded to the trailer panel with #8 awg, hooked up to the ground bar. If there is, you still may want to check the connection at the chassis, it should be in an accessible area, i've seen a lot of loose lugs, corroded connections here that have given trouble in the past.
 
  #11  
Old 04-07-05, 06:29 AM
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Originally Posted by Jedi9
good morning, this would be considered a mobile home service, the service pole is within 30 ft of the trailer. The ground rod should be at the pole. You may find the chassis is already bonded to the trailer panel with #8 awg, hooked up to the ground bar. If there is, you still may want to check the connection at the chassis, it should be in an accessible area, i've seen a lot of loose lugs, corroded connections here that have given trouble in the past.
Hi Jedi9,

Thank you for your suggestion.

There is a 5/8" driven ground rod at the service panel location. It has a #8 bare copper wire connected to it, which runs back to the ground bus in the service panel.

I did look under the chassis when I was there 2 weeks ago. There were 2 #500 beam clamps, clamped to the lip of the beam. A ground wire was not attached; I assume they may have been used for grounding. I am going to get 2 new suitable clamps and bond a #8 bare copper wire from the beam to the ground bus in the trailer's sub panel. I guess that 2 were used for redundancy because of safety. It may be an OSHA requirement for construction sites.

Regards,
Mike
 
  #12  
Old 04-07-05, 08:29 AM
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I checked both the neutral & ground bus with a continuity tester. There are not bonded. There is no continuity between the neutral bus and the enclosure.
This is the comment that concerned me. If there was a bond at the service, there would be continuity at the panel, right?
 
  #13  
Old 04-07-05, 09:07 AM
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Originally Posted by John Nelson
This is the comment that concerned me. If there was a bond at the service, there would be continuity at the panel, right?

Hi John,

Thank you for your follow-up.

I apologize for being vague in my reply concerning the above. I should have emphasized that the 4 wire feed from the existing service panel on the post to the subpanel in the trailer will not be installed until the weekend of April 23 & 24.

When the feed is installed, the neutral and equipment ground will be terminated (married) in the <b>service panel on the post. </b> The connections of the neutral and equipment ground will be isolated from each other in the <b>subpanel of the trailer.</b> When continuity is tested between the <b>trailer's neutral and ground bus,</b> it will then show continuity because of the marriage of the neutral and ground bus at the <b>service panel on the post.</b>

Again, thank you for your follow-up and apologies for my initial vagueness.

Regards,
Mike
 
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