grounding multiple services

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scroot

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I am working at a high school where 5 mobile home (trailer) type classroom outbuildings are being installed. The power company would not provide 5 drops for us. Instead they made us install a distribution panel so they could provide one larger service drop. The distribution panel has a main breaker and 5 branch breakers. We will be bonding neutral and ground at this panel. The question is: Do we have to run a separate ground to each trailer? Currently the drawings show the 2 phases and a grounded conductor from the distribution panel to each trailer. At each trailer, a ground rod will be installed and the neutral and ground bonded just like a service entrance in the usual means.
Should we be including a ground wire (4th wire) in these branch service feeds?
 
You would have to meet the requirements laid out in 250.32(B)(2) to not include an equipment grounding conductor with the feeders brought to each trailer.

Should we be including a ground wire (4th wire) in these branch service feeds?
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I would suggest including an equipment grounding conductor in the feeder.

JMHO,

Chris
 
These units will probably have some other conductive paths bonded to the grounding system in each building or structure which will mean the fourth conductor will be required as pointed out by Chris.

These other conductive paths could simply be Phone, Data or TV cables.

Roger
 
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550

550

I beleive 550 applies to mobile homes being used as dwelling units..not classrooms. (look at the definition of mobile home in 550)
 
scroot said:
Should we be including a ground wire (4th wire) in these branch service feeds?
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In my opinion, absolutely. While it's arguable whether eliminating the EGC is meant for existing installations, since this is a new install, there's no good reason to do so here. Run the EGC.
 
augie47 said:
I beleive 550 applies to mobile homes being used as dwelling units..not classrooms. (look at the definition of mobile home in 550)
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550.4(A) Mobile homes not intended as a dwelling unit. Farther on down the paragraph......it shall,however, meet all other requirements of this article....That is why I believe 550.33 requires an insulated EGC.
 
I would be suprised if these trailers were really a mobile home or a manufactured home as defined in Article 550. I rather suspect that there are mobile classrooms, which wouldn't fall under Article 550.

Chris
 
scroot said:
I am working at a high school where 5 mobile home (trailer) type classroom outbuildings are being installed. The power company would not provide 5 drops for us. Instead they made us install a distribution panel so they could provide one larger service drop. The distribution panel has a main breaker and 5 branch breakers. We will be bonding neutral and ground at this panel. The question is: Do we have to run a separate ground to each trailer? Currently the drawings show the 2 phases and a grounded conductor from the distribution panel to each trailer. At each trailer, a ground rod will be installed and the neutral and ground bonded just like a service entrance in the usual means.
Should we be including a ground wire (4th wire) in these branch service feeds?
Click to expand...

The ground wire (4th wire) in the branch service (I call it feeder) is absolutely required as the effective ground fault current path. A ground rod shall be installed at each trailer for lightning protection. But you cannot bond neutral and ground at trailer like service entrance. The only bonding point for the system is the distribution panel. Just my opnion.
 
dahualin said:
The ground wire (4th wire) in the branch service (I call it feeder) is absolutely required as the effective ground fault current path.
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David, with no more information than what was given, making the statement "the 4th wire in this particular feeder is absolutely required" could very possibly be wrong.

If there are no other possible neutral paths, a three wire feeder could be used and the Neutral could be regrounded at the individual buildings.

See 250.32(B)(2)

Roger
 
raider1 said:
I would be suprised if these trailers were really a mobile home or a manufactured home as defined in Article 550. I rather suspect that there are mobile classrooms, which wouldn't fall under Article 550.

Chris
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If the trailers don't fall under art. 550, what is the purpose of 550.4(A)? The examples given in the section are not dwelling units,yet, they still must comply with the article.
 
rcarroll said:
If the trailers don't fall under art. 550, what is the purpose of 550.4(A)? The examples given in the section are not dwelling units,yet, they still must comply with the article.
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True, the examples given are not dwelling units, but for Article 550 to apply you have to start with a mobile or manufactured home.

I don't believe that the OP ever had a true mobile or manufactured home as defined in Article 550 to begin with.

I believe that if I have a mobile home or a manufactured home and I choose to use this as a construction trailer or to display merchandise, then 550.4(A) would apply.

The definitions of mobile and manufactured home, both include the term "designed to be used as a dwelling". A mobile classroom that was never designed to be a dwelling wouldn't be a mobile or manufactured home.

JMHO,

Chris
 
In my opinion, whether the trailers are/were for use as dwellings is not relevant. What is relevant is that these will be sub-panels and the cables have not yet been run.

The odds are that some additional wiring will be run, whether phone, coax, PA, etc. What is a good reason for not using EGC's? The difference in cost of the wire?
 
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