seperate building

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duke70

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I am preparing to supply power to a separate building @ the manufacturing plant were I work. One general lighting circuit and one heating circuit.The separate building is metal framed and is utilized as a smoking area for employees.

Feed is a 4 wire(2 phase conductors,1 grounded conductor/neutral,and 1 equipment grounding conductor), 50A 240v 1ph circuit breaker, from a remote location inside the existing building, supplying a outdoor sub-panel w/ (1) 20A 120V GFCI & (1) 30A 240V GFCI circuit breaker (used as disconnects for separate building), which will be mounted on the outside wall of the existing building. The separate building is 6ft. away from the outside wall(sub-panel) and I am using direct burial cable to supply the fixtures & equipment in the separate building. I will use ground rods to establish ground at the sub-panel and terminate Grounding Electrode Conductor and Equipment Grounding Conductors @ the sub-panel and maintain separation of grounded conductor/neutral. I will bond conduit (housing cable to required burial depth) @ sub panel to the established ground @ sub panel, & bond incoming conduit @ separate building.

Questions:
1. Should I install an additional ground rod(separate of the grounding electrode @ sub-panel) and bond the metal frame of the building through the grounding electrode conductor, since there is no metal path way between the sub-panel and the separate building?

2. Is there anything that I have overlooked or misinterpreted concerning this installation?
 
Re: seperate building

1. Not required.
2. Nope. :)
The separate building is 6ft. away from the outside wall(sub-panel) and I am using direct burial cable to supply the fixtures & equipment in the separate building.
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Do you mean you're using the direct bury cable to feed the panel, and that panel is feeding the heat & lights?
 
Re: seperate building

Thanks for your input.
To clarify:
The sub-panel is located on the outside wall of the exsisting building and fed from inside of the plant. The direct burial cables will supply the equipment inside the separate building from the sub-panel. I did not want to install the sub-panel to the separate structure if possible.
 
Re: seperate building

The only thing I could see as a problem is the disconnect being located on the existing building but exception 1 to 225.32 will allow it since it is under under single management. And the fact it is only 6' away.

Exception No. 1: For installations under single management, where documented safe switching procedures are established and maintained for disconnection, and where the installation is monitored by qualified individuals, the disconnecting means shall be permitted to be located elsewhere on the premises.
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Re: seperate building

Thanks hurk27.
225.32 exception 1, was my basis for prefered location of sub-panel, but created concern of proper grounding and lightining protection of the metal structure (separate building),since I was using direct buried cable and did not have a physical metallic path (ie: conduit) between the metal parts of the sub-panel & metal frame of separate building.
 
Re: seperate building

Originally posted by duke70:
...but created concern of proper grounding and lightining protection of the metal structure (separate building)...
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The grounding electrodes serve the electrical system, not the structure.

With the panel residing on the originating building, the building is fed by two branch circuits as permitted in 225.30(E). Since there is more than one branch circuit, then 250.32(A) will require you to use existing electrodes or install a ground rod (or two), and connect them to the EGC's of the two circuits.

IMO.

But, that does sound a little off. :D
 
Re: seperate building

I don't see why you would need ground rods at the sub panel since it is part of the premisis wiring where the service equipment feeding the sub panel is located. If you ran the sub panel to the second building, then you would need the ground rods.
 
Re: seperate building

Great point Tom. I cant find a reason to install the additional rods since the building itself is effectively grounded.Thanks for comments.
 
Re: seperate building

Believe it or not, most of the protection methods prescribed in the NFPA 780 are designed to protect the structure itself and not the electrical service or other systems such as communication systems.

I for one don't understand how lightning knows not to strike a building or structure supplied with one branch circuit but will strike one supplied with a feeder. :eek:
 
Re: seperate building

Originally posted by bphgravity:
I for one don't understand how lightning knows not to strike a building or structure supplied with one branch circuit but will strike one supplied with a feeder. :eek:
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The same way that tornados know where the mobile home parks are. :p
 
Re: seperate building

Originally posted by m73214:
I don't see why you would need ground rods at the sub panel since it is part of the premisis wiring where the service equipment feeding the sub panel is located. If you ran the sub panel to the second building, then you would need the ground rods.
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No electrodes are required to be connected to the sub panel, since it's attached to the originating building.

Electrodes are required at the detached structure by 250.32(A), because there are more than one branch circuit serving this detached structure. So, despite the lack of a panel, connection to electrodes is required.

Don't ask me why. I'm just reciting it as I see it. An odd installation such as this calls out the oddities in the code. :D

Originally posted by bphgravity:
Believe it or not, most of the protection methods prescribed in the NFPA 780 are designed to protect the structure itself and not the electrical service or other systems such as communication systems.
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But in terms of the NEC, the grounding electrodes required are required for the electrical system irrespective of the structure itself, right?
 
Re: seperate building

George thanks again for your continued input. Am I to understand that that the exsisting building is not considered effectively grounded through the grounding electrode system?

Would mounting the sub-panel on the separate structure make for a less odd installation? I would prefer more standardized/accepted practices observed over location preference.
 
Re: seperate building

Duke.......If I were you, I'd put a sub panel in the detached building. Based on the info you provided, I would run #4 AL SER to a MLO panel backfed with a 70 A main breaker. Drive two ground rods, connect the GEC to the ground bar and be done with it. Be sure to look at Table 300-5 ( I hope that is still accurate ) for minimum cover requirements for any raceway you install between the two buildings.
 
Re: seperate building

Tom, as long as the supplying panel has the properly-sized breaker to protect the feeder, the sub-panel can be a simple 100-amp MB panel, which might be cheaper than an MLO-panel and a 70-amp breaker.

The sub-panel requires a main disconnect, but not a main OCP device, so this breaker can be bigger than the feeder's rating. Unless I'm wrong, of course.
 
Re: seperate building

Originally posted by LarryFine:
Tom, as long as the supplying panel has the properly-sized breaker to protect the feeder, the sub-panel can be a simple 100-amp MB panel, which might be cheaper than an MLO-panel and a 70-amp breaker.
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Great point Larry. That would definitely be the less expensive way to go.

Also, maybe I shouldn't be so presumptuous as to think you could use SE-R in your building. If not, install a raceway for the entire run and use THWN.

[ January 25, 2006, 02:26 PM: Message edited by: m73214 ]
 
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