feeder conductors for subpanels for detatched buildings

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steelersman

steelersman

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Lake Ridge, VA
Hi guys. I was hoping to get some clarification about the types of cabling allowed to feed sub-panels in detatched buildings. I was told that you must use 3-wire instead of 4-wire and drive a ground rod for the new sub-panel if it's a detatched building, but if it's attatched then 4-wire is fine. Is this true and also if so which year of codebook did that change, because I've always used 4-wire and never driven a ground rod for the new sub-panel. Also if 3-wire is fine then can you use USE for direct burial and just protect it with pvc where it comes up from the ground? I just want to get a better understanding of this and also the USE. I've never used it and don't understand where and how it's able to be used. It seems like the kind of cable the power companies use. Thanks.
 
Until 2008 a three wire feeder was allowed if there were no other grounded paths between the structures. You would treat the installation as if it were a service.

In 2008 this was changed and an EGC must be included which is bonded to the remote panel and the Grounding Electrode at the detached building.

A gorund rod (GE) was required in the past so you were actually in violation.

See 250.32(B)

Roger
 
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roger said:
Until 2008 a three wire feeder was allowed if there were no other grounded paths between the structures. You would treat the installation as if it were a service.

In 2008 this was changed and an EGC must be included which is bonded to the remote panel and the Grounding Electrode at the detached building.

A gorund rod (GE) was required in the past so you were actually in violation.

See 250.32(B)

Roger
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so for the 08 you do need 4 conductors, deeping the ground and neutral seperate in the remote panel and also will need a ground rod (electrode)?
 
steelersman said:
so for the 08 you do need 4 conductors, deeping the ground and neutral seperate in the remote panel and also will need a ground rod (electrode)?
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Yes you will need 2 ground rods connected to the egc and a main disco.
 
steelersman said:
so for the 08 you do need 4 conductors, deeping the ground and neutral seperate in the remote panel and also will need a ground rod (electrode)?
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Yes, and probably two ground rods as Dennis mentions.

Roger
 
steelersman said:
so do they make USE in 4 conductor?
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Yes they do.

6065809.jpg
 
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steelersman said:
slammin. now would the OCPD in the main panel count as the main disco?
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No -- you need to read art. 225 Part II. Basically it needs no more than 6 handles to disconnect the building as you would in a home. Generally I use a main breaker panel or I use a breaker on the bus with a main breaker kit to hold the breaker in place.
 
steelersman said:
this is only per 08 code though right? 05 code this wasn't the case correct?
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No this was always the case as long as I could remember. Unless you mean the 4 wires then I would say yes that is new in the 08 code.
 
steelersman said:
this is only per 08 code though right? 05 code this wasn't the case correct?
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It was the same in 05

Roger
 
Dennis Alwon said:
No this was always the case as long as I could remember. Unless you mean the 4 wires then I would say yes that is new in the 08 code.
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well I've always used main lug sub-panels and they were almost always out of sight of the main panel (which had the only means of disconnecting it) and it's always passed. Also a while back I started a thread and asked about an disagreement a friend and I were having. He said that sub-panels had to have a main breaker or a breaker lockoff on the breaker in the main panel if it was out of sight. I said no way and posted it on here and from what I remember everyone agreed with me. I'm going to try to search for that thread now and post a link to it.
 
steelersman said:
well I've always used main lug sub-panels and they were almost always out of sight of the main panel (which had the only means of disconnecting it) and it's always passed. Also a while back I started a thread and asked about an disagreement a friend and I were having. He said that sub-panels had to have a main breaker or a breaker lockoff on the breaker in the main panel if it was out of sight. I said no way and posted it on here and from what I remember everyone agreed with me. I'm going to try to search for that thread now and post a link to it.
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here it is: http://forums.mikeholt.com/showthread.php?t=102354
 
steelersman said:
well I've always used main lug sub-panels and they were almost always out of sight of the main panel (which had the only means of disconnecting it) and it's always passed. Also a while back I started a thread and asked about an disagreement a friend and I were having. He said that sub-panels had to have a main breaker or a breaker lockoff on the breaker in the main panel if it was out of sight. I said no way and posted it on here and from what I remember everyone agreed with me. I'm going to try to search for that thread now and post a link to it.
Click to expand...

A sub panel in a house is a very different animal than a panel in a detached building.
 
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