Feeder Questions

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  #1  
Old 12-08-12, 04:16 PM
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Feeder Questions

My mother bought a house recently which has a detached garage served by a 20A feeder. The feeder is 14/2 NM-B run through PVC conduit for about 15 ft. underground until it enters the crawlspace. There is a 14/3 NM-B running through the same conduit,which is a three-way-switch loop. The feeder runs into a fused disconnect switch in the garage.

I am a woodworker so I am converting the roomy two-stall to a modest workshop. I want to upgrade the service to 120/240V 50A. I wish to run 6/3 nonmetallic sheathed cable from the service panel to a junction box in the crawlspace where the conduit enters. There I will splice. Through the conduit I plan to pull four conductors total, but three being stranded 6 AWG THWN. Will 8 0r 10 AWG be appropriate for my EGC?

Also, I wish to keep the three-way switch in the house. Is it acceptable to pull my 2-14 AWG travelers and 1 switch leg conductor in the same raceway, or should I just run 14/3 W/GND UF-B adjacent to the conduit? I would use 1in. for the first case, and 3/4in. for the latter. Also, is it correct that I only need a neutral present in one of the boxes? If so, that already is met in the garage.

It should be said that the circuit with the three-way switches is a branch circuit derived and fused in the garage disconnect. There are not two branch circuits feeding the garage.

I look forward to any feedback and for regulatory purposes, this residence is located in the County of Oceana, MI. More specifically for good measure, Leavitt Twp. In the Village of Walkerville
 
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Old 12-08-12, 04:37 PM
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If I ran all conductors in the raceway, would I need to derate? As I have seen everywhere, I would. So is the UF-B my best bet?
 
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Old 12-08-12, 06:09 PM
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Number 10 copper is the correct size for the equipment ground when the supplying circuit breaker is 60 amperes or less.

Yes, technically you DO need to derate the conductors when there are more than three current carrying conductors. However, in this case you do not count the neutral as it only carries the unbalanced current of the two "hot" conductors and only two of the 3-way switch loop will be carrying current at any one time. Still, that leaves four current carrying conductors but the good thing is that you derate from the 90 degree C. column and for four to six conductors the factor is 80%. That means that you are covered with the #14 switch conductors AND the #6 feeder conductors.

In other words, you are fine and can put all the conductors in the single conduit.
 
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Old 12-08-12, 07:45 PM
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Thanks for your expertise.

I understand neutral and ground must be isolated. Is an additional ground electrode(ground rod) required to be bonded to the ground bus in the subpanel? Is it correct practice to drive an 8' rod, run 6 AWG solid copper to the ground bus, which is bonded to the enclosure, and also connected to the feeder egc? It makes sense to me. All my senses say yes. There are no metallic paths between the garage and house. So what do you say?
 
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Old 12-08-12, 07:55 PM
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I understand neutral and ground must be isolated.
In the subpanel, neutral must be isolated and ground must be bonded.

Is an additional ground electrode(ground rod) required to be bonded to the ground bus in the subpanel? Is it correct practice to drive an 8' rod, run 6 AWG solid copper to the ground bus, which is bonded to the enclosure, and also connected to the feeder egc?
Yes. To be on the safe side, drive two rods, 6' apart, and run the wire through the acorn nut on the first rod before terminating it at the second rod.
 
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Old 12-08-12, 09:08 PM
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That's what I figured. I'll be sure to do that.
 
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