4-wire feeder line vs. 3-wire feeder line


I have a question that I can't seem to find an answer to.
The task is adding a new sub-panel in an outbuilding. I understand that new sub-panels now require a 4-wire feeder line, however this feeder will be coming from the service disconnect. Specifically, it will be coming from a small lug box on the side of the service disconnect; because this is how the existing outbuildings are being fed.
So, my quesiton is: Is the fourth wire required in this situation, coming off the disconnect. If it is required, what is it connected to??
Thanks in advance for any advice! scrapwood.
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scrapwood wrote:

Are you running 120 volts to the out building or 220 volts?
--
Blattus Slafaly ? 3 :) 7/8

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On Oct 8, 9:36 am, scrapwood_at_hotmail_dot snipped-for-privacy@foo.com (scrapwood) wrote:

Run four. It never hurts to upgrade and it is always far more bother and expense to change it later when the need, that you thought would never happen, happens.
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I'm not completely sure I understand your situation, however, if this feeder to the outbuilding is connected to the "load" side of the service disconnect, it will require four wires for a 120/240 volt feeder. Two hot legs, one neutral, and one ground. You may have to drive additional ground rods at the outbuilding as well
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The ground line can be bare and is sometimes wrapped around the others to make a sturdy cable.
But there's another possibility if you have heavy motor loads. What you heard could apply to a 3-phase system and, specifically, a 3-phase "Y" system which has 4 wires.
TKM
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That is not the ground. It is the neutral conductor of an "SEU" type cable

Even if the OP had a 3 phase wye service, it would still require a fifth conductor as it would require three hot legs, one neutral, and one ground

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or run a empty conduit for a future use. cheap choice
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scrapwood had written this in response to http://www.thestuccocompany.com/maintenance/Re-4-wire-feeder-line-vs-3-wire-feeder-line-335437-.htm :
Thanks for all the suggestion guys. After doing further research today, and consulting a knowledgable electrician, I think I have my answer.
First, I have to change out the breaker box and put a load center there so I can have three breakers. The two existing ones plus the new one. Run 3-wire with equipment ground to the new barn. Grounding rod at the sub-panel in the barn. Apparently, grounding rod at the other end is not required. . . unless of course the inspector says it is :)
Thanks for all the suggesitons guys. I sure do appreciate it!
scrapwood. -------------------------------------
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So, what would a delta have? My house has 240V 3 Phase Delta service, four wires come from the pole to the house. Three are standard single phase, two hot, one common. The other is the so called "wild" leg. No ground. Ground is bonded to the water line and tied to a ground rod just under the meter.
Al
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Big Al wrote:

You'd still have 5 wires feeding a sub panel, your three hots (including the "wild" one), your neutral a.k.a. your common, and the ground which is bonded to your neutral at your service entrance. The key thing here is we're talking about what is required to be feeding a sub panel, not what is feeding from the utility to your service disconnecting means.
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