Wiring a shed

Old 03-13-04, 02:19 PM
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Wiring a shed

I want to run power to a shed at the back of my property. I will be running shop equipment table saw, drill, etc. The shed is about 200ft from my house. I plan on wiring a sub panel in the shed with 2 circuits. I need to know what gauge of romex to use and any suggestions on what kind of breaker I should use or any thing else would be greatly appreciated.

Thanx in advance
Old 03-13-04, 07:04 PM
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There are lots of tradeoffs. Cost vs. difficult vs. extensibility.

The design considerations also involve how well you can balance the loads on the two circuits. Strange as this may soulnd, 10-amps of load simultaneously on each of the two circuits will cause less voltage drop than running 10-amps of load on only one of the circuits.

Unfortunately, with one person running a table saw on one circuit and a few lights on the other, the load is not very well balanced. So that means that you really need to compute the voltage drop as a 120-volt feeder, even though it is really a 240-volt feeder.

200 feet is a pretty long ways. I'm not sure whether that's 200 feet of cable length panel to panel, or 200 feet as you walk it. Either way, it's a long ways. I suggest you run at least 8/3 UF-B. If you ever think your needs will grow, consider 6/3 UF-B instead. Bury it 24 inches deep.
Old 03-14-04, 06:10 AM
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For this application, you might want to find out if your table saw motor can run at 240V. In many cases motors are 'dual voltage', and can operate at higher voltage simply by changing some internal connections. You would additionally have to change the control switches to double pole switches, and change the sort of cord on the saw.

The reason is that _for the same power_ the higher voltage motor will draw less current. The less current drawn on a line, the less the voltage drop caused by the resistance of the line. On top of this, the higher the voltage of the load, the greater the tolerable voltage drop. The net result is that the effective voltage drop is reduced by a factor of 4.

Consider that if you were running a saw that took 15A at 120V. You have 200 feet of 8/3 wire. The voltage drop works out to be 4.6V or 3.8%. Run the same saw (properly rewired, of course) at 240V. The current required is 7.5A, the voltage drop is 2.3V, and the percentage voltage drop only 0.9%. Under full load, these voltage drops don't make much difference, but when starting the motor the current demand is momentarily much higher than 'full load', and switching to 240V might mean the difference between a momentary 20% voltage drop and a 5% drop.


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