what to do?


Old 12-02-05, 01:55 PM
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Location: Taylorsville, MD
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what to do? *UPDATE*

OK, in the process of running electric to a pole barn. Have the line trenched and 2/2/2/4 AL wire from trench to a junction box in basement.

Was going to run 2/2/2/4 grey sheathed wire in basement to load center in my MIL's portion of the house (its the closest to the barn). We are actually two houses joined together...so we have 3 panels in our house, 2 on our side and hers is a subpanel off of ours...Her panel is filled, so I figured I would use some tandem breakers to free up enough room for a 60 amp breaker for the barn. Turns out the Square-D panel she has won't accept tandems.

so now i'm in a quandry...

- I can run the 2/2/2/4 sheathed wire over to my panel adding another 78 feet to the run, bring the total distance breaker-to-breaker at 250ft. I've read that the max voltage drop is either 2, 3, 4, or 5%. Depneding on which online vltage drop calculator you use, the drop would be between 2 and 4.5%...Is voltage drop only a concern when you are using all 60 amps at a given time? I'm only planning to have 2-20a breakers in the barn for lights and such, the only thing that would be on a lot is the fan in the summer and the trough heater in the winter, and they would most likely have a dedicated circuit for them.

- Add a small subpanel off of the MIL's panel to house a few breakers.

- Is there anyway to "piggyback" onto her subpanel without using a breaker there...the only 60a breaker would be at the barn.

thanks for any input...right now i'm at a standstill!

*UPDATE* I went to the panel on my side of the house...there were 2 tandem breakers that were spares...they had been tweaked to fit any panel by the electrician who did the house originally...what are the risks of using them in my MIL's panel, since they will fit?

Last edited by mathey; 12-02-05 at 04:17 PM.
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Old 12-02-05, 02:12 PM
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Adding a subpanel off a subpanel is okay, but it further partitions the available power, and doesn't offer much flexibility in the use of that power. So it's much better to run the barn feed from the main panel.

The electricity has to travel all the way to the barn whether it runs from the main panel to the subpanel to the barn, or straight from the main panel to the barn. In fact, bypassing the subpanel will probably reduce the voltage drop.

And yes, the actual instantaneous voltage drop is proportional to the amount of power used at that instant. So the voltage drop would be less when you are using less power. Based on what you said you plan to run in the barn, and the size of the feeder you are using, it doesn't seem like voltage drop will be much of a problem.

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