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Power to Detached Office

leafer3's Avatar

Join Date: Mar 2018
Posts: 3

03-06-18, 04:22 PM   #1  
Power to Detached Office

Hi All!

I had a company build a 12X20 foot shed in the yard for me to use as an office. I am having a hard time trying to figure out what type of sub-panel and feed to install. The office is two hundred feet away from my house. (main panel) I'm having a hard time calculating the AMP requirements. Someone sent me an actual electrical calculator to plug in numbers and figure out the load but that is all very confusing. Am I supposed to track down every device I plan to plug in and look for a sticker to get the electrical draw for that device then come up with a total?

I'm not even exactly sure what I would use at the end of the day but I know that I would have six to eight LED light bulbs, laptop, three monitors, large flat screen TV, 500 watt AMP / speakers, Portable AC/Heat Pump Unit (prob 10 amps), and various electronic equipment. (smaller things like phone charger, laptop docking station, modem)

I was thinking I may need 100AMP sub-panel, but I've been told that is overkill. Would 60 AMP do the job? If so what wire should I use for the 200 feet run? I used to work as an electrician's assistant so I am very well acquainted with the "work" involved. I never really designed layouts or had to deal with load calculations before.

Any suggestions would be great!

Thank you

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PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 41,959

03-06-18, 05:39 PM   #2  
Welcome to the forums.

A 60A 240v sub panel should be more than enough for your needs.
2-3) 20A 120v receptacle circuits.
1) 15A lighting circuit.

Because of the distance.... the wiring will need to be upsized due to the voltage drop.
Are you looking for direct burial wiring or will you be using conduit ?

I'd recommend 1-1/4" or 1-1/2" PVC conduit and at least #4 copper. You will need 4 wires.... two hots, a neutral and a ground. The ground can be smaller than the hot wires. You will also need a ground rod at the shed/office.

Others will add input.

~ Pete ~

leafer3's Avatar

Join Date: Mar 2018
Posts: 3

03-07-18, 05:32 AM   #3  

Yes I'm going with 1 1/2 inch PVC. That is pretty much the setup I was looking at. I was just worried that the 60AMP wouldn't be enough. It looks like I might be OK with the 60. What are your thoughts on aluminum wire vs copper? I'm on a pretty tight budget and just looking for any way I can cut cost or if its even worth it.

Thank you for your warm welcome.

pattenp's Avatar

Join Date: Feb 2016
Posts: 701

03-07-18, 06:17 AM   #4  
At 200ft I would seriously consider aluminum wire. If your max load is 60A or less you can get by with #2 Al. If using conduit the whole run l would use XHHW-2 in sizes of #2 for the phase and neutral conductors and a #4 for the ground. Because you are upsizing the current carrying conductors for voltage drop the ground conductor also needs to be upsized proportionately to the other conductors..

AllanJ's Avatar

Join Date: Mar 2010
Posts: 2,738

03-07-18, 11:17 AM   #5  
Get out (or buy) a copy of the National Electric Code book (NEC) and a crystal ball. At the back of the NEC is one set of rules to compute the power needs for your entire house including the office outbuilding. This in turn will determine what ampacity you need for the outbuilding and also whether the main house service needs to be upgraded to accommodate that load.

A good sized outbuilding or barn with a lot of activity or even a workshop can get by with 60 amps (at 240 volts) with no problems provided you are not using electric space heaters or water heater.

leafer3's Avatar

Join Date: Mar 2018
Posts: 3

03-08-18, 05:09 PM   #6  
Thank you for all your help.

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