70 amp service to shed

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Old 05-01-19, 06:21 AM
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70 amp service to shed

Hello,
I'm hoping someone can offer some advice, I'm really stuck at this point.

I planed to build a shed and run a 70 amp service out to it, which is a 75' run.
I looked at my breaker panel and saw that I had 4 slots open and didn't give that much more thought. I then built the shed and I'm ready to run the electrical.

The problem is, the four slots are unusable, and at closer look, the previous owner has put in a few mini breakers.I don't know how to proceed at this point.

Any help would be great.
Dan
Can I add a 70 amp breaker to this panel? If so, what is the best way to proceed?
 
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Old 05-01-19, 06:45 AM
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This is called a split-bus panel. The upper section of the panel is always hot. The top left breaker (1,3) is the main breaker for the lower section of the panel.

You could add a double-pole breaker to feed the shed in either of the open spots (11,13) or (12,14); however it's not yet clear that you should. One catch with split-bus panels is that all of the 6 breakers in the upper section combined together make up your service main breaker. Adding another breaker to this section essentially increases the size of your incoming service, which should only be done if you know the service wiring is large enough to handle it. The panel is listed at 150A and the incoming wiring appears consistent with that.

How much actual load are you adding in the shed? Appx how big is the house and are you using the large electrical appliances (water heater, cooking, HVAC)?
 
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Old 05-01-19, 07:19 AM
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An electrical project of this size should have a load analysis done. One set of rules is at the back of the NEC.

It is possible that you will need a larger (higher amperage) service.

Unlike for the breakers in the lower half of the panel, the sum of the ratings for the (up to) 6 breakers in the upper half of the split bus panel must not exceed the service amperage rating (for service entrance cable, meter, service drop).

There is also a limit on the number of breakers and/or breaker handles in the lower half. This spec should be on the panel label. This will limit how many full width breakers may be replaced with half width (tandem) breakers.
 
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Old 05-01-19, 07:38 AM
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The 4 installed mains already exceed the listed 150 max amps. ???
 
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Old 05-01-19, 09:07 AM
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Hello,
Thank you all for the information, it is a 150 Amp service coming into the house. The Water heater is Gas but the HVAC, stove, and other normal appliances are electric. It is not a huge house about 2000sf.

Because I haven't bought anything yet, I could go lower on the service to the shed, 60 or 50 amp is as low as I would like to go.

I didn't think I could add a breaker to the 11,13 or 12,14 because it does not have a lip for the breaker to hook onto in that space. But I'm not familiar with this. I have added and replaced breakers in previous homes, so I thought this may not be that big of a job.

I'll take any further advice you have for me, but it may just be time to call a pro and go from there. I want to be safe, and I'm going to get it inspected by Fair fax county, so I want it to go well.
Dan
 
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Old 05-01-19, 09:12 AM
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Those 2 spaces are just like the spaces the existing 4 breakers are in. The breaker hooks on to the metal lip of the panel back plate.
 
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Old 05-01-19, 09:51 AM
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The 100% correct way to do it is to keep the sum of the breaker handles in the upper section at or below 150A; or to replace the split-bus panel with a modern main breaker panel, at which point you can have as many breaker handles as you want as long as actual load doesn't exceed 150A. I don't think that you're actually in danger of going over, but the code doesn't care about guesses.
 
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