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Old 03-16-2011, 03:24 PM   #1
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How to get 200 amp subpanel in garage


I want to get a 200amp sub in my detached garage (because I am converting the loft in that garage to a 600 sq ft apartment with 3 electric wall mount heaters, electric HWH, jetted tub, W/D, range, microwave, TV, reefer, dishwasher, freezer, also outlets in garage that will occasionally power a medium compressor, tablesaw and other power tools).

My home is gas heated, has a Square D all-in-one main with meter on the outside of my home, and powers a 200 amp sub inside the home. The service panel has a 200 amp disconnect for the 200 amp sub.

Reading the labeling on the service panel, it seems that the max breaker I can add is 100 amp, and further reading indicates that the combined rating of service disconnects shall not exceed 250 amps, which would further limit me to a 50 amp breaker.

I really don't want to get a meter for the garage/apartment because the utility has a $92 base charge per month for the extra service. I hope there is some option like tapping into the meter side of the all-in-one and installing a 200 disconnect box near the service that would feed the garage panel. Here's to hoping....

Any advice or ideas on layout would be great!

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Old 03-16-2011, 05:53 PM   #2
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How to get 200 amp subpanel in garage


Your feed from the transformer to your meter has to be capable of supporting 400 amps. I think you need to have a discussion with your power company.

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Old 03-16-2011, 07:02 PM   #3
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How to get 200 amp subpanel in garage


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I want to get a 200amp sub in my detached garage (because I am converting the loft in that garage to a 600 sq ft apartment with 3 electric wall mount heaters, electric HWH, jetted tub, W/D, range, microwave, TV, reefer, dishwasher, freezer, also outlets in garage that will occasionally power a medium compressor, tablesaw and other power tools).
Are you going to rent it out? If so it's worth the extra meter.
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Old 03-16-2011, 10:04 PM   #4
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How to get 200 amp subpanel in garage


No plan to rent, although family may stay. I have no need for a meter, especially at $1100 per year. Besides, a few hundred would get me my own private meter if I needed to know the difference in power usage.
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Old 03-16-2011, 10:11 PM   #5
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How to get 200 amp subpanel in garage


You bring up a good point; I assumed that the service drop (which they upgraded last year) would be sufficient, but that is based on no evidence. I will call them-thanks for the tip.
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Old 03-17-2011, 12:20 AM   #6
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How to get 200 amp subpanel in garage


BEFORE YOU DO ANY OF THIS: CONTACT YOUR AHJ AND MAKE SURE THIS IS ALLOWED AND IF YOU NEED ANY SPECIFIC TYPE OF CONNECTIONS. Your AHJ ALWAYS has the FINAL say in these matters. I strongly suggest that you get an electrician to do this AND have a permit pulled. If you desire to do this yourself with limited knowledge then it is your prerogative.

You do not need to have a 400 amp service.

You can split your feed coming off the all in one. As long as there is a breaker protecting your meter side that is no larger than 200 amps, you are fine. You said "Service Disconnects" to my knowledge this means the breaker DIRECTLY after the meter...

Now, the hard part is splitting your service. You will need to actually rewire between the all in one and your sub panels.

You will probably have to make this connection inside a tangle box (NEMA 3R), but use something like the "IT" series connectors to split your wires. You will need one that has 3 ports for all 4 wires. Make sure that it is rated for the type of wire (Al or Cu).

Make the connection at your lugs on the All in one, bring it to the tangle box and then to the splice blocks. Bring in your two subpanel feeds into the blocks.

Make sure your wire sizes are calculated for voltage drop and using the standard table, NOT service entry sizing for the Out building.

http://www.tork.com/Catalogs/ePolaris.pdf

Its relatively easy and simple. The theory behind this is to remember that the main on the all in one will not allow more than 200 amps to be drawn through the meter, all in one on on the service from the all in one. If this is maintained, you can split wires to your hearts delight as long as voltage drop is accounted for.

You will almost NEVER pull 200 amps regularly, so why put a 400 Amp service in?

Now, remember I say this assuming you are not using a resistive heat system in both buildings, just in the out building. 600 sq ft doesnt require more than maybe 6-7kW which is about 30 amps @ 240vac.
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Old 03-17-2011, 08:34 AM   #7
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How to get 200 amp subpanel in garage


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Reading the labeling on the service panel, it seems that the max breaker I can add is 100 amp, and further reading indicates that the combined rating of service disconnects shall not exceed 250 amps, which would further limit me to a 50 amp breaker.
I re-read your first posting and caught this.
Adding a breaker to feed a sub panel is not a service disconnect. I think you should calculate your load to this building and and look at whether a 100 amp feed would be enough. It sure would simplify your project.
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Old 03-17-2011, 11:56 AM   #8
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How to get 200 amp subpanel in garage


Why not use gas everywhere you can in the apartment and install a 100 amp feeder to a 100 amp main lug panel. 100 amps is what many homes in the 1500 square foot range have installed. 100 amps may/should be all you need for your present plan.
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Old 03-17-2011, 01:58 PM   #9
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How to get 200 amp subpanel in garage


Wow, you folks are a huge help. First, thanks to Leah: the new meter is the smart longterm path because we all know apartments tend to get rented by someone. I simply can't afford to let the city get their hands in my pocket.

Thanks A7eCorsair, I will check on the 250 amp maximum for service disconnects at the all in one. After reading Lyons reasoning (re: as long as the amp draw on the meter, all-in-one and feeds are limited by the service disconnect), I believe you are right; my only concern would be nuisance tripping, and I don't see that kind of power usage.

Thanks J.V., I will do a more careful load calculation today. It would simplify life to go with a 100 amp panel. I think I recall that my load would have to be 80 amps or less to use a 100 amp panel, and my quick math suggested I would have a load of just over 100 amps (if everything was on and I was in the garage using the table saw and compressor at the same time!)

Lyons, thanks for the tip on splitting the feed (and subsequently correcting my bonehead idea of tying in upstream of the 200 amp service disconnect rather than downstream where the load is controlled). Should I calculate that 100 amps won't suffice, I can see going that direction. I will pull a permit but I can't afford a good electrician. I always talk to my inspector first; they are helpful as long as I don't ask them to lay out my work. I'm pretty capable and should be able to pull it off. Of course I'll turn a three hour job into two days.
To clarify, the tangle box is used to house the block where the splice occurs? And could I re-route the feed (serving my 200 amp sub in the main house) to the tangle box? The wire is the aluminum stuff we see on all the service stuff, 4-0,4-0,2-0 I believe.

Thanks again, all. I'll repost when I know more.
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Old 03-17-2011, 02:27 PM   #10
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How to get 200 amp subpanel in garage


After looking at a chart of common appliances and average wattage, figuring everything in amps gets me to 180 amps. It seems insane to me; there will never be a time when all of this is on simultaneously. Am I going about this wrong? I mean, when the weather is cold and my wife is baking a pie, can't I just refrain from drying clothes, running the compressor and table saw while vacuuming?
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Old 03-17-2011, 03:19 PM   #11
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How to get 200 amp subpanel in garage


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Originally Posted by chuck willis View Post
After looking at a chart of common appliances and average wattage, figuring everything in amps gets me to 180 amps.
house + garage, right?

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Originally Posted by chuck willis View Post
It seems insane to me; there will never be a time when all of this is on simultaneously. Am I going about this wrong? I mean, when the weather is cold and my wife is baking a pie, can't I just refrain from drying clothes, running the compressor and table saw while vacuuming?
Trust me on two things:

1. People are NEVER sorry they have more electrical capacity than they need. Just think about how our demand for more Amps, outlets, lights, etc in our houses has changed in just 10 years. Heck, when my house first got power (in the 1890s) it had four circuits and 60 amps - now I've got 200 and I'm saving up for 400.

2. Just 'cause you are willing to refrain doesn't mean you will always be home to enforce this. Family can do some crazy things when you aren't looking....

3. You WILL likely exceed your capacity in the middle of something really, really important.

I know it's hard to spend the money (or impossible) just think about it. And let us know what you decide.
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Old 03-17-2011, 05:05 PM   #12
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Roger that, Leah. I am certainly better served with a 200 amp sub in the garage, and typically when I build I over-engineer and provide for as many future options as practical.

I have, however seen many larger homes run on 100 amp panels (and many older homes making do on 60 amps), so I should not get stuck on 200 amps if there is little likelyhood of nuisance tripping.

A quick calculation reveals that the dryer, range, HWH, freezer, fridge, microwave, dish washer, washing machine and 4000 watts at 240V (heaters) would load about 89 amps if simultaneous. I think there is sufficient power with a 100 amp sub, but I am still open to learning more about splitting my feed with the tangle box Lyons mentioned.

Thanks for the input!
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Old 03-19-2011, 09:18 AM   #13
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How to get 200 amp subpanel in garage


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I really don't want to get a meter for the garage/apartment because the utility has a $92 base charge per month for the extra service.
Holy Cow! I'm adding a second 200Amp service to my garage for apt/shop very similar to what you mentioned. I checked with the CoOp in my area beforehand and my second meter will run $16 per month.
But I intend to run 275' lateral of 4/0 4/0 2/0 URD which was pricey.
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Old 03-19-2011, 09:43 AM   #14
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How to get 200 amp subpanel in garage


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my only concern would be nuisance tripping, and I don't see that kind of power usage.
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You can split your feed coming off the all in one. As long as there is a breaker protecting your meter side that is no larger than 200 amps, you are fine. You said "Service Disconnects" to my knowledge this means the breaker DIRECTLY after the meter...
Your house, apartment, and shop will be limited to a combined 200 amps.
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Old 03-19-2011, 12:35 PM   #15
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How to get 200 amp subpanel in garage


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Originally Posted by chuck willis View Post
After looking at a chart of common appliances and average wattage, figuring everything in amps gets me to 180 amps. It seems insane to me; there will never be a time when all of this is on simultaneously. Am I going about this wrong? I mean, when the weather is cold and my wife is baking a pie, can't I just refrain from drying clothes, running the compressor and table saw while vacuuming?
Thats not how you size a panel. You do not add up all the wattage and convert it to amps. Imagine the service for an apartment building if they used your method.
A load calculation is what is required.

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