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Old 12-29-2010, 12:28 AM   #1
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Upgrade panel, add subpanel, add tandem breakers?


I am doing an addition to my house and am wondering if I should upgrade to a 200A panel, add a subpanel, or just add more breakers to the current panel.

I have a 150A service now, 3 empty breaker spots, but have several breakers that could get changed to tandem breakers. I have 1400 sq ft now and I'm adding another 900 sq ft living space and another 420 sq ft garage space. I have gas hot water and gas furnace.

I am applying for my permit soon and need to describe the work I will need to do, so I need to have a plan. Will they make me upgrade the service size?

If I upgrade the panel from 150 to 200A I will need to change panel feed wires from meter correct? This is about a 20 ft. distance from meter to panel w/ underground service to meter.

Thanks in advance for the help
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Old 12-29-2010, 06:43 AM   #2
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Upgrade panel, add subpanel, add tandem breakers?


You need to do a load analysis. The guidelines are in the National Electric Code.

Among other things it calls for three watts per square foot of your entire house. This covers lighting, consumer electronics such as televisions, and small plug in appliances. Include portions of basement and garage used as living space, workshop, etc. You will take into account the wattages for major appliances, "continuous" or 100% of the wattage of items like air conditioners, "intermittent" or 80?% of the wattage of some appliances.

The total wattage you come up with may dictate that you upgrade the service.

Panels have a limit to the number of breaker handles. In some cases you will be able to fit in single wide double handle (tandem) breakers and stay within the total. Not all makes and models of panels accept tandem breakers.

If you don't have to upgrade the service, a subpanel is usually the simplest way to go. Upgrading the service and upgrading the main panel require two separate permits in some cities. Upgrading the main panel usually requires having the power company shut off the power at your meter. Adding a subpanel usually does not need an "additional" permit over the permit for adding wiring, and the electric company does not have to come over.

A subpanel merely requires commandeering two slots of your main panel for a (double wide double) breaker. If the main panel was full, you would reroute a few circuits into the subpanel to free up the breaker slots. Separate neutral and ground conductors are run from the main panel ground/neutral busses to the subpanel neutral bus and subpanel ground lug respectively.
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Last edited by AllanJ; 12-29-2010 at 06:55 AM.
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Old 12-29-2010, 08:30 AM   #3
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Upgrade panel, add subpanel, add tandem breakers?


Allan is close but not entirely accurate. Do a google search and you should find some free online calculators to help with your load analysis.
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Old 12-29-2010, 09:05 AM   #4
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Upgrade panel, add subpanel, add tandem breakers?


after you get total wattage added up,first 300 watts at 100%,the rest at 35%.say your total is 10,000 watts.take 3000 at 100%,the 35% of the remaining 7000 watts.that is 2450 watts.add to the 3000 gets 5450 watts.then5500 for dryier.you get 10950 watts.divide by 240 volts.your load is 45.6 amps.this does not include ac or range which would be added at name plate rateing.it van get complicated but not hard.you could have 18500 computed watts or about 75 amps.then comes neutral calcs if this is a main service to house.

Last edited by oleguy74; 12-29-2010 at 09:08 AM.
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Old 12-29-2010, 10:10 AM   #5
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Upgrade panel, add subpanel, add tandem breakers?


If you change the main panel, there is a good possibility you will need to change the meter can and the wires from the utility to the meter can.

I would think you have plenty of power with 150 amps, after these calcs you'll probably decide not to upgrade that part.

The tandem breakers are iffy. I think they removed the limit on circuits in the box, but those things aren't cheap, and I still don't like to use them to cram pack the box even if it's legal. Just putting 10# of wire into a 5# box.

I would look into one of those fairly cheap 100A boxes at Home Depot, and feed off of a smaller breaker in the main panel. That would probably be easiest and cheapest. Say, maybe a 60 amp feeding the 100 amp panel would be plenty, there's nothing wrong with that except you'll blow the 60 amp first. In fact, it would be legal to remove the 100 amp breaker altogether and direct wire that panel, if you had the breaker in the other panel. I'm not too sure if those cheapies are capable of that, though.
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Old 12-29-2010, 02:22 PM   #6
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Upgrade panel, add subpanel, add tandem breakers?


I used an online load calculator and came up with 108A and I added wattage for possible air conditioning in the future.

So there shouldn't be any reason for inspector to require larger service correct?


My panel is rated in six breaker positions to use tandem breakers, you are saying this may not be accepted?? or not good?

If I decide to add a subpanel and feed it with a 60A breaker, am I correct in thinking I can run several breakers in sub panel that add up to more then 60A correct?
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Old 12-29-2010, 02:35 PM   #7
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Upgrade panel, add subpanel, add tandem breakers?


Quote:
Originally Posted by oregondiy View Post
I used an online load calculator and came up with 108A and I added wattage for possible air conditioning in the future.

So there shouldn't be any reason for inspector to require larger service correct?


My panel is rated in six breaker positions to use tandem breakers, you are saying this may not be accepted?? or not good?

If I decide to add a subpanel and feed it with a 60A breaker, am I correct in thinking I can run several breakers in sub panel that add up to more then 60A correct?
I'm not a fan of tandem breakers. They are expensive, have limited installability (although you have already identified the capacity of your main panel for tandems) and tend to invite "crammed" panels by introducing more circuits into the box. That being said, I don't think they are unsafe (as long as they are installed in accordance with the panel specfications), just inconvenient.

The total capacity of the breakers in the subpanel can exceed the subpanel disconnect breaker capacity. Obviously, you don't want to connect circuits to that sub in such a way as to frequently draw 60A through the sub, or the sub breaker will trip (instead of killing one circuit, you could shut off the half the house).

You mentioned adding AC in the future? Did your 108A calculation include that AC, or are you assuming that you'll have 42A left to play with? Since you are doing an addition, the inspector may require an outside disconnect if your meter can does not already have one. Some jurisdictions are requiring these now.
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Old 12-29-2010, 02:43 PM   #8
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Upgrade panel, add subpanel, add tandem breakers?


I am including the possible future AC in the 108A.

So will the inspector do a load calculation to determine if he tells me to upgrade the service, or just say well you adding 900 sq ft. you have to?

I don't see any reason to add larger service if it is not really necessary. I just want to be able to have all my ducks in a row before I go to get my permit. As I am not a professional electrician at least I want to seem like I know what I am doing.

In reading I think I have to add hard wired smoke detectors to addition, and wired so when one goes off they all do. Do these need to be wired to my existing detectors in the old part of the house or is this considered seperate?
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Old 12-29-2010, 02:50 PM   #9
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Upgrade panel, add subpanel, add tandem breakers?


Quote:
Originally Posted by oregondiy View Post
I am including the possible future AC in the 108A.

So will the inspector do a load calculation to determine if he tells me to upgrade the service, or just say well you adding 900 sq ft. you have to?

I don't see any reason to add larger service if it is not really necessary. I just want to be able to have all my ducks in a row before I go to get my permit. As I am not a professional electrician at least I want to seem like I know what I am doing.

In reading I think I have to add hard wired smoke detectors to addition, and wired so when one goes off they all do. Do these need to be wired to my existing detectors in the old part of the house or is this considered seperate?
Quite frankly, it depends on the inspector. He may do some calculations and come to a similar conclusion as you, or he may say it needs to be upgraded because of the size of the addition. You can always ask him to explain his load calculations if he pushes for upgraded service.

I'm sure you will be required to use hard-wired SDs in the addition and retrofit your existing structure with them also (interconnecting them). Most jurisdictions are all over that one.
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Old 12-29-2010, 03:25 PM   #10
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Upgrade panel, add subpanel, add tandem breakers?


It's hard to say exactly what they'll want. Get your ducks in a row, come up with a tentative plan, and call the inspector and see if he has time to answer some of your questions. Most of them are pretty good at telling you ahead of time what they want, people just never bother to ask. Don't ask him how to do it (as in installation hints) though- that ticks them off. Just ask how he wants it. Ask here for the hints.

I did an addition in my house and never even thought about the smoke detectors, it never got mentioned by the inspector, either. I put in a battery one like the rest of the house.
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Old 12-30-2010, 10:17 PM   #11
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Upgrade panel, add subpanel, add tandem breakers?


Thanks to everyone for the replies, I think I will try to keep my existing 150A service and add a subpanel.

I understand that my new circuits will need to have a AFCI breakers, but I shouldn't be required to upgrade any of my old circuits in the main panel to AFCI correct?
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Old 12-30-2010, 10:45 PM   #12
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Upgrade panel, add subpanel, add tandem breakers?


Typically you would only need to change out the older breakers to AFCI breakers if the old circuits were modified like by extending them or other work.
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