Merging 2 Breaker Boxes into Panel + Subpanel

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  #1  
Old 09-17-15, 09:16 AM
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Merging 2 Breaker Boxes into Panel + Subpanel

Hey everyone,

First post here. I have just purchased an 8,000 square foot mixed-use residential/commercial building that my wife and I are moving into. It is two stories, with the upstairs having 2 condo-style apartments and the downstairs having commercial units, and it is in need of fairly significant work/upgrades/improvement.

Each of the apartments used to be broken down into 2 very small units (i.e. there were 4 ~800 square foot apartments upstairs originally), and because of this, my current living space has 2 separate breaker boxes. Each box originally had an A/C unit, water heater, and then all of the other breakers for the usual house odds and ends (bathroom GFIs, lights and outlets, etc.); however, we now have one larger A/C unit and all of the kitchen appliances running off a single breaker box, while the other breaker box now only has 4 15 Amp breakers running our bedroom lights/fans and outlets, our library lights/fans and outlets, a bathroom GFI circuit, and a circuit for a jacuzzi bathtub.

Because there were originally 2 apartments, there are two service connections from the utility company to each breaker box, meaning we will be paying two bills, and although we have not received our first bill yet, I am all but certain we will be using less than the minimum charge per day on the 2nd breaker box (because of the small number of things it runs and how much we are currently using them). For the sake of convenience, and money in the long term, I would like to eliminate one service, and have a single service running to the main box supplying the "big" appliances, and then turn the second box into a subpanel running from the main, thus eliminating having 2 bills, etc.

Would that be something that is possible, assuming the right wiring/amperage is running to the "main" panel (which I have not had the chance to dive into yet, but will be doing so this weekend)?

Obviously I know more details are probably needed, but I do not have them available just yet. I have done quite a bit of electrical work over the years, but it has mostly been fairly routine items, or something done from scratch (running an entirely new breaker box, service panel, etc.), and I have limited experience changing around already existing wiring systems.

Thanks, and I will get any additional info as quickly as possible.
 
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Old 09-17-15, 09:24 AM
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This should be a pretty straightforward project. You need to feed the "other" service with a cable from your current main panel, and separate the ground and neutral wires onto their own bars in the subpanel. This will require buying an add-on ground bar ($10) for the panel and removing the bonding screw or strap which connects the neutral bar to the metal box.

The bare minimum to do this with is 10-3/g cable with a 30A double-pole breaker. If you anticipate need for expansion use #6-3/g cable with a 60A breaker. The subpanel does not require a main breaker, but you can have one if you want.

Before doing the work you'll need the power company to come out and glass out the meter box and do a permanent disconnect. If you already have the new cable pulled when the power company does the disconnect, you should be able to have power back on in the subpanel in an hour or two.
 
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Old 09-17-15, 09:31 AM
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Yes, as you suggest simplest would be to remove the service to one panel and connect that to the other panel as a subpanel. It might help us help you if you post pictures of the panels with the covers removed. http://www.doityourself.com/forum/li...rt-images.html
 
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Old 09-17-15, 12:44 PM
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The bare minimum to do this with is 10-3/g cable with a 30A double-pole breaker. If you anticipate need for expansion use #6-3/g cable with a 60A breaker. The subpanel does not require a main breaker, but you can have one if you want.
I was planning to use #6-3/g with a 60A breaker. I thought that would be best to ensure not having any issues in the future with available current. The panel as it is now (with direct feed to the meter) does not have a main breaker (I believe that is in violation of code?), so I will not be worrying about having a main breaker on it as a subpanel.

Before doing the work you'll need the power company to come out and glass out the meter box and do a permanent disconnect. If you already have the new cable pulled when the power company does the disconnect, you should be able to have power back on in the subpanel in an hour or two.
As I said, I have done new service hookups and run wiring for new breaker boxes that did not have service, but never tried to rewire an existing breaker box that already had electric service... point being, why would I have to get the meter disconnected rather than just cutting off the main breaker below the meter box? If I have to cut it off, it is not a huge problem, but I was just curious on the reasoning behind it in order to further my own knowledge...


Ray, I will have some pictures up tonight.
 
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Old 09-17-15, 01:05 PM
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If you have abandoned wiring, it has to be disconnected on both ends to prevent accidental energizing, or accidental cross connect between the different services. I suppose it would be ok to do the work if you lock out the main breaker until the power company physically disconnects the service. I wouldn't want to leave the wiring just hanging if the main breaker could potentially be flipped on.
 
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Old 09-17-15, 06:39 PM
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why would I have to get the meter disconnected rather than just cutting off the main breaker below the meter box?
To keep from continuing to get a bill for a minimum service charge.

The panel as it is now (with direct feed to the meter) does not have a main breaker (I believe that is in violation of code?),
No code violation, the main breaker is at the meter location.
 
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Old 09-18-15, 08:10 AM
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Ok, here are the pictures requested. First, the outside of what would become the "main" box:
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Then the outside of what would become the subpanel:
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Internals of the "main" box:
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I believe this is #3 wire? But I haven't dealt with "big" wires enough to know just from the look... (well, I have, but it's always been 3/0 or 1/0 and I know that's much smaller)
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Internals of the subpanel... I believe it also has #3 wire. Additionally, I just noticed that all of the wiring to the old water heater, air handler, and condeser are still attached, which I definitely need to take care of, because if their breakers are accidentally flipped, there would be live wires running into the attic.
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So, a couple of problems I can forsee... the "main" panel is only a 100A service with #3 wire, so I'm not sure it would be able to handle adding on the second panel? Although, again, as I mentioned, we are running very few items off what would be the new subpanel, so I'm not too concerned about it. In general, my wife and I try to be very mindful of conserving electricity, so we usually keep lights off, etc. if not in the room.

If you have abandoned wiring, it has to be disconnected on both ends to prevent accidental energizing, or accidental cross connect between the different services. I suppose it would be ok to do the work if you lock out the main breaker until the power company physically disconnects the service. I wouldn't want to leave the wiring just hanging if the main breaker could potentially be flipped on.
To keep from continuing to get a bill for a minimum service charge.
Ok, I thought that's what you were probably referring to, but that is going to be my next little project (probably done at the same time). If I can pull off this subpanel hook up, I will be commandeering the second service hookup currently into the apartment to create an entirely new hookup with a breaker box in the attached garage. The property currently has an attached garage, a separate 2,000 square foot warehouse, and a large boat/rv shed with electricity running from one of the downstairs commercial units. This setup is not good for me, so I am planning to have a separate service to those 3 outbuildings in order to write them off as a business expense (I am moving my CrossFit gym into the warehouse). So that's why I was not as concerned about having the meter disconnected. But I get the safety concern and it is something to think about. As I said, I'm used to hooking up boxes and outside service wires BEFORE the electricity is ever on...
 
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Old 09-18-15, 08:50 AM
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It all looks reasonable to me. #3 copper is the correct size for a 100A subfeed in a multi-use building (at least it was a few years ago); some modern code revisions would require #2 in this case, nothing to be concerned about. You can do a demand load calc on the service panel that feeds your residence, but given the apartment sizes you mentioned, I would be surprised if 100A is too small.

The only thing that looked a little concerning is in the close up shot it looked like you might have two white wires under one screw. The white neutral wires must always be one per screw due to thermal expansion. Bare grounds can be doubled.
 
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