200 amp subpanel feed from 200 amp main panel

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Old 01-17-19, 07:44 AM
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200 amp subpanel feed from 200 amp main panel

I currently have a 200 amp main panel on my home. The model of this is a GE PowerMark Gold Load Center TM2020RCUBK1. This panel was just upgraded from an old 100 amp panel.

I am looking to get an electric tankless hot water heater installed in my crawlspace. This specific unit I am looking at says it requires (4) 40 amp circuits to go to it (240v). Due to where the water heater will go in comparison to the main panel, it would be much easier to install a subpanel closer to the water heater, then run the 4 circuits from the subpanel directly to the water heater.

In addition, my house has some old aluminum wiring in places, two of which goes to my electric stove, and to my electric dryer. I am also looking to get those circuits replaced with new copper wire.

I am wondering if I am able to get a 200 amp circuit breaker that will install into my main panel, then feed directly to the main lugs of a 200 amp sub panel. From the subpanel I would eventually like to run the hot water heater, as well as the dryer and stove (once the wires get updated).

I have been looking around and have found replacement main breakers for my existing panel like these:

https://www.homedepot.com/p/GE-Power...00DP/100165515

https://www.ebay.com/p/GE-Distributi...d=153340810787

Which according to my panel these types (THQMV) can only be used for the top main breaker of the panel.

Do they even make such a thing that will allow me to branch out 200amp from a 200amp main panel? I have seen that you can use a lug pass-through panel in order to feed a sub panel, but I am really looking to be able to shut down power to just the subpanel, and not the entire house when doing work in the subpanel.

 
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Old 01-17-19, 08:27 AM
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There is TQDL21200 https://www.homedepot.com/p/GE-Q-Lin...1200/100188498 It should fit but need to check your panel's label to see if it accepts TQDL type breakers. Note picture is squashed. It is a large breaker taking up both sides of the panel/4 spaces.

Also for that size water heater you likely need 320/400 amp service. Do a load calculation to check.
 

Last edited by Astuff; 01-17-19 at 08:49 AM.
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Old 01-17-19, 08:50 AM
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What is the actual full load amps of the water heater? Sounds like they should have upgraded to 400 amp main panel. Even in the old days a house had a 60a panel. Your water heater leaves only about 40 amps for the whole house. The dryer and the stove are at least 70 samps. Of course the total for branch circuit breakers usually does exceed the main breaker but in your case you have multiple heavy draw items.

O/P wrote:
my electric stove, and to my electric dryer.
 
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Old 01-17-19, 08:57 AM
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Agreed your service is probably too small for that heater. Usually when installing this class of tankless we would put in a 400A service which immediately splits into two 200A panels. One dedicate just to the tankless and one to the rest of the house.

The service from the pole or transformer pad to your house also may not be big enough as the power company sizes based on actual load not panel size. You'll have to notify them of the significant increase in load and let them decide if service work needs to be done.

Finally, there is no specific problem with aluminum wire feeding the stove and dryer as long as it is physically in good shape and terminated on receptacle blocks rated for Al. Addition of an anti-oxidation compound is best practice but not strictly required. It's still very common in new construction. The problem with aluminum wiring is only in receptacle and lighting circuits where splices cannot be made safely.
 
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Old 01-17-19, 08:57 AM
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The data sheet in the panel should list the max size breaker that can be used for a branch feed.
 
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Old 01-17-19, 10:47 AM
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Thanks for the replies so far.

Astuff: I dont believe that this type of breaker will work in my panel. I have attached an image of the inside label. Almost all of the compatible breakers start with THQ*

Ray2046: here is the information form the water heater manufacturer:
HEATER INPUT: 36kW
ELEMENTS: 4
VOLTAGE: 240 V
MAX kW: 36 kW
kW PER ELEMENT: 9 KW
MAX AMPERAGE DRAW: 150 AMPS
REQUIRED BREAKERS: 4 X 40 AMP
REQUIRED WIRE GAUGE: 4 X 8 AWG

ibpooks: It does seem that the over all service may not be big enough. The next sized down water heater has a max amp draw of 112.5, and only requires (3) 40amp circuits. That might be the way to go. But this still brings me to the question of being able to run a higher amp subpanel off my main, or more so finding the right circuit breaker to feed that.

As far as the AL wiring, its in rough shape, and needs to be replaced anyways. Having this new panel give me the opportunity to do this, in addition to move some appliances around the house.

With all that being said, is it even possible to run a 200amp sub panel off a 200 amp main panel? I do not see anywhere on the panel label about max sized breakers, only that you cannot exceed 220a on any one stab

Thanks everyone!
 
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Old 01-17-19, 10:55 AM
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The 220A limit per stab is the max breaker amperage that can be used on that stab. Some panels may limit stab amperage to 125A.
 
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Old 01-17-19, 11:00 AM
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What exactly is a stab? Is it one side of the panel?
 
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Old 01-17-19, 11:22 AM
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Originally Posted by minnino View Post
Astuff: I dont believe that this type of breaker will work in my panel. I have attached an image of the inside label. Almost all of the compatible breakers start with THQ*
Upper left on label shows TDQL so you could use that breaker.

Generally people are not happy long term with tankless water heaters unless they are in warmer climates.
 
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Old 01-17-19, 11:29 AM
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Thanks Astuff, i see that up there now. i was looking at the right side of that label where it had breakers listed for main and branch breakers. The reason I am looking at tankless is to free up some space. Currently my water heater is sitting in my kitchen, and I have no other good place to put one. It was also my understanding that I cannot put a gas tankless in my crawlspace due to not having enough clearance around it
 
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Old 01-17-19, 11:44 AM
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Where are you located? What are your groundwater temperatures? Gas tankless have outdoor versions.
 
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Old 01-17-19, 12:02 PM
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I am in Denver, CO so I cannot use an outdoor one due to the temperature
 
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Old 01-17-19, 12:20 PM
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Originally Posted by minnino View Post
What exactly is a stab? Is it one side of the panel?
It's the point where the breaker pushes on to the buss bar.
 
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Old 01-17-19, 12:42 PM
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In Denver to get 110 out of faucets at 5 gpm (2 things happening) you need 50KW or 200+ amps. So large tankless might work if you live alone. Not so much if you have a family.
 
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Old 01-17-19, 12:49 PM
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Too late now but if you are going to take 200 amps off a 200 amp panel best is use a panel with main breaker and main lugs. That way no additional breaker needed. You just come off the main lugs which are protected by the main breaker.
 
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Old 01-17-19, 01:49 PM
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Its just me and the wife in the house. We dont own a dishwasher, and wash all our clothes in cold water. This is a smaller 1500sqft single story house with 2 full baths.
 
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Old 01-17-19, 01:52 PM
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ray2047 - would this mean i would have to shut down the power to the entire house if i wanted to do any work in the subpanel? I looked at those types of boxes, but it was already too late, the electrician had already picked out the new box.
 
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Old 01-17-19, 03:00 PM
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The subpanel could be a main breaker panel with the main breaker serving as your disconnect.
 
 

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