100A Sub to addition/attached garage MC

[ibilisi]

Hey all, I have done a bunch of searching but I thought I'd throw this out because it is a bit different.

I just put on an addition and replaced my attached garage. I currently have 100Amp service and I'm going to do an upgrade to 200amp.

My thought is to leave my current 100Amp panel untouched due to potential issues with having to mess with current house wiring. I would rather leave that for another time. My current Idea is to use this 200 Amp disconnect with 2x100amp breakers.

I have two 125 amp lug centers, one for a 100amp sub in the basement addition and then use the other for a 60amp in the garage.

Now, unfortunately the way the grade changes and structural I don't have a clear path from my existing panel to my sub location(s). Mainly a huge lvl blocking path. I don't want to drill the LVL. I could get around it with tighter bends.

I am wondering if I could use the 4/3 MC-Copper cable referenced in the attached file. What I see is that it is rated @ 95 AMP in the 90 degree column. My understanding is that you would be able to step up to the next size breaker or 100 AMP in this case. Or is the 90 degree column only used for derating in this instance.
MC-copper pdf link.

The MC would not be in insulation.

Thanks

 

[Mustang51js]

I'm having trouble understanding what your trying to do. Basically what you need to do is get a 200 amp main breaker panel, run 2-2-2-2 ser cable to the old panel. In the main panel you will need a 70 amp breaker to power old panel. In the old panel you need to remove bonding between ground and nuetral and separate all the grounds to its own ground bar. You will also need to run a #4 thhn from water meter to the new main panel and also a #6 from the ground rods to the main panel.

 

[Mustang51js]

Can you replace 100 amp panel with a new 200 where it's at or is the new garage in the way

 

[ibilisi]

I'm having trouble understanding what your trying to do.

Sorry-

I have two subpanels.

One subpanel is going to be on the interior wall of addition. One inside the attached garage.

The issue with the updating the "old" 100 amp service is that the city may require me to bring whole house wiring up to current code (House built 1931, lath, plaster, stucco, not fishing wire here). This way, I'm not touching existing wiring.

So, I split new 200 amp service at the disconnect box. Run 100amp to current/existing panel, second leg to new 100amp panel inside addition. Then I'm just running 6/3 from addition panel to new panel in garage for 60amp service.

 

[Mustang51js]

I would still go with a 200 amp main breaker panel instead of two 100 amp breakers, this way you can add to that panel also and price different prob isn't that much. Just remember you need your grounds to the main panel now and your old panel would be a sub panel. You don't have to upgrade the rest of house if you replace the panel. How far are all the other panels going to be from where you plan on putting main breaker. Could you run the circuits to new addition to a main panel where power comes in. Do you have to move service because of the addition.

 

[ibilisi]

Could you run the circuits to new addition to a main panel where power comes in. Do you have to move service because of the addition.

Hmmm.... I actually hadn't thought of this. I could go new 200amp service drop to attached garage from the overhead lines. Then run 2-2-2-4 to the old panel with say 90 amp breaker.

That would be a cleaner install.

 

[Mustang51js]

Hmmm.... I actually hadn't thought of this. I could go new 200amp service drop to attached garage from the overhead lines. Then run 2-2-2-4 to the old panel with say 90 amp breaker.

That would be a cleaner install.

Yeah that would be better and look much neater than having boxes all over. Only reason I would even do the garage panel is in case you want to add more stuff in the future, but the new addition on the house will prob stay the same over the years if you plan it right the first time.