Can I swap out and downsize just the main breakers & not the whole panel?

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Flicker

Member
Location
Washington
I own a duplex where I swapped out the panels inside the apartments but I did not take note that the incoming feeder to the panels was 2/0 and I mistakenly put in a new 200 amp panels.

But, each of the panels in the apartments are feed by their own double 100 amp breakers.

My questions are:

1. Since the 200 amp panel is feed by the double 100 amp breakers, even though the feeder wire is undersized for 200 amps, is there any risk since the supply through the feeders will be limited by the 100 amp breakers feeding it?


2. The 200 amp panels that I put in are Siemens and even if the answer to the above question is "there is no risk", it would be nice to have the main breaker match the feeder wire for anyone looking.

The 125 amp main breakers in Siemens panels seems to connect to the busses in the same way as the 200 amp breakers. Instead of going through all the trouble of replacing the entire 200 amp panel with a 125, does anyone see any problem with just swapping out the main breaker for a 125?

Thanks for your help.
 

jeremy.zinkofsky

Senior Member
Location
nj
What is the panel itself rated for?

And could you explain what you mean by double 100A breakers?

Your post is kind of all over the place, do you have any pictures?

Generally, you size the conductors so that they can handle the maximum amount of current available. If you have a 200A main breaker being fed by 2/0 then you will run the risk of the cable being compromised if the load in the 200A panel exceeds 175A. You can't rely on one breaker "catching" another breaker as you can't guarantee that the breakers will work in perfect coordination. As a side note, the rating of the panel itself is just a frame size. For example, you are allowed to put a 50A main breaker in a 200A rated panel enclosure. You just can't put a 250A main breaker in a 200A rated enclosure or any breaker rated higher than the panel enclosure rating.
 
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charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
What I understand (rightly or wrongly) is that you have two separate feeders, each sized at 2/0 copper, each providing power to a separate panel. Each of the panels is rated at 200 amps, and each has a 200 amp main breaker. Finally, when you say "double 100 amp breaker," I think you mean a 2-pole, 240 volt breaker. Is that much right?

Assuming that is right, my next question is what is on the other side of the 2/0 conductor? Does each 2/0 come directly from the utility meter? If so, then is there an overcurrent device at that meter, and what is its rating? Or does each of the 2/0 come from a distribution panel, with a feeder breaker providing power to the 2/0? If so, then what is that breaker's setting?

There are two separate and equally important requirements at play here. One is that you have to protect the 2/0 against overcurrent. A 200 amp breaker will not satisfy that requirement, even if it were upstream of the 2/0. A breaker downstream of a conductor is allowed to protect the conductor, but only under very limited circumstances. For the most part, you will need an overcurrent device rated no higher than 175 amps upstream of the 2/0.

The other requirement is that every panel has to be protected against overcurrent at a value no higher than the panel's rating. That protection can be a main breaker within the panel, or it can be a breaker somewhere upstream. In your case, a 200 amp main breaker would certainly serve to protect a 200 amp panel. So there would be no need to replace it with a 125 amp breaker.

I need you to explain what you mean by, "But, each of the panels in the apartments are feed by their own double 100 amp breakers." Are you saying that there is a 100 amp, 2-pole breaker on the upstream side of each of the 2/0? If that is the case, you are OK as is. That would satisfy both of the requirements I just described.
 

Flicker

Member
Location
Washington
And could you explain what you mean by double 100A breakers?

See a breaker example below (sorry the picture is so big). Each apartment is fed by one of these.



153395_front500.jpg
 

Flicker

Member
Location
Washington
What I understand (rightly or wrongly) is that you have two separate feeders, each sized at 2/0 copper, each providing power to a separate panel. Each of the panels is rated at 200 amps, and each has a 200 amp main breaker. Finally, when you say "double 100 amp breaker," I think you mean a 2-pole, 240 volt breaker. Is that much right?

You are correct above except it is 2/0 AL (not copper) and see my recent post for an example of the breaker.
 

Flicker

Member
Location
Washington
Does each 2/0 come directly from the utility meter?

Each 2/0 comes directly from the double 100 amp breaker pictured above and that breaker is fed from the meter.

I need you to explain what you mean by, "But, each of the panels in the apartments are feed by their own double 100 amp breakers." Are you saying that there is a 100 amp, 2-pole breaker on the upstream side of each of the 2/0? If that is the case, you are OK as is. That would satisfy both of the requirements I just described.

Yes, there is a 100 amp breaker like the picture above on the upstream side of each 2/0. In other words, each apartment/200 amp panel has their own breaker like the one pictured above.
 

jeremy.zinkofsky

Senior Member
Location
nj
Ok, so each 200A panel is fed from a two-pole 100A breaker via 2/0 cable.

Are the 200A panels main lug or main breaker?

If main breaker, what is it's rating? If it is less than 175A you're ok with 2/0. Otherwise you have to switch out the main breaker to something smaller or replace the cable with something larger.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If the #2/0 feeder is protected by a 100 amp OCPD at it's origin it doesn't matter what size breaker is in the panel.
 
Each 2/0 comes directly from the double 100 amp breaker pictured above and that breaker is fed from the meter.



Yes, there is a 100 amp breaker like the picture above on the upstream side of each 2/0. In other words, each apartment/200 amp panel has their own breaker like the one pictured above.
As long as you're protecting the 2/0 wire on both ends with the same rating (i.e.- 100 amps) you should be fine with a 200 amp max. Can. In fact, even better! Now, each unit will have a large capacity for solar! Just make sure you don't overload the bus bar given the extra slots.

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If the #2/0 feeder is protected by a 100 amp OCPD at it's origin it doesn't matter what size breaker is in the panel.
It would be risky in the case that someone with not so much electrical design knowledge one day decides to up the source breaker given the fact that a 200 amp sub is already installed.

Someone might just think 2/0 is suitable.

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Ingenieur

Senior Member
Location
Earth
Should be OK as is

depending on service/feeder conductor type I might
replace the existing 100/2 with a 150/2
and the new main 200/2 with a 150/2
that's just me
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It would be risky in the case that someone with not so much electrical design knowledge one day decides to up the source breaker given the fact that a 200 amp sub is already installed.

Someone might just think 2/0 is suitable.

My response was based solely on the NEC not potential DIY tinkering. :D
 
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