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Comment by lisper | Hacker News Reader

Did you upgrade your wiring? Your old breakers were the size they were for a reason.

That's not a consideration here. They were just replacing a smaller 100A panel with a larger one. with more circuit spots. That is always allowed.

As long as you you use a panel that accepts the same type of breakers, you can also re-use the existing breakers, unless code require upgrading to AFCI breakers. Otherwise you swap them for new breakers of the same rating. (Assuming the US: There are some inspectors who would ok a panel swap that reused the existing breakers without requiring upgrades, but technically upgrading is supposed to be required, unless your state amended out the AFCI requirements in the state version of the code). Note: technically many breakers can fit in competitor panels, but they are not legal. They were not designed nor tested to trip at proper ratings in those panels, and using them violate the labeling of the panel.

Now obviously the reason for upgrading the panel is to add more circuits, and it is possible that these additional circuits if added would need more power than the 100A service can provide. To technically comply with code, you need to follow the rules to calculate the expected loading of existing circuits plus planned new circuits.

"That is always allowed."

The last sentence you wrote is the killer. You are technically correct that changing the number of circuits in the panel is not itself disallowed. But .... you would also be hard pressed to get an AHJ to pass a number-of-circuits upgrade without knowing how many circuits you are planning on adding, and doing the feed sizing calculation to make sure you don't have to upgrade the incoming feed to support it.

The panel and the breakers in it are different things. If you get the right size breakers, that's fine, and even a good idea (breakers go bad over time from what I know. Maybe due to number of trips?).

Putting in a new panel can get you more space, or just update to a currently maintained standard for breakers so you can find and put new ones in.

He said he wasn't upgrading amperage, so wire size requirements for existing breakers should not change.

It sounds like he was adding circuits which means he's running wires for those new circuits anyway.

I didn't touch the wiring; just made sure to use the same exact amperage (though I bought all new breakers just in case, and upgraded one to an AFCI - Michigan doesn't require AFCI on everything as the rest of the country seems to mandate). I checked the wire with wire gauge with my wire strippers to make sure 15amp wire is never behind a 20amp breaker.

Sorry, I mis-read your original post. I read it as "upgrading to 30-amp circuits" rather than what it actually says, "upgrading to 30 circuits." My mistake. (In retrospect I should have realized that 30-amp circuits were unrealistic.)

Even with the same size breakers you have to be careful. Many circuits in the US are wired using a shared neutral. These circuits must not share the same phase and when rewiring an entire panel this seems like it'd be an easy mistake to make.

Multiwire branch circuits must be wired with tied breakers. If the person rewiring doesn't understand that this must be duplicated in the new panel, they definitely has no business upgrading their own panel.

This doesn't appear to have been the case until 2008, at least with multiwire branch circuits that supply separate outlets. Many if not most 100A panels with multiwire branch circuits will have been wired with breakers without ties.

I'll take your word for it, but I thought that at least as far back as 2002 it was required that the breaker for a MWBC trip both sides if one trips.

I really don't like MWBCs myself, if I would've known the electrician for my house was going to utilize a bunch of them, I'd have happily paid him not to do that.

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