Alternatives to replace tandem single pole MWBC breakers?

Question

Thinking about making some panel wiring changes and have some questions I could use some wisdom on.

Background: - House built 1979. Two panels in the unfinished garage (Murray plug in panels). Both are mains with what looks like 200 amp service to both (they both have feeds from the outside coming into the panel, both have a bonded neutral/ground bar, when I flip the service disconnect on the left panel, the right panel is still hot and vice versa etc). Panel on the left is the “big boy” panel for electric range (no longer used), electric furnace (no longer used), AC and some 240 circuits for my table saw, dust collector etc. Right panel handles basically everything inside the house and the garage other than the big boy circuits. Meter and utility box just on the other side on the outside wall. Haven’t been able to open up the utility box yet (painted shut) but will. I’m assuming I will find the master cutoff (or in my case perhaps two).

The right panel has no main service disconnect as the left panel does. Instead, it relies on what I understand to be the now defunct “6 throw” rule. The top part of the panel is always hot unless I were to throw the master cutoff and service to the bottom part can be disconnected with the 60 amp double pole breaker on the right. As you can see, the original wiring made ample use of MWBCs and several tandem single pole breakers (the ones on the left are both MWBCs and no breaker ties). There are no open breaker slots on the bottom of he panel and 2 each right/left on top (presumably because of the 6 throw rule. The face plate of the right panel clearly labels that upper section as “service disconnects”).

Problem:

I was thinking about upgrading some of the breakers in the right panel to accommodate some AFCI/GFCI but now I’m rethinking/questioning this. Specifically what I was thinking about doing was getting rid of the two tandems on the left and replacing with double pole breakers (retaining the MWBC). I can’t find a combo AFCI/GFCI double pole breaker and one of those is for the washing machine so I would just go AFCI breakers and throw a GFCI receptacle on the washing machine outlet.

Initially I was thinking that I would move one of the tandems up top and soak up the two open slots on the left with the double pole (which would then leave room for the other double pole where the two existing tandems are) but then I realized I would run afoul of the 6 throw rule (which doesn’t exist anymore regardless from what I’ve read). That means that I’m stuck (I think…). Siemens now makes a single pole tandem AFCI breaker but it’s really not designed for a MWBC that I can see because I’m not seeing anything about a common trip and I’m not big on breaker ties if they can be avoided.

There are other problems in the panel but some are fairly easy to solve (i.e. replace some of the single pole (non-tandem) MWBCs with a double pole). In fact, I threw both legs (two breakers) on one of the MWBC’s yesterday and my voltage tester was still going nuts on a circuit receptacle and for the life of me couldn’t figure out what was going one so reflipped the breaker and all was well (which very likely indicates I’ve got a sketchy breaker).

Questions:

Is it possible just to replace the “inside” of a panel (i.e. the hot bar that runs down the middle the breakers attach to) and add a master disconnect at the top. While I realize that even with a master disconnect the service lines coming in are still hot (unless the master cutoff is thrown), I’m not super thrilled being around a panel where about 1/3 of it is always hot. Hard for me to tell from my panel how it’s constructed (i.e. can the middle part just come out) and I’ve been looking at pics of new panels but can’t tell either. Obviously a major project but if possible seems far less work than replacing the entire panel. This also seems like potentially less work that moving some of the circuits in question over to the other panel. This question is about addressing the problem noted above but also peace of mind.

Irrespective of first question, are there any other alternatives to my dilemma on the two tandems on the left (other than moving over to the other panel)? The tandem on the right side is fine btw in the sense that it’s not a MWBC but still lacks a breaker tie. Maybe there is a tandem single pole breaker with a built-in switch tie or a common trip that I haven’t been able to locate?

Some of this work could get complicated and I would get a pro in but I like to understand what I’m dealing with regardless.

I’ve read lots of stuff on Stack which has been very helpful (and have scoured everything I could find on this topic). This is my first post and apologies for the length and probably stupid questions but wanted to be as detailed as possible. And "you're chasing your tail" is perfectly welcome

Answer 1

What you have there is 400A service, and this is the usual way that was distributed: splitting from the meter to dual 200A panels. The two panels are main panels.

Consult the panel labeling for which breaker types are allowed.

"Rule of Six" panels

Indeed you have a "main breaker" panel alongside a "Rule of Six" panel. The 6-throw rule still applies, no more than 6 hand movements to shut the whole house off. What changed is you're no longer allowed have the breakers add up to more than the service size, which defeats the purpose of Rule of Six (but still allows dual 200A main breakers).

You are already in violation of the Rule of Six, because you have 1 breaker in the left panel and 6 breakers in the right panel to throw (four of them single-pole breakers). This can be fixed by replacing two single-pole breakers with a 2-pole (or two handle-tied breakers). Not those; those are obsolescent breakers and you won't find a listed handle-tie for them.

FYI, handle-ties do not provide common trip. An internal mechanism on those breakers does that. Handle-ties are for common control so that a maintainer turns off the whole MWBC and doesn't need leave half turned on by mistake. MWBCs are one circuit not two.

Initially I was thinking that I would move one of the tandems up top and soak up the two open slots on the left with the double pole (which would then leave room for the other double pole where the two existing tandems are) but then I realized I would run afoul of the 6 throw rule (which doesn’t exist anymore regardless from what I’ve read).

That's not out of the question. You could handle-tie (read: totally replace) all four of the single-poles, bringing you to 5 throws in both panels. That gives room for 1 more.

For that matter, you could obtain triple-handle-ties (i.e. for 3-phase circuits) and handle-tie three single-poles, making them count as 1 for Ro6 purposes.

Meters and mains

Meter and utility box just on the other side on the outside wall. Haven’t been able to open up the utility box yet (painted shut) but will. I’m assuming I will find the master cutoff (or in my case perhaps two).

"Utility box" eh? It's unusual on such an old installation to have additional main breakers outside. But if they are present, that is wonderful and will let you de-energize the panel fully. If so, you need that panel to be accessible, it is a fire safety requirement. Get that unstuck ASAP!

Be warned that meter boxes are sealed with a power company seal. Breaking that seal, and getting caught, can result in hefty fines (they assume you've been stealing power). If you break it by accident, call them immediately and report it.

Since you think you might have outside disconnects, how about getting them for sure? Get a meter-main or ranch/farm panel which has two 200A "main breakers" right on the meter assembly. Now you shut those off and entirely de-energize the inside breaker panels. That will facilitate easier panel replacement.

As far as finding more "innards" for the panels, notice the gray assemblies with the "tangs" on them the breakers lock into. Everything in the panel bolts to that, so we're talking about the whole shebang. There are two ways to swap that whole bus assembly out.

• Fit an Eaton retrofit kit, which does replace the entire bus assembly and "universal fit" panel cover. It's quite an expensive assembly.
• Carefully identify the "Box Size" either from stickers or out of vintage Murray catalogs. Any given Box Size is used for a variety of panel models. Find a used panel of that era which use that same exact Box Size. Get the whole thing, cover included, and swap the bus assembly and cover. Not easy to do - you probably have to work with a company that specializes in old panels, and they may charge a pretty penny.

Tandem availability

Irrespective of first question, are there any other alternatives to my dilemma on the two tandems on the left (other than moving over to the other panel)? The tandem on the right side is fine btw in the sense that it’s not a MWBC but still lacks a breaker tie. Maybe there is a tandem single pole breaker with a built-in switch tie or a common trip that I haven’t been able to locate?

There's no such thing as a tandem that is factory handle-tied. That defeats the entire purpose of a tandem. Even so, all tandems are dangerously wrong for MWBCs.

Let's review: Why doesn't sharing neutral result in double current on neutral, setting it on fire? Because MWBCs (Multi-Wire Branch Circuits) must place their two hot wires on opposite poles of 240V. This means the neutral carries the difference in current, not the sum. This is the essence of MWBCs. You can see where that doesn't play nice with tandems.

In fact, I threw both legs (two breakers) on one of the MWBC’s yesterday and my voltage tester was still going nuts on a circuit receptacle and for the life of me couldn’t figure out what was going one so reflipped the breaker and all was well (which very likely indicates I’ve got a sketchy breaker).

For each cable, you need to follow the red-black pair to their breakers. You may find each MWBC takes 1 wire from each tandem, indeed placing them on opposite poles. This would've been more obvious if both red wires were on 1 tandem and both black wires on the other. (which is a fine way to do it).

So how do you get best of both worlds: Double-stuff breakers and handle-ties? A special breaker called a Quadplex breaker. This would be a drop-in replacement for the two red-handled tandems. They are made in every line except GE.

On a quadplex, one of the 240V circuits is on the inner terminals, and the other is on the outer terminals. Not all quadplexes handle-tie the outer terminals, so shop carefully.

In the Rule of Six area, a quadplex would count as two throws.

Siemens now makes a single pole tandem AFCI breaker but it’s really not designed for a MWBC that I can see because I’m not seeing anything about a common trip and I’m not big on breaker ties if they can be avoided.

The Siemens breaker is slick as a whistle, but useless to you unless these panels are Murray, ITE or specify a MP type breaker on their labeling. Yes, it's two AFCI breakers double-stuffed. Yes, the AFCI doesn't require the neutral wire! (Actually GE did this first; and they did it specifically to support MWBCs, with a listed handle-tie).

The problem is, you still need the handle-tie, and there are no field-applicable outer handle-ties to turn two tandems into a quadplex. Some make an inner handle-tie to turn two adjacent tandems into a center-only quadplex; that would work but you'd need a stack of three tandems for two MWBCs, and you'd have two leftover independent breakers on the ends.

Again you can't use brand X handle-tie with brand Y breaker with brand Z panel.

If you don't like handle-ties because of the way they love to fall out and be lost when handling the breakers, easy peasy - tape the breakers together with a couple loops of electrical tape. No more, you don't want it too thick.

Answer 2

Getting away from the Rule of Six

Our first challenge here is migrating you away from your current, nonconforming configuration with 1 service disconnect on the left, but 6 on the right, thus violating the Rule of Six. The good news is that whoever set up the right-hand panel thoughtfully left four free spaces at the top for us to use, so we'll put them to good work.

In particular, to get this panel up to anything resembling a minimum standard, you'll need to fit a QN2200(R) into those top four spaces, with its main lugs oriented towards the left side of the panel, and bolt it down with the included screw so that it can't come loose. From there, you'll need to have your power utility cut power to your house briefly so you can move the main wires in that right-hand panel over to the new main breaker, thus converting the Rule of Six panel to a backfed main breaker configuration. This is possible because the QN2200 is the Siemens equivalent of the Murray MPD2200, which your panel appears to be able to accept.

Now that that's out of the way...

Once that's done, you can get a Q22020CT2 to replace the existing pair of 20A double-stuff breakers in the top right of the lower section, thus providing a common maintenance shutoff for your MWBCs. Now, we can move on to the left-hand panel, where the various Eaton BR breakers that snuck into what appears to be a Siemens panel need to be replaced with their Siemens QP counterparts.

A postscript on that box on the outside of your house

As a sidenote, the box on the side of your house is what is called a current transformer cabinet, or "CT can" for short. It houses special calibrated step-down transformers that enable a 20A meter to handle a 400A service, and is sealed by the utility as you have observed, with the meter mounted in a separate socket that is connected to the CT can by wires in the conduit you see between the two.

This is similar to how a commercial or industrial electrical service is metered, and has the advantage that it can be used for much larger services, even up to massive industrial services in the multi-kilovolt and multi-kiloamp range. It does come with a major downside though, and that that's your utility can't just "pull your meter" to shutoff power to your panels; instead, they have to physically disconnect your incoming service drop, which may require more coordination (and trucks) than a normal setup would.