Tandem breakers

[nizak]

I was told something today from an electrical inspector that I believe is incorrect.
In taking about adding a sub panel for additional circuitry, the inspector said that I could add tandems to the existing load center. I said that it was a 40 space 40 circuit panel and that tandems weren't allowed. He told me that tandems were " listed" and that I could legally put 40 tandems in and essentially have 80 single pole circuits.



I'm familiar with load centers that are specifically designed for tandems.
Thoughts?

 

[AC\DC]

check The sticker on the panel and look for random slots

 

[brantmacga]

You are technically correct. While the CTL restrictions have been removed, if your existing panel is labeled as 40/40, and it’s a stab-on bus, it won’t be slotted for tandems.

I’m not familiar with every panel out there. I know SqD offers a QO tandem without the hook that will fit in any QO panel space.


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[nizak]

check The sticker on the panel and look for random slots

You are technically correct. While the CTL restrictions have been removed, if your existing panel is labeled as 40/40, and it’s a stab-on bus, it won’t be slotted for tandems.

I’m not familiar with every panel out there. I know SqD offers a QO tandem without the hook that will fit in any QO panel space.


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It is a QO panel. 42 years old. I am familiar with $70 QO stab on tandems , but didn't think you could simply fill a load center with 40 of them just because they fit.

 

[curt swartz]

You are technically correct. While the CTL restrictions have been removed, if your existing panel is labeled as 40/40, and it’s a stab-on bus, it won’t be slotted for tandems.

I’m not familiar with every panel out there. I know SqD offers a QO tandem without the hook that will fit in any QO panel space.


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The CTL requirement has not been removed. You are still limited to the maximum number of overcurrent devices the panel is listed for. The maximum of 42 circuits is what was removed from the NEC.

While SquareD now lists most Homeline loadcenters for tandems in all locations they don't list all of them that way. QO's are often listed for only full size breakers. When I built my house a couple years ago I used 42 circuit plug on neutral loadcenters. They are not listed for any tandems.

I know Siemens still list many loadcenters for full size breakers only too.

 

[brantmacga]

It is a QO panel. 42 years old. I am familiar with $70 QO stab on tandems , but didn't think you could simply fill a load center with 40 of them just because they fit.

It all depends on the listing of the panel. There are two versions of QO tandems.

QO2020 - non-CTL, will fit any space.
QOT2020 - CTL, will only fit in the lower spaces with notches for the rejection hook.

At 42 years old, your panel is probably a class CTL, and if the listing is for 40 circuits only you wouldn’t have rejection hook slots. The QO2020 will fit anywhere, but you technically aren’t supposed to install it.

It sounds like you’ve already verified the listing but take a look at the lower 5 bus spaces and see if there is a slot on the base rail. It’ll probably be filled with a small piece of metal that can be punched out to accept the rejection hook. The QOT version is a few dollars less expensive.


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[MTW]

QO tandems were made in three styles
No rejection feature- earliest type
Molded rejection bump on the breaker bottom
Metal rejection hook

I have all three types, in my collection.

 

[mtnelect]

Don't forget to use the ties if it is a 3-Wire circuit.

 

[Fred B]

Don't forget to use the ties if it is a 3-Wire circuit.

Word of caution, be sure to use a 2 pole tandem if wireing a MWBC and be sure to land each wire on seperate poles in addition to the handle ties.

Had an Eaton panel marked as 40/80, no rejection slots anywhere on bus only option for tandem was the higher priced tandem without the rejection clip. Kind of sucks.

I think OP is correct if panel is marked as only 40, then mfg didn't design and test to have tandems and would be a technical violation to use them. Another factor as to fully loading panel with tandems, load calculations would also have to be figured in to prevent overloading. Also AFCI requirements might restrict how many tandems you can use. Siemans is making (only one that I know of) a tandem AFCI.

 

[jaggedben]

Word of caution, be sure to use a 2 pole tandem if wireing a MWBC and be sure to land each wire on seperate poles in addition to the handle ties.

One does NOT wire an MWBC to a single 2 pole tandem. Ever. You wire it to poles on separate phases, either a two pole full space breaker, or separate breakers. Just want to make sure no one is confused by what you said. Seen it enough in the field to know a lot of people are confused.

 

[wwhitney]

One does NOT wire an MWBC to a single 2 pole tandem.

I think you are taking "2 pole" to mean "2 branch circuit connections" while the person you responded to meant "2 pole" as "2 bus connections".

Cheers, Wayne

 

[jaggedben]

I think you are taking "2 pole" to mean "2 branch circuit connections" while the person you responded to meant "2 pole" as "2 bus connections".

Cheers, Wayne

He said '2 pole tandem' which by definition is only one bus connection.

Like I said, I just don't want people to get confused. Because people do. I've seen lots of MWBCs improperly wired to a 2 pole tandem (1 bus connection) and on occasion I've seen the charred neutrals that result from it. This one of the most dangerous commonplace mistakes in residential wiring.

 

[wwhitney]

He said '2 pole tandem' which by definition is only one bus connection.

If "pole" = "number of switches you can throw" then I agree it's very rare for such a tandem to have more than one bus connection (although I seem to recall there might be one manufacturer where it's possible).

But the word "tandem" already implies more than one switch. So if the comment is to "be sure to use a 2-pole tandem" rather than just a regular tandem, the modifier "2-pole" is obviously meant to convey something extra. In the usage you were responding to (whether or not "pole" was the correct word to use), I took it to convey 2 bus connections, typically a tandem (quad) that would take up 2 spaces.

Cheers, Wayne

 

[Fred B]

One does NOT wire an MWBC to a single 2 pole tandem. Ever. You wire it to poles on separate phases, either a two pole full space breaker, or separate breakers. Just want to make sure no one is confused by what you said. Seen it enough in the field to know a lot of people are confused.

That is what im saying.

 

[Fred B]

He said '2 pole tandem' which by definition is only one bus connection.

Like I said, I just don't want people to get confused. Because people do. I've seen lots of MWBCs improperly wired to a 2 pole tandem (1 bus connection) and on occasion I've seen the charred neutrals that result from it. This one of the most dangerous commonplace mistakes in residential wiring.

My view of a 2 pole tandem is the same as any other 2 pole breaker. A single pole tandem is 2 handle on one pole, a 2 pole tandem will have 4 handles, an connections on 2 seperate poles.

 

[jaggedben]

I call that a quad. I would never call that a tandem, just to avoid the confusion.

I never would have thought that people would consider the number of 'poles' on a tandem to be the number of connection to the bus instead of the number of circuit handles. I would say a tandem is a device that contains two single pole breakers. But I guess this all just shows that clarification of terms is necessary.

 

[jaggedben]

My view of a 2 pole tandem is the same as any other 2 pole breaker.

You might want to consider that they are actually different. Common trip devices are true 2-pole devices and a tandem is not.

Typically the number of 'poles' refers to the number of electrical connections that are switched by the same handle or trip mechanism. I assembled a 3 pole 12 position rotary switch once.

A single pole tandem is 2 handle on one pole,

A tandem is two single pole circuit breakers in a device that has a single connection to a panel busbar. Referring to tandems as 'two pole' or 'single pole' is just confusing IMO.

a 2 pole tandem will have 4 handles, an connections on 2 seperate poles.
View attachment 2561599

See above.

 

[tortuga]

Zinsco type Z tandems can grab both busses, also FPE and GE tandems are designed so a tandem can grab 240V.
Challanger also made a bizarre tandem with little hooks to grab the other buss.
Also bulldog or pushmatic might have grabbed both buses.
Most all but GE are long obsolete now.

 

[jim dungar]

Also bulldog or pushmatic might have grabbed both buses.

No, they did not. To get 240V, the breaker had to be built as a 2 pole device.
Although they may have made a 2 pole with a tandem single pole on each side, like the 'Quad breaker' others mentioned.

 

[Fred B]

I call that a quad. I would never call that a tandem, just to avoid the confusion.

I never would have thought that people would consider the number of 'poles' on a tandem to be the number of connection to the bus instead of the number of circuit handles. I would say a tandem is a device that contains two single pole breakers. But I guess this all just shows that clarification of terms is necessary.

Ge makes a quad, it has 4 single pole breakers together just like a 2 pole has 2.
This is why you cannot use a single pole tandem for a MWBC, a double pole tandem you can actually have 2 mwbc so long as each is terminated on seperate poles.
Generically what is a 2 pole breaker? Generally we speak of a breaker that lands on 2 seperate buss tabs. What is a single pole breaker? Generally It is only landing onto one buss tab.
But I think mfg terminology also lend to some confusion. In some advertising the 2 pole tandem is also called a quad, but I have always seen the quad being like the 4 pole GE breaker below.