I had to replace this old Bryant 20/20 tandem circuit breaker but could not find any with the deep-set contacts and the metal “guard” at the outer edge of the case [see picture]. I bought a Murray 20/20 tandem breaker and it installed just fine.
Electrical dept guy at Lowe’s said it is a “limiting breaker” made so the panel cannot be over-loaded by installing too many breakers. When I asked how this prevents installing too many breakers in a panel he hadn’t a clue. I Googled “limiting breakers” and came up with links about current limiting devices.
So what was this guy talking about, anyway?
Oh, and I noticed an interesting stencil on the old breaker specifying CU wire sizes 10-14. Under what circumstances might 14ga wire be allowed on a 20A breaker?
Thanks,BruceT
Edited 5/15/2008 4:50 pm by brucet9
Edited 5/15/2008 4:51 pm by brucet9
Replies
The metal guard is to prevent the circuit breaker from being installed on the standard panel busbar. The bottom 2-4 busbars in a service panel have slots cut in them allowing the installation of a few mini-breakers.
The idea was to limit the amount of mini-breakers that could be installed so that an inexperienced person would not jam the panel full of breakers and cause an overload of the main breaker or cause overheating of the busbar and surrounding breakers.
In a jam we used to take a hacksaw and carefully cut out the tab, now they make the mini breakers with and without tabs, I have no idea why except they charge a little more for the tabless mini's.
I think the 14-10 is just the lug rating and does not directly apply to the breaker capacity. But I also remember that back in the days before HACR breakers (which have a built-in delay for motor surges) it was common to install a larger breaker on a smaller wire to compensate for starting surges.
Thanks, for the explanation. So if I looked at the upper positions in the panel I would find wider connection tab?Sorry for the duplication. First nothing happens when trying to upload a pic, then if you click again it uploads twice and there is no way to delete the extra one before posting.BruceT
If you look at the listings on panels you find ones like 12/24, 6/12, 20/40, 30/40, and 40/40.
The first number is the number of breaker slots. The 2nd is the number of poles that the panel will handle.
The wiring diagram will show which spaces will take the tandem. A panel like a 12/24 all of the splace can use tandems. For the 30/40 it is the bottom 10. And the 40/40 can't have any.
None limiter breakers are produced for use with older panels that did not have the restrictor system.
Bryant is now the Cutler Hammer BR series and they are an exact replacenent.
About the wire size dedicated motor circuit do have different rules from general purpose circuits. Since the load is known, unlike with receptacles where any load might be connected, the breaker does not need to protect the wire from overload, only faults.
Going through the calcualtions you can use a larger breaker size than that allowed for general purpose circuits.
For AC compressors this information is printed on the lables. They will have a minimum circuit rating which is used to determine the wire size. And a Max HACR breaker size.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks Bill, for the complete and concise explanation. Would I find that listing on a label in the panel somewhere?BruceT
Maybe, in some format or another.This is what you will find on new panels. Look starting on page 31.http://www.schneider-electric.com.mx/opencms/opencms/SchneiderElectric/modules/Productos/resources/SquareD/documents/Cat-CC-QO.pdfYou see the maximum number of CIRCUITS. That counts the total of
both full size and tandem. On the next page they should a
electrical layout. The rectangular boxes represent the breakers. And
those with 2 bars represent ones that can accept tandems.Pages past that show the electrical diagrams for all of the
different pages.If you compare the part numbers with the diagrams you will see
the replation ship. In general the part number is of the
form xxxSSCCxxxAAAxxxSS - slots
CC -circuits
AAA - amp rating.So the QO12024L125G os a 20 slot, 24 circuit, 125 amp panel.
With tandems allowed in the last 2 slots.And the QO112L125G is 12 slots, 12 circuits, 125 amp panel.
No tandems allowed.It seems that many other brands follow a similar numbering scheme.Futher down they show the homeline series.This shows how to visual tell about older panels.http://www.squared.com/us/applications/residential.nsf/LookupFiles/Retailink_Jun03.pdf/$file/Retailink_Jun03.pdfNote that the Homeline is one of the "compatable" series that
use "similar" breakers with Murry, Siemens, Cutler Hammer BR
(Bryant, Westinghouse) and GE. So the clues should be the same.Cutler Hammer CH is a propritory line and I don't know about them.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.