1/2" Or 1" Circuit Breakers (Residential Load Center Box) ?

Nipple Clamp boy!

There may be all sorts of building code and NEC code limitations, etc. I particular, I saw postings a couple of months ago about 42 breaker limits.

However, electrically, using the 1/2 size breakers works.

All of those that I have seen have a smaller breaking capacity, but I am not an electrician. Typically a full size 20 Ampere branch breaker in the USA is rated 10000 Amperes; the half size ones are 5000 Amperes. Here too there may be rules that require minimum fault limiting capacity.

| There may be all sorts of building code and NEC code limitations, etc. | I particular, I saw postings a couple of months ago about 42 breaker | limits.

The 2008 NEC has lifted that limit.

| I see that circuit breakers are offered in 1/2 inch and 1 inch sizes.

The only ones I've seen in 1/2 inch are doubles in a 1 inch space.

Cutler-hammer CH series and Square-D QO are 3/4 inch (but not compatible with each other).

| Obviously, I think, assuming one doesn't exceed the main breaker capacity, | it is possible to have more (independent) branch circuits utilizing the 1/2 | inch variety. | | So, my question is: why hasn't the industry standardized on (just) the 1/2 | inch size. ?

You mean the doubles? Until recently, there was a limit on breakers in a box and even so, the new 2008 NEC that lifted the limit would need to be adopted in your area/city/state.

| Seems like they would fulfill most every need. | Why use the 1 inch at all ?

A 1/2 double is a 1 inch with 2 circuits on the same pole.

| Are they as reliable, or safe, as the 1 inch types ?

That's questionable. They certainly do not have the variety.

There are a few singles. I have seen them in GE and the ever popular FPE.

UL tests a panel with a specific number of breaker "poles". A 2 pole breaker is 2 "poles". Two half sized breakers are 2 "poles". Previously, both the NEC and UL also limited the maximum number of "poles" to 42. The NEC limit is gone (as phil said), UL should be disappearing if not gone. But, as before, the number of "poles" will be limited to the maximum number the panel was tested with ? which may be well under the old 42 limit.

Panels have, for a long time, been required to limit the spaces where half sized breakers can be installed. If all the allowed half sized breakers are installed, along with the rest full sized, the panel will be at the maximum number of "poles" allowed by the UL listing for that panel. All of the spaces may allow half sized breakers, or none of them. These are called class CTL (circuit limiting) panels. (This was not changed).

------------------- For your amusement - the way I am reading the 2008 NEC you can have 2 main breakers, with one supplying a split bus that still has a limit of

| UL tests a panel with a specific number of breaker "poles". A 2 pole | breaker is 2 "poles". Two half sized breakers are 2 "poles". Previously, | both the NEC and UL also limited the maximum number of "poles" to 42. | The NEC limit is gone (as phil said), UL should be disappearing if not | gone. But, as before, the number of "poles" will be limited to the | maximum number the panel was tested with ? which may be well under the | old 42 limit.

Just because the NEC limit is gone does not mean the number of breakers in a panel can be allowed to exceed the listed limit. For example, a panel might be designed for, tested for, and listed for, no more than 72 poles in use, and have 48 slots to put them in. Putting in enough doubles to exceed the 72 poles listing of the panel would make it a panel not in compliance with the listing, and thus not in compliance with the NEC rule requiring them to be listed. There is one of those, right? I didn't go check before writing this.

| Panels have, for a long time, been required to limit the spaces where | half sized breakers can be installed. If all the allowed half sized | breakers are installed, along with the rest full sized, the panel will | be at the maximum number of "poles" allowed by the UL listing for that | panel. All of the spaces may allow half sized breakers, or none of them. | These are called class CTL (circuit limiting) panels. (This was not | changed).

It's a matter of how the panels are designed. There's (probably) a reason we don't have small 22 space panels that could be filled to the 42 circuit with doubles in all but 2 spaces.

There are panels with as many as 84 spaces I found in a Schneider catalog (they own Square-D) for Canada. It's a BIG TALL panel. I had original planned on smuggling a couple of these across the border to put in the house I'm planning to build ... not to get 168 circuits ... but rather so I can space out the breakers and better heat dissipation with more AFCI breakers in there. I think maybe that should be an issue UL might want to look at: the heat buildup when panels have a LOT (mostly) AFCI in there.

Anyway, in theory, Square-D could now market those panels in the USA with no complications from the NEC. They already have panels up to 54 spaces, and note on the specs to follow the NEC 42-circuit limit. That would be for perhaps the above spacing idea, or breakers with added features such as switched neutral, shunt trip, etc.

| For your amusement - the way I am reading the 2008 NEC you can have 2 | main breakers, with one supplying a split bus that still has a limit of | 42 poles. Probably not what you intended to install.

Maybe an overlook of the intent of removing the limit?

Thats what I said. That is the point of class CTL panels.

Nope, it is clearly intentional. But I don't have any idea where it is useful.