They didn't used to be, however, Square D now has a "homeline" line of circuit breakers which interchange with gould. They are available at Lowes, Home Depot and other hardware stores. Make sure you purchase the identical amperage Square D "homeline" breaker.
Breakers are build to snap onto a buss bar in a breaker panel. If they look the same on the back end then they will likely work. If not do not try to force a fit. To add a little more to this: 1st of all it depends on what kind of Square D you are talking about. Square D Homline breakers will fit in a GE panel but GE breakers will not fit into a Homeline panel in my experience. Square D QO is not compatible with either.
No, if you have a Square D distribution panel only Square D breakers will fit in it.
No, only Sq D breakers will fit into a Sq D panel. I believe Square D makes at least two styles of breakers. Home and industrial. I have a GE entrance/distribution box that has Square D (home), Murray, Bryant, Westinghouse, and GE breakers, all working together. I hope this helps.
sqaure D
No, Sq D and Cutler Hammer breakers are not interchangeable.
Square D circuit breakers can be purchased from various homeware and DIY stores such as Home Depot or Lowes. Websites that specialise in circuit breakers such as Circuit Breaker Service or All Breakers do sell them as well.
Square D was founded in 1903 and was called Detroit Fuse and Manufacturing. They made breakers that very first year.
Square D breakers can be bought online on various websites that specialize in the electronics and electronics accessories such as Best Buy and Amazon.
Only a Square D designed breaker can be installed in a Square D manufactured panel.
GE circuit breakers with catalog numbers ranging from THQL1115 through to THQL1150 can be substituted like for like with Cutler-Hammer circuit breakers coded CL115 through to CL150, ITE Siemens circuit breakers coded Q115 through to Q150 and Square D circuit breakers coded HOM115 through to HOM150. These are single pole breakers. GE circuit breakers with catalog codes from THQL2115 through to THQL2150 can be substituted with Cutler-Hammer circuit breakers CL215 through to CL250, Square D circuit breakers HOM215 through to HOM250 and ITE Siemens circuit breakers Q215 through to Q250 of the same amperage and voltage. These are double pole breakers.
The big yellow "D" is the logo for Square-D, a manufacturer of circuit breakers.
GE circuit breakers with catalog numbers ranging from THQL1115 through to THQL1150 can be substituted like for like with Cutler-Hammer circuit breakers coded CL115 through to CL150, ITE Siemens circuit breakers coded Q115 through to Q150 and Square D circuit breakers coded HOM115 through to HOM150. These are single pole breakers. GE circuit breakers with catalog codes from THQL2115 through to THQL2150 can be substituted with Cutler-Hammer circuit breakers CL215 through to CL250, Square D circuit breakers HOM215 through to HOM250 and ITE Siemens circuit breakers Q215 through to Q250 of the same amperage and voltage. These are double pole breakers.