How is that even possible? The CH's mounting rail is made altogether different.

They just bent the back of the qo cb and the cover held it in place
Ob

The panel looks like a Cutler Hammer CH loadcenter, the breakers with tan hanhles are Cutler Hammer CH model same mount as a Square D QO, and the double pole in the bottom right side appears to be a QO breaker. Other than being mis matched according to brand whats the trouble?

I don't think this will fly .....

Sq D has gone to great lengths to have a 'unique' style of breaker with the QO. It's a pretty large part of their corporate ethic that only their breakers, only their panels be used.

We're not talking about the 'classified vs. listed' breaker debate here .... I don't think the QO breaker 'fits' in that load center .... I think it was 'made' to fit! As such, I say it's a 'no go' situation,

Sq D HO style will fit.
Insatlation is a Violation of Section 110.13 (B)

I don't think so. The Homeline product is more in-line with Siemens/GE, et. al. standard 1" stab.

I will admit that I got a Square D QO series GFI breaker to fit in a Cutler-Hammer "CH" series panel on a fire job. It was an emergency call at night, I had to disconnect all branch circuits and install a single GFI circuit before the POCO would turn the power back on. At 2:00 in the morning, I figured it was safe until we could return the next morning with the correct breaker. It can be done.

We don't have that style C&H up here although from the picture it looks like the front line clips on the breaker would fit over the busswork, BUT the rear clip to hold theload side of the breaker in would have had to been modified to fit over that metal rail, OR removed completely..

I guess square pegs DO fit in round holes.. You gust have to hit them hard enough!

A.D

A square D breaker switch in Cutler Hammer panel, that's a new one on me.

I hope that double pole breaker switch at the top labeled MAIN is not being back fed to the panel bus bars.

I'm sure it is.
Why do you think it is a problem?

How else would the busses be powered? Backfed mains are fine as long as a hold down bracket is used.

That panel predated the requirement for a hold down on plug in backfed breakers, as 384-16 (f) showed up for the 1st time in the 1990 NEC.

The CH 100+ amp breakers used to take four pole spaces (two adjacent two-pole positions). On the right side, the breaker clipped along the rail. On the left side, there was a screw/clip that was installed to lock it down. If you look very close, you'll see the locking screw on the left side rail.

Living in a tiny tiny town, I get to see every breaker that'll fit in every box. :P

A SquareD Homeline breaker will fit in ALMOST every other manufacturer's panel, but others' breakers won't fit in the homeline panel, due to a slightly different shape of the mounting rail.

QO breakers usually aren't interchangeable with anything.