Bypassing CB's? Klixon 7277 Circuit Breaker Clearance

[pecanflyboy]

My instrument panel was professionally built and installed by the original builder. It uses several rows of Klixon 7277 circuit breakers (CB's). These CB's are .75" tall. The rows are separated by 1" which gives at least 1/4" between each breaker. Seems like plenty, until.....

During some behind the panel maintenance, I discovered that the brass bus bar screw heads, and the screw heads from the output side of the row above, were making contact with each other:

https://drive.google.com/file/d/1G4x...ew?usp=sharing

As you can see, the screw heads on the output side of the CB row above, were touching the bus bar screw heads below, essentially by-passing the CB. My temporary fix was to install flatter headed screws which are shown in these pictures, and plastic insulators between the CB's.

https://drive.google.com/file/d/1o46...ew?usp=sharing

The permanent fix was going to either involve a re-fab of the CB panel, or creating separation between the screw heads. I decided to start by removing the bus bars, and installing flat head screws.

Bus bar with pan head:

https://drive.google.com/file/d/1PNF...ew?usp=sharing

I countersinking the bus bars:

https://drive.google.com/file/d/1HKR...ew?usp=sharing

And installing flat head screws:

https://drive.google.com/file/d/1rjP...ew?usp=sharing

The result is much better clearance:

https://drive.google.com/file/d/1LG9...ew?usp=sharing

https://drive.google.com/file/d/1omE...ew?usp=sharing

I may even try to install the flat heads on the output side to increase the clearance. I think you would need at least 1 1/4" between the CB's to make clearance between the hardware. You could also group the bus bars together.

Check those CB's!

[John Tierney]

Can you fit strips of rubber baffle materials between each row of CB's/bus bars?

[pecanflyboy]

Originally Posted by John Tierney

Can you fit strips of rubber baffle materials between each row of CB's/bus bars?

That was my initial, temporary fix. However, I was worried that vibration might wear through the insulator, or shake it out. Also, it caused the CB's to be stressed as they were being forced out of alignment.

[BobTurner]

How about inverting the middle row? Buss bar to buss bar, don't care if they touch. Without the thick buss bar, the "fused" sides may have a bit more clearance.

[DennisRhodes]

Sorry I didnt look at all your pictures but an idea may be while the buss bar is off to put a piece of heat shrink on it then open it up at the hole for each of the screws. Any close space could be at least insulated with the shrink.

[pecanflyboy]

Originally Posted by DennisRhodes

Sorry I didnt look at all your pictures but an idea may be while the buss bar is off to put a piece of heat shrink on it then open it up at the hole for each of the screws. Any close space could be at least insulated with the shrink.

That?s a great idea. I?ll do that next. I considered inverting the bus bars as mentioned, but the would have been issues with avionics bus isolation and possibly requiring some areas.

The main point of the thread is that you need a lot more clearance with these CB?s than you think.

[keitht]

Ran into a similar problem. My solution was to run the bussbars so that they were on the bottom contact on the top row of breakers and the top row of contacts on the next down row of breakers. Then even if the bussbars touch it doesnt bypass the breakers. It does require a redo of the wiring on the downstream side of the breakers in your case which may be a bigger problem than the solution you chose.

KT

[Carl Froehlich]

As a side note - I never use bus bars. All that bare copper waiting for a nut or screw to fall and short it out always bothered me.

Carl

[sf3543]

You can also remove the copper strips and use wire with terminal ends.

[RV7A Flyer]

As an observation, you have no service loop in those wires. Had that been available, one part of the solution may have been to rotate the ring terminals to avoid interference of the crimped portion and wire with other elements.

Probably too late now unless you rewire it, and may not have helped anyway, but it's good practice to add sufficient service loop (normally, enough to cut and recrimp a new connector 3 times before having to run a new wire).