GE Spectra bus fingers

[chris kennedy]

I have a 125A breaker frame (came without the hardware) to bolt on to the fingers in a 480V 1000A dist pnl. Looks like 10/32 but that doesn't feel right when you try to bolt it in. Anyone know for sure?

Thanks

 

[shepelec]

10-24??

 

[G._S._Ohm]

M5 x .08?
http://www.precisionscrewandbolt.com/metric.htm

 

[G._S._Ohm]

Trying wedging some toothpicks into the hole. The outer ones will have marks from which you can measure or judge the thread pitch but you'll need a magnifier.

 

[LarryFine]

All of the bolt-in breaker bolts I ever had reason to determine the thread of were 10-32's. I've found that grounding screws are the same thread, length, and hex size, and fit like they were made for them.

If you're concerned with damaging the bus by forcing a 10-32, I'd try it in a bottom finger. You could try running a 10-32 tap as a thread chaser. The worst that can happen is the bus has to be re-tapped.

 

[chris kennedy]

Its definitely a fine thread (32). There are no extra fingers to experiment on, I'm using the last three. I am thinking about running a 10/32 tap through them first but its a ?" copper bus and if I break off a tap in there, well that will make for a bad day.

 

[masterinbama]

Take a screw out of one of the other breakers to measure/match your new ones to.

 

[cadpoint]

If you had some taps you could identify the threads... Maybe a clearer understanding of Threads per Inch is required...

 

[GeorgeB]

M5 x .08?]

you mean M5 x 0.8, but that's not the issue. If it were M5 x 0.8, a 10-32 would screw in easily at only 1/4 thick. M5 is 0.196 inches, #10 is 0.190 inches. 0.8mm pitch is 31.75 threads/inch.

IN GENERAL, with a well tapped part and good male thread, a 10-32 male will screw into a M5 x 0.8 female about 1/2" before any resistance is felt. They'll get really tight at about 3/4".

I'm basing this on tests I used to run, in the late 1970's, with hardened tool steel female in a tensile testing machine where we regularly tested proper pairings, and one tech was given a bunch of 10-32 and told they were M5-0.80 ...