Batboard

Quick question, what would happen if to much power is run through a duplexer? Let's say I have a duplexer rated @ 50w and I run 55w throught it. Fry the duplexer? Blow the PA on the radio?

If you are only going 5 watts above rated, you should be fine.
If you go WAY above rated power usually ya' fry or melt items in the duplexer, or the excess heat causes the duplexer to de-tune, and maybe fry your PA, or again, the components in the duplexer.

1) Heat, duty cycle and thermal inertia. Doubling the power through the device might be OK for a very short duty cycle. The heating effects are averaged over time. Heat will melt certain components, and can cause rapid oxidation in others. Power has to flow long enough to heat things up... followed by no power at all to allow things to cool.
2) Voltage ratings of the components, tx line, capacitors, etc could be exceeded with a resulting breakdown (flashover).

In your 10% excursion over the 50W duplexer rating, heating would be the limiting factor. Really depends how accurately the manufacturer determined that 50W rating. And you must consider your duty cycle.

RF Dude

Personally, I would never run 50 watts through a 50-watt duplexer, especially if it's in ham (yack yack yack) or P/S service. I generally purchase a duplexer that's rated for double the expected power.