PD 52 transfer switch hum normal?

They buzz when the relays get dirt inside and the two parts of the armature cannot "seal up" tight. Once you are home and have time, dismantle the relay and clean it out. If necessary, sand the mating surfaces against a sheet of fine sandpaper on a flat surface. With alternating current relays, if the two metal surfaces cannot solidly connect with each other in addition to buzzing it also can make the relay coil run hot and eventually fail. You can also buy new relays fairly inexpensively to replace it once you get it out and can identify it. eBay is your friend. If you buy a completely new transfer switch, get the PD52DCS model as they utilize internal rectifiers to furnish DC (direct current) to a DC coil relay that will not buzz when it gets dirt in it and will not burn out from not "sealing up" properly like is very necessary with an AC coil. A hazard of using AC coils in an RV that gets exposed to a lot of dirt and dust.

enblethen wrote:
Check for loose connections.
Think about replacement as it will fail when you need it the most.

I tightened connections. No change

Is there a better model available?

Check for loose connections.
Think about replacement as it will fail when you need it the most.