What is this symbol near an AC motor?
The capacitor symbol inside it may be a clue; the block next to it is one way of representing a resistor, and the staggered lines above it suggest there are three.

Given this, I suspect it's three R-C snubbers, wired in delta, to reduce noise and switching transients on the 3 phase supply. This IS a guess, but there's not much else it could be.

Component values? Resistors in the tens of ohms, capacitors a fraction of a microfarad (e.g. 47R,0.1uF) would be typical. The physical unit is probably a sealed metal can, and may or may not have such useful information printed on it.