Why am I still seeing a voltage ?

Greetings,

I am in the process of wiring up my controller cabinet and have
decided to incorporate a servo drive e-stop circuit that
was created my Mariss of Gecko Drives. In his circuit he has the
e-stop button disconnecting the "common" side of 110vac. I have
wired the coolant pumps "common" in series with the "common" from
the e-stop button so that if an e-stop condition occurs the coolant
pump will shut down. Ater doing this I started the controller and
measured the voltages and when the circuit was complete my
multi-meter showed 117vac, great ,however after I hit the e-stop
switch I decided to mesure the voltage to verify that it was 0 at
the coolant pump, To my surprise it measured 17vac.I am not
accustomed to breaking the "common" leg of a curcuit as my AC
wiring skills are limited to house things.Can anybody tell me why
I still see a voltage?

Thanks
Jeff