[ Luke Myers wrote in 151216 MMDigest:

"I am wondering whether I can use a 5 ampere, 120 V.A.C. variable
speed fan control switch on a 6 ampere 120 V.A.C. vacuum motor ..."

Why not use a slightly larger speed controller like this 8 ampere
controller to give yourself a bit of safety margin?

http://www.amazon.com/KBWC-18K-H9011-Mount-Motor-Control/dp/B007YA2YW6/ref=pd_sim_60_3?ie=UTF8&dpID=21uU6Eqd6lL&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=1A7DWV54QCTBG3AMC1KA 

I'd think it's a generally good idea to use such devices at no more
than 80% of their rated capacity.  Starting off over capacity is a
recipe for an overheated device (at best).

Cheers,
Roger Wiegand
Wayland, Massachusetts
http://www.carouselorgan.com/