If this pump is running 24/7 (I'm assuming a permenant installation) wouldn't a cable gland with the flex entering into an isolating switch be a better solution than a plug & socket?
The NEC is pretty restrictive about using cables or cords without plugs.
In this case another option might be to use a flexible conduit but then a disconnecting switch would likely be required.
Bob Badger Construction & Maintenance Electrician Massachusetts
