I know this has been done but cant locate exact parts. I need a 15amp or 20amp ACrelay that can be controlled by the arduino 5v output. I dont understand why solid states are the preferred over the cheaper mechanical ones? I live in the USA so hopefully if anyone puts links to a store that ships here. Thank you all for helping with my first project and cheers
Soild state relays have no contacts to wear out due to arcing when switching an inductive load like a motor.
Gotcha that makes sense. Just had a thought. should I buy two 110v relays to control both hots going to the pump?
Lakes:
Soild state relays have no contacts to wear out due to arcing when switching an inductive load like a motor.
But SSR relays can have much difficulty switching high inductive loads such as large motors unless you equip them with a properly size snubber circuit. SSRs work much better with pure resistive loads. Also if actually running at 15 to 20amps they require a very large heat sink to keep from destroying the SSR. Most SSRs have about a 2 volt drop across them and at 20 amps that is 40 watts of heat that needs to be removed from the package. Actually at the 15-20 amp range you should be looking at 'motor controllers', which are large multi-pole electromagnetic relays designed to turn motors on remotely. They often contain built in 'overloads' and/or fuses.
15 to 20amps of AC current powering a motor is not something to fool around with unless you have the proper knowledge and experiences working at such power levels.
Lefty
this is the standard in the industry Zodiac Relay, 3 H.p. (r0658100) - INYOPools.com
I figured i should be able to find it cheaper if I do it myself. Any Ideas ??
This is not stuff to mess with unless you really know what you are doing.
The way I would do it would be to have the arduino drive a smaller relay which controlled a mains contactor relay
Again, do not attempt this unless you really know how to wire high current circuits.
Thank you for all the "you shouldn't mess with high voltage" . But I am and I understand it and work with it daily for a living and install manufactured systems that do what I am trying to do. I am new to arduino and I'm trying to get help with the relay portion as this part is not my specialty. I will use relays as this is the industry standard but was curious if anyone had experience with this type of scenario. Part numbers would help if anyone can. 
For example:
or
Google 
Check out digikey.com they have that relay you linked to earlier except it hasn't been dressed up with a wire and marked up 300%
The pump relay that Jeffmans speced out looks like a solid state. I have had no trouble with high current solid states, but then I run only resistive loads that don't kick back. The trick I use to avoid lots of heat is to use a relay rated at twice the amps. That way I only need a good heat sink and a little ventilation. The cost isn't that much more. The old kiln relays were all duty cycle contacts and they were always needing replacement... but they were switching probably a lot more than most applications.
RPCoyle:
The pump relay that Jeffmans speced out looks like a solid state. I have had no trouble with high current solid states, but then I run only resistive loads that don't kick back. The trick I use to avoid lots of heat is to use a relay rated at twice the amps. That way I only need a good heat sink and a little ventilation. The cost isn't that much more. The old kiln relays were all duty cycle contacts and they were always needing replacement... but they were switching probably a lot more than most applications.
No, it's a standard electromechanical relay available from Mouser for $14 and is probably the rest device to use.
Lefty
retrolefty:
RPCoyle:
The pump relay that Jeffmans speced out looks like a solid state. I have had no trouble with high current solid states, but then I run only resistive loads that don't kick back. The trick I use to avoid lots of heat is to use a relay rated at twice the amps. That way I only need a good heat sink and a little ventilation. The cost isn't that much more. The old kiln relays were all duty cycle contacts and they were always needing replacement... but they were switching probably a lot more than most applications.
No, it's a standard electromechanical relay available from Mouser for $14 and is probably the best device to use.
Lefty