My pool uses a 110V, 20 amp pump motor, specifically a Hayward Super Pump. Not sure on the HP rating but I believe it's the 1HP model based on the amperage. The pump uses a NEMA 5-20 plug, into a 20 amp GFCI socket, into 20 amp dedicated circuit.

In between the plug and the socket, I've added an Intermatic HB114 Heavy Duty timer, rated for up to 2HP motors. Ideally, I'd like the pump to turn on and off three times a day at various times, which I tweak depending on season, usage, and weather. The problem with that is, each time it turns off, there is a large arc. It seems unreasonably large to me. The arc is clearly visible through the opaque plastic housing of the timer, not just through gaps, but it actually illuminates the plastic. I believe the arc is destroying my timers, as their reliability significantly decreases after a month or so of operation, to the point that the mechanism doesn't turn properly and they no longer reliably turn the pump on or off and have to be replaced.

After giving up on the timer idea, I tried plugging and unplugging the motor manually, usually on a daily basis. Unfortunately, the arcing continued, and a month or so of doing that appears to have damaged both the socket and the plug. The tips of one of the prongs is visibly shortened from what it was before, and looks like it has been attacked by an angle grinder. Speaking with the previous owners, they confirmed the problem and explained that they simply left the pump plugged in 24/7. Due to rising electricity prices, this is not a reasonable option for me.

Aside from repairing all this damage that I did last year, I want to avoid a repeat of the situation this year. Is there anything I can do to avoid this situation in the future? Would a more expensive digital rather than mechanical timer help? Would hard-wiring the pump help? Is there some kind of arc-suppressor device or some kind of switch or power supply or capacitor that would help? Do I need a new/different pump? Should I consult an electrician?

  • \$\begingroup\$ I think something is wrong with your motor. Maybe something to do with the starting capacitor or relay. \$\endgroup\$
    – mkeith
    Apr 2 '18 at 6:26
  • 1
    \$\begingroup\$ Look up MOV's. Metallic Oxide Varistors. Snubbers you put across the contacts to absorb inductive kick-back. The should be the 40mm size with a voltage above your line voltage. Large motors always have a nasty back-emf when cut off. \$\endgroup\$
    – user105652
    Apr 2 '18 at 6:33
  • \$\begingroup\$ I agree. MOV’s and snubbers ought to divert the arc energy created from stored mechanical energy are needed . Active suppression methods can be used too. The contacts must be rated for > 2HP motor if there is more inertia not Every 2HP motor is the same \$\endgroup\$ Apr 2 '18 at 7:09
  • \$\begingroup\$ 110V 20A supplies comfortably over 2HP to the motor, so it may not be 1HP as you suggest. Tony has a point. \$\endgroup\$ Apr 2 '18 at 9:51
  • \$\begingroup\$ According to the owner's manual ecx.images-amazon.com/images/I/91iT7XXYyBS.pdf, the only Super Pump Hayward makes that recommends 20 amp/115V wiring is the 1HP model. Unless it has been installed grossly incorrectly, that's why I believe it is the 1HP model. It certainly shouldn't be any higher than that, or I assume it would be tripping the circuit breaker? \$\endgroup\$
    – cecilkorik
    Apr 3 '18 at 3:18

You need a motor contactor rated for 1-1/2 or 2 Hp. Use a timer to turn the contactor on and off. A timer rated for the contactor coil current should be much less expensive. MOVs are really designed for occasional high voltage spikes. They are not a substitute for a properly rated contactor.

Here are a couple of contactor examples:



Note that these are 2-pole contractors that will open both power lines simultaneously.

  • \$\begingroup\$ Those look great, but would it be possible to connect those to a timer? And I presume I would need an electrician to install them? \$\endgroup\$
    – cecilkorik
    Apr 3 '18 at 3:14
  • \$\begingroup\$ Don't use your existing timer to switch a contactor. Just get a larger intermatic timer. Not the plug-in kind, but the hard-wired kind. You should probably hire an electrician. \$\endgroup\$
    – mkeith
    Apr 3 '18 at 6:19
  • \$\begingroup\$ Yes, it would be possible to connect a contactor to a timer. If you can find an intermatic timer with a 1-1/2 or 2 Hp rating you would not need an electrician. If you add a motor contactor, an electrician may need to evaluate how to properly enclose it. Local electrical code may require an electrician. An electrician or pool service technician may be able to evaluate the motor. A 1 Hp motor should not require a 20 amp circuit. If the motor is 1 Hp, it may not be a very efficient one. The manufacturer may recommend a 20 amp circuit because they can't depend on the use of a dedicated circuit. \$\endgroup\$ Apr 3 '18 at 12:29
  • \$\begingroup\$ In any case, it would probably be a good idea to have a pool technician evaluate the condition of the pump and motor. \$\endgroup\$ Apr 3 '18 at 12:31
  • \$\begingroup\$ A contactor plus timer will work. I just advise against it because why have two things when you could just have one? Intermatic timers are very commonly used to control pool pumps and well pumps, and they have models that will do the job by themselves without an additional contactor. But if you decide to use a contactor plus timer, it will certainly work. \$\endgroup\$
    – mkeith
    Apr 3 '18 at 15:38

You got the wrong timer.

A 2Hp 240Vac rating is only 1Hp at 120V rating, so you are overloading it.

You probably won’t like the cost of a reliable 2Hp relay with Arc suppressor

  • \$\begingroup\$ It's only a 1HP pump, so I don't think I'm overloading it. I'm pretty sure that it's maximum rating is actually just the maximum of 120V 20 amps. I understand that running it at maximum rating is not ideal. I doubt I'm going to find a 120V 20amp timer with higher wattage. Are you implying I should upgrade the circuit to 30amp or 240V, and then find an appropriate timer for that? \$\endgroup\$
    – cecilkorik
    Apr 3 '18 at 3:12
  • \$\begingroup\$ A 120V 1 HP motor uses the same current as a 240V 2 HP motor. That is all he is saying. \$\endgroup\$
    – mkeith
    Apr 3 '18 at 6:22
  • \$\begingroup\$ Yes maximum rating means it lasts for 5000 cycles instead of 50k for a mechanical rating of 1million from some suppliers of silver oxide contacts. But these may not be that quality rating. If your results are much less then an RC snubber is advised. ( like a PP motor run cap \$\endgroup\$ Apr 3 '18 at 6:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.