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Old 05-28-2014, 05:28 PM   #1
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Pool Pump Motor Switching


A question came up on a home automation (HA) forum regarding a pool pump motor. Today currently controlled via a mechanical timer (dial type Intermatic) for so many hours of operation a day. The change desired is to make this controlled under a home automation systems so it can be programed and used more flexibly.

All that said the question came as to whether a 240VAC pump motor needed to switch both phases on and off on the pump motor of if just a single pole switch would be adequate. I thought I'd post this over here where more licensed folks can chime in.

My thinking is a single pole switch to control the motor is fine if some sort of disconnect is local to the pump motor. That disconnect can be a DPST switch or a disconnect like an AC disconnect panel. Whatever disconnect used it would have to disconnect both phases to the motor. Furthermore I would argue, since the HA switch is remote controllable, it should be disallowed as a disconnect since it can be inadvertently switched remotely. Not exactly fail safe....

Thoughts?

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Old 05-28-2014, 08:13 PM   #2
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Pool Pump Motor Switching


Most 240V equipment is indeed controlled through the switching of just one leg. Some equipment for reasons of safety only use double pole switching. Of course if you have wired your pool with safely in mind then it would include a gfci breaker, which would take care of the safety side of things.

But if you're talking automation, then you're talking about controlling the system from a distance (not being present to ensure everything is working properly). That being the case, why take a chance. Double pole relays aren't that much more expensive than a single pole.

Is this a hot tub or an actual pool?

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Old 05-28-2014, 08:19 PM   #3
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Pool Pump Motor Switching


It comes down to what is the disconnect, a controller only needs to break one leg, but if you are using some device as a disconnect it MUST break both legs...
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Old 05-28-2014, 09:13 PM   #4
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Pool Pump Motor Switching


You'll need a double-pole disconnect (manually activated, not a contactor), but the switching device for control only needs to break the circuit at one point. A solid-state relay is your best bet these days, since they are so cheap and reliable, and much easier to interface to digital devices.
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Old 05-28-2014, 11:21 PM   #5
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Pool Pump Motor Switching


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Originally Posted by stickboy1375 View Post
It comes down to what is the disconnect, a controller only needs to break one leg, but if you are using some device as a disconnect it MUST break both legs...
430.84 The controller shall not be required to open all conductors to the motor.

430.103 The disconnecting means shell open all ungrounded conductors and shall be designed so that no pole can be operated independently.

So yes, as noted, whatever turns the motor on and off can be either one or two pole, but the disconnecting means needs to open both lines.
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Old 05-29-2014, 04:14 PM   #6
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Pool Pump Motor Switching


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Most 240V equipment is indeed controlled through the switching of just one leg. Some equipment for reasons of safety only use double pole switching. Of course if you have wired your pool with safely in mind then it would include a gfci breaker, which would take care of the safety side of things.

But if you're talking automation, then you're talking about controlling the system from a distance (not being present to ensure everything is working properly). That being the case, why take a chance. Double pole relays aren't that much more expensive than a single pole.

Is this a hot tub or an actual pool?
Pretty much, all the electronic timer systems have gone to switching one leg to save room and keep the system as small and cheap as possible. This includes the HA designed pool timers. I do agree, if you're building you're own HA system, just install the double pole and break both legs. As you pointed out, the price difference is small, sometimes the same.
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Old 05-29-2014, 04:19 PM   #7
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Pool Pump Motor Switching


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You'll need a double-pole disconnect (manually activated, not a contactor), but the switching device for control only needs to break the circuit at one point. A solid-state relay is your best bet these days, since they are so cheap and reliable, and much easier to interface to digital devices.
Both types of relays are easy to interface. For the electro-mechanical, you just need a power supply with a little more power. Both will require glue logic circuits and both come in 5VDC coil (gate on SSRs) versions.
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Old 05-29-2014, 09:42 PM   #8
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Pool Pump Motor Switching


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Both types of relays are easy to interface. For the electro-mechanical, you just need a power supply with a little more power. Both will require glue logic circuits and both come in 5VDC coil (gate on SSRs) versions.
A mechanical contactor adequate for a pool pump load will require a 12, 24, or 120V coil circuit with a decent amount of current (an amp, more or less). That will require its own control device to interface with the logic - either another smaller relay or a power semiconductor. If you use an SSR, many microcontrollers can drive it directly (it's just an LED, internally), but those that can't will work fine with just a single small open-collector transistor as a buffer. It's way easier.
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Old 05-29-2014, 10:45 PM   #9
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A mechanical contactor adequate for a pool pump load will require a 12, 24, or 120V coil circuit with a decent amount of current (an amp, more or less). That will require its own control device to interface with the logic - either another smaller relay or a power semiconductor. If you use an SSR, many microcontrollers can drive it directly (it's just an LED, internally), but those that can't will work fine with just a single small open-collector transistor as a buffer. It's way easier.
The 6V Omron GL7s work fine at 5VDC and drive 3HP just fine. Want more, then use a latching relay that can drive 5HP such as the Hongfa HFE10. A GP medium duty transistor is adequate enough to drive these and I did mention glue logic. Using a smaller relay to drive a larger relay is not the best method, but it will work, but you still need a transistor to drive it, unless your talking HV coil. And these do not require an amp or more (GL7 is 320mA, HFE10 is 250mA). I don't know why you'd think so much current, since 20A relays draw up to 200mA.

An SSR is not an LED internally unless it is an optical SSR. But the thyristors inside an SSR are silicon diodes with a wire bonded to the P-N junction (the gate).

Most uCs cannot source or sink typical indicator LEDs unless the current is about 10mA or less or you drive them less than or equal to 1/2 their rated current. Many PICs can source and sink, because they were desigined for >=20mA, still too low for lighting type LEDs (unless you're going to include any GP high brightness, but these are not really considered lighting LEDs).
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Old 05-30-2014, 02:15 AM   #10
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Pool Pump Motor Switching


I suppose there are some suitable relays with very low coil power requirements. You don't usually see relays capable of switching that much load with that little coil power. It's still enough to always require an intermediate switching device though. I'll stick the my SSR recommendation. They are more inherently reliable and even easier to drive. They are LEDs internally - regardless of what type of thyristor is used (many are photothyristors), every line-voltage SSR I've used has been optically isolated. Most do not require more than 10mA for full turn-on, and it's not hard to find a microcontroller than can drive that directly. Simpler, more reliable, about the same price... solid state relay.
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Old 05-30-2014, 06:13 AM   #11
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Pool Pump Motor Switching


Oddly, around here, people never turn their pool pumps off, they run 24/7... so i always chuckle when people want to integrate their pump into home automation.
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Old 05-30-2014, 07:00 AM   #12
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Pool Pump Motor Switching


Why not use a small cheap digital timer a wall wart
And a contactor with a 12v coil.
Easy as, and cheap !
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Old 05-31-2014, 09:27 AM   #13
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Oddly, around here, people never turn their pool pumps off, they run 24/7... so i always chuckle when people want to integrate their pump into home automation.
Let me add...

For the life of me I can't understand WHY anyone who want's to "automate" their home would take a pool pump or a water heater, devices that are already automatic, and integrate them into a "system." This isn't "home automation" but more like re-integrating automation into the hands of a control freak.

Just because you CAN doesn't mean you SHOULD.
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Old 05-31-2014, 11:32 AM   #14
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Let me add...

For the life of me I can't understand WHY anyone who want's to "automate" their home would take a pool pump or a water heater, devices that are already automatic, and integrate them into a "system." This isn't "home automation" but more like re-integrating automation into the hands of a control freak.

Just because you CAN doesn't mean you SHOULD.
I concur, people with just too much time on their hands....

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