How to control high power HOA switch with a relay shield?

Hello kind people of the Internet,
I’m attempting to figure out how perhaps to use a relay shield to control an HOA switch (Hand/Off/Auto switch). Full disclosure: I have zero experience with an HOA switch.

The HOA switch would be controlling the power to a 220V / 440V AC water pump which pulls significant amps and is several hundred horsepower.

An example HOA switch would be perhaps, a Square D Control switch:
[link to Square D switch][1]

I noticed the discussion of the Ada fruit 120v controller (power switch tail 2) [link to Adafruit power switch here][2] …but need to handle significantly more power than 120V.

Any help/advice would be mucho appreciated…

thanks in advance

Hi @woody2shoes

Wow! That is a big switching problem, for sure. A pump motor that is rated 100HP at 440V would have a nameplate running amperage of around 135A and would require a very large relay or contactor to control it due to the locked rotor amperage, which should be 726A. This is not something that you should try to do unless you are very experienced! Very bad things happen very quickly when switching that much wattage. There are likely to be “lock out” requirements too to prevent accidental turn-on while someone is working on it.

I think the control switch you linked to is designed to be hooked up to the large relay or contactor that actually controls the high current pump, probably with starting capacitors and a starting relay or contacts too. The idea is that you change the selector which switches 110V (or 24V or 220V depending) to the big relay’s coil which in turn pulls in the contacts and turns on power to the pump. The control switch itself just has two normally-open contacts, one for each position, that are relatively low current (5A in the one you linked to).

If you are just trying to control an existing pump and contactor system, you have a chance of wiring in your own relay connected to a Core/Photon, but if you are designing from scratch you should hire an engineer to design it for you.

Do you have a contactor that controls this pump already? Do you know if it is 110V or 24V or 220V on the coil?


Hi bko, really appreciate the feedback!
… as it very much helped illuminate the scope challenge.

I’m fairly sure the motor has a contactor system in place (with starting capacitors, relays, coils, contacts, etc)…but full understand you’re advice for extreme caution regarding working with on this.

I’ll probably be actually looking at the set up sometime this summer, which is an agricultural water pump, way down several miles of dirt road…which the farmer has to drive out to, manually turn on, then remember hours/day-or-so-later, to go back and turn off. At this point I don’t have to many details, but again, you’re descriptions above have very much help shed light on the subject.

So far my discussions indicates there is a ‘normal’ on/off switch which controls the high power. I’m also told there are industry available radio controllers, but are fairly costly that has a specialized radio transmitter & reciever. So, given there’s cell signal out at the pump, it seems reasonable an Electron could do the trick (which I’ve already pre-ordered!..and lookn forward too).

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