Hello,
I am rewiring switched for two pool pumps. The old set disintegrated so I cannot tell how they were wired. The two pumps are recirc and booster and are both 230v. I would like to wire them so that the booster can only turn on when the first pump is on. How can I manage that wiring with no loss of voltage?

Add a contactor to the recirc pump circuit to close when the recirc pump is on. Wire the contacts of the contactor into the circuit of the booster pump. This way if the recirc pump is not on the booster pump cannot come on.

Thanks! So there is no way to do this simply based on wiring the 2 30 amp dbl pole switches?

What turns on the pumps? A switch? A breaker? Where is it located? What is the HP rating of the pumps?

The problems are protecting both motors separately and having them both turn on together.

I am thinking on the lines of a NEMA class enclosure for wet environments and two DIN rail breakers and a watertight switch on the outside of the enclosure. You would need two contactors to do this. One for each motor.

Motor starters would be a better choice to protect the motors. You have to look at replacement costs and wheter it's worth it. I would get a case large enough to put in two DIN rail motor starters.

DIN rail is basically an erector set for controls.

Kiss's points are well taken. If the controls are in a potentially wet area use the proper enclosure. Most of these pumps are thermally protected. They have a thermostat right in the motor housing to protect it from overload. They generally have some sort of strainer to keep big stuff out of the impeller so stalls are not a big concern. Watertight enclosures are expensive, if you can keep the controls in a dry place you are better off. The motors should be on separate circuits if possible. They are not wired in series at all.
Another way to do this is to use a three pole switch for the circ pump, using the third pole to make a break one leg of the boost pump. Then use a double pole switch, one leg through the circ pump switch, to feed the boost pump. In this case these pumps should be on one circuit. It is most likely a code violation to have feeds from two different circuits in the three pole switch. If KISS knows for sure let me know.

Switching one leg won't work if this is a disconnect.

Good point about the internal thermals, very good motor protection.

I guess the one issue is that there is a disconnect nearby. Plugs can serve as one and so can a disconnect. Nice thing about disconnects as that they are lockable off.

As long as the system is protected by a GFCI and metal is properly grounded to the pull pump and a LOCAL disconnect is available and the power requirements are OK then you should be able to:
1. put pump controls in a water tight encloseure (see Lowes/Home Depot)
2. You need a HP rated switch and/or contactor (waterproof is tough to achieve)
3. Two contactors rated for the motors is easy to achieve.
4. 230 V coils is easy to achieve
5. A watertight On/off switch is easy to achieve with two independent contact blocks.
6. DIN rail construction is easy to achieve
7. You could make one pumps power switch the other contactor.
8. You could make it current sensor based, then if the first pump failed, the other would turn off.
9. You could put DIN rail mount breakers sized for the motors.
10. You could use motor starters instead of breakers.

You MUST:
1. ground properly
2. Have a local disconnect means (can be plugs).
3. Be protected by a GFCI
4. Have a properly sized supply(s).

We really can't help much further without motor sizes (FLA/HP) and service size to the pool and what's currently in place.

I read your post again and saw "Can be turned on If the other pump is on"

Is it CAN? MUST? One or two switches? Where are they now?

You can also post pictures using "Go advanced/Manage attachments"
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