Switching 8 parallel a.c. Contactors with one pressure switch
Switching 8 parallel a.c. Contactors with one pressure switch
(OP)
I am redesigning a circuit which currently uses two DPDT pressure switches; both at the same setpoint. Each switch pole actuates two contactors, for a total of eight contactors,each with a 120VAC coil rated at 96 VA.
I need to modify the circuitry so that a single pressure switch pole simulateously energizes all eight coils. I am trying to avoid adding an interposing relay to the circuit if at all possible. The pressure-switch contact is rated at 15 amps for 120/240 VAC, so I don't think there is a capacity issue.
What gives me pause though is operating all eight coils in parallel. Where there are currently two contactor coils in parallel for each pole of each pressure switch pole, quadrupling the number of coils makes me wonder if the inductive kick might be too much, or if some other unknown (to me) reason exists to make this a poor engineering decision. These devices operate very infrequently, perhaps once or twice a year during plant start-up or shutdown.
Any thoughts or comments?
I need to modify the circuitry so that a single pressure switch pole simulateously energizes all eight coils. I am trying to avoid adding an interposing relay to the circuit if at all possible. The pressure-switch contact is rated at 15 amps for 120/240 VAC, so I don't think there is a capacity issue.
What gives me pause though is operating all eight coils in parallel. Where there are currently two contactor coils in parallel for each pole of each pressure switch pole, quadrupling the number of coils makes me wonder if the inductive kick might be too much, or if some other unknown (to me) reason exists to make this a poor engineering decision. These devices operate very infrequently, perhaps once or twice a year during plant start-up or shutdown.
Any thoughts or comments?





RE: Switching 8 parallel a.c. Contactors with one pressure switch
You will have inrush issues but a pressure switch with contacts rated for 15 amps @ 120/240 volts AC is frequently used for direct control of a pump motor or compressor motor.
If your contacts have an HP rating they will probably be suitable for the inrush.
Bill
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"Why not the best?"
Jimmy Carter
RE: Switching 8 parallel a.c. Contactors with one pressure switch
Use the interposing relay...
Or, add auxiliary contacts to some of your contactors and have them close other contactors.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Switching 8 parallel a.c. Contactors with one pressure switch
RE: Switching 8 parallel a.c. Contactors with one pressure switch
Overall, it is a difficult load to switch. If you use an interposing relay then you just have to swap a relay out when it fails instead of changing the pressure switch. They are usually plug-in devices that are simple to change.
RE: Switching 8 parallel a.c. Contactors with one pressure switch
So I agree with itsmoked - put in the interposing relay AND also the surge suppressor.
If your concern is reliability, put in two interposing relays.
What is your objection to an interposing relay.
RE: Switching 8 parallel a.c. Contactors with one pressure switch
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If we learn from our mistakes I'm getting a great education!
RE: Switching 8 parallel a.c. Contactors with one pressure switch
Thanks to all for taking time to reply. Chuck
RE: Switching 8 parallel a.c. Contactors with one pressure switch
(I'd also use dc motor operated valves, but that's just me.)