20 amp circuit blows on 220 pump

[jchealey]

I have an irrigation pump that runs off a pressure switch. There is a subpanel about 4 feet from the pump. The pump is listed as 220 20 amp. The sub panel has a 20 amp breaker. The sub panel is fed from the house main panel where there is a 20 amp breaker. The breaker at the sub panel clicks off every few days. The main panel never clicks off. The wire run is 8 guage for about 100 feet. No loose wires have been found.
Choices:
1. 20 amp sub panel breaker is not accurate. (brand new) Replace
2. Replace sub panel breaker with larger amp.
3. Pressure switch is activating the pump too often. There is a 200 gal bladder tank next to the switch. (New switch also)

Any other ideas?

Jerry

[HayZee518]

Any motor that starts from stop to full speed theoretically is a dead short. If this motor is started and stopped frequently eventually the breaker will trip.
Are the bearings of the motor well lubricated? Is the pump free to turn? Water lubed pump bearings?
If you have access to a clamp around ammeter take a reading when the pump starts and when it is running.
You'll find the amperage on start is about 150% of the nameplate rating.
Is there a motor starter in the circuit? If so check the motor heater elements. Maybe they're too small or too big. Should be the nameplate motor amps. The heater elements of the starter makes up for the initial starting current, if current draw is constant enough the heaters heat up and trip the effected line.

[jchealey]

My neighbor has an amp guage that I will try. It does start and stop as the sprinklers run the pressure down. The motor is about 4 years old and has no visable lube fittings. It is a Gould pool pump, 2 HP. I will check the amp pull.

Thanks

Jerry

[SSN596]

Is the 20 amps listed on the motor referred to as starting current or full load current? A 20 amp FLA motor should be on a 30 amp circuit. A 20 amp circuit is woefully undersized for that load.

[LazyPup]

Is the piping properly matched for the pump specifications? A pump is rated to move a specified Gal/min flow at a specified dynamic head pressure. If the discharge line from the pump is too small, or as in the case of an irrigation system, if the irrigation heads are not sized correctly that would increase the dynamic head pressure of the pump, which would result in an increased amp draw.

As Hazee stated, the only way to be sure the pump is running at its rated load would be to take an amp reading while the pump is under load.

Also, if it is a capacitor run 220v motor both the run winding and capacitor winding are supplying power so you must take the amp reading on the common wire to get an accurate reading of the combined feeds.

[HayZee518]

Because the pump is going on - off so often I can just imagine what the pressure switch contacts look like. Have you considered installing a magnetic starter into the circuit? The starter will protect the motor as it has motor heater elements in the start circuits, and the breaker feeding the circuit exhibits overload protection and short circuit protection. Think of the starter as a sacrificial unit between the source ( breaker ) and the load (motor)

[HayZee518]

Here is a pictorial on how to hitch up a contactor (magnetic starter) for the pump motor. A 30 amp sized starter will be sufficient. The heater elements are sized according to motor nameplate FLA data Slightly over is better than undersized.
The coil is rated 240 volt 60 cycle and the circuit uses the available 240 for the control circuit.

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[jchealey]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4660&item=7519290544&rd=1

Is this what you are talking about as a magnetic starter?

Jerry

[HayZee518]

yes

[HayZee518]

Yes same thing - if I can blow up the pix and incorporate it into a drawing on how to wire it I'll do that.

[HayZee518]

the .gif picture won't let it me cut n paste it. I'll see what I can come up with.

[HayZee518]

I found this image on a siemens/furnas page. The wire going to the coil I am not sure of - the diagram/picture isn't too clear as to where the coil circuit is. Should be an empty screw though.

[jchealey]

I looked on the internet as to how these work and it sounds like they make sure a switch reverts back to the off stage if power is interupted. There must be another use for you to recomend its use here in my pump circuit. Can you explain a little more to me?

By the way, I changed the circuit breakers to 30s and no more blown problems. The pump does cycle on and off a lot and I think that is going to be more wear and tear on the pump. At least this way, I can open a hose bib and expect water to come out. I was a little worried in case of fire, that the pump being off, would cause a delay in fighting the fire. We don't have fire hydrants out here in the country.

Jerry

[HayZee518]

The pressure switch is used as a control device for the magnetic. It's current flow is way lower than if the pressure switch was used for direct control of the motor circuit. Say the coil of the magnetic uses a quarter amp to energize it then a quarter amp will flow between the contacts. But because you're using it for motor control, whatever amps the motor is drawing will flow between the contacts and will pit the contacts badly. You'll end up replacing the pressure switch more often.
The purpose of the magnet starter is to control (interrupt) high starting & run currents of motors. the starter also offers intermittent overload protection for the motor, as the [raw] breaker does not.

[drifter12]

Any motor has a 150% plus starting current. When placing a motor in a circuit the installer must consider this. The Fla is used to make this consideration.