Cistern pump tripping breaker.

[Boerdoc]

I have a 1/2 hp 10 gpm pump in my 4000 gallon cistern. When the pressure switch activates the breaker trips. This pump is protected by a pumptec which does not trip.

I OHMed the pump and it measured 5 ohms, normal for this pump.

I switched the breaker with the one from the deep well, (same amps). It tripped as well. The tripping is immediate.

I bypassed the pumptec electrically and it tripped similarly.

Where do I look next? It seems to me that the breaker, pumptec and switch are good. If the pump trips the breaker but ohms correctly, could it still be bad?

The pump is 8 years old and there is a cycle stop valve before the pressure switch.

Any advice welcomed and appreciated.

BTW. We are bypassing the cistern and using the wells directly so we have water, just not enough to irrigate.

 

[Reach4]

Does the pump pump any water before the trip? Is this a 3-wire pump?

Submersible pump or jet pump? I presume submersible. "The Pumptec is not designed for jet pumps."

Immediate tripping (under one second) of a breaker is unusual. Could be a ground fault.

 

[Sponsor]

 

[Boerdoc]

It is a 2 wire submersible pump mounted horizontally. No shroud (I learned about this after install). Tripping is under a second. How do I check for ground fault?

 

[Reach4]

Isolate the wires at the breaker. Check first for voltage on the loose wires to a ground (to save the meter in case of a short to a power line) and then check resistance to ground. Should be over 100,000 ohms on either of the 240 volt wires. To be really sure, you should have an ommeter that puts over 500 volts across the wires, but a regular ohmmeter would pick up most ground faults.

Another check would be to remove the hot wires one at a time at the breaker. With either of the two hot wires disconnected at the breaker, the breaker should not trip.

If you don't show a ground fault, I would take the Pumptec out of the circuit. If the pump works then, ....

 

[Boerdoc]

When I removed one wire the circuit tripped still. When I removed the other wire I could hold the pressure switch closed/contacting and the breaker would not trip. This means......?

Removing the pumptec from the circuit still tripped.

When checking OHMS should I be checking the wires from the pump itself to ground so that I can keep the switch and pumptec out of the equation?

 

[Reach4]

When I removed one wire the circuit tripped still. When I removed the other wire I could hold the pressure switch closed/contacting and the breaker would not trip. This means......?

Removing the pumptec from the circuit still tripped.

When checking OHMS should I be checking the wires from the pump itself to ground so that I can keep the switch and pumptec out of the equation?

You are on track to a fix! Since the breaker reliably trips, you can use that as a troubleshooting tool.

When you disconnected one hot wire at the breaker and the breaker still blew, let the orange in the drawing represent the wire that you disconnected. Let the red represent the one that stayed attached.

You know the fault is between A and F. If the pressure switch was held open and the breaker still tripped, the problem would be between A and D. Suppose you lift the wire at B and the breaker still blows. That means the problem is between A and B. If the breaker does not blow, the problem is beyond B. So pick a spot in the path, and you will figure out where the short is. You could restore the B connection, and open the C or D connection. Then go with visual inspection on the problem segment.

If the problem disappears mysteriously, the shorting was probably in the area that you last diddled with. Inspect extra hard there.

There are ohmmeter ways that could help maybe, but visual inspection will probably do the job.

Remember whenever you use the ohmmeter, the breaker needs to be off.

 

[Boerdoc]

Thank you for the help. Tremendously useful info. I will do a complete check for this after a round of golf this morning. If the fault is between E and F and everything is underground except in the cistern is there perhaps a leak in the splice or pump connection? We had a trench dug above and around the wires last winter. Could settling pulling the wires cause this?

 

[Reach4]

If the fault is between E and F and everything is underground except in the cistern is there perhaps a leak in the splice or pump connection? We had a trench dug above and around the wires last winter. Could settling pulling the wires cause this?

A really wet wire or very leaky splice would not cause this symptom. It is pretty sure that there is a metal-to-metal short.

If you temporarily pulled the connection for the bare/green protective ground wire and the breaker did not trip, you would be confident that the short was to the protective ground wire. If the breaker still tripped, the short would be to something that is grounded otherwise, such as a metal water pipe or a metal conduit, or a metal well casing, OR to a different circuit. I don't know how separated this circuit is.

If you can hold the pressure switch open (with a strong-enough plastic piece etc) and not get the trip, that will quickly eliminate your path out to the pump. You could put a fragment of a plastic bottle between each contact, for example.

 

[Boerdoc]

The breaker trips as soon as the pressure switch closes. So that means that it is the path to the pump, correct?

 

[Reach4]

Yes. It could in theory be the pressure switch itself, but the path to the pump seems by far more likely.

I presume that the system was working fine for a good while. Did you do any work after it was known to work and before it stopped working?

Do you have some access points in between where the wire goes through boxes or conduits? Metal boxes? Is your protective ground wire bare or green? Any metallic conduit in use?

You may have to cut some splices open to continue the troubleshooting.

OK... get a clamp-around ammeter. When you clamp around a single wire (not more than one wire in a cable) that is carrying the short circuit current, you should see a spike in current in the brief time before the breaker blows. That would include the protective ground wire if it is the protective ground wire that the short is to. If you clamp around a wire after the short, you will not see the big spike. So you may be able to continue troubleshooting without cutting splices.

Clamping around a single splice is good. What you don't want to clamp around is 2 or more separate conductors at the same time. In other words, think of the splice making the two spliced wires into a single wire.

 

[Boerdoc]

I traced the fault to the black wire underground by bypassing that wire alone, connecting straight from the pumptec to the junction box outside the cistern.( about 40 feet) I contacted the pressure switch and the circuit did not trip and the pump started. Fortunately, the distance underground is only about 32 feet. I am off to get a trencher, wire and conduit to bury a new wire.

The settling must have pulled the wires and connected the black to the ground wire.

Thanks for all the help. I could not have done this without it.

 

[Boycedrilling]

Buy thhn wire, not Romex. Install it in conduit. If the wire ever good bad, you can replace it without digging it up.

All the wire for center pivots is installed in conduit, not because it's not rated for direct burial, it is rated DB. but it's done for protection of the wires from rodents.

 

[Boerdoc]

Thanks for the advice. The job is done. I put romex DB inside conduit and buried. Only 28 feet. All is good for now.