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-   -   Well pump trips breaker at start, but then starts when breaker reset (http://www.diychatroom.com/f18/well-pump-trips-breaker-start-but-then-starts-when-breaker-reset-134273/)

J. David 02-19-2012 03:17 PM

Well pump trips breaker at start, but then starts when breaker reset
 
I have a Jacuzzi convertible jet pump powered by a 1 HP, GE capacitor start motor; identical to the one found here: http://www.emotorstore.com/productde..._skuID_E_28402

The pump is used primarily for water supply to my heat pump; but I do have it plumbed for watering my lawn. The pump is over 17-1/2 years old, and aside from replacing the mechanical seal last summer, has run flawlessly.

After the pump has set idle for an extended period of time, the breaker has tripped when the pump first turns on. Then, as soon as the breaker is reset, the pump starts just fine.

The shaft turns easily by hand.

All connections are tight and clean.

I have replaced the start capacitor and 20A breaker.

I have cleaned and lubricated the centrifugal switch. The switch is closed when the pump is at rest.

I have observed the shaft turn slowly and not even a full revolution before the breaker trips. But, there is no hesitation when I reset the breaker: the pump comes up to speed quickly.

At least once, the breaker has tripped while the pump was running.

I suspect there is something wrong with the start winding on the rotor, but thought to try posting this topic here in hopes someone might have an idea of what the real problem is and a possible fix.

Thanks for any help in advance.

Dave

fa_f3_20 02-19-2012 03:41 PM

My guess is, you need to replace the capacitor.

zappa 02-19-2012 03:56 PM

I was going to suggest the contacts on the start switch becoming slightly oxidized when sitting for a while and the first start current is making them conduct again. But then I read the part that the breaker opened while it was running which doesn’t fit the rest of the symptoms. Maybe it’s time for a new motor.

Yoyizit 02-19-2012 04:14 PM

After the pump has set idle for an extended period of time, the breaker has tripped when the pump first turns on. Then, as soon as the breaker is reset, the pump starts just fine.
>bearings start to seize?

I have replaced the start capacitor and 20A breaker.

I have observed the shaft turn slowly and not even a full revolution before the breaker trips. But, there is no hesitation when I reset the breaker: the pump comes up to speed quickly.
>bearings start to seize?

At least once, the breaker has tripped while the pump was running.
>?

>Unlikely, but maybe the trip curve of your breaker is not suited to the startup surge of this motor?

mpoulton 02-19-2012 04:33 PM

Sounds like a problem with the centrifugal switch not actually being closed when at rest, or a bad capacitor. Considering the intermittent nature of the problem, I'd guess the switch. I know you said it is closed at rest, but are you sure it ALWAYS is? Have you measured current flow through the start winding during startup?

micromind 02-19-2012 04:48 PM

Several possibilities here;

1) A 1HP motor operated at 120 volts is pushing a 20 amp breaker pretty close to its limits. The fact that it ran for 17 years could be due to the original breaker being at the top end of its magnetic trip curve. The new breaker is likely a bit further down the curve.

2) It's possible that the POCO has increased the incoming voltage a bit. They can give you any voltage they want, as long as it's within NEMA specs.

3) The motor windings, particularly the start winding, could be breaking down. A megger test would confirm this.

What brand is the breaker?

If this motor is on a circuit of its own, and it operates at 120 volts, the code maximum breaker would be 40 amp. The code minimum wire size is #14. Yes, 14s on a 40 is completely compliant if it is a single motor circuit with nothing else. If you want the code references, just ask and I'll post them, but it's a bit lengthy.

Rob

rrolleston 02-19-2012 06:05 PM

Quote:

Originally Posted by micromind (Post 857572)
If this motor is on a circuit of its own, and it operates at 120 volts, the code maximum breaker would be 40 amp. The code minimum wire size is #14. Yes, 14s on a 40 is completely compliant if it is a single motor circuit with nothing else. If you want the code references, just ask and I'll post them, but it's a bit lengthy.

:confused1: Would like to see the info backing this up.

mpoulton 02-19-2012 07:25 PM

Quote:

Originally Posted by rrolleston (Post 857641)
:confused1: Would like to see the info backing this up.

Article 430 supersedes all other conductor and OCPD sizing rules when dealing with motor circuits. For a thermally protected motor (which this is), the conductors can be sized to the normal load and the OCPD sized to the locked-rotor current of the motor. Overload protection for the conductors is actually provided by the thermal protector in the motor rather than by the OCPD.

Yoyizit 02-19-2012 07:27 PM

Just two days ago I had the privilege of replacing my 1982 Bryant furnace blower motor. The old one sounded like birds chirping in the days before it finally pretty much refused to spin at all.

Anyway, by spinning the shafts I could easily notice a difference in bearing friction between the old one and the new one, but I was surprised at how little the difference was. But it was enough for motors that do not have start capacitors.

You might try spinning the shaft of your existing motor and then comparing that feeling to that of a replacement motor.
Also, listen to the bearings of the existing motor while you spin it by hand.

Hardway 02-19-2012 07:57 PM

NEMA Sepc for risdental 120 and 240V

Missouri Bound 02-19-2012 09:01 PM

Quote:

Originally Posted by mpoulton (Post 857733)
Article 430 supersedes all other conductor and OCPD sizing rules when dealing with motor circuits. For a thermally protected motor (which this is), the conductors can be sized to the normal load and the OCPD sized to the locked-rotor current of the motor. Overload protection for the conductors is actually provided by the thermal protector in the motor rather than by the OCPD.

Running a motor which draws 14.2 amps on #14 wire is a mistake, especially a motor for pump usage. 12 ga. would be the minimum for this application, and depending on the length of the run, 10ga wouldn't be out of the question.:yes:

J. David 02-19-2012 10:24 PM

Many thanks to all those who responded.

With regards to the start capacitor, I replaced it, but then had the original one tested at Grainger and it was found to be good. There was no evidence of leakage, either. I am fairly confident that is not the problem.

With regards to the centrifugal switch, I cleaned the contacts and also checked the resistance across the switch at rest and it was a small fraction of an ohm. Thought it may have been sticking, so I cleaned and lubricated the mechanism. I am now fairly certain that is not the problem.

With regards to the bearings, there is resistance to turning, but it does not feel excessive. Since the motor is still assembled to the pump, I would expect there to be some amount of drag.

With regards to the breaker, it is a Homeline by Square D. I believe that I have 12 AWG conductors which I think are rated at 20A for 600V and 100 feet of conductor. Again not positive of conductor size and rating. The pump is on the opposite side of my garage from the breaker panel. So I have much less than 100 feet, probably closer to 30 feet. I will measure the cable tomorrow to be sure. Home Depot has a 30A breaker for my panel, which I may try.

I am suspicious of the start windings, but do not have a megger to test. I am not sure my multimeter can handle the current.

Again, thanks for all of the advice. Need to avoid needlessly changing out a motor or pump if I can fix what I have. Every penny counts.

Missouri Bound 02-19-2012 10:32 PM

Don't use any breaker larger than a 20amp for #12 wire. Get an ammeter and see what the pump draws when it starts (or attempts to start) and what it draws when running. I'm thinking that the motor itself may be the issue. You can always remove it and take it to a motor shop and let them test it. Perhaps the pump itself is dragging.

micromind 02-19-2012 10:42 PM

Quote:

Originally Posted by rrolleston (Post 857641)
:confused1: Would like to see the info backing this up.

Ask, and you shall receive.......

lol.

All of this is based on the 2005 version of the NEC.

First, 110.14 (C) (1) (a) (4) states that wire for motors must be rated for at least 75șc, and that would also be the column you'd use in table 310.16 (Wire ampacity).

430.6 (A) (1) states that the tables of article 430 are to be used for all calculations except for overload protection.

Table 430.248 gives the current of a 1HP single phase motor operating at 115 volts as 16 amps. Remember this figure, we'll use it twice.

430.22 states that wire size is to be 125% of the motor current. In this case, 16 X 1.25 = 20.

240.4 (D) states that #14 is to be protected at not more than 15 amps, but table 240.4 G exempts motors from this requirement.

Table 310.16 lists the ampacity of #14 as 20 amps.

Therefore, #14 is the smallest wire that can be used for a 1HP single phase motor operating at 115 volts.

Now for the breaker size;

430.51 states that the rules in part IV of article 430 add to or amend the provisions of article 240 (240 is overcurrent)

430.52 states that table 430.52 shall be used to determine the maximum rating of fuses or breakers.

Table 430.52 lists the maximum rating of a breaker for a single phase motor as 250% of the motor current. 16 X 2.50 = 40.

Therefore, 40 amp is the largest breaker allowed by code for a 1HP single phase motor operating at 115 volts.

The reason here is that all motors (with a few exceptions) are required to be protected against overload by a device responsive to current. These devices are nothing more than extremely accurate circuit breakers. They can directly interrupt the motor current or they can be connected to the control circuit.

This will protect the wire from the source all the way to the motor.

The breaker here is not intended to trip on long term overcurrent, only short circuits and ground faults. In fact, most breakers that are factory installed in motor control equipment don't have long term trip units at all. Only instantaneous.

If a normal size breaker is installed, it would very likely trip on the starting current. This current is roughly 6 times the running current.

Hopefully, this isn't too complicated to understand. But it's typical of the run-around you need to do in order to be code-compliant.

Rob

P.S. A lot of inspectors have no clue about how to properly connect a motor. I've educated (tactfully) a number of them in my 22 years as an electrician.

P.P.S. The same goes for HVAC equipment.

mpoulton 02-20-2012 01:42 AM

Quote:

Originally Posted by Missouri Bound (Post 857859)
Running a motor which draws 14.2 amps on #14 wire is a mistake, especially a motor for pump usage. 12 ga. would be the minimum for this application, and depending on the length of the run, 10ga wouldn't be out of the question.:yes:

Quote:

Originally Posted by Missouri Bound (Post 857954)
Don't use any breaker larger than a 20amp for #12 wire.


#14 wire on a 40A breaker may not be your preferred installation, but it is code compliant and there's nothing wrong with it in this specific circumstance. He says the run is only about 30 feet, so voltage drop is unlikely to be an issue - especially since he actually has #12 installed. Using a 30 or 40A breaker is perfectly fine for this application and may fix his problem. However, it seems likely that either the motor or the breaker has a problem because an upsized breaker really shouldn't be necessary to start this motor.


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