Breaker Trips But Fuses Do Not Blow

OliLt

Member
Recently, the service panel circuit breaker for my irrigation pump trips after the pump runs for a few minutes. If I immediately reset it, it trips again, but if I wait a few minutes it will reset and trip after a few minutes. The pump and service panel breaker were replaced 3 years ago with no problems until recently. The pump is 2 HP, 220 volt, draws 15 amps at full load and is thermally protected. When actually running, the pump draws 10 amps when measured with a a clamp-on amp meter. The pump is connected to a fused disconnect box. The 2 fuses in the disconnect box are slow-blow, 15 amp fuses rated for motor start-up loads. The wiring from the disconnect box goes to my service panel and connects to a 2-pole, 20 amp, HACR rated breaker. I have checked all the wiring connections from the pump connection at the fused disconnect to the service panel and they appear fine. The wiring is #12 and runs for approx. 100 ft. underground from the pump disconnect to the service panel. I checked the resistance with a DVOM which indicated 0.9 ohms on the 200 ohm scale. Why would the 20 amp breaker in the service panel trip before the15 amp fuses in the disconnect box blow? Should I just replace the 20 amp service panel breaker, or check further?
 
Check for a crappy ground. You could also have a high line but I'd bet on the ground. Do any of your wires run under ground? Still bet you got some thing that is going to ground . Run some heavy extension cords above ground to the pump. Might just work. Get back to us.
 

15.0 FLA rated motor is supposed to use 20 amp wire and 30amp breakers. Fuses are supposed to be also 30amp time delay.
Odds are the breaker has gone soft from repeated motor starting inrush current .
What brand of breaker ? There is a notorious brand here called FPE Stab-Loc, best stayed away from.
 
First I would check the connections to the breaker, I had a loose screw cause enough heat to trip a breaker once. Then I would turn off the main and pull the breaker and check the contacts where it plugs into the hot bars. If that doesn't do it I would try a different breaker. This is where a !R heat gun from HF might come in handy!
 
I agree, could be a bad breaker, or a loose/corroded connection at the breaker panel.

Look for evidence of overheating, discolored connections, corrosion. If the breaker is the plug in type, pull it and look at the back where it connects to the buss bars. If any evidence of a bad connection, move the breaker to an unused space, if available. If not, you may need a new panel.

Another test you can run, turn the fuse disconnect off, turn the breaker on. Check for amp draw at the breaker. Should be zero. If there is a draw, there is a problem in the underground wiring.
 
B&D is right, the circuit was not designed correctly, so breaker is probably worn out from being worked too hard.
 
100 ft of 12 gauge wire drawing 15 amps can lower the voltage actually getting to the motor is one concern. When I was a power distribution design engineer I preferred fuses over breakers on motor branch circuits. Its quite possible the breaker is getting weak and trips too easy you might try a new breaker and see what happens and of course check for loose connections and evidence of heating and burning in the panel and all the motor circuitry

John T
 
(quoted from post at 20:00:31 08/09/17) First I would check the connections to the breaker, I had a loose screw cause enough heat to trip a breaker once. Then I would turn off the main and pull the breaker and check the contacts where it plugs into the hot bars. If that doesn't do it I would try a different breaker. This is where a !R heat gun from HF might come in handy!

Good point on the breaker connection to the buss bar and the wire termination from the breaker . Had that problem with the main breaker on the &$&@-@:&(&:mad:. FPE panel that used be in my house .
Those SEEK thermal cameras that plug into the smart phone work very well.
Tossed the FPE turkey in the junk and installed a square D with the built in generator transfer switch.
 
The circuit breaker is Eaton, and is in a Cutler Hammer service panel. Apparently Eaton took over Cutler Hammer. The buss connection to the circuit breaker looks OK, no burning, or pitting. Connections are tight. According to a voltage drop and wire size calculator at southwire.com, I am OK with 100 ft. of #12 wire carrying 220V / 15 amps. I will try Steve@ Advance suggestion. Thanks for everyone's input.
 
I have a 4" well with 220 volt 1HP pump about 80 Foot from breaker box running #10 underground wire and a 20 amp breaker in a Square D main box and use no fuses just 20 .amp breaker. Been running this way for all most 40 years.
 
With the risk of being crucified here I have a Question. Did I read this wrong you said that 20 amp wire (12 gauge) should have a 30 amp breaker and 30 amp time delay fuses. I don't know of any electrical inspector who would past on a 30 amp circuit with 20 amp wire.

You are probably right that it is a bad breaker.
 
When I built my house in 1979 the panel and breakers I chose were FPE (Federal Pacific). Been there ever since and have not replaced one
of them.

I agree on questioning the 30A with 20 AWG dedicated.
 
My generator transfer switch is made by my standby generator mfgr. who also mfgrs. the engine contained therein: GenerAC.
 
When I put my transfer switch I looked and called Generac and Reliance. Reliance was much more helpful in answering my questions.I found a supplier that handled both and they said the reliance was a better switch but does cost more. I use a 8,000 watt generator that runs everything we need and not out of electric that much to make a standby worth while.
a168533.jpg
 
(quoted from post at 08:37:42 08/10/17) With the risk of being crucified here I have a Question. Did I read this wrong you said that 20 amp wire (12 gauge) should have a 30 amp breaker and 30 amp time delay fuses. I don't know of any electrical inspector who would past on a 30 amp circuit with 20 amp wire.

You are probably right that it is a bad breaker.

Yup that is how motor loads are wired as most of the general public plus half the electricians don't know the difference between short circuit protection and thermal protection. This Confusion and concern over wiring damage occurs.
The 30 amps provides short circuit protection and prevents spurious trips during motor starting inrush loads. The motor's thermal protection prevents overheating of the motor windings and supply conducors. Not going to exceed 18.5 amps continuous as the thermal protection in the motor or starter will open the supply circuit.
Info is all in the charts and tables of the National Electrical Code.
 
B&D help me out here.

2 HP = 1500 watts / 220 volts = 7 amps.

Why is the motor listed at 15 amps FLA?
 
I assume by FPE, you're referring to Federal
Pioneer. There must be millions of those breakers in
the country. What's wrong with them?
 
Your retarded. 12 gauge wire is good for 25 amps max at 75C.
Maybe he should wire in some screw in fuses and put some
penny's in the bottom.
 
Years ago I could only use half a stick with my welder or it would trip the breaker. Over the years the wires had become a little bit loose and after i tighten the set screws, the problem went away. Check the connectors??
SDE
 
(quoted from post at 18:06:07 08/10/17) B&D help me out here.

2 HP = 1500 watts / 220 volts = 7 amps.

Why is the motor listed at 15 amps FLA?

Less than 100% efficiency turning electricity into mechanical power. Reactive current flowing through motor windings that does not make shaft power. The Power Factor for the motor is probably 0.6 to 0.7 .
The motor could be drawing 5.0 amps on the ammeter however there would be about 4.0 amps of working current and 3.0 amps of lagging reactive current . The 3.0 and 4.0 add up to 5.0 because of the phase angle.
 
(quoted from post at 19:49:15 08/10/17) The well company that put the well in told me what was needed.

Was the well company's spokesperson a master electrical, an electrical code inspector or an engineer? Did he or you read the National Electrical Code?
 
Check your grammar. Actually the Code book states the conductor has to be good for 18.75 amps with 15..0FLA but I rounded up to limit the confusion.
Has nobody here ever opened an Electrical Code book?
 
My whole house is wired in #12 wire and everything around the kitchens counter tops are wired in #10 wire.
 
The pump/motor can draw over 50 amps at max draw. Fuses and breakers have built in overload and time delay. Just sounds like your 15 amp fuses are handling the load better then the 20 amp breakers. A 20 amp breaker can usually handle 40-50 amps for short time. I'd suspect a bad breaker
 

I had a central vacuum motor blow the 20 amp breaker. After much investigation, it was the breaker. I swapped breakers with a circuit that didn't have any motors on it, and that fixed it.
 
Hey Buick did you read the NEC or did you really read the CEC which is not as cautious as the NEC. Which book are you in because you are speaking a different code?
 
Usually what I do for sizing motor conductors is on the name plate of the motor is get the horse power rating. Then look at the tables in the NEC in the motors article (in the back of that section).

So for a 2HP motor that would be 12amps at 240volts.
Them multiply that by 125% to get conductor size. I come up with 15amps. So a 14 gauge or a 12 gauge wire should work.
 

Both codes are close on the protection however the CEC goes surprisingly high on the wiring average in particular with the 90C temperature rated insulation. Most breakers however are rated for use with 75C wire insulation.
 
Please post a picture of your copy of the NEC next to your copy of the CEC so I know you are studying both books . You seem to know it all . Amazing how you have studied you the code from two different counties .
 
Actually I didn't say a word to Generac. I shopped around. They caught my eye being the name of the corporation was "Generating AC" power, having made and sold over a million power units also was a go sign to buy. Then, for my sized unit at least, they designed and built the V twin that runs it....another attaboy.

Read their specs, figured what I needed for kWHrs. running in case of a week without power. Went to their www, ordered it and the switch. Got here via freight delivery. Manual was very thorough. Had no problem installing and setting it up myself. Called the local Propane dealer and had them install a 250 gallon tank and connections and all. Called the power company and asked if they wanted to inspect it. They asked me a few questions and were happy. That was that back in Feb. 2014. Best money I ever spent. Only problem since then was the spin on oil filter developed a drip at the seam. Since it was time to change the oil anyway that was a no brainer.
 
(quoted from post at 19:22:36 08/11/17) Please post a picture of your copy of the NEC next to your copy of the CEC so I know you are studying both books . You seem to know it all . Amazing how you have studied you the code from two different counties .

Had it online at work. How about you post the NEC motor charts ?
 

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