breaker tripping over time

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rushfan

New member
I am trouble shooting a 20 amp breaker that feeds 11 light poles. It's 277 volt, draws 8 amps, after in rush. Controlled by a photocell/contactor with a bypass. It has been raining consistently and have found that all j boxes at the poles do not have wp gaskets (they do now) and have been getting water (in most). The circuit only trips at night, after it has been on for a considerable amount of time. I'm going to open 2 j boxes at a time, separate the wires, read resistance (to ground) and document (looking for insulation break down). Then I'm going to clean the wires (with salt and vinegar solution) and resplice with the wire nuts with that stuff inside designed to protect splice in exterior applications. My question(s)?
Am I on the right track? What happens to current draw in the hot conductor when it's subjected to underground conduit filled with water? If the wire nut connection has water in it, will that cause the current to increase, eventually tripping the breaker?
 

gar

Senior Member
100122-1944 EST

rushfan:

You did not mention the breaker rating.

Water is a very good insulator, distilled. As you add salts to the water these become ionized and increase the conductivity. The more salt concentration the greater the conductivity.

Here are some relative values of resistance for a test probe that has two plates somewhat over 1 sq-cm and spaced somewhat over 1/10 cm. I believe the calibration constant is about 10 time the resistance reading to obtain the ohm-cm value. The following values are the resistance measurements from the probe at 1 kHz.

Distilled water exposed to air has limited conductivity resulting from CO2 dissolved in the water from the air.

Kroger distilled 90 to 100 thousand ohms.
Absopure filtered 67 thousand ohms,
Arbor Springs filtered 12 thousand ohms.
Arbor Farms store does own filtering 4.9 thousand ohms. Not very good.

Our city tap water 205 ohms.
Our same city water after two days of boiling for humidification 44 ohms.

Lets use the city water for an example. If you had two plates 1 sq-cm in area and spaced 1 cm apart the resistance would be 2050 ohms.

If you have a large surface area exposed to water of this resistivity and fairly close spacing between the exposed hot and neutral or ground surfaces, then assume the resistance is 100 ohms between said conductors. At 277 V this would be 2.8 A.

If possible I suggest you connect a recording ammeter to the circuit and see if you can identify how much current is causing the breaker to trip, and how this current may vary with time leading up to the trip.

.
 

kwired

Electron manager
Location
NE Nebraska
water is probably not as big of trouble as you think, your conductors should be of a type with a W in the name THW, THWN, etc, water in connectors may cause connectors to fail over time, but if water creating a current path to ground it will most likely dry itself out unless there is a constant supply of water. you may want to check temperature of breaker terminal and buss connection after several hours of operation bad connection could cause heat and tripping. otherwise put supplemental fuses at each pole and maybe you will blow one of them and narrow down where the problem is.
 

a.bisnath

Senior Member
suggestion

suggestion

the lamps are apparently wired in parallel,one or more of them is pulling down the entirecircuit, what I have done when I meet this problem is install a fuse, rated less than the breaker,at diifferent points in the circuit and use a process of elinimination as to where the problem lies
actully I fuse each pole so the entire string of lights does not have to go down for one faulty sub-circuit,it is commonly known as circuit discrimination,it saves time ,effort and cost
 

jeremysterling

Senior Member
Location
Austin, TX
I just went through this whole ordeal. Isolated the poles, changed ballasts, resplice pole handholes and inground handholes, megger the conductors (600 megohm). 15A on 30A breaker. Overnight the breaker trips.

Save yourself a lot of time and replace the breaker.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
If you've actually metered the current flow at 8A, then I concur with Jeremy.

It is _possible_ that the problem is with the circuit wiring or one of the lamps, but my guess is that the problem is related to the breaker, either a bad breaker, or a bad termination that is producing heat which causes the breaker to trip. Since it is easier to swap breakers than check all the other things that you describe, this is the first thing that I'd do.

Note that the problem might be the bus bar where the breaker is attached, not the breaker itself.

-Jon
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Is the breaker HID rated?

We had a store that the breakers would trip as you indicate. For us it was combination of maximum load, max conduit fill, and heat from a whole panel of siimliar circuits. Replacing the existing breakers with HID rated ones made a world of difference. I do not know if there is a difference internally but the load lug on CH plugin HID breaker is considerably bigger. (208v MH fixtures).
 
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