I have a 30 amp double pole breaker in my main panel that feeds a sub-panel for the pool equipment. A days ago, I noticed the pool pump was not on. Tracked it back to a tripped 30 amp DP supplying power to the pool sub-panel. Turn off the breakers on the sub-panel and 30amp DP breaker in the main still trips after a few seconds of being reset. After a time or two of testing this, the 200amp Service Disconnect tripped. Since there was no power being drawn by the pool equipment (breakers at the sub all off), I replaced the DP 30amp breaker in the main panel to see if that was the problem, but got the same results. I next disconnected the wires feeding the sub panel (at the sub-panel) and capped them, reset the breaker and again trips after a few seconds. This was leading me to believe there may be a short in the wires between the Main and Sub panel, but I am looking to see if there are any other possible culprits before pulling new wire to the pool sub-panel. I also disconnected the wires from the Main panel, capped them and used an Ohm meter (from sub-panel side) to test the 4 wires (each to each other) for any shorts with no results. Any thoughts on next steps or possible issues here? Any other test on the wires I can run before replacing them? Any other possible issues at the main panel?

The run to from the main to the pool panel is about 20 years old and has been working until recently. Its about 60' liner distance between panels. No new work was performed in the sub-panel or main-panel in the last 9 to 12 months, and no recent digging near the conduit. This is a Square D Homeline main panel/breakers.

 

Welcome to the forums.

I agree 100%..... especially being underground.

You need to check from each wire to a known good ground. At the sub panel end... the filter should be grounded. You should not measure any continuity. Since you're tripping a breaker in the main panel.... the short to ground will be on one of the two hot wires. This short to ground will change based on moisture in the ground.

 

Woodchuck digging a burrow chewed the wire or cable.

Whatever the reason, finding the break underground will not be easy. xxxx, er, break underground requires replacement of the wire in question.

Any significant distance and junction boxes between the main panel and where the line exits the house on the way to the pool? This could give one last chance to narrow down on where the problem is although if the part in the basement is not at fault then the difficulty of fixing it has not been reduced.

 

Thanks for the responses! There is no junction box between the main and sub panels. Just conduit that runs under a sidewalk and single driveway. Unfortunately, I am not having any luck tracking down which wire is the problem. I do have both ends of the wire disconnect (main side and sub side). Any other methods to try and test the problem. One thought which I am not crazy about is to temporarily run a new wire above ground to the sub panel and replace one hot at a time to see which combination does not trip. Leaning towards just replacing both hot wires, but given that I am not sensing a short with the multimeter, I am a little concerned replacing the wires may not solve the problem. I would really like to confirm a short to ground before replacing. In the desert so no woodchucks here

 

"simply" pull out every conductor, and pull in new conductors. Arcing enough to trip out a 200A breaker is a serious, damaging fault to the insulation. And, it very likely has affected at least 2 conductors.

 

Hi, if it takes a few minutes to trip the breaker, it’s a hi resistance ground and you may not see it with a meter, (Been there), pull the conductors out and install new, connect a pull line to the old conductors to use to pull in new.
Geo🇺🇸

 

I recognized and added a picture of your meter.

Typically digital meters are auto-ranging. Yours is not. You used the 200Ω scale.
You need to use a much higher/more sensitive scale.
You should be using the 200kΩ or 2mΩ scale.

 

Thanks guys. I was able to identify both hot wires and the common are bad. Changing to 2m helped, but only detectable when I had the red lead on ground and black (comm) to the conductor. Vise versa did not produce any detectable results. I am planning on replacing all 4 wires, but I also believe the conduit is compromised somewhere. The wires are stuck pretty good, particularly pulling form the sub panel side. Also, tried blowing air through from sub panel side and could not detect any at the main. I can get a fish tape in about 3 feet and then I get stuck. In the process of dining up the conduit from the panel end, but no obvious issues yet. The conduct is wrapped and looks pretty well intact, but the 90 runs through concrete poured for the sub panel supports. Howerver, I am certain I my fish tape extends beyond the concrete portion. I am hoping to find the issue within 10 to 15 feet of the sub panel or I am probably saw cutting concrete to install a new line. At this point, I am going to keep digging for a bit.

 

You most likely need to pull and push simultaneously on the wires. ie; a helper is required on the other end.

 

Conduit was rusted out and bent near the main electrical panel as it goes under a concrete drive. Can't get under the concrete enough to find the end of the corrosion, so I am going to saw cut and run all new conduit (and wire).