User: JoeNorm, Location: WA
Asked on: Monday, June 2, 2025 at 2:00 pm EDT
Answered on: Monday, June 2, 2025 at 2:03 pm EDT
Question: troubleshoot. One outdoor panel fed from another within site. Feeder breaker ON but getting no voltage at load panel. Breaker is good. I get continuity hot to hot with wiring disconnected. 120/240. Residential setting. Why is this breaker not instantly tripping? I only have basic meter at the moment. No meggar or underground locater. Thanks
Okay, let's break down the troubleshooting process for this frustrating scenario. You're getting continuity between the hot conductors with the wiring disconnected at both ends, and your breaker isn't tripping, but you're getting no voltage at the load panel. That points to a serious problem. Here's a step-by-step approach
1. Confirm Breaker Operation (Again):
Double-Check
Even if you think the breaker is good, test it specifically for its ability to trip. A multi-meter on ohms can give a clue. Disconnect the feeder wires completely from the breaker. Use a known fault to trip the breaker. Use a jumper wire from one of the hot terminals to ground. Does the breaker immediately trip? If not, replace the breaker. A breaker can feel like it's working (switch action) but be internally damaged.
Voltage Drop Across Breaker
With the breaker ON and the feeder wires connected to the supply panel, carefully measure the voltage on the line side of the breaker (where the power comes into the breaker) and then measure the voltage on the load side of the breaker (where the power goes out to the feeder). Is there a voltage drop? If you have full voltage on the line side but no voltage on the load side of the breaker, the breaker is defective, even if it doesn't look tripped.
2. Identifying the Short and Continuity
Clarify Continuity Test
When you say "continuity hot to hot," are you referring to the two hot wires between the main and sub panels?
Neutral and Ground Isolation
This is critical. You need to isolate the neutral and ground wires at the load (remote) panel. Disconnect the neutral wire from the neutral bar and disconnect the ground wire from the ground bar in the remote panel. Now, re-check for continuity between: Hot to Hot Hot to Neutral Hot to GroundDocument each reading. The results of these tests will dramatically narrow down the fault location. Walk the Run
Visually inspect the entire run of the feeder wires between the two panels. Look for any obvious damage to the conduit, junction boxes, or the wire insulation itself. Pay close attention to any points where the wire might have been compromised (e.g., where it passes through a wall, underground, or near any metal objects).
3. The Most Likely Scenario
Given your symptoms (continuity between hots, no voltage, breaker not tripping immediately), the most probable cause is a
high-resistance short somewhere in the feeder wiring. Here's why: High-Resistance Short
A direct, low-resistance short (e.g., bare wire touching a grounded metal enclosure) would usually cause the breaker to trip instantly. However, if the short involves some degree of resistance (e.g., partially damaged insulation allowing current to leak between the conductors, or a corroded connection), it can create a scenario where current flows, but it's not enough to trigger the instantaneous trip mechanism of the breaker.
Voltage Drop
The resistance in the short will cause a significant voltage drop along the feeder wires. By the time the voltage reaches the load panel, it will be very low or nonexistent.
Continuity Reading
Your meter reads continuity because there's a conductive path between the hot wires. The resistance of the damaged insulation or connection isn't high enough to register as an open circuit on your meter.
Why the breaker doesn't trip
Breakers are designed to trip when they detect an overcurrent (too much amperage) or a short circuit (a direct path between hot and neutral/ground). The resistance in the short limits the current flow. It's not high enough to trigger the breaker's instantaneous trip, but it is high enough to cause a voltage drop and no voltage to be received.
4. Specific Areas to Investigate Based on Wiring Type
Underground Feeder (UF) Cable
Dig Carefully
If any portion of the feeder is buried, this is the most likely location of the fault. Rodents, rocks, or improper burial depth can damage the cable over time. Carefully excavate along the path of the cable, looking for any signs of damage to the insulation.
Splices
Underground splices are notorious points of failure. If there are any underground splices, carefully inspect them for water intrusion or corrosion.
Conduit
Moisture
Water can accumulate inside conduit, leading to corrosion and insulation breakdown. Check for any points where water might be entering the conduit (e.g., loose fittings, cracks, or where the conduit enters the ground).
Sharp Edges
When wires are pulled through conduit, they can be damaged by sharp edges or burrs.
5. Without Advanced Equipment
Divide and Conquer
If you can safely access a midpoint in the feeder run (e.g., a junction box), disconnect the wires at that point. Then, test for continuity and voltage from the supply panel to the midpoint and from the midpoint to the load panel. This will help you isolate which section of the feeder contains the fault.
Look for Heat
If you can safely energize the circuit for a brief period (with extreme caution!), carefully feel along the feeder wires for any areas that are unusually warm. This can indicate a point of resistance and potential short. Do this briefly and monitor closely.
Important Safety Notes
Turn off Power
Always turn off the breaker feeding the circuit you are working on and verify it is off with your meter before touching any wires.
Lockout/Tagout
Use a lockout/tagout device to prevent someone from accidentally turning the breaker back on while you are working.
Grounding
Ensure proper grounding throughout the electrical system.
Call an Electrician
If you are uncomfortable performing any of these tests or if you cannot locate the fault, it is best to call a qualified electrician. Working with electricity can be dangerous, and a professional has the training, experience, and equipment to diagnose and repair electrical problems safely.
Working Live
Never work on live circuits! The tests described above should only be performed with the power off, unless specifically instructed to do otherwise (e.g., measuring voltage drop with extreme caution*).
In summary, the combination of hot-to-hot continuity, no voltage at the load panel, and a breaker that doesn't trip immediately strongly suggests a high-resistance short in the feeder wiring. Carefully inspect the wiring, isolate the neutral and ground, and use a process of elimination to pinpoint the fault location. Flag for review