Mike Dolt Enterprises
Mike Dolt Enterprises
User: topend, Location: Parma, Ohio
Asked on: Monday, April 25, 2011 at 8:13 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:37 am EDT
Question: Hello. Last week I did a panel change, which included consolidating a 4 ckt sub-fusebox into the new loadcenter. I ran 2 - 12/3 RX to the fusebox and shared the neutrals. Everything was working when I left the job, now there is a dead short situation due to 120v on one of the existing knob&tube neutrals. Anybody have any ideas?Thanks,Rich
Possible Causes
Miswiring
Ensure that the two neutrals shared on the 12/3 RX cables are indeed from separate circuits in the old fusebox. A mix-up could cause a short.
Damaged Neutral
Inspect the knob-and-tube neutral that has 120V for any nicks, breaks, or loose connections. A damaged neutral could create a fault.
Overload
Check if the shared neutral wires are overloaded. Excessive current draw could heat up the wires and cause a short.
Grounded Neutral
Ensure that the neutral wires are properly connected to the neutral bus bar in both the new loadcenter and the old fusebox. A loose or improper connection could allow current to flow through the neutral to ground.
Voltage Imbalance
If the shared neutrals are carrying unbalanced loads, it could cause a voltage imbalance and lead to a dead short.
Troubleshooting Steps
1.
Isolate the Faulty Circuit
Disconnect one of the 12/3 RX cables from the old fusebox and see if the short persists. If so, the short is most likely within the old fusebox or its associated wiring.2.
Check Neutral Connections
Verify that all neutral wires are securely connected to the neutral bus bars, especially in the old fusebox where the knob-and-tube wiring interfaces with the new wiring.3.
Test Neutral Continuity
Use a multimeter to test the continuity between the shared neutral wires at the old fusebox and the new loadcenter. If there is continuity, the neutrals are connected correctly.4.
Check Fusebox Wiring
Inspect the wiring within the old fusebox for any damaged or loose connections, especially where the two shared neutrals are connected to the circuit breakers.5.
Inspect Knob-and-Tube Wiring
Look for any exposed wires, broken porcelain insulators, or loose connections in the knob-and-tube system. A damaged neutral in this wiring could cause a short.
Additional Considerations
Ground Fault Protection
Install ground fault circuit interrupters (GFCIs) on the affected circuits to protect against shock hazards.
Circuit Breaker Tripping
If the circuit breakers in the new loadcenter or the old fusebox are tripping, check for overloaded circuits or a persistent short.
Professional Inspection: If you are unable to identify and resolve the cause of the dead short, contact a licensed electrician for professional assistance. Flag for review