A borrowed neutral occurs when the return path for an electrical load is tied into the neutral conductor of a completely separate circuit. This creates a severe shock hazard because turning off the breaker for the borrowed circuit does not de-energize its neutral if the other circuit is still live. It also causes safety devices like RCDs or GFCIs to trip instantly due to the current imbalance.
Heard on the job
The GFCI keeps popping because whoever wired these hall lights grabbed a borrowed neutral from the bedroom circuit.
Insider tip
Always test neutrals for voltage before touching them in older buildings, especially near multi-gang switch boxes where borrowing was a common shortcut.
Also heard as
- shared neutral