Flickering or Dimming Lights

Lights that blink, dip when a load starts, or rise and fall together are a voltage problem until proven otherwise. Related guides: open / backfed neutral, dead outlet / lost circuit, hot or buzzing breaker, voltage-drop calculator.

⚠ An open or loose service or feeder neutral can put about 240 V on 120 V loads and start a fire in the panel, the meter, or a splice. If lights throughout the house go bright and dim together when a large 120 V load starts, or if some rooms look too bright while others look too dim, treat it as an open-neutral emergency. See the open-neutral guide and involve the utility if the problem is on the line side of the service point.

General field practice for qualified electricians. The equipment manufacturer's instructions, your adopted code edition, and the AHJ govern where they differ.

1 · Pattern first

Whole house, bright and dim, 120 V loads acting strangely: suspect the grounded conductor (neutral) at the service, meter, weatherhead, or a lost bond. Do not keep resetting breakers. Measure line-to-neutral at the service (qualified persons, proper PPE) and compare both legs.
One room or one circuit: loose hot or neutral on that run, a failing switch or dimmer, a backstab, or a poor splice in a box.
Dips only when a motor, compressor, or EV charger starts: voltage drop, an undersized conductor, a loose lug that opens under load, or a utility-side issue. Measure voltage at the panel and at the load at the moment of the dip.
LED lamps on a dimmer or a shared neutral: incompatible dimmers, a reverse-fed switch loop, or an MWBC with a lost or overloaded neutral.

2 · Measurements that settle it

Record no-load voltage at the panel (L1-N, L2-N, L1-L2, N-G). Then start the load that causes the flicker and record again at the panel and at the light.
A large L1-N vs L2-N split that grows with load is a classic loose or open neutral. N-G voltage that climbs under load points the same way.
If the panel voltage is steady but the branch voltage collapses, look at that circuit’s terminations, conductor size, and length (use the voltage-drop calculator). A 3% branch and 5% feeder+branch figure is a design target, not a hard Code limit in Article 210, but it is a useful field check.
Infrared or a careful temperature check on breakers, neutrals, and meter jaws (with the required training and PPE) finds loose connections that only fail under load. Also see hot or buzzing breaker.

3 · Common repairs (after you have found the loose point)

Retorque or replace a loose breaker, neutral bar lug, or meter-base connection (utility side belongs to the utility).
Move backstabbed conductors onto the screw terminals or a listed pigtail.
Replace a failing dimmer with one listed for the LED load, and confirm the neutral is where the dimmer instructions require it.
Do not “fix flicker” by oversizing a breaker or bypassing an AFCI/GFCI.

Reference only — not engineering, legal, or code-compliance advice. Results are estimates for qualified persons and must be verified against the NEC edition adopted where the work is done (your selected edition), manufacturer instructions, and the local AHJ. Use is subject to the Terms of Use & Disclaimer. — Morningstar Electric LLC