A dead outlet and a $20 multimeter
A dead outlet, a first multimeter, and a lesson in what a voltage tester can and can't tell you.
The situation
An outlet that had worked fine was suddenly dead. I had never used a multimeter, and a cheap non-contact voltage tester told me the slot was “live”, which only made things more confusing.
Why the tester misled me
A non-contact detector senses the field around the hot conductor and says nothing about the neutral. An outlet can have hot present and still be dead, because the return path is broken. That is the classic signature of an open neutral, or of an outlet downstream of something that has cut power.
The order that worked
- Learn what normal looks like first. Before probing the dead outlet, I measured one I knew worked. Seeing about 120 V there meant I knew the meter, the probes and my technique were right.
- Check upstream GFCIs. A tripped GFCI in the garage, bathroom or kitchen can kill outlets in other rooms without tripping a breaker. Press Reset on every one, even ones that look fine.
- Flip every wall switch in the room. Switch-controlled outlets are common, and the switch may be one you never use.
- Measure the slots:
| Measurement | Reading | Meaning |
|---|---|---|
| Hot to neutral | about 120 V | Outlet is fine; the problem is the device |
| Hot to ground | about 120 V, but hot to neutral near 0 V | Open neutral: broken return upstream |
| Both near 0 V | none | Open hot, or an upstream GFCI or connection |
| Hot to neutral reads 120 V but drops under load | sags | Loose or corroded connection |
The answer
It was a wall switch. The outlet was switch-controlled, and the switch was off. With the switch on, the outlet read 121 V. No tools were needed to fix it, only to prove it.
What I took from it
- Test a known-good outlet first. A reading means nothing until you know what a good one looks like.
- Rule out the free explanations (GFCIs, switches) before opening anything.
- Test with a real load. An LED strip draws so little that a marginal connection can look dead.
- If you do get to the wiring: breaker off, confirm it is dead, and look for backstabbed wires (pushed into the holes in the back instead of wrapped around the screws), which fail constantly.
Stop and call an electrician for any burnt smell, melted plastic or scorch marks, or an open neutral you can't find in the box. A floating neutral can carry dangerous voltage even when everything looks dead. I'm not an electrician, and this is what worked for one outlet, not advice for your wiring.
This is entry 11 of AI Lab Work.