CODEX
406.4

Receptacle Grounding and Mounting

Grounding-type receptacles must actually be grounded, and replacements in old ungrounded boxes have specific allowed options like a GFCI.

Introduced
1962
Level
NEC (National)
Why this code exists
Shock / electrocution
Current status
Active

Why this code exists

A three-prong outlet with no ground gives a false sense of safety; appliances trust that ground pin to carry a fault away from the user.

If a receptacle has a ground slot, it needs a working ground — unless you use one of the code-allowed fixes for old wiring, like a GFCI marked 'No Equipment Ground.'

The worst thing I find is a three-prong outlet screwed onto two-wire cable with no ground at all. Someone did it to fit a plug, and now the whole circuit lies about being safe.

When it applies

Grounding-type receptacles must actually be connected to an equipment grounding conductor. When you replace a receptacle in an older box that has no ground, the Code gives you defined options rather than leaving you stuck.

Common mistakes

In the field

In a 1950s house I found three-prong outlets everywhere with no ground behind them. Somebody swapped them to fit modern plugs. I put GFCI protection ahead of them and applied the labels the Code requires, so the outlets are safe and honest about what they offer. If you cannot ground it, protect it and label it.

Field note
When I find a three-prong outlet on ungrounded knob-and-tube, I put in a GFCI and label it honestly. The old one was pretending to be safe, and pretending is what gets people hurt.
— Priya · Journeyman · 12 yrs
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