Electrical – What reasons are there to rewire an ungrounded circuit instead of adding GFCI protection


The NEC allows replacing non-grounding-type (2-prong) receptacles with grounding-type (3-prong) receptacles by adding GFCI protection at the breaker or first outlet.

What reasons might there be for wanting to upgrade the circuit wiring to include an equipment grounding conductor (EGC) instead of, or in addition to, adding GFCI protection? (alluded to in this answer)

Specifically, I'm curious about:

  1. Safety – In what scenarios does an EGC provide protection (from electric shock, fires, etc.) where a GFCI does not?
  2. Can an EGC help prevent damage to computer or audio equipement?
  3. Could an EGC reduce noise/static from audio equipment?

Best Answer

  1. A GFCI is the best protection against shock you can reasonably put on a 120V mains circuit, grounded or not.

  2. Surge suppressors absorb surge energy as well as attempting to divert some of it back to the source—even without a ground, they can function just fine.

  3. The mains ground is ineffective at RF as it is long enough to be highly inductive (or even a transmission line!) at typical EMI frequencies. Local (i.e. as part of the computer, AV, et al installation) bonding is what provides effective RF suppression due to the equipment chassis being equipotential to both AC and RF relative to the other chassis it is connected to—cable shielding is an extension of the chassis when terminated to the chassis correctly.

Note: Leave the ungrounded outlets ungrounded if you cannot put a new home run in! In other words, don't run individual EGC wires to outlets or ground outlets to water pipes. Bootleg or otherwise improper grounding can be very dangerous to life, limb, and equipment when combined with reversed polarity due to 120VAC flowing through equipment chassis and cable shields.