Two Circuits Sharing Ground Circuit

[zakthor]

Originally Posted by jyl

Currently the room is like yours: no ground, GFCI in first position. Eventually I’ll ground the first receptacle, and all the subsequent receptacles have ground wires connected to the first.

Or, I’ll power and ground that room’s receptacles from the adjoining room.

Here is a table of the different circuit conditions and their risks.

That’s a cool chart. And yikes a great incentive to add gfi.

One thing, the gfi are specified with a current to response time curve to react fast enough to avoid causing a heart attack. Curve was set by studying human body. Small amount of current through the heart can kill you dead so reaction must be in milliseconds. Idea of the only safety being a vintage breaker tripping… it’d be like that scene from young frankenstein with the hair standing up and the smoke.

I was mad one time because an electric motor startup was tripping a gfi, turns out the gfi was an early design that tripped faster than the response curve required and wouldn’t let the startup capacitor energize. New gfi and motor was fine. I’m a believer in gfi.

[jyl]

Yeah and I’m reading if the breaker is 15A it will take at least like 10 ms to trip at any amperage, and if the amperage is not much higher than 15A it can take seconds or minutes to trip.

https://forums.mikeholt.com/threads/at-what-amperage-is-a-breaker-designed-to-trip-at.142990/

I guess breaker trip is designed to protect circuits not people. It takes time for conductors to overheat, so the breaker takes it’s sweet time.