GFCI by-passed?

[always-learning]

When a oil filled space heater is plugged in....or a shop vac....either / or both. into a GFCI duplex and the breaker trips in the main panel...but NOT the GFCI.... isn't that defeating the purpose of the GFCI?

Or am I misunderstanding how GFCI's work? You would think the GFCI would be more sensitive than the main panel circuit breaker?

[jwelectric]

A GFCI will not protect against an overload. The protection from overload is the job or the breaker or fuse.

What a GFCI does is open the circuit when there is a difference in current between the hot and neutral conductors.

[always-learning]

JW,

SO if I understand you correctly...

As long as the current remains constant between the hot & the neutrals the GFCI won't trip?

An overload, such as a heater / shop vac running at the same time overloads the circuit breaker in the panel, but because there is no difference in current between the hot & neutrals- such as a person grounding themselves in a tub / sink or toilet, then it gets by-passed.

Thanks, I never knew it worked that way..... Most appreciated.

[David Meiland]

Inside each GFCI receptable is a little man with a test meter. He also has a bed, a small kitchenette, a TV with satellite service, and books to read. When you are running something on a GFCI outlet he gets out of his chair, grabs the meter, and makes sure that 100% of the current going out on the black wire is coming back on the white wire. If the white wire is missing any current at all he kicks this foot pedal that makes the GFCI pop.

Sometimes he notices that you are using a device that draws too much current. He can tell, the wires are getting too warm. "Not my problem", he says, "Union rules. This one gets handled by the overcurrent protection guys."

Last time I was in Florida I went by the retirement home for guys that used to work inside GFCI receptacles. There are a lot of them and they deserve our thanks. In case you are wondering, they have relief shifts and don't have to spend all day every day inside your receptacles. They also get new books periodically.

[gregoryj]

Finally an explanation I can understand! Thanks David. Now can you explain how the little men work in AFCIs? And why do electricians sometimes say naughty words when working on AFCIs?

[ajnsue]

Damn - I was hoping someone would explain why our GFCI outlet will pop whenever my wife plugs her curler and hair dryer in simultaneously. IANAE (i am not an electrician) But I always assumed they will overload and pop if the outlet rating is less than the circuit rating.

[David Meiland]

Originally Posted by gregoryj

Finally an explanation I can understand! Thanks David. Now can you explain how the little men work in AFCIs? And why do electricians sometimes say naughty words when working on AFCIs?

Those guys are part of the same union, but they don't hang out together much. They don't even have to get out of their chair much, they just sit there and listen for the telltale sound of an arc... an arc creates a pulsing that they can sense, as the electrons go from flowing smoothly to this sort of herky-jerky flow caused by the arc. If they hear that they pick up this big mallet and strike a plunger that is mounted in the floor next to their chair. Some of the better AFCI guys can tell something's wrong by the look on the faces of all the electrons. Frown=no good.

[OGR8ONE]

David, Now that's clever. I take back everything I ever said about you. Well, maybe not everything.

[James Eggert]

"A GFCI will not protect against an overload. The protection from overload is the job or the breaker or fuse."

As a GC, I didn't understand this facet, and appreciate this info!

Now, I also know they make both 15a and 20a GFCI units, and I know they are priced differently. I think in many cases, I have been provided 15a GF outlets on 20a circuits, because I noticed a difference the first time I saw a 20a GFCI.
It also appears to be pretty common to use 15a outlets on 20a circuits. I will review this a little more in the NEC for my own benefit, but any extra comments to understand the possible reasons for interchanging would be appreciated!

[always-learning]

Originally Posted by James Eggert

"A GFCI will not protect against an overload. The protection from overload is the job or the breaker or fuse."

As a GC, I didn't understand this facet, and appreciate this info!

I'm glad I wasn't the only one who found this useful

[jwelectric]

210.21 allows 15 amp devices on 20 amp circuits as long as there is more than one device. Take note that a single duplex receptacle is in reailty two receptales.

[Wizard]

Originally Posted by jwelectric

210.21 allows 15 amp devices on 20 amp circuits as long as there is more than one device. Take note that a single duplex receptacle is in reailty two receptales.

Though most of the quick wire 15 A receptacles will only take 14 GCU wire so it it the more costly screw terminals to take the 12 GCU. Personally I prefer the 20 Amp circuit over the 15.

[James Eggert]

OK, I see under the exception 1 now why the washing machine 20amp always had the 20a receptacle. However, when subsequently adding to that circuit(washing machine relocated) then the 15a receptacles can be used.

And the lampholder, recessed lights, can also be on a 20a circuit, even though it's internal wire is smaller, ie 14 or 16. I guess the more I think about that, it's no different than the plug-in lights we buy today, and who knows what size wire is internal!

[Wizard]

I tend to wire my light strings on a 15 Amp circuit and receptacles on a 20 Amp (residential). I do not mix them, so when you blow the circuit you are not in the dark!

[jwelectric]

Originally Posted by Wizard

I tend to wire my light strings on a 15 Amp circuit and receptacles on a 20 Amp (residential). I do not mix them, so when you blow the circuit you are not in the dark!

So when a 15 amp circuit opens your lights don't go out.
This is one of the silliest things I have ever heard. It don’t matter how it is wired when the light is off it is off.

EDITED TO ADD

I wouldn’t matter if the lighting circuit carried the receptacles or not. If the circuit that carries the lighting outlet opens the light goes out.

The only way that “you are not in the dark!” is to turn on a light that is plugged into one of the receptacles at the same time that the light is turned on. How many people do this?

The key is to not wire the circuit so heavy that the circuit is over loaded.

How would wiring two circuits keep a light on when the bulb blows?

Just plain silly.