Pelican electricians.. educate me on GFIs..

[Nostril Cheese]

Got a problem relating to a blocked dishwasher drain and a non-functional disposal

The switch for the garbage disposal is on a GFI and a 15amp breaker. My understanding is that if a GFI detects water, it shuts down, right?

I've cleared the drains and the disposal. I reset the breaker on the GFI and I hear my Denon receiver power up (click) for a sec and shut down at another plug about 10 feet away. I immediately went to the panel and shut off the breaker. I unplugged the receiver as well.

Looking for my circuit tester now.

How do I test a GFI? Why would the stereo power up for a sec on another plug? Any ideas? Wet wiring somewhere? Wet disposal internals? Procedures?

Days like this really make me miss my father..

[look 171]

your stereo shouldn't turn on by itself unless that plug is wired off of the GFI. Trip the GFI and see if there's power to the plug where your stereo is plugged onto. Forget the tester, just plug a hair dryer or a lamp in it. Around here code is that the disposal needs its own dedicated circuit, but in a lot of older homes, creative wiring may have started way before you moved in.

Lets find out what else if hooked up off that GFI. If the stereo plug isn't hot, pull the GFI and pig tail the hot and neutral wire off before it enters the GFI. Depending what's on that GFI. you should be OK.

[look 171]

When you said reset the bbreaker, you are talking the little reset button on the GFI outlet itself and not at the main panel?

[Cajundaddy]

A GFI measures current between hot and neutral and if there is a difference, typically +/- 5mA it opens the circuit because stray current is shunting to ground and could present a hazard. Bad wiring, wet wiring, grounded electric appliance or simply failed GFI are all possibilities.

To test it, I would remove one appliance at a time from the circuit and retest. I have a test rig that eliminates ground so I can use a meter and test for mA current directly. A simpler way to test an appliance is with an ohm meter from hot to ground. It should always be open. Any ohms across this means a possibility for stray current and a failed appliance.

More than you ever wanted to know about GFIs:
https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf

https://www.osha.gov/SLTC/etools/construction/electrical_incidents/gfci.html

[Nostril Cheese]

Originally Posted by look 171

When you said reset the bbreaker, you are talking the little reset button on the GFI outlet itself and not at the main panel?

Correct. the red reset button on the GFI outlet with incorporated switch.

[Nostril Cheese]

Originally Posted by Cajundaddy

A GFI measures current between hot and neutral and if there is a difference, typically +/- 5mA it opens the circuit because stray current is shunting to ground and could present a hazard. Bad wiring, wet wiring, grounded electric appliance or simply failed GFI are all possibilities.

To test it, I would remove one appliance at a time from the circuit and retest. I have a test rig that eliminates ground so I can use a meter and test for mA current directly. A simpler way to test an appliance is with an ohm meter from hot to ground. It should always be open. Any ohms across this means a possibility for stray current and a failed appliance.

More than you ever wanted to know about GFIs:
https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf

https://www.osha.gov/SLTC/etools/construction/electrical_incidents/gfci.html

Thank you sir. On to testing.

[flyenby]

They sometime fail with age...

[rusnak]

If there is power to the outlet, then you have a bad or jammed disposal. You might be able to take a broomstick and spin it gently, being careful not to dislodge the seal at the sink.

[flyenby]

There is a Allen wrench hole in the center of the unit on the bottom, you use that to free it up. You can also sense how easily it moves by turning the wrench

[john70t]

I second the turn it w/ the allen and it should spin freely. There is a reset button on the bottom of the disposal as well. In this case the GFI outlet tripped first which is a good thing but they can wear out and get sensitive, same with main box breakers.

It's possible that old disposal is pulling close to the maximum 15 amps and needs to be replaced anyways.
It's an hour or two job but not too complex.

Disposal should be on it's own circuit. It's dirty electricity full of spikes and drops for anything else running on that leg. The big box stores sell a lot of new appliances after brown or black outs when motors and electronics have been running off of bad juice. It's also worth having the electrician take a look at the box for other separations or breaker upgrades.

To find what is on that circuit:
Klein Tools Non-Contact Voltage Tester-NCVT-1SEN - The Home Depot Outlets and wires
Commercial Electric 120 VAC GFCI Outlet Tester; 1/Clam, 5 Clams/Master-GFI-3501 - The Home Depot Outlets. Has a trip button for testing gfi trips
Plugging in a cheap radio (or two) helps when the outlet is upstairs.

[Cajundaddy]

Agreed. Spin the disposal motor first and see if it frees up, then retest. A stuck motor draws a lot of juice.

[bickyd]

When you turn on your disposal , you will have a momentary inrush of current . if your disposal is old and binding, the inrush will continue and maybe increase, but this should trip your OVERCURRENT breaker in you panel. The ground fault circuit interupter will detect current leakage to ground because the hot and neutral pass through a window transformer and if the current in each wire is equal [ no leakage], then the current flux is cancelled out. if there is leakage to ground in the circuit, then the current is not equal and a flux is generated in the gfci and said flux will transform into the window transformer and interupt your circuit. gfci,s do not like motor circuits. my guess is that if your not tripping the breaker at the panel, then buy a new gfci. the new ones are improved. Allso for general info, new arc fault circuit interupters are now made to sense series and paralllel faults. much safer.

[Nostril Cheese]

It was a bad GFI. I replaced it and the disposal fired right up.

I knew about the code for the isolated disposal circuit, hence my concern. Turns out that the stereo plug is on the same circuit as the GFI.

Thanks for the input guys.

[look 171]

Originally Posted by Nostril Cheese

It was a bad GFI. I replaced it and the disposal fired right up.

I knew about the code for the isolated disposal circuit, hence my concern. Turns out that the stereo plug is on the same circuit as the GFI.

Thanks for the input guys.

It should be fixed. All you need is to isolate the GFI and be done with it. It can be done as I described in the thread above.

[john70t]

Code around here is GFI within 6ft of water (meaning all kitchen and bath).

There are also GFI breakers substituted inside the box for outlets which can't be changed easily(i.e.historic or 2wire).
A label is put on the outlet noting this.

[Nostril Cheese]

Originally Posted by look 171

It should be fixed. All you need is to isolate the GFI and be done with it. It can be done as I described in the thread above.

Yeah, I thought the same thing and kept the stereo plug off the new GFI.