How much protection does GFI really provide?

jacmyoung · #1 10/27/2005, 04:58 PM

While I was working on one of my powerheads, a cup of saltwater spilled on the plug which was plugged in on an extension cord. The sparks flied and the power was out. To my surprise my GFI did not trip, rather the circuit breaker. A close inspection revealed that my powerhead plug and the extension cord receptacle were badly burnt.

I then remembered someone mentioned GFI only protects the items with three-prong plugs, and my powerhead has no ground connection, only the two-prong plug.

Is this why we continue to hear stories of powerheads burning the whole tank down? I know by adding a ground probe in the tank such melt down can be avoided, but what about people working around the tank where a two-prong device is damaged and we accidentally get our wet hands on it?

I know many things used around the tanks are two-prong plug-ins, such as powerheads, the cheap lights we buy from the HD for our fuges, UV sterilizers, air pumps...

Am I worried for nothing? Is there an easy way to ground every electrical device so they are all protected by GFI outlet? I sure was glad I was not near where the sparks were, but next time I may not be as lucky.

Crusty Old Shellback · #2 10/27/2005, 05:04 PM

I pluged in a 2 prong fan into my powerstrip that was pluged into a GFI and the GFI tripped. The powerstrip is a 3 prong plug so I don't know for sure if that made a difference.

I also had a PC light w/ a 2 prong plug that fell in my sump and the GFI triped. Maybe you have a bad switch. have you tested it? Mine is on a 20 amp circuit as well.

I know that it's supposed to trip if the power is grounded, that's what it's for. Not for sure how it works when there is no ground. Maybe it's not installed correctly or maybe your electrical service is not grounded correctly.

Be thankful though that at least your breaker tripped.

reefmarker · #3 10/27/2005, 05:08 PM

It compares the power going out the hot to the power coming back into the neutral. If they are not the same then it trips.

In the case of an arc all the power is going between hot and neutral so no trip. If you take some of that power to ground, either with a 3rd prong, or with by some other method (through your body) it will also trip.

If you want to stop arcs there is an arc fault circuit interupter now. They are required by code in bedrooms now due to the chance of getting shocking being much less than the chance of an arc burning your house down in a bedroom. But, for fish tanks and other wet areas, you must have a GFCI. It will kill you if you are the faults path to ground.

Blazer88 · #4 10/27/2005, 05:56 PM

Get a GFCI. I replaced the outlet with one but they can easily be purchased in power strips if you don't want to mess with the wiring. A ground probe (though I've never used one) would seem to allow a path for any stray electricity to exit the tank, but it's far better to just have a GFCI trip and avoid the whole situation.

jacmyoung · #5 10/27/2005, 06:27 PM

Quote:

Originally posted by reefmarker
It compares the power going out the hot to the power coming back into the neutral. If they are not the same then it trips.

In the case of an arc all the power is going between hot and neutral so no trip. If you take some of that power to ground, either with a 3rd prong, or with by some other method (through your body) it will also trip.

If you want to stop arcs there is an arc fault circuit interupter now. They are required by code in bedrooms now due to the chance of getting shocking being much less than the chance of an arc burning your house down in a bedroom. But, for fish tanks and other wet areas, you must have a GFCI. It will kill you if you are the faults path to ground.

Yeah I am pretty sure it was an arc on the two prong plug from the powerhead. My GFCI was tested fine.

What you are saying is in the case like above some water gets between the hot and neutral, but not enough heat to trip the breaker, also not tripping the GFCI because no leak to the ground since there is no 3rd prong on the two-prong plug, but if I touch the water that will certainly leak some power to the ground through my body, then the GFCI will trip?

If you are 100% sure then I can sleep tight

I knew the breaker was for fire prevention not my protection, so when I found out the breaker tripped but not the GFCI, I started to feel dizzy

Gudwyn · #6 10/27/2005, 06:59 PM

That's how it works. GFCI won't stop arc'ing between hot and neutral.

[EDIT: I personally worry about the part where I become path to ground before the GFCI trips. So I use grounding probes. This is controversial, so do your own research into the opinions]

jacmyoung · #7 10/27/2005, 07:08 PM

I use a ground probe also. But in the case of any danger outside of the tank or sump where you put the probe in, your body still has to act like a ground probe to trip the GFCI.

I wonder if anyone had tripped a GFCI could tell us how bad it felt. I bet it was nothing compared to me once being electrocuted by a leaking plug until I was able to pull myself away from the plug, but not until my finger was badly burnt

old salty · #8 10/27/2005, 07:08 PM

GFCI's do not detect short circuits (usually sparks fly when circuits are shorted), but electrical imbalances (so to speak.)

For example, your standard circuit in your house is rated at 15 amps. Plug something in that draws 20 amps, and the circuit breaker will trip. Even if the item that you plugged in was plugged into a GFCI outlet, the circuit (not the GFCI) will trip.

Sleep well!!