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Old 01-09-2009, 07:24 PM   #1
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GFCI Power Usage


This came up a while back, regarding how much power GFCIs use.

I finally got a meter that could measure milliamps AC.

I measured a cheap harbor freight GFCI at 6.1 milliamps with nothing plugged into it.

So a little less than a watt.

When you "reset" it after tripping though, it draws a huge amount for a short time, I don't know if it's charging caps or what, but it was enough to blow the 250ma fuse in my meter.

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Old 01-09-2009, 07:31 PM   #2
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That's interesting. I never thought of a GFCI as drawing current, but then, I did take a bad one apart and found a circuit board, so it has to draw something.
Doesn't your meter have a high current (10A) range that you could use to measure without blowing its fuse?

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Old 01-09-2009, 07:54 PM   #3
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I wanted to get an accurate measurement of idle current, I didn't know it was going to draw several amps when I pressed test and then reset or I would have put it on the higher range.

I'm going to replace that fuse with a 250ma polyswitch anyway, I hate replacing fuses.
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Old 01-09-2009, 11:35 PM   #4
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Originally Posted by Gigs View Post
I wanted to get an accurate measurement of idle current, I didn't know it was going to draw several amps when I pressed test and then reset or I would have put it on the higher range.

I'm going to replace that fuse with a 250ma polyswitch anyway, I hate replacing fuses.
What kind of meter did you get?
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Old 01-10-2009, 11:42 AM   #5
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Originally Posted by Gigs View Post
I wanted to get an accurate measurement of idle current, I didn't know it was going to draw several amps when I pressed test and then reset or I would have put it on the higher range.

I'm going to replace that fuse with a 250ma polyswitch anyway, I hate replacing fuses.
So you pressed test, then reset. I kind of suspected that. Perhaps the higher current spike is caused by the relay operating to open the circuit.

Polyfuses are great. Not expensive either.
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Old 01-10-2009, 07:24 PM   #6
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GFCI Breakers (2 X 20amp) won't set in sub-panel at pier. Feed is 8/2 from 50amp breaker at another sub-panel feed from the 200 amp disconnect in basement at house with black to two hot blocks with jumper and white to the neutral bus and ground to the ground block/bus in a load center at pier being used for the sub-panel. There is no main breaker. In addition, a ground rod is 8 feet into the sand and mud under the pier with a #6 ground wire up to the ground block/bus. Ground at house sub-panel is separate from neutral. Someone give me an answer before Monday please!!
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Old 01-10-2009, 08:05 PM   #7
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What is the question? How are you feeding a sub-panel with 8/2? Start a new thread with this question and get some pictures if possible.
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Old 01-10-2009, 08:13 PM   #8
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Originally Posted by jerryh3 View Post
What is the question? How are you feeding a sub-panel with 8/2?
He is supplying 120 V to the subpanel and has jumpered the two hot busses. And apparently the GFCI breakers he has won't reset. This should have been posted in a separate thread. Maybe a mod can move it.

But first, you should swap the breaker feeding it with a 40 A, a 50 is to big for the wire size. Second, how do you have the two 20 A circuits wired in? Did you place both the black and white wire on the breaker? If not, this could be the problem. GFCI breakers have a screw for both circuit conductors and they both must be hooked up or it won't function.

And wiring a dock or pier is no joke, be careful.
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Old 01-10-2009, 08:48 PM   #9
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He is supplying 120 V to the subpanel and has jumpered the two hot busses. And apparently the GFCI breakers he has won't reset. This should have been posted in a separate thread. Maybe a mod can move it.

But first, you should swap the breaker feeding it with a 40 A, a 50 is to big for the wire size. Second, how do you have the two 20 A circuits wired in? Did you place both the black and white wire on the breaker? If not, this could be the problem. GFCI breakers have a screw for both circuit conductors and they both must be hooked up or it won't function.

And wiring a dock or pier is no joke, be careful.
Thanks for the translation. What is the power requirement at the pier? Lights? Lifts? I have three circuits on mine. A two pole feeding two lift motors, a pole lantern, and a GFCI receptacle. Seems like a lot of work just for 2 20A receptacles.
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Old 01-11-2009, 03:42 PM   #10
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Originally Posted by KE2KB View Post
So you pressed test, then reset. I kind of suspected that. Perhaps the higher current spike is caused by the relay operating to open the circuit.

Polyfuses are great. Not expensive either.
Yes, I pressed test to see if it drew anything when tripped: It didn't. So if you are really anal and want to save that 1 watt you can trip your GFCIs when you aren't using them.

I had no idea the "reset" process would cause such a large surge though. Oh well. It wasn't "test" that surges, it was "reset".

Jamie: I got the best one harbor frieght sells, $30, It's still cheap junk, but I still use my analog for most things, so this one will only see light use as my second meter. Analog didn't have AC amps/milliamps.
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Old 01-11-2009, 07:27 PM   #11
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Thanks for the translation. What is the power requirement at the pier? Lights? Lifts? I have three circuits on mine. A two pole feeding two lift motors, a pole lantern, and a GFCI receptacle. Seems like a lot of work just for 2 20A receptacles.
Thanks to both of you for trying to help me with this. I intended to feed each sheathed wire of the 8/2 with 120v and use the bare copper ground as common/neutral, then ground the sub-panel and branch circuits under the pier with a 10' 5/8" rod and a #6 ground wire to a grounding block in the sub-panel. When that didn't work, I fed 120v through the black wire and used the white for neutral. To feed both 20amp GFCI breakers, I intended to use a jumper wire between the two hot blocks. Didn't get that far 'cause I couldn't get the breaker to set on the first one. The pier will have a boat lift using a 3/4 hp motor, one 100 watt light, and a dual recepticle. I am using UF 8/2 which run underground 600 feet should carry the 50 amp feed resulting in about 25-30 amps at the pier. So far, the only way I could get 120v of power was a direct connection to a GFCI recepticle w/20 amp rating. It works, but don't believe it will pass inspection. How do I get the orignially intended 120/240 volt feed to work with two 20amp GFCI breakers so I can power the lift on one breaker and the branch circuit on the other for light and recepticle?
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Old 01-11-2009, 07:44 PM   #12
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Originally Posted by Mobjack Pete View Post
Thanks to both of you for trying to help me with this. I intended to feed each sheathed wire of the 8/2 with 120v and use the bare copper ground as common/neutral, then ground the sub-panel and branch circuits under the pier with a 10' 5/8" rod and a #6 ground wire to a grounding block in the sub-panel. When that didn't work, I fed 120v through the black wire and used the white for neutral. To feed both 20amp GFCI breakers, I intended to use a jumper wire between the two hot blocks. Didn't get that far 'cause I couldn't get the breaker to set on the first one. The pier will have a boat lift using a 3/4 hp motor, one 100 watt light, and a dual recepticle. I am using UF 8/2 which run underground 600 feet should carry the 50 amp feed resulting in about 25-30 amps at the pier. So far, the only way I could get 120v of power was a direct connection to a GFCI recepticle w/20 amp rating. It works, but don't believe it will pass inspection. How do I get the orignially intended 120/240 volt feed to work with two 20amp GFCI breakers so I can power the lift on one breaker and the branch circuit on the other for light and recepticle?
I think you may be in a little over your head with this one. You can't provide 240/120 with a XX/2 wire(not safely). Is the lift motor 240v?
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Old 01-11-2009, 07:48 PM   #13
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Mobjack it is not polite to hijack other people's threads.
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Old 01-11-2009, 07:54 PM   #14
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I think you may be in a little over your head with this one. You can't provide 240/120 with a XX/2 wire(not safely). Is the lift motor 240v?
No, it is 120v.
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Old 01-11-2009, 08:04 PM   #15
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I don't need 240volts. Can I feed the two 20amp GFCI breaker from a single 120volt black (from 8/2) with a jumper to second breaker hot lug?
I know to keep the neutral bus separate from ground. The white (from 8/2) goes to neutral bus, and the ground (bare copper in 8/2) goes to a ground block secured to the metal sub-panel, further grounded to the rod under pier...as much for lightening protection as for ground purposes. At present, this is what I have hooked up and cannot get the first 20amp GFCI breaker to set. What is wrong?

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