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Author Topic: salvaged a 240VAC GCFI plug off a dead air conditioner, cord wire shields NOT  (Read 1231 times)
WA2ISE
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Posts: 1294




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« on: May 22, 2019, 12:19:12 PM »

Saw a tossed big air conditioner, salvaged the power cord.  This cord has a 240VAC 20A plug that has inside it a ground fault circuit interruptor.  Maybe good for that linear...  Stripped the far end of the cord and found what looks like shielding on each of the hot wires.  Humm, should be good to keep switching power supply RFI contained.  I put a 240V female plug on this end, and connected the shields to the ground wire.  The circuit interruptor kept kicking out.  Damm, maybe a stray wire shorted a hot to ground?  No.  Separated the shields from the ground, no trip.  If I touch a grounded object with the green ground wire of this cord, no problem.  But if I touch the grounded object with the shields, then it trips.   Maybe this "shield" was meant to detect the cord getting cut into by some metal object and shut the GCFI plug dowm...   Huh And who knows what an RF field might do to it...    Huh

Mentioned this in case another ham salvages a cord like this, or maybe the air conditioner keeps shutting down when you key up..   Angry
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KD0REQ
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« Reply #1 on: May 22, 2019, 01:09:15 PM »

what does the ohmmeter say about those shields to... anything...

use a high range, not beep-continuity or 1x range, in case they ARE sense leads to the lovely Chinese GFI chip inside that plug. it's possible the thing doesn't like ground at both ends because the sense circuitry doesn't see current flow. it's a black-box device, so it takes a little gentle poking to find out what the gozintas-gozouttas are.
« Last Edit: May 22, 2019, 01:13:40 PM by KD0REQ » Logged
WA2ISE
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« Reply #2 on: May 22, 2019, 02:50:26 PM »

I measure an open circuit on ohms, even on the megohm range, from ground to shield.  I measured about 200pF capacitance with a cap meter, between the shield and the ground.   I did measure 0.0011uF from the shield to either hot wire.  No attempt was made in the cord to keep one hot wire's shield from touching the other hot wire's shield, so there is near zero resistance there. Using a DVM on ohms, I get about 24 megohms between the two hot wires.  And around 0.05uF between the hot wires (I get 0.098 when using 120Hz setting on the cap meter, and 0.028uF at 1KHz, which seems a bit strange, so it must be seeing something more than a simple cap and resistance.  

Why don't I just take the plug apart, you ask.  Well, they used anti tamper screws, ones I don't have the bit for.   Angry  

It's made by Ele Mfg Corp, cat no. 00022000 and I don't see "China" or any other country name anywhere on it.  Maybe it was made in USA, but I didn't think that could happen anymore...   Wink



I did find a web page about a very similar product (what I have probably is out of production but this web page is likely the new version) http://www.elegrp.com/english/productShow.asp?id=79 and that company is in China, so that answers that question...  
« Last Edit: May 22, 2019, 03:00:14 PM by WA2ISE » Logged
W5CPT
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« Reply #3 on: May 22, 2019, 05:00:04 PM »

You can get a set of "security" bits from Harbor Freight ".  Very handy to have.
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KD0REQ
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« Reply #4 on: May 23, 2019, 08:41:04 AM »

almost any hardware store has anti-tamper bits that look like the packages that Harbor Freight brings over from Tariff Central. you will pay two to three times the HF price. that's a different looking screw for sure, might need the larger kit for it. my Vermont set won't have it.
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WA9AFM
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« Reply #5 on: May 25, 2019, 08:53:32 AM »

Screws look like Robinson heads.  Very common in Canada; also used in 'manufactured housing' (trailers).
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W6EM
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« Reply #6 on: May 27, 2019, 08:22:53 AM »

Using the highest capacitance you measured, .098uF, and assuming 120V to ground, that works out to about 4mA.  More than enough capacitive current to trip a decent GFCI.  FWIW, get the right bits to take the plug apart, and change out the cable.  Or, just let the shields float, disconnected.  You don't need a neutral if only connected hot to hot.  The round pin is just for grounding purposes.

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