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Measuring electrical current?

Discussion in 'General Plant Topics' started by Detritus Mulm, Oct 11, 2009.

  1. Detritus Mulm

    Detritus Mulm Guru Class Expert

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    I was reconnecting a powerhead after a water change tonight and I'm pretty sure I got zapped. It could have been the sharp edges on the PH, but I did not think so. The GFCI did not trip though, but I'd still like to disprove my paranoia. If I measure from ground to the tank water will this detect any stray current? I've got a ground probe connected too, if that matters.
     
  2. Biollante

    Biollante Lifetime Charter Member
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    Definitely Check

    Hi,

    Definitely check.:)

    Test your GFIC before you do anything else.;)

    The ground probe should be pulling any stray voltage. It is always possible your ground isn’t. If you have aground probe (a good idea ;) ) confirm the ground in fact is at ground potential.:)

    Set the voltmeter to the lowest AC setting, probably ‘10 volts’, one probe to the ground in your outlet, the other into the water. The meter should continue to read ‘0’, now remove the grounding probe (the one that is always connected), the meter should continue to read ‘0’.

    If the meter continues to read, ‘0’ make sure that all of your electrical devices are on and that the heater(s) have cycled ‘on’ and ‘off’. move any in tank devices.

    If you see any movement, any reading above ‘0’, turn ‘off’ all the power to tank electrical devices, if the voltmeter reads or continues to read above ‘0’, make sure you have everything associated with the tanks ‘off’. If the voltmeter reads anything other than ‘0’, your meter is likely defective or you live in Canada. If your voltmeter is defective, you cannot assume the tank is safe.

    If the voltmeter returns to ‘0’ when the power is turned off, start turning equipment on one at a time starting with your main filter or pump. Then when you find the item, replace or repair.

    In tank heaters are the usual suspect. Most catastrophic failures, bare wires and such, usually will trip the GFCI’s, which I will assume you test at least once a month and anytime you are fooling with electrical equipment in your tank.

    Biollante
     
  3. Detritus Mulm

    Detritus Mulm Guru Class Expert

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    Haven't played with the grounding probe yet, but voltage from tank to electrical ground read about .08 when I started. Unplugging everything (including probes) brought it down to .065+/-, but it was jumping around quite a bit. The only thing that might have caused a drop was the UV/Cannister. With everything plugged back in (heater cycled) again it's below .06. The HOT was cavitating a bit before the restart and has stopped now. Cycling the heater may actually be the cause for the drop below .06, but I can't be sure. I want to play with the one PH tomorrow as I was likely wiggling the power cord when I thought I got zapped. I'll need my third appendage for this, so it will have to wait until tomorrow.
     
  4. shoggoth43

    shoggoth43 Lifetime Charter Member
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    Ground Probe and GFCI

    The ground probe is a good idea but you should strongly consider using one ONLY in conjunction with a GFCI. It is entirely possible for a neutral wire to be cut in a tank with a ground probe and have the current flow out through the ground probe wire vs. the neutral wire. Everything will continue to work just fine unless/until you interrupt the flow with your body as part of the circuit which is how you'll find out about it.

    A properly working GFCI will prevent this as it will "see" the current going in on the hot side but not enough coming back out on the neutral and will trip. Test these fairly often. Once a month is not a bad idea. Bear in mind they need to be replaced fairly often ( every couple of years ) as they do fail. Any hint of a shock means you should go through and check everything.

    -
    S


     
  5. Biollante

    Biollante Lifetime Charter Member
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    Hey In There, Are You Okay

    Hi,

    What is going on, you tell us about a 'minor' electrical problem.:(

    We give advice...:eek:

    Opps:eek:

    Are you okay?

    Biollante
     
  6. Detritus Mulm

    Detritus Mulm Guru Class Expert

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    LOL, I was never OK, ask anyone. :D

    But I haven't received any new electrical shocks. I do know that the voltage fluctuates wildly about zero when the grounding probe is disconnected. But stays between .06v to .08v generally. I will try moving the probe and electrode around the tank to see if I can see any differences. I almost think something in the house wiring is leaking to ground.

    I grew up working in my Grandfather's motor repair shop, so I learned a few things the hard way. Liked the time I stuck the screwdriver in the 220; never did that again, but it might explain item one above. Then there was the time I picked up the pulley after it spun off the motor shaft; learned about friction that day. Never did that again either. They were greatly amused both times though. :-0
     
  7. Biollante

    Biollante Lifetime Charter Member
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    Whew, No Fatalites

    Whew…

    Thought I had lost another one… well, er, one…:eek:

    Sounds like a funky ground to me.:eek:

    What happens when you disconnect everything (from the tank)?

    Occasionally the meters themselves, in particular the newer digital meters will leak a certain amount, 60- 80 millivolts may be what your meter does.

    A pitcher of aquarium water, the grounding probe and the meter may tell you.;)

    Biollante
     
  8. Detritus Mulm

    Detritus Mulm Guru Class Expert

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    Yeah, it never goes to zero even with everything off. I just used the freebie for my testing. I've got a fancy one (meter) around here somewhere. I'll try that next. Could also try my analog meter.
     
  9. essabee

    essabee Prolific Poster

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    If the ground is funky, there would be no potential difference between it and the neutral. If you get a voltage reading on the multimeter between the neutral and the ground the ground is working.
     
  10. Biollante

    Biollante Lifetime Charter Member
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    Okay

    My operating assumption is that the reading is from ground to the tank water.:)

    In the US the National Electrical Code requires a neutral-to-ground connection to be made at service equipment only and there shall not be any neutral-to-ground connection on the load side of service equipment [250-23(a), 250-24(a)(5)], except as permitted in Section 250-61 [250-142].

    All of that means it is not uncommon to see a potential difference between ground and neutral at the outlet of at least 50 millivolts and throw in computers and other nonlinear devices of the modern world and a couple of volts would not be unexpected.

    If with the ground probe in the aquarium and at ground potential and the voltmeter plugged into the neutral on the GFCI and the other to the aquarium water then 60 or 80 millivolts seem acceptable. ;)

    If the test is between the ground and the tank, the possibilities come down to the meter, questionable ground or some radio frequency interference; a couple of 1k ohm resistors in parallel should handle that.

    Biollante
     
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