stray voltage/confusing dmm readings?

[spamreefnew]

i happen to be an electrician but this one stumps even me?

all power off= 4.7 v to ground
1 powerhead=11 v
both powerheads=14v
all equipment running=39.5v

holding the prob with one hand and putting other in tank=7v

how can this be?

and i am not sure a ground probe would help the living things in this aquarium because that would just give the voltage a path to ground causing whatever was in that path to become part of that path and be shocked. the same as the helicopters that touch the hi-voltage transmition lines,,they are not harmed because they are NOT grounded.

 

[Chris27]

Voltage in the tank with all equipment off is indicative of a capacitive charge leaking from a piece of equipment - you wouldn't by chance be measuring VDC instead of VAC would you?

 

[Paco]

I'm tagging along on this too because I have exactly the same situation -- my very sensitive digital multimeter is reading over 30 volts in the VAC setting. I don't even have to ground it -- just hooking the other lead to a long extension cord (not plugged in) is enough of a "current path" to make the meter read that high. I think it's due to a lot of magnetic fields around the tank -- two MH ballasts, four power heads, two pumps, two fans. I tried measuring the "current" and it didn't detect anything.

 

[spamreefnew]

ok i did some reading and thinking and it seems that the 30volts i am reading is not much for concern. because it is only voltage and not current,,i re checked the tank using the amp and miliamp function on the meter and there is no current flowing in the tank water. so voltage without current is harmless ,,in fact it could be 10,000,000,000 volts and if there is no current it is harmless. a ground probe would give that voltage a path to flow on and create current causing harm to living things in the tank. IMHO

 

[Paco]

in fact it could be 10,000,000,000 volts and if there is no current it is harmless.

I'm not disagreeing with your general idea, but remember that what matters is volts x amps (current). 1 millamp at 10,000,000,000 is going to kill you. At 30 volts or even 120, it's not. :lol2:

 

[reefergeorge]

I know you said all power off, but were your lights sill on? They will induce a voltage, but usually over 5v.
My 90 has around 30vac with everything on.

 

[spamreefnew]

lights wear off

 

[iamwrasseman]

a ground probe will help you in the event that there is electrical current it will seek the path of least resistance and that would be the ground probe not you . without a probe you will feel tingling in cuts when your shoes are off . in extreme cases you will get shocked . in very extreme cases you will die .

 

[Reef obcession]

even with lights off you can have a positive charge do to the ballasts, make sure your lights do not touch the tank, keep all wires neat and dry. My wet room and lighting wires were a mess, sometimes giving me a shock when I touched the water. I recently took the time and wire tyed all the wires neatly out of the way and wala no more voltage strays

 

[dpcham]

Help! I stumbled on this thread. Last Mon. I had a cleaning and water change done on my 135 gal. reef tank. 30 gal change and the glass cleaned. On Tue morning most of the 15 fish were dead, by Wed morning all were gone and most of the corals were not opening and look bad. I took a water sample to the dealer that I use and the biggest in town to have a analysis done. No problem found every test within spec. I tested for stray voltage with a multimeter set on 300mv range. I got between 155 and 255 mv's no matter if I had all of the electrics on or all off or any combination of them. But from your posts I may have been doing it all wrong. I put both of the probes into the water at the same time, think that it would mesure any current in the water. This may have been a mistake. Any help would be appreciated.

 

[shifty51008]

put the neg. probe into the ground part of an outlet and the red probe in the water.

 

[Paco]

I doubt it's voltage. I suspect the water they gave you was contaminated.

 

[Mike31154]

A couple of links I like to use for good info on stray voltage, GFCI & grounding probes.

http://angel-strike.com/aquarium/GFI&TechnicalDetails.html

http://angel-strike.com/aquarium/GroundingProbes.html