Using Digital Multimeter

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debdp

Premium Member
Due to getting shocked went and picked up a digital multimeter at HD...by Commercial Electric. Questioned the sales guy on usage and he said that the black lead would go into the neutral plug. But when going over the Reef Addicts instructions it shows to insert into the ground plug... so that's the instructions I followed.

I had to use a three-prong extension cord but I'm getting mixed results. The first test resulted in a 7.8 in the display but 0 in the sump. Then my 6g registered 7.8 in the sump and 0 in the 6g display. The 40g registered 0. But the problem I see is if I move the black probe around it gives a reading or goes to 0. Also on the refugium of my 6g setup while I never got shocked if I use the extension cord I get a 7.8~7.6 reading which fluctuates with moving the black probe. There is a wall plug close by so I unplugged the UPC backup and used the wall plug and it fluctuated from .0 to 2.6 back and forth.

So at this point I'm not feeling too confident about these readings. Any additional pointers on using this would be great. BTW I really hate working with electricity so I'm very intimidated working with it, which doesn't help.
 
You have it on ac or dc? Should be ac. Also make sure you are right setting their should be V or mV When you touch probes together do you get 0.


If all test good test the voltage of outlet? Just plug straight into them. Should read close to 110 v


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Might be in display as it is finding a way to ground in sump it isnt. Electricity follows path of least resistance. So my guess wherever you are testing voltage that equipment in there is the cause of electricity


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I did test a couple of outlets and the extension cord. And while the instructions didn't tell me what went where...just says "connect the test leads across the source load being measured"... at least one of my home improvement books had more info...so I checked using the hot and neutral slots.... and got readings close to 120 +/- ... it did fluctuate as well.

Each range on this meter is sort of separated by color bands underneath...nothing says AC on the meter. The instructions simply lists the ranges for DC Voltage, DC Current, AC Voltage, and Resistance. Those ranges are listed in the sections on the meter and identified by symbols ...AC is identified with a lightening bolt and V~, DC current is symbolized with an A and a solid line and broken line underneath, etc.

What I don't get is I'll test and get 00.0. Take the probes out, try again and then get 7.6 +/-
 
I have it pointed to the setting I use as well as the leads.

[attachment=0]METER IMAG0508.jpg[/attachment]


I played around with it testing batteries and found that if I hold only the very tip of the leads on the connections then I get a steady read, otherwise the reading fluctuates. I tried testing a couple more things last night, one being the heater, the other the light. I tried touching the metal housing on the light and did find a 'hotspot' near the cord. But like everything else I test, one minute I'll get a reading and then when I move the red probe to the water and test, and then dry it and put it back on the light, I got no reading. But going back and forth with different items I would get a reading then nothing. The only tank I've tested that no matter what I do stays 00.0 is my 40 gallon tank. I played around with my 6g sump and removed an extra pump I just added, but I'm still getting a .4 reading...again it bounces sometimes .1, sometimes .6. And after turning everything off nothing changed. On all these tests I used the same extension cord. And I'm still using my finger as a second verification, which by now is really sore....but the feeling now is only a mild tingle in the display as opposed to a knee jerk type response that I was getting before, and no feeling in the sump. And again I can go check it and get no tingle for a couple hours and then go back and get shocked... just like the readings 0 sometimes numbers the next.

I also had my mom help out by turning the heater on and off while I had the lead in the sump and what was weird when she turned the heater off, the reading went up and when she turned the heater back on the reading dropped. I'm sorry I didn't write down the reading and I don't remember what it was.

Right now there are three items running. The MP10 in the display, Jaeger 250W heater in the refugium section; 2+/- month old Mag5 in the sump. The heater and Mag 5 are plugged into a Chauvet power panel which is plugged into a GFCI cord, the MP10 is plugged into a UPS backup (not on GFCI circuit).
 
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