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another common curiosity

2294 Views 17 Replies 4 Participants Last post by  1idejim
we've talked about the hot common without much resolve so i have another common question to keep us going.

when russ was finding the elusive fried solenoid we decided to separate the common wire shunt that was in a 10 inch can, he had 4 wires to test and we had an extended earth ground as we were getting a major interference (from his friggn bluetooth we found out) so he touched the black lead to the earth ground wire and the red lead to the common wire to get a resistance reading on each wire.

my hope was that we would be able to get a reading similar to a TDR reading.

the wire that the valve was on read 4 or 5 ohms or a short reading.

as he was testing the other 2 wires i could hear the multimeter tone going off and asked him what he was touching and what he was reading...?

i told him that since there were no other valves connected and they were future expansion wires they should read OL for open....they were reading 0.0 and giving an audible tone.....continuity. with what the earth?

i'm not catching something here, and so far no one can give me an explaination that makes sense.........i know what we're reading, but it doesn't make sense yet.

any takers?
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Why not construct a circuit diagram for us?
not that computer savvy boots,

2 wires for expansion, running an unknown distance buried under the mainline

1 wire connected to a valve

screwdriver with same gauge wire as system used as a lead to the testing area serving as an earth ground.

the black lead touching the earth ground and the red lead touching the common wire = continuity tone

i've done many resistance tests in my life and have never gotten continuity from a wire that is not connected in a complete circuit or a loop

i may be confusing in my description, but i think not

i know what i'm reading, but do not have the answer why?
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if there is a link to a drawing aid that i can use i'll draw you a pic

i'm not on my computer (mine crashed the other night, tooo much intergalactic midget porn i guess) and have an appt. soon but i'll be back later today

what was the cause of the hot common?
The 'hot common' was a result of a zone wire being grounded, so a person touching the common would complete a circuit, and get zapped. Current must travel in a loop, so grounding one lead of a multimeter, and touching the other lead to a wire, and getting a beep, would mean that wire is grounded.
yes and i realize that this is the situation with the 2 common wires tested but never hav i gotten continuity readings from an earth ground to the wire in question and the loop being completed by the earth it'self.

this is how a pulser or Aframe works, but they work using an introduced current bleeding into the earth.

i also understand the resistance readings using the earth, if i understood how to read resistance without earth ground i'd be rich.

if i can get you a drawing i will

thanks boots
I would think some wet California soils would have enough minerals and salinity to make a very good electrical conductor. The same phenomenon might not happen after six months of drought.
that is what i'm thinking, this happened in washington state
We typically have had no problems, but the site in question is very sandy; I'll be interested in what happened; of course, pilot error is always to be looked at, though my tech that installed it was pretty damn good then; but.....:dizzy:
forget pilot error boss.

i know what i'm reading, it's just that i've never seen continuity on a multimeter attained through the soils. i know that it's possible, i just want to know why here?

even though we had a few miscommunications about the way i wanted to isolate the wires this was a smooth run....and fun as could be :)
Speaking of fun, here's coming east to west today over WA highway 12.
those mountains do call :)

i've asked the question op from here to locators forum to electricians forum, i belong to a few :confused:

this is the best so far:

"If the wires are removed from the equipment and you were measuring from conductor to EARTH, and got a low reading, I guess you have defective insulation and the ground might possibly be very moist."

i think that since i've never gotten this kind of reading before (and no one else wants to really get into it) that this is either the perfect storm for the resistance or russ needs to buy an adjustable multimeter.

i take resistance readings quite often and have never gotten a tone from an earth ground / resistance test. my dad said that if you had the same amount of cover, and the moisture was right that it seemed to make sense to him, what's he know he's my dad :laugh::laugh::laugh:
If you really want to delve into this, you need to get a signal source and a load resistance and a current meter, and see what can actually flow through the wire.
my expectations exceeded the desire of the masses to participate.

all forums are represented by a few well informed individuals (you in this case) that desire to help solve unanswered questions.

the electrical forums answer was posted here........

the locators forum is still thinking that a multimeter is a locator, for some reason.........

your answer is quoted above.........

here is the best:

"there are some guys on this forum that will have a good answer to that good question but i am not one of them.....good luck on getting an answer! "

thanks to all
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Open wires in a wet valve box with wet soil will get a reading here frequently. I've actually stuck one of the meter leads in the ground 2 feet away from a valve box and read AC voltage. Kinda makes your knees tingle.

I don't know how the salty soils works into the issue, Boots. But we do have high PH soils here.
if you're getting AC readings bill, i'd think that there's an electrical ground fault...i'm sure that you've touched a metal building when the grass is wet, i get calls for those once in a while.

page 18 of the manual IrrigationTroubleshootingGuide.pdf
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