I am getting 90 volts in one line, 140 in the other and 20 in my common line. These overhead lines run to my farm yard cattle water trough.

Why does this happen? They say it is because I have a loose connection somewhere in my common line. Why does this cause the volt fluctuation in all of the lines?

  • \$\begingroup\$ Are these all measurements to local earth or are some live to neutral? Also, what do you have connected to the lines when you make your measurement? \$\endgroup\$ – Andy aka Feb 18 '14 at 22:41
  • \$\begingroup\$ @Andyaka 90 and 140 are live to neutral. The neutral is to earth. At this breaker box I have nothing connected while testing. There are yard lights and breaker boxes connected before the power gets to this box as well. \$\endgroup\$ – Nelson Feb 19 '14 at 2:08
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    \$\begingroup\$ Fortunately cows can't read voltmeters, so don't worry about it. \$\endgroup\$ – Olin Lathrop Feb 19 '14 at 15:00
  • \$\begingroup\$ I wish that was the case. The power goes to a water trough heater element. Right not it is shocking the cattle as they drink with 20 volts. \$\endgroup\$ – Nelson Feb 19 '14 at 19:16
  • \$\begingroup\$ Be careful you don't become the return circuit, if the load changes or goes further out of balance. Get it fixed. \$\endgroup\$ – Optionparty Aug 3 '14 at 23:05

A bad neutral connection can cause overvoltage in one side of the line (and undervoltage in the other) if the loads on each side of the line are unbalanced.


simulate this circuit – Schematic created using CircuitLab

If R1 = R2 then no current flows in the neutral, and it does not matter if there is a good connection or not.

However, in the case shown, if the neutral is broken, then R1 sees 192V (VM1) and R2 sees 48V (VM2). The total voltage from red to black wire (VM4) is still 240V.

If the neutral is intermittent or has a high resistance connection, then the situation will be somewhere in between.

Since neutral is about at ground potential at the panel, if you see 20V at the far end (to earth), that indicates the neutral line is not making a good connection. Note that the 90V and 140V you measured add up 230V (close enough to 240), and that if you add 20V to the 90 and subtract it from the 140, you get about 120V each.

  • \$\begingroup\$ subtract from 240 spehro! \$\endgroup\$ – Andy aka Feb 18 '14 at 22:39
  • \$\begingroup\$ @Andyaka Not sure how to explain it any more clearly. \$\endgroup\$ – Spehro Pefhany Feb 19 '14 at 0:23
  • \$\begingroup\$ It's your last sentence - add 20 to 90 and subtract from 140 - shouldn't it be 240 you subtract from? I'm confused now!!! \$\endgroup\$ – Andy aka Feb 19 '14 at 8:04
  • \$\begingroup\$ @Andyaka The neutral should be 0VAC (relative to panel neutral and Earth, but it's 20VAC, so you subtract (or add, depending on what phase it is) to the voltage on either of the 'hot' lines, each of which are 120VAC relative to the panel neutral (and Earth). The fact they don't add up exactly might be round-off error or it could reflect a power factor that isn't 1.0. \$\endgroup\$ – Spehro Pefhany Feb 19 '14 at 13:48

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