Big Voltage Drop Under Load

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You most definitely have a neutral issue and it is usually on the poco side due to small aluminum conductors old and minimally maintained. I have sometimes had to call as many as 3 or4 times before the poco actually found the problem on thier end.

It is up to the quality of the lineman who they send out. The catch 22 is that it only rears its ugly head under a load. The tendancy is to load up the circuit to see the voltages rise and fall on each side.

What is important is that the problem get fixed asap before it starts a fire. It will damage motor and electronic loads first so remove them from the equation before you start horsing the loads in the house around.

Use only resistive loads like incandescent lights and high ampereage heaters like you are noticing the problem with these are less easilly damaged.
 
heres something a little off topic but about ACSR. if you plan on cutting the ACSR messenger cable you need a pair of bolt cutters or a sawzall. i ruined a pair of 200 dollar cutters not knowing it was steel
 
UMMMM come on EP you could have asked me I would have sent you the pair I ruined years ago and saved yours. Hard lesson to learn, once caught an apprentice trying to cut re-bar with cable cutters.
 
electricalperson said:
heres something a little off topic but about ACSR. if you plan on cutting the ACSR messenger cable you need a pair of bolt cutters or a sawzall. i ruined a pair of 200 dollar cutters not knowing it was steel
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Well, the center strand is. Expensive lesson, eh?
 
brian john said:
UMMMM come on EP you could have asked me I would have sent you the pair I ruined years ago and saved yours. Hard lesson to learn, once caught an apprentice trying to cut re-bar with cable cutters.
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we had an apprentice cut a SEU cable on the side of the house because he "forgot" the cable was still connected at the top. he ruined the cable cutters and the siding on the house. luckily he wasnt hurt
 
electricalperson said:
we had an apprentice cut a SEU cable on the side of the house because he "forgot" the cable was still connected at the top. he ruined the cable cutters and the siding on the house. luckily he wasnt hurt
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Yikes, we need a new smiley for that, one with soiled drawers:grin:
 
Lxnxjxhx said:
This was a lot harder to figure out than I remember it to be.

With 10 ohms in series with the center tap due to loose connections or corrosion, with a 15 ohm load on one side and a 25 ohm load on the other,
the 15 ohm load should see 105 v and the other one should see 135 v. They'll be 1.6 amps (the difference between the 15 ohm load current and the 25 ohm load current) flowing through the neutral, so 16 watts is dissipated in this bad connection.
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Hi Lxnxjxhx, just wondering if you could show your math on this VD problem, thanks.
 
Also, today I stopped by a co-workers house to replace a gfci and notice a voltage reading of 107 at that location. I pulled the panel cover off and got the same reading from the feeder itself. I had to run out to the store and when I came back I was reading 120 after I hooked up the new gfci. Most of the co-worker's appliances are gas and their A/C's nameplate says 24 amps, which was running when I first got there but not upon my return. After viewing this thread I'm going to have them contact the power co to evaluate their drop. Thanks
 
This is a good one to take the time to understand fully.

Somewhere there is a really good video clip explaining this. Now if I can just find it.

Add: Go back to the Forum home page, find free stuff, scroll down to bottom of page to Open neutral 2 & 3 wire. Not the video but a start.

Some day, maybe, I will figure out & remember how to link.
 
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080725-1143 EST

redhorserider:

Almost certainly you have a neutral problem as most other responders have said.

To understand this consider an ideal center tapped transformer secondary with exactly 120 V on either side of the center tap. Place all source impedances from the transformer to the main panel including the service drop into three elements with one in each line from the transformer. For convience assume all impedances are resistive. Further assume each resistance is the same value, and is 0.025 ohms.

At the transformer put a ground rod connected to the transformer center tap (neutral).

At the main panel connect the neutral to its own ground rod. Assume the resistance between the two ground rods is 10 ohms. This might be low for may locations.

Effectively we have between the transformer center tap and the panel neutral 10 ohms in parallel with 0.025 ohms which equals 0.024937656 ohms. In other words 10 ohms contributes virtually nothing to the normal current flow, but if the neutral path current was 200 A, then about 0.5 A flows thru the earth.

With the neutral working correctly and ignoring the shunt ground, then the loop resistance for one phase is 0.025 + 0.025 = 0.05 ohms. Assume we load only one phase with 200 A and the other with zero, then at the main panel the 120 V hot to neutral voltage is 120 - 200*0.05 = 110 V.

If the neutral wire opens and we only have 10 ohms in the neutral path, and load only one phase, then the maximum possible current is approximately 120/10 = 12 A. If the current was 5 A thru the 10 ohm ground path and with the assumption that the neutral resistance was the only neutral path from the transformer to the main panel, then the voltage drop in the ground path is 50 V. That means one phase has a voltage of 120-50 = 70 V and the other has 120+50 = 170 V.

Adding additional ground rods would not greatly change the results and could never allow much unbalanced current. For almost any application the ground path resistance is high in comparison with the resistance of a reasonable wire in its place.

If the GECs are wired correctly and there are no shorts to the GECs, then there is no current in the GECs. Even if there was a short to a GEC this has nothing to do with the unbalanced voltage problem. Note the GEC is bonded to the neutral at the main panel and thus only originates at the main panel.

Normally the only way to have the voltage on one phase to go above its correct value and the other to go below at the same time is a neutral problem between the transformer center tap and the main panel neutral bus.

.
 
fireryan said:
What do you mean the gec wired correctly. How could they be wired incorrectly. Are you talking about the bonding of in the main panel
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If you're responding to me, the neutral should only be bonded to the EGC, the electrodes, and basically the earth itself, in the enclosure containing the main disconnect. (The utility side of the service is irrelevant (with one exception; later.))

Any sub-panel with a 4-wire feeder should have no connection between the EGC and the neutral, so no amount of neutral current, or neutral voltage drop, should impart any current on the EGC.

The exception I mentioned is the possibility that a voltage drop on the neutral between the utility transformer and the house main, causing a voltage gradient in the earth. That might develope current in the feeder's EGC, between electrodes.
 
LarryFine said:
If you're responding to me...
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Umm.... fireryan referred to the GEC earlier, not EGC.

It is quite likely an abnormal-for-the-case amount of "neutral" current will flow on the GEC when the service neutral is bad.
 
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