I cannot figure out the source of some wild voltage fluctuations.

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
For a small meeting hall we have, I cannot figure out the source of some wild voltage fluctuations. Very basic electrical system. 2 circuits used to power lights, outlets, some fans and a small public address system. Two more circuits used to power two portable AC units. The AC units use about 11a each and are 120v units.

On a regular basis, the AC units start to shake. They sound a little like a machine gun. It is very distracting and annoying. To try to figure out the problem, I have been using my meter to try and figure out what is going on. Didn't take long to find out that the voltage going to the two units is all over the place. Each unit is on a separate leg of the service. So both legs have the issue. Voltage can range anywhere from 90v all the way up to 120v. But really anytime the AC units are in use, the maximum we see on either leg is about 110 to 115.

We have to use AC as the building gets very hot when there are many people inside. We want to install a couple of 240v mini-split AC units but not sure they will work any better. Initially I thought it would be the same issue.

Then the other day I put my meter on both legs while the building was under full load. What was strange is that when metering between both hot legs, the voltage is pretty consistent at about 230v. Even when the individual legs would drop low, the two hot legs didn't have much change. At one point I had 105v on one leg, 110v on the second leg and 230v on both legs. Now I am starting to suspect a bad neutral wire.

Any suggestions or thoughts? Power company has been out several times and can't seem to find any issues. Thanks in advance for any help!
 

bwilliams60

Joined Nov 18, 2012
1,386
You havent said where you are or what your actual test point were but it sounds like you may be on the right track. How old is the building, the panel, where is it grounded, and how far did the hydro company go? To the buiding ot just the street?
 

Reloadron

Joined Jan 15, 2015
5,875
Now I am starting to suspect a bad neutral wire.
Based on what you mention that is where I would start looking. The power company will generally look to where their responsibility ends. I would be looking at the neutrals from the panel to the loads. When you mention:
Each unit is on a separate leg of the service.
I assume one unit is like L1 to Neutral and the remaining unit is L2 to Neutral. I would start with the two neutral lines for each unit at the panel.

Ron
 

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
Thanks bwilliams60 for the quick reply! Building is probably about 20 years old. New service was installed about 2 years ago so everything on the service side is relatively new, including a new panel inside the building. The wiring to the AC units is new also - I installed that myself. Those are dedicated circuits run from the panel to the location of each AC unit.

Test points for the 120v side of things has been at the outlet for each AC unit, the main panel and the meter. On the 240v side, just tested that at the main panel and the meter.

New ground rod was installed in the same area as the meter when the service was replaced a couple years ago.

The power company tested at the meter also but didn't see any issues. Then they replaced the wire from the pole to the meter as they said it wasn't sized correctly. Unfortunately, that didn't help at all.

Hope the extra details are helpful.
 

BR-549

Joined Sep 22, 2013
4,938
To some extent, depending on your location, and the accuracy of your circuit description, the audible effects and your electrical measurements, seems correct and normal.

You will certainly improve the situation if you properly install 240 AC units.
 

mvas

Joined Jun 19, 2017
538
Thanks bwilliams60 for the quick reply! Building is probably about 20 years old. New service was installed about 2 years ago so everything on the service side is relatively new, including a new panel inside the building. The wiring to the AC units is new also - I installed that myself. Those are dedicated circuits run from the panel to the location of each AC unit.

Test points for the 120v side of things has been at the outlet for each AC unit, the main panel and the meter. On the 240v side, just tested that at the main panel and the meter.

New ground rod was installed in the same area as the meter when the service was replaced a couple years ago.

The power company tested at the meter also but didn't see any issues. Then they replaced the wire from the pole to the meter as they said it wasn't sized correctly. Unfortunately, that didn't help at all.

Hope the extra details are helpful.
First, the Ground Rod cannot be the root cause of this problem.

The key to a "Bad Neutral" is an inverse change in voltage between L1-to-N and L2-to-N.
When the Neutral between the Main Panel and Pole is open or too high a resistance ...
One Line-to-Neutral will have a higher voltage, while the other Line-to-Neutral will have a lower voltage.

You have not stated ... when one Line-to-Neutral goes higher, then the other Line-to-Neutral always goes lower.

Also, do both AC Units always experience this problem simultaneously?

Typically, the nominal 120 Volts AC should be between 114 Volts AC ( -5% ) and 126 Volts AC ( +5% ) at the panel .
90 Volts from Line-to-Neutral at the Main Panel is not acceptable and needs to be fixed,
because every circuit in your building is experiencing this too high a voltage or too low a voltage issue.
How many amps is your Service Entrance rated for?
How many amps is your building consuming?
 

mvas

Joined Jun 19, 2017
538
Based on what you mention that is where I would start looking. The power company will generally look to where their responsibility ends. I would be looking at the neutrals from the panel to the loads. When you mention:

I assume one unit is like L1 to Neutral and the remaining unit is L2 to Neutral. I would start with the two neutral lines for each unit at the panel.

Ron
How can a bad neutral in the branch circuit ( between the Main Panel and the Load ) cause the voltage at the Main Panel to repeatedly drop to 90 volts without tripping the breaker?
 

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
Thanks for the input. I didn't think the ground rod was related to this issue but good to confirm that.

I also thought we should see a higher voltage on one line when the other lines drops but that does not happen. Typically what we see is a drop on one leg and the other leg stays basically the same. It certainly does not increase.

The problem never happens at both units at the same time. It is one or the other.

Currently it is just a small 60A service. Current load, with everything running is about 42A. We are planning to upgrade the service to a 100A service and if we replace the current two, 120V AC units with two, 240V AC units, the load will change to about 39A. So not much of a change.
 

mvas

Joined Jun 19, 2017
538
OK, with this new information this does not sound like a Bad Neutral type problem.
How many amps does the AC Unit pull when you have this Brown-Out condition?

It now appears to be too many Starting Amp from one AC unit on one Leg.
 
Last edited:

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
I am not sure what the starting amps are on the units. I could meter that to find out. But if that was the case, would it cause the voltage drops like that?
 

Reloadron

Joined Jan 15, 2015
5,875
How can a bad neutral in the branch circuit ( between the Main Panel and the Load ) cause the voltage at the Main Panel to repeatedly drop to 90 volts without tripping the breaker?
Well, I figure it this way. Typical line to line (L1 to L2) is about 240 VAC. When the problem exist the Line to line voltage doesn't drop but each unit is a 120 VAC unit running off L1 to neutral and L2 to Neutral.
Then the other day I put my meter on both legs while the building was under full load. What was strange is that when metering between both hot legs, the voltage is pretty consistent at about 230v. Even when the individual legs would drop low, the two hot legs didn't have much change. At one point I had 105v on one leg, 110v on the second leg and 230v on both legs. Now I am starting to suspect a bad neutral wire.
So since the L1 to L2 voltage remains constant but at the units the L1 to Neutral and L2 to Neutral reflect a large drop that leads me to believe the drop is on the 120 volt branches neutral side. This is purely a guess but where I would start looking.

Ron
 

Tonyr1084

Joined Sep 24, 2015
5,802
One question I didn't see asked: Do both lines share the same neutral? If so, a weak neutral could account for the teeter-totter voltages you seem to be seeing.

I remember my fathers first air conditioner. It rattled the whole house. Did so for years. Then one year we took it out to clean it and noticed that the compressor, which is spring mounted, was bolted tightly down. Meaning it was transmitting all its vibrations to the house, and sounded like a Mac Truck bearing down on the house. Once the compressor bolts were loosened and allowed the compressor to float on the springs it was very nice and very quiet.
 

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
Hey Tony41084 - what do you mean when you ask do they share a neutral? Each unit is in a different part of the room with a home run back to the panel.

One other thing to add to this - the units will work just fine for a while. They will be working fine for anywhere between 10 minutes and 2 hours (we have had occasions when they work fine without any issues at all but that basically never happens now). Then the voltage drops on one of the legs causing the unit on that leg to shake uncontrollably for about 3 - 5 seconds. At that point the compressor shuts down, the voltage returns to normal and the units fan just runs for a few minutes. A few minutes later, since the voltage is back to normal, the sensor in the unit turns the compressor back on and we repeat the process.
 

Tonyr1084

Joined Sep 24, 2015
5,802
What I mean is that all neutrals come back to the panel in the same spot. Sometimes people run a common neutral to numerous plugs for the sake of saving a buck. Since none of us know you or your level of skill or knowledge of the EEC (which I know little of myself), AND since we've seen some people do some pretty questionable stuff here, it's always worth asking what may otherwise be the obvious question.

If each outlet has its own dedicated line, neutral and ground then my question is answered - "No, they don't share the same neutral anywhere but in the fuse box." But I've seen people run 12/3 (one Red, one Black, one White and one Green) and use the red/white as one circuit and the black/white as the other circuit, sharing both the neutral and the ground. I believe that's not per code.

I don't know the codes. I know what little I've picked up here and there. And the reason for the code is largely for safety - the prevention of shock hazards and fire. Both can be unpleasant, and I've experienced both. Fortunately my fire was not electrical related, but I did come close once. In an OLD OLD house, up in the attic, I took my TV (CRT type) up to the attic to test why it blew the fuse. Yes, fuse, not breaker. When I plugged it in upstairs all the lights in the house dimmed but the fuse did not blow. The reason for that was old wiring not up to current code. The house had at one time been "Tube & Knob" wiring, which some of that still exists to this day. My TV was dead shorted in its power circuit, turning the house wiring into a giant heater. Fortunately I shut down the TV before any damage could result. Shortly after that I ran a dedicated line from the fuse box in the basement all the way up to the attic. A 12/2 with proper ground. None of the house was properly grounded. And there were many times I got a shock when I thought a circuit was de-energized.

The point is that none of us here want you to get hurt, hurt someone else or burn down a building. We know people do strange stuff; and since we don't know you personally we may choose to err on the side of caution. In my current home a former owner added a built in desk with built in lamp. He (assumed gender) ran lamp cord inside the wall to the light. Dumb stuff in deed. He also did flying taps where he'd open one sheathed wire and select the black wire, strip the insulation, wrap copper wire around it and another sheathed wire and select the white wire and wrap copper around that. Then solder them together then bury them in black cloth tape. OK, would probably outlast the house. But NOT the right way to do it. And if there were ever an electrical fire, the insurance would decline to cover it due to improper wiring practices.

We think you're on the right track with the bad neutral thing. I was just asking to make sure the problem wasn't a shared neutral (in the walls). ALL neutrals come back to the box, where you can make sure the connection is properly tightened. It might also be worth wile making sure the electrical connections at the outlet are also tight. It might just be that simple. Just make sure to turn the breaker off before you open the plug on the wall. Be safe. Hang around a while.
 

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
Thanks Tonyr1084! I thought you may be referring to that way of running a 12/3 and sharing the neutral but wasn't sure. I know that used to be done but I have not done that personally for probably 20 years. To be honest, I don't know if it is allowable in any situation per code or not - I just stopped doing it because I didn't like that setup personally. I wanted all my home runs to be standalone circuits - no sharing of neutrals.

In any case, thanks for looking out for my safety - I do appreciate that very much!
 

bwilliams60

Joined Nov 18, 2012
1,386
Toby it does sound like you are losing neutral as previously stated. As Tony mentioned, always good to err on the side of caution so I am only going to state what I would do, and not what anyone else should do as we are working with mains voltage here and I do not want to be responsible for any injury to anyone.
If you are measuring erratic voltage at the plugs and proper voltage at the panel, one would assume a voltage drop between panel and plug. If you are measuring erratic voltage at the panel, and the 230 is working okay, one could assume that there is a problem between the connection point outside (meter) and the panel or a problem with the connections in the panel (neutral side). I have in the past shut down my house completely and went in and tightened up all the neutral connections and repaired a voltage problem to my table saw. All the lights would momentarily dim every time I turned it on. Tightening all the neutral connections fixed this.
Again, that is what I have done and would not recommend anybody do this as you are working with voltages and amperage enough to cause you harm or death.
The last thought I have is checking the amperage draw on your AC units? Not likely that two are going bad at once but stranger things have happened.
 

Thread Starter

Toby Pischieri

Joined Apr 21, 2019
11
Totally understand bwilliams60. I will go back and check all those connections. I will turn everything off first. I will try to get the power company to come out and check their connections again though they keep telling us their service is fine. But I will see what I can do. I think we are going to upgrade to the 240V units also so if it is a bad neutral it would eliminate that issue. We still want to get the issue fixed but we need to get the AC working as soon as possible.
 

mvas

Joined Jun 19, 2017
538
Well, I figure it this way. Typical line to line (L1 to L2) is about 240 VAC. When the problem exist the Line to line voltage doesn't drop but each unit is a 120 VAC unit running off L1 to neutral and L2 to Neutral.

So since the L1 to L2 voltage remains constant but at the units the L1 to Neutral and L2 to Neutral reflect a large drop that leads me to believe the drop is on the 120 volt branches neutral side. This is purely a guess but where I would start looking.

Ron
But you actually stated "... The problem was in the Neutral Wire in the Branch Circuits - between the Main Panel and the Load ..."
And I still disagree with that statement.
Each branch has its own Hot Wire and its own Neutral from the Main Panel to the Load.
So, I still do not see how you can claim the Neutral Wire in either of the two Branch Circuits for the two A/C Units can cause this problem.

And the TS stated that only only one-side of 120-N-120 circuit drops at of the Main Panel, but the other side does not increase.
If true, this conflicts with a "Bad Neutral" between the Pole to the Main Panel.
 

MaxHeadRoom

Joined Jul 18, 2013
22,627
But I've seen people run 12/3 (one Red, one Black, one White and one Green) and use the red/white as one circuit and the black/white as the other circuit, sharing both the neutral and the ground. I believe that's not per code.
.
Keep in mind where a centre tap split phase L1 and L2 circuits share a common neutral, the neutral current will be the difference between the two not the sum.
Max.
 

mvas

Joined Jun 19, 2017
538
Thanks for the input. I didn't think the ground rod was related to this issue but good to confirm that.

I also thought we should see a higher voltage on one line when the other lines drops but that does not happen.
Typically what we see is a drop on one leg and the other leg stays basically the same.
It certainly does not increase.
Something is very wrong, with the symptoms that you are providing ...
If one Leg has a lower voltage at the Main Panel then the other Leg must have a higher voltage, given that you stated "the Voltage between L1-to-L2 remains constant"

How is it possible that only one Leg has lower voltage at the Main Panel,
while the other Leg stays at the same voltage and the voltage across L1-to-L2- stays the same ?
How can you have 90 Volts on one Leg, 120 Volts on the other Leg and still have 240 Volts from L1-to-L2 ?
This literally does not add up - Why?

( the L1-to-Neutral Voltage ) + ( the L2-to-Neutral Voltage ) must equal ( the L1-to-L2 Voltage ) but you claim this is not true, at the Main Panel.
 
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