Electrical question, here we go again!

fixerupper

Well-known Member
Years ago, back in the seventies, over on the other farm, whenever a 110V motor was started up the lights would brighten a bit over the whole farm. By whole farm I mean five buildings with old 120 volt service through copper wires to every building but the shop which was newer 240 with aluminum triplex. Whenever I'd hit the trigger on the big drill or the bench grinder in the shop the lights would brighten barely noticeably in every building. My welder was a Lincoln 225 AC buzz box and it worked OK but the lights flickered a bit on the whole farm when I used it. The service to the farm was initially 60 amp but was upgraded to a whopping 100 amps which stopped the flickering from the welder, but that didn't solve the light brightening problem. Two local electricians were stumped but both of them mumbled the word Neutral meaning a bad neutral somewhere. When the service was upgraded to 100 amps the triplex coming into the farm was replaced as was the meter box and everything on the meter pole was re crimped so the problem had to be somewhere else. Overhead wires to every building came off of that one meter pole except for two sheds that were subbed off the next building nearby, as far as I can remember. Today all of the original buildings are gone with some new ones put up with new buried wiring on the whole place so the problem is long gone, but sometimes that nagging question with no answer comes to mind; what made the lights go brighter? Do any of you guys have an idea? John? Buick?
 
"Bad neutral" is the correct diagnosis, but obviously your electricians were unable to track it down.

Here's what was happening: The lights were on one leg, and the 120 volt outlets were on the other. If everything is wired properly, there should almost no voltage drop, so the neutral stays at about zero volts referenced to ground. But if there's a bad connection, you'll have voltage drop, and voltage drop can occur in either the hot or cold wires (or both). So, for the purposes of discussion, let's assume your lighting circuits have a five volt drop in the neutral. Now if you add a heavy load on the opposite leg, that will cause the neutral voltage to swing to that leg. So now, maybe the voltage drop in the neutral is five volts, but 180 degrees out of phase with the lighting circuits. five plus five is ten, so the voltage across the lighting circuits increased by a whopping ten volts when you started the motor.
 
I assume this is single phase stuff. Could you explain a little more about the 180 degrees out of phase between the neutral and other circuits.

single phase and 180 degrees out of phase needs a diagram to help explain. Can you draw some diagrams or tell us where to look to find some?

Thanks.
 
Actually, this must not be all that uncommon, as I have lived in at least two houses where this occurred. In fact, the house I live in now does it.

When the clothes dryer starts up, the lights in the bathroom get real bright during the spool up time.

In decorative lamps that are not all that bright, only a two or three volt difference will be noticeable.
 
Sounds like the problem is a poor
connection. As we all know a completely
bad connection is easy to diagnose, if not
find. In this case it sounds like the
neutral is still making connection but not
as efficiently as going through another
phase. That problem could be yours or on
the transformer end. The fact that a new
service didn't fix it leads me to believe
that it could be an issue from the power
company, but don't tell them I said that
lol. Easiest way to find it is to put a
load on one phase and do a voltage test to
see if there is a difference in voltages
ie. 122 vs 118 volts on each leg. Follow
this back until the numbers match, then
you have passed your bad connection. As
always I can make it sound easy but it is
usually more difficult in reality.
 
Hi Greg.. Well, in my case, it is the ground bar in the breaker box that I measured, years ago with a digital VOM.

It has been years ago, but, I remember that it showed zero volts just like it should, when I measured for AC voltage between it and a cold water pipe that is nearby.

But, when a heavier load such as the clothes dryer kicks on, during the second or so that the motor is speeding up, I can measure a few volts, not much, maybe a couple or three, between the ground bus and the water pipe.

I remember asking an electrician when I had one here installing a welder outlet, and he told me it was nothing to worry about, in fact, he said it was nearly what he would call common.
 
Sounds like you have a very good ground and that is the path of least resistance under a heavy load. The difference with yours is that it goes awaway, and one with a bad or weak neutral will not go away unless somehow the loads on both phases are evenly matched. Your electrician was right, just different situations.
 
(quoted from post at 12:02:37 07/27/14) I assume this is single phase stuff. Could you explain a little more about the 180 degrees out of phase between the neutral and other circuits.

single phase and 180 degrees out of phase needs a diagram to help explain. Can you draw some diagrams or tell us where to look to find some?

Thanks.

Ron, this is pretty basic stuff. One leg of a single-phase service is 180 degrees out of phase with the other. So whatever the instantaneous voltage is on one leg, the other is the same, except with the opposite polarity. Otherwise you couldn't get 240 volts rms across both legs.

mvphoto9603.png

[/img]
 
(quoted from post at 06:07:38 07/28/14)
(quoted from post at 12:02:37 07/27/14) I assume this is single phase stuff. Could you explain a little more about the 180 degrees out of phase between the neutral and other circuits.

single phase and 180 degrees out of phase needs a diagram to help explain. Can you draw some diagrams or tell us where to look to find some?

Thanks.

Ron, this is pretty basic stuff. One leg of a single-phase service is 180 degrees out of phase with the other. So whatever the instantaneous voltage is on one leg, the other is the same, except with the opposite polarity. Otherwise you couldn't get 240 volts rms across both legs.

mvphoto9603.png

[/img]
owever, Ron, don't start thinking two phase, because it isn't. L1 to L2 (240v) is a single phase voltage. L1 or L2 when observed, relative to the center-tap Neutral are also single phase voltages L1-N or L2 to N (each 120v). When L1 and L2 are observed with respect to the center-tap neutral, they are 180 degrees out of phase as per Marks drawing.... No contest here, just making the point that this is not a two phase system , as too many loosely

refer to L1 and L2 incorrectly as the 'two phase legs' or the 'two phase wires'.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top