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fw2007 07-15-2008 07:46 PM

Does this make any sense?
I've been wanting to know for a very long time whether my thinking is genius, or totally off<g>
For 20 years I lived in an apartment in a relatively small complex in New Jersey.
The electrical service was 220V, and the panel was in the kitchen. There was a 220V air cond in the living room.

I always noticed that when I ran my microwave oven, the kitchen light got brighter.
Measuring the voltage on a receptacle that I assume was on the same leg as the light, revealed that the voltage was jumping up by a few volts (I don't recall the exact number, but I believe it was around 5V or so).

On the other hand, when I ran the toaster oven, the light in the kitchen became slightly dimmer, and the voltage dropped a few volts.

Note that my unit was the last in the building, approx. 200ft of wire from the meters.

Because there are currents of opposite polarity flowing in the neutral of any 220V single phase system, the current caused by leg A will cause a voltage drop with polarity A, and that from leg B will be the opposite polarity.
Because of this, the voltage drop in the neutral wire caused by current flowing from leg A, will in effect, lower the voltage in the neutral with respect to leg B, therefore increasing the potential between leg B and neutral, and thus increasing brightness of a light, or the speed of a fan, etc.

I believe this theory is correct, as I am pretty well educated in the theory of electric current, and cannot come up with a better explanation.

Has anyone ever experienced this with long runs of feeder at 220V single phase?


Yoyizit 07-15-2008 08:14 PM

a 1 ohm resistance in the neutral (way too high)
a 13 ohm load on one side of the 120-n-120 input service
a 38 ohm load on the other side of the 120-n-120 input service.
that the voltage across both must always total 240v.

Solving two equations for two unknown loop currents, the voltage across the 13 ohm load is 113v and the other voltage is 125v.
These two added give 238v, due to rounding errors in my calculations.

The voltage drop across the bad neutral connection is 5.4v, some of which is used up by the drop in the 200' of cable.
You can find this bad connection with a voltmeter.
Also, it will be hot because it is dissipating 29w.

If the brighter light is running on this 125v and it normally runs on 120v it will appear to be (125/120)^(3.5)= 115% of normal brightness, but will last 60% of its normal life.

fw2007 07-16-2008 05:55 AM

Further, this effect will only occur when the load on one leg is higher/lower than that on the other, causing an imbalance between the two legs.

I don't believe there was actually a "bad" connection in the neutral, just more resistance in it than in either hot leg. I'm not sure why that would happen. Assuming all three wires are of the same gauge, there should be the same resistance in each.
If that were the case, the drop in the hot leg would balance out the drop in the neutral, and we would not see the effect I described, no?

It's been a while since I've been exposed to circuit theory, so I'm a bit rusty on things, although this is pretty straight-forward ohm's law.


Yoyizit 07-16-2008 03:47 PM


Originally Posted by fw2007 (Post 139753)
I'm not sure why that would happen.

Bad connection?

I found a link on the Internet that said that bad connections in comm circuits can actually rectify. Dunno' if this is possible at resi voltages and currents.

The default fix is to tighten all connections down at the panel. Supposedly only the black or red wires are hot.

The short circuit current from the pole xformer is probably 200,000A, so, before doing much of anything on this, please read

joed 07-16-2008 03:48 PM

Lights getting brighter as loads are turned on is a classic symptom of a loose connection on the neutral. It means the voltage is going higher on one leg. This can be very damaging to electronics and is not something to be ignored.

fw2007 07-16-2008 06:26 PM

This situation existed in the apartment I rented for 20 years, ending last June.
I never reported it to the management, because I didn't consider it serious. It was not very noticeable unless you measured the voltage. Most people probably wouldn't have noticed the lights going brighter, and would have written off the change in voltage as "normal".
I was lucky to get a plumber when the bathtub drain became clogged. I don't think I would have had any response if I had told them that my kitchen light was getting brighter when I ran my microwave.

In the 20 years I lived there, I never saw the problem get any worse (or better).

BTW; I have heard that a bad connection in the ground can rectify. I used to hear about strange things happening in homes where there was an amateur radio station operating.
The RF signal would get into the power lines, or telephone lines, get rectified, and produce all sorts of results, mostly resulting in RFI being picked up by TV and radio receivers.

I think that a connection so bad that rectification is taking place would become apparent in power supply wiring. Then of course that doesn't mean that the homeowner will do anything about it. It's amazing what people can learn to "live with" for a long time, and only take action when a complete failure or a catastrophe occurs.


nap 07-16-2008 08:20 PM

I doubt the RF signal would result in any appreciable increase in voltage.

In your situation, chances are it was simply a poor neutral connection.

btw; poor connection= increased resistance

your theory in reality.

Not sure where you are going with the poor ground connection and rectification of the power. Ideally, you do not want any current flow on the ground connection. The ground is intended only to provide a low impedance path for unintended high voltages that are not meant to be on the power system and to stabilize the voltage to ground, so, with no current flow, there is no rectification.

BigJimmy 07-16-2008 10:23 PM


Originally Posted by Yoyizit (Post 139881)
I found a link on the Internet that said that bad connections in comm circuits can actually rectify.

Please share. But don't bother if the source is Wikipedia.

Yoyizit 07-17-2008 08:37 AM


Originally Posted by BigJimmy (Post 140007)
Please share. But don't bother if the source is Wikipedia.

Wasn't wiki.
Can't find right now.
I did hear that if you don't have a "cat's whisker" you could have used a rusty razor blade, but these all worked at micro signal levels.
Of course, I'm too young to know what a cat's whisker is/was.

Yoyizit 07-17-2008 11:54 AM


Originally Posted by BigJimmy (Post 140007)
But don't bother if the source is Wikipedia.

Frequent Spanking Of The Wiki is generally frowned upon.

Couldn't find it.


in various ANDed and ORed combinations.

Anyone know how I can ask Google for a list of my previous searches? This one didn't show up on my dropdown arrow.

Yoyizit 07-24-2008 04:48 PM

finally. . .

Originally Posted by BigJimmy (Post 140007)
Please share. But don't bother if the source is Wikipedia.

Search on the word "diode" within the article.

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