voltage drop

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  #1  
Old 11-27-05, 05:44 PM
deby77
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voltage drop

I have an out building wired with 220 volts. The electricity works but the voltage drops as the load increases. This is on one leg (110 volts). As the voltage drops on one leg, the voltage increases on the other leg. The wires are run underground. Is it possible that there is a leak to ground (nicked wire underground) that causes the vltage to drop as the load increases? Why does the voltage increase on the other leg when the voltage drops on the load leg?
 
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  #2  
Old 11-27-05, 05:50 PM
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Before I take a stab at the answer, I would like some additional information.

How far is the sub panel in the outbuilding from the main panel? How much current are you pulling through one leg, and how much voltage drop are you seeing?
 
  #3  
Old 11-27-05, 05:55 PM
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deby,
I assume you mean it has a 120/240 feeder to the out building.

It sounds as if you have an open or compromised neutral.
A load on one leg it would not affect the other leg unless there was already a balanced load to begin with.

How are the voltages at the connections? Line to line and line to neutral.
 
  #4  
Old 11-27-05, 05:58 PM
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Just a first response theory:

You might be having a backfeed situation that adds voltage from line 1 to line 2. You see, the way 220 works is that you don't need a neutral/ground because the alternating current pulsates back and forth at 60 hertz so that when line 1 is in sin mode the line 2 is in cosine mode so that line 2 becomes line 1's ground and vice versa.

So, I am thinking that somehow or another that say when line 2 is in a forward current sending mode, when line 2 should be in the return mode, that some of line 1's juice is also going forward and clashing with line 2. But don't ask me WHY this is doing it. I'm as curious as you and I am in no mood to think any deeper on this tonight as I am getting ready to go home now and I have had a long day. I spend too much time thinking.
 
  #5  
Old 11-27-05, 06:15 PM
deby77
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voltage drop

I actually have a barn 100' from the main and the out building is run from the barn panel and is about 150'. the barn is on a 100 amp breaker at the house main panel and I have the out building on a 50 amp breaker on the barn panel. I have run the kind of wire that is used for service from the transfomer to the house (it is huge aluminum wire but I don't know what size) so I think it is big enough. Line to line is 250 volts with no load at the out building sub panel. Line to ground is 125 volts with no load at the outbuiding sub panel. 95 volts with 1 light on, 85 volts with 2 lights on and 75 volts with 2 lights and a ceiling fan on.
 
  #6  
Old 11-27-05, 06:18 PM
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You have a problem with the wiring somewhere. Either the neutral is bad or the hot wire in question is bad.
 
  #7  
Old 11-27-05, 10:04 PM
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Those voltage drops are massive. You have some very serious problem with your connections, or with your wire.
 
  #8  
Old 11-28-05, 03:50 PM
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What a moron, I a can be sometimes. I said sin/cosine in above post. Duh. That's for geometry/trigonometry. I believe though that they talk in "sine waves" though, about the pulsations of 220.
 
  #9  
Old 11-28-05, 03:53 PM
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I have seen power company rated underground aluminum wire turn to "froth", underground (stood over trench and watched as the power company dug up the break in the line, and watched/saw the damaged area). Aluminum corrodes easily and can turn to a whitish powder. A nick in the wire during the laying of the wire could have been a festering wound that now is coming to fruition. Just a thought.
 
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Old 11-29-05, 07:10 PM
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Check for a bad neutral. The voltage going up on one leg is the clue.
 
  #11  
Old 11-30-05, 06:18 AM
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That "froth" is aluminum oxide which is, ironically, a very good insulator.
 
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Old 11-30-05, 08:39 AM
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alittle-So then, if the wire is coroding away underground, it might help restrict the current from electrifying the ground as much?
 
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Old 11-30-05, 08:55 AM
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Originally Posted by WFO
Check for a bad neutral. The voltage going up on one leg is the clue.
Could you explain how?

Remember that 220 doesn't really need a neutral in the sense 110 does. You can put a volt tester on each leg of a 200 and get a volt read without ever touching a neutral wire. I could be wrong here, but I believe the main reason you find neutral with 220 is for both grounding reasons, like so a case(the box of the appliance itself) has a way of being grounded, AND so that in the case of appliances, with motors, with light bulbs, timers, safety switches, etc., that these things are on one leg (110). But as far as the theory that 220 needs a neutral to carry the current, I do not believe this is so.

I think with a lot of things in life, a lot of us become experts on things and can successfully worlk on things without truly understanding the theory behind how certain things work. But that's okay, usually. It's like I'm sure doctors don't fully understand heart tissue, how irt got there and the elements of it's construction; yet they can repair damaged hearts.
 
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Old 11-30-05, 09:17 AM
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I haven't detected anybody mentioning any 240-volt loads in this thread, so the question of whether a 240-volt load needs a neutral is unrelated to this thread (and of course the answer is no).

We have talked about voltages going up, but we don't know how high they go up, or whether or not they go up above 125. A voltage that goes up from 90 to 100 when a new load is added to the other leg doesn't necessarily have anything to do with a bad neutral. It could just be less voltage drop due to a reduction in the unbalanced current.

If we have a bad neutral, then when the voltage drops from 125 to 75 on one leg, it should increase from 125 to 175 on the other. Does it?

Something is very, very wrong here. A voltage drop of 50 volts over 100 feet in the presence of only two lights and a fan is amazing.

We have far too little information in this thread to make any intelligent guesses. We don't know the gauges of the wire. We don't know the wattage of the loads. We don't know how high the voltages increase. Further speculation is not productive until we get more information.
 
  #15  
Old 11-30-05, 10:23 AM
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If there is an open Neutral on a 3-wire 220/120 circuit, the result is two 120-volt loads "in series" across 220 volts.

There is only one path for current-flow-- Line "A" to load "A'
----thru load "A" to where load "A" and load "B" connect to the Neutral bar,----- thru load "B" to line "B"

voltage-drop across load "A" + voltage-drop across load "B" = 220 volts = voltage across lines "A" & "B"

If the resistance of load "A" = 20, and the resistance of load "B" = 10, then the voltage-drop across load "A" = 2 X the voltage-drop across load "B", because the resistance of load "A" = 2 X resistance of load "B".

v-d load "A" = 140 + v-d load "B" = 70 = 210 volts = line-voltage A-to-B
 
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Old 11-30-05, 11:26 AM
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"alittle-So then, if the wire is coroding away underground, it might help restrict the current from electrifying the ground as much?"

Probably not. At least I doubt that the aluminum oxide ever completely seals off the conductor and you'll always have leakage current to earth. Some types of fault locators use leakage current and the resultant step potential to pinpoint underground cable failures.
 
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Old 11-30-05, 12:40 PM
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I think the confusion is stemming from the OP stating the out building is fed with "220". This is a very generic term, especially to the DIY'er.

I think ecman1 is reading this literally as "220". I also think the rest of us are seeing that it is feeding an out building and assuming it is actually a 120/240 feeder we are talking about. In this case, yes, an open or compromised neutral will act exactly as the OP states.
The "220" appliance example that ecman1 is using in his last post is actually also 120/240.
Again, we'll save this for another thread.

I do agree we need the OP to clear up some issues before going any further.
 
  #18  
Old 11-30-05, 02:13 PM
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I re-read the OP. What I make out of it is that he ran 220 underground to some outbuilding. Then when he uses power (I am assuming 110), there is volt drop on the circuit he is using (because of tell tale signs like motor slows down, lights dim, or whatever.) And at the same time he noticed that other lights got brighter (just a guess here). So, he went to the panel box to test the legs and noted that on the circuit that had dimming, that on that leg, he noted lower voltage on his test meter. But when he tested the other leg, it was higher by the amount that the other leg was lower.

IF that is true (until we hear differently, if he comes back, which I hope he does), then what can you make of this?
 
  #19  
Old 11-30-05, 03:27 PM
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Originally Posted by ecman1
Could you explain how?
Because he made reference to 110 readings on each leg. Of course you are correct that a bad neutral would not effect a 220 volt load. But since one leg is INCREASING in voltage, he has lost his reference to the source (center tap of the transformer) and whatever loads he is running (lights, for example, which probably aren't 220) are now operating in series. So Kirchoffs law applies depending on the combined impedance of each leg.

Open hot legs, partial shorts to ground, etc. can all cause decreases in voltage. I can see no other reason, other than the bad neutral, for an INCREASE in voltage unless he has some really bizarre situation where he actually has a center tap on a 220 volt inductive load, has one leg open, and the load is actually acting as an autotransformer and stepping it up in the open leg. Far fetched, but possible.
 

Last edited by racraft; 11-30-05 at 07:36 PM.
  #20  
Old 11-30-05, 03:29 PM
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.....and, obviously, I have no clue as to how to use the "Quote" button...
 
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Old 11-30-05, 06:06 PM
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Seriously? You're joking? In case not - push quote button. Begin typing under persons quote on the reply page.

Ohhhh _ *I* see what you did wrong. You forgot to include the [/QUOTE], which causes the post to "unquote" and turn to nice pretty yellow for us all, up on the screen.
 
  #22  
Old 11-30-05, 07:37 PM
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WFO

...Is that what you wanted? You're welcome.
 
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Old 12-01-05, 03:40 AM
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.....and yet, the company turns me loose in a substation. Go figure!!
 
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