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sushiboy 04-02-2008 09:14 AM

Voltage Drop Issues
 
Hello,

I am having some voltage drop issues on pretty much all of the electrical recepticals in the house I just bought. Most are at around 7%. One, however, is around 11%. I have read that voltage drop should idealy not be above 5%. The person who owned the house before me told me that the once receptical (the one that I found to be at 11% voltage drop) would get hot to the touch if she plugged something in to it. I personally have not used it since she told me that.

So, in my case, what exactally is voltage drop anyway? I found some info on what can cause voltage drop (http://ecmweb.com/mag/electric_diagn...ower_problems/ ), but I dont fully understand what it actually is. Can someone explain it to me? Am I having power consumption even when nothing is plugged in? Where do I start to remedy this? My first thought is to try a higher guage wire, but I dont really know what I am talking about.:confused1:

Thanks in advance!

HouseHelper 04-02-2008 09:30 AM

I would think this is not a voltage drop issue, but a connection issue: You have poor connections between your wiring and the receptacles. Turn off the power to each circuit and start pulling receptacles to check the wiring. Each wire should be wrapped clockwise around the screw and the screw tightened securely.

jrclen 04-02-2008 02:06 PM

The voltage drop you are referring to is a reduction in voltage due to a bad connection or the resistance in a given length of wire.

If we use a volt meter to measure voltage from one side of a bad connection to the other side, we will read a voltage. That voltage is the drop across the connection. On a good connection, that voltage will be zero.

Every wire has resistance. The longer the wire, the more resistance. Measuring the voltage at the source end and comparing it to the voltage at the load end will show the voltage drop on the wire.

In your case you would measure the voltage at the source, in the electric panel, and then again at the end of the circuit, such as the receptacle outlet. But to get an accurate idea of the voltage drop, you will need a load on the circuit. The voltage drop will increase with the load.

I hope this helps.

sushiboy 04-02-2008 02:11 PM

Quote:

Originally Posted by jrclen (Post 113224)
The voltage drop you are referring to is a reduction in voltage due to a bad connection or the resistance in a given length of wire.

If we use a volt meter to measure voltage from one side of a bad connection to the other side, we will read a voltage. That voltage is the drop across the connection. On a good connection, that voltage will be zero.

Every wire has resistance. The longer the wire, the more resistance. Measuring the voltage at the source end and comparing it to the voltage at the load end will show the voltage drop on the wire.

In your case you would measure the voltage at the source, in the electric panel, and then again at the end of the circuit, such as the receptacle outlet. But to get an accurate idea of the voltage drop, you will need a load on the circuit. The voltage drop will increase with the load.

I hope this helps.


So, it is not power that is constantly being wasted even if nothing is plugged in to that outlet? I am still having a little trouble understanding this. If my tester shows a voltage of 121 or so, it is actually 11% lower than that if the voltage drop is 11%?

jerryh3 04-02-2008 02:25 PM

Quote:

Originally Posted by sushiboy (Post 113228)
So, it is not power that is constantly being wasted even if nothing is plugged in to that outlet? I am still having a little trouble understanding this. If my tester shows a voltage of 121 or so, it is actually 11% lower than that if the voltage drop is 11%?

Why don't you start over with this question. What are the voltage readings at your outlets? And where did you get the 11% and 7% figures?

sushiboy 04-02-2008 03:31 PM

Ok, I have a SureTest Circuit Analyzer. It says all the power jacks in my walls have at least a 7% voltage drop. One shows an 11% voltage drop. I have been told that the one with the 11% voltage drop gets warm when something is plugged into it. I want to understand what voltage drop is, to know if power is being used even if nothing is plugged in due to voltage drop, and what I can do about it. I already got some suggestions of where to start to lower the percentage, but anything further would be helpful as well.

jerryh3 04-02-2008 04:00 PM

Quote:

Originally Posted by sushiboy (Post 113260)
Ok, I have a SureTest Circuit Analyzer. It says all the power jacks in my walls have at least a 7% voltage drop. One shows an 11% voltage drop. I have been told that the one with the 11% voltage drop gets warm when something is plugged into it. I want to understand what voltage drop is, to know if power is being used even if nothing is plugged in due to voltage drop, and what I can do about it. I already got some suggestions of where to start to lower the percentage, but anything further would be helpful as well.

What load was the drop tested at?

sushiboy 04-02-2008 04:13 PM

Sorry, but I don't know what that means. The only thing plugged in to that outlet was my tester. It showed around 120-121V with 0 Ground to Neutral.

chris75 04-02-2008 08:45 PM

I was waiting for one of these threads to start... :yes:

nap 04-02-2008 09:31 PM

to accurately read voltage drop, your circuit has to be under load.

It can be calculated given a resistance reading though. Not sure what a SureTest Circuit Analyzer is and what it can do but unless it is somehow measuring the resistance in the wire or applying a load, it cannot tell you what the voltage drop is.


Typical voltage drop at no load is typically 0 volts. Under load, that can change greatly.

Did a quick look and it seems the tester used does in fact apply a load somehow or calculates the drop.


Unless your house is very big, chances are you have some bad connections somewhere that are highly resistive. That would cause your voltage drop.

jrclen 04-03-2008 11:21 AM

Quote:

Originally Posted by sushiboy (Post 113260)
I want to understand what voltage drop is, to know if power is being used even if nothing is plugged in due to voltage drop, and what I can do about it. I already got some suggestions of where to start to lower the percentage

I already explained what voltage drop actually is. No power can be used with nothing plugged in. Voltage drop has nothing to do with your electric bill. And I would really like to hear the suggestions you got to lower this percentage you are referring to.

Many people buy testers that they should just toss in the trash. They cause undue stress in some people. :laughing:

Quote:

Originally Posted by chris75 (Post 113354)
I was waiting for one of these threads to start... :yes:

I'm thinking I should have passed it up. But then, it might be fun. :whistling2:

InPhase277 04-03-2008 11:55 AM

For some reason, this sounds like a homework question... But I'll bite.

Sushiboy, voltage is the potential across a circuit to do work. In this case, the work is moving electric charge through a resistance, or load. In effect, any load is in series with the two wires that supply it, and the voltage drop across a load is equal to the source voltage. Which means that current enters a lamp at 120 V and leaves that lamp at 0 V. Sometimes the wires themselves have enough resistance to be part of the load, so some of the voltage is dropped just overcoming that resistance. This is what usually is referred to as voltage drop.

Under load, the amount of voltage that is dropped across the circuit conductors is the voltage drop. And that drop is equal to the resistance of the wires (in ohms) multiplied by the current (in amps). So, if the wires to the receptacle have a total of 1 ohm of resistance, and you turn on the vacuum cleaner which pulls 10 amps, the voltage drop in the conductors will be 1 x 10 = 10 volts. With no load, you will read 120 V. With the vacuum on, you will read 110 V.

Voltage only drops when current flows. In your case if you have 120 V, that is nominal, but if you have an 11% voltage drop, which would be about 107 V, either you have a heavy load, or a high resistance connection. Check your connections.

InPhase277

BigJimmy 04-03-2008 10:01 PM

Quote:

Originally Posted by InPhase277 (Post 113522)
In this case, the work is moving electric charge through a resistance, or load.

InPhase: This is one of the best explanations of voltage drop that I have ever read. Also, I highlighted one important and often misunderstood point that you correctly made. Current is charge flow, not electron flow. The drift current is actually very slow, esp. in ac where the direction of the electric field is changing 120 times per second. Charge moves very fast, however the electrons do not.

Great response,
Jimmy


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