Electrician Talk banner
1 - 20 of 20 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 ·
I have a customer who has been having problems with severe dimming of their lights and voltage drop on a general lighting and receptacle circuit, when running heavier loads like their vacuum cleaner. I suspected a bad splice or possibly a back stabbed receptacle was the cause. I have opened up every device that I have found on the circuit and moved any wires that were backstabbed to the screw terminals, but the problem persists. I have taken a piece of new Romex and used it as a test piece to replace each section of wire between the receptacles. What I find odd is that when I replace a section with this new wire I am getting a slight increase in the voltage at the end of the line, but I haven't found a section where I see a significant change. Also, if I put a load at the end of the circuit (vacuum) and I test throughout the circuit, the voltage increases incrementally from point to point as I get closer to the panel. I would expect that the location of the bad connection would show up as a larger decrease between those two points. It's almost like there is too much resistance in the wire itself, which just sounds bizarre. Has anyone here run into a similar situation? I'm not sure what to try next.
 

·
Registered
Retired EC and Fuel distribution contractor
Joined
·
1,576 Posts
How long is the circuit from the panel to where you plug in the outlet? Conductor routing, not direct route. I worked for a guy once that would rather us drill one hole above the receptacle and use more wire going up/down for each outlet, that would add a lot of wire.

I think your troubleshooting skills are correct. The next thing would be to do VD calculations and see if they match up with what you are seeing.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #3 ·
You raise a good point. I used a locator and the wires from each outlet go up the stud bay, into the attic and back down the next stud bay to the next receptacle. I would guess the wire length total between breaker and the last receptacle to be about 150'
 

·
Tool Fetish
Joined
·
889 Posts
Replace all of the receptacles on the circuit. Voltage drop is greater the farther away you get from the source, especially with any bad or loose connections.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #6 ·
Thanks Steve. I have confirmed that the voltage is good at the panel. They actually had the utility install a recording device on the meter to check for problems on their end, they found none.
 

·
Tool Fetish
Joined
·
889 Posts
Make sure you test it right on the buss bars in the panel. I encountered a problem like this many years ago. The service was copper SEU cable. The original installer never removed the clear wrapping on the copper conductors, under the insulation. Guess they didn't know it was even there. They even stripped the cable to use the SE conductors through the conduit into the panel. When the lugs were tightened originally the set screws tore the clear wrapper just enough to have proper voltage until loads were attached. Worked OK for 10 years, they lived with dimming lights, until they added central air. The A/C contractor, who also happened to wire the new A/C unit couldn't find anything wrong. If all else fails, then call an electrician.;)
 

·
Hackenschmidt
Joined
·
11,667 Posts
It's almost like there is too much resistance in the wire itself, which just sounds bizarre. Has anyone here run into a similar situation? I'm not sure what to try next.
That's exactly what voltage drop is from - resistance in the wire - you expect to see it depending on the length of the wire. Put the approx wire lengths in a voltage drop calculator and see if it's dropping more than expected for that AWG and load.
 

·
Registered
Power distribution and controls
Joined
·
730 Posts
Is this the only circuit?
Have you changed the breaker?
I do not like words for electrical descriptions. Number really help me.

What is the voltage at the first device from the breaker without any other wiring?
 

·
Tool Fetish
Joined
·
889 Posts
OK, what is the load?
There is no such thing as a perfect connection. Especially push in receptacle connections. Need an expensive tool to test across individual connections. A DRLRO meter. Were always required to use these to commission battery bank connections. (direct read low resistance ohm meter)
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #11 ·
The
That's exactly what voltage drop is from - resistance in the wire - you expect to see it depending on the length of the wire. Put the approx wire lengths in a voltage drop calculator and see if it's dropping more than expected for that AWG and load.
I just put the numbers in the calculator. Looks like i should be seeing a drop to around 111V. I am seeing 106V
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #12 ·
Is this the only circuit?
Have you changed the breaker?
I do not like words for electrical descriptions. Number really help me.

What is the voltage at the first device from the breaker without any other wiring?
This is the only circuit where I am seeing this large of a drop. I swapped the breaker with another in the panel to rule that out. I have almost exactly 120V at the first receptacle unloaded. I am getting about 106V at the last when loaded.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #13 ·
OK, what is the load?
There is no such thing as a perfect connection. Especially push in receptacle connections. Need an expensive tool to test across individual connections. A DRLRO meter. Were always required to use these to commission battery bank connections. (direct read low resistance ohm meter)
The load in this case is a vacuum cleaner at about 8.8 A. I have replaced any back stabbed connections with hooks on screw terminals.
 

·
I like ceiling fans & EMT
Former commercial, occasional (small) residential
Joined
·
874 Posts
How much of a load is on the circuit, normally? Is this all incandescent lighting?

Some voltage drop is normal with a ~10a appliance.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #16 ·
There are 3 light fixtures on the circuit with the energy saving compact fluorescent lamps in them. Other than when they run the vacuum, there is only an amp or 2. When they turn on the vacuum the lights dim dramatically. One of these is at the tail end of the circuit and goes almost completely out. In hindsight, I wish I had checked voltage at the fixtures. Are these type lamps more susceptible to voltage drop that it could show more obviously. The last thing I wanted to do was switch to incandescent and increase the load, but perhaps LED should be tried.
 

·
Registered
Joined
·
9,062 Posts
I have a customer who has been having problems with severe dimming of their lights and voltage drop on a general lighting and receptacle circuit, when running heavier loads like their vacuum cleaner.
This is perfectly normal. This is not a problem until someone notices, brings it up, then everyone thinks it's a problem and tries to solve something that is normal and just complying with the laws of physics. Go take a voltage meter and stick it in a receptacle with a lamp and turn on the vacuum - voltage will drop.

I suspected a bad splice or possibly a back stabbed receptacle was the cause. I have opened up every device that I have found on the circuit and moved any wires that were backstabbed to the screw terminals, but the problem persists. I have taken a piece of new Romex and used it as a test piece to replace each section of wire between the receptacles. What I find odd is that when I replace a section with this new wire I am getting a slight increase in the voltage at the end of the line, but I haven't found a section where I see a significant change.
You are bypassing the route of the installed cable and using a shorter cable. Shorter cable is less voltage drop.
Also, if I put a load at the end of the circuit (vacuum) and I test throughout the circuit, the voltage increases incrementally from point to point as I get closer to the panel. I would expect that the location of the bad connection would show up as a larger decrease between those two points.
You think there is a particular point where there IS a problem. What you are describing is resistance and voltage drop. There is no problem. I know you registered here in 2012 but are you an electrician? Do you have any theoretical schooling? Do you know all wire has resistance?
It's almost like there is too much resistance in the wire itself, which just sounds bizarre. Has anyone here run into a similar situation? I'm not sure what to try next.
The resistance is collective, there is more and more the further you go towards the end of the circuit.
Thanks Steve. I have confirmed that the voltage is good at the panel. They actually had the utility install a recording device on the meter to check for problems on their end, they found none.
They did huh? You didn't?
This is the only circuit where I am seeing this large of a drop. I swapped the breaker with another in the panel to rule that out. I have almost exactly 120V at the first receptacle unloaded. I am getting about 106V at the last when loaded.
Oh... you mean voltage drop?
There are 3 light fixtures on the circuit with the energy saving compact fluorescent lamps in them. Other than when they run the vacuum, there is only an amp or 2.
How are you reading an amp or 2 with only 3 compact flourescents? Each would have to be 80 watts to see 2 amps load. Where are they getting these anyway? They sound old because LEDS have been the go-to for the last 10 years.
When they turn on the vacuum the lights dim dramatically. One of these is at the tail end of the circuit and goes almost completely out. In hindsight, I wish I had checked voltage at the fixtures.
Yea 12 year old CFLs will do that.
Are these type lamps more susceptible to voltage drop that it could show more obviously. The last thing I wanted to do was switch to incandescent and increase the load, but perhaps LED should be tried.
I think you need to get an electrician to put eyes on the problem.
 

·
Registered
Retired EC and Fuel distribution contractor
Joined
·
1,576 Posts
This is the only circuit where I am seeing this large of a drop. I swapped the breaker with another in the panel to rule that out. I have almost exactly 120V at the first receptacle unloaded. I am getting about 106V at the last when loaded.
What is the reading on the 1st receptacle when the last one is 106V?
 

·
Registered
industrial E,I&C
Joined
·
3,518 Posts
I like numbers.
all tests with vac left running on the same receptacle.

L1 to N
L1 to ground
L2 to N
breaker to N
L1 to L2
 
1 - 20 of 20 Posts
Top