Not enough juice at receptacle

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Hey yal! So have a customer that has low power to their fridge. They had a tech come out and he determined that the fridge is fine, but the power at the receptacle is not. He measures 120v across both bottom and top, but once the fridge is plugged in it is underpowered, and the bottom face on the receptacle measures 7v-20v. I believe it is a dedicated circuit and will check out the wiring and panel tomorrow, but figured I would ask ahead of time for any ideas!
 

JFletcher

Senior Member
Location
Williamsburg, VA
although the refrigerator could be on an individual branch circuit, the overwhelming majority of them are wired onto one of the small appliance branch circuits to save money when building the house.

while the appliance Tech has been there, I would take what they say with a grain of salt the size of Rhode Island.

Though there are many ways to troubleshoot this, I would start finding out if the circuit and or the refrigerator are new, if there have been any recent modifications to electrical circuit, Etc. if it is an individual branch circuit, which will usually narrow down to three points... The refrigerator, the receptacle, or the connection to the breaker.

with an extension cord to the refrigerator off another circuit to eliminate it as a problem, and then a shop light with a 100-watt bulb in it plugged into the receptacle and observe what it does.

If the 120 volts measured at the outlet is not a phantom reading, it would take virtually a short circuit to create a 100 + voltage drop at the receptacle given the typical distances involved in houses. This would have certainly have tripped any ocpd.

I would not test the refrigerator again on the circuit until the problem is found... Last thing I want is to blow up somebody's brand new $3,000 refrigerator.
 

mopowr steve

Senior Member
Location
NW Ohio
Occupation
Electrical contractor
First off———— juice comes in a can!

And what is top and bottom of receptacle?
Sounds like a loose connection somewhere.
 

JPinVA

Senior Member
Location
Virginia
A drop in voltage by that much under load is a sign of high resistance somewhere along the line.

Test for high resistance on the neutral. If that's OK...test for high resistance on the high side.

Quick and dirty neutral test: With load applied, check neutral to ground. If you find your lost 100V there, then your neutral is faulty down stream. You can also check for neutral/ground continuity...but ensure the circuit is de-energized...and that you're not dealing with a shared neutral. If you see high resistance...that can confirm your faulty neutral.

If that all shows OK. Remove the hot from the breaker...and run a continuity check to the outlet. If that shows high resistance, you have a hot side issue.

If an issue is found...start with the connections first...receptacle and panel...and any receptacles along the way.
 
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JPinVA

Senior Member
Location
Virginia
The following is purely hypothetical...I'm an engineer...so I have fun doing this stuff. Until we have more test data, we don't have much to go on...but I'll just throw out an example of what "could" be the problem.

Let's say we have a 100 ohm resistance somewhere in the neutral from the outlet back to the panel. Without a load (i.e., an open circuit at the outlet), the voltage across the outlet (hot to ground) will read 120V.

For sake of argument, let's say the refrigerator runs off 720W (ignoring PF for the sake of simplicity) and pulls 6A, resulting in an equivalent resistance of 20 ohms. That is, Power is 120V X 6A = 720W. The main thing here is the 20 ohms.

When the load is connected, the open circuit that once existed at the outlet (showing 120V) now has the 20 ohm at the outlet. And if the resistance to/from the outlet back to the source is nigh zero, then we have 120V @ 6A, and the fridge happily churning at 720W within spec.

But if we have 100 ohm of resistance in the neutral...in series with the outlet, then the 120V is now impressed across 120 ohms (100 from the neutral resistance and 20 from the Fridge). 120V and 120 ohms means 1A will flow. The 1A across the fridge 20 ohms will result in a 20V reading across the outlet...and the 1A across the neutral resistance will show the remaining 100V.

As the EGC is connected to the neutral at the SE, If there is a 100V drop on the neutral on the way back to the SE panel, then 100V will show between the neutral and the ground at the outlet when the 20 ohm load (Fridge) is connected.

The same problem can occur if the 100 ohm resistance is on the hot side, but checking for that occurrence is slightly more complicated.

Basically, if you see 120V in open condition (no load) and 20V in closed condition, then the other 100V is somewhere in series. Be it along the neutral as described above...or along the hot. It could manifest in the wire itself...or more likely...in a bad connection (including bad connection of hot or neutral in the panel or a receptacle in the circuit)....not bad enough to be open...but bad enough to induce approximately 100 ohm of resistance or there about.
 

480sparky

Senior Member
Location
Iowegia
......... They had a tech come out ...........

red-flag.jpg
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
First....... the HO should take a lamp and plug it in at the fridge receptacle, if it comes on a full bright, the receptacle is probably fine
2nd........ Do as someone else suggested and run an ext. cord to a known working outlet and plug in the fridge, if the fridge works then the problem is either at the receptacle or the path back to the panel.

This should have been done before calling anyone, tech or electrician. Maybe an elderly person might not could do this but certainly the tech could have, if for nothing else, just to show that it was the power and not the fridge.

Electrician should have no problem determining what is happening here.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
First off———— juice comes in a can!

And what is top and bottom of receptacle?
Sounds like a loose connection somewhere.

That seems pretty plain to me. You have a duplex receptacle. when the refrig is plugged in to the top, there is easy access to the bottom, where the tech is reading 7-20V. Which does translate to a resistance in series with the refrigerator. To assume it is a loose wire may be jumping the gun. My first guess with just the information available is a bad breaker, mostly because it is easier to eliminate.
 

growler

Senior Member
Location
Atlanta,GA
To assume it is a loose wire may be jumping the gun. My first guess with just the information available is a bad breaker, mostly because it is easier to eliminate.

I certainly would check the breaker and connections (neutral buss) at the panel. But I would also want to pull that frig and check the receptacle for bad back stab connections.
 

growler

Senior Member
Location
Atlanta,GA
Folks I don't see the fact that they had an appliance tech come out as a red flag.

If their frig stopped working an appliance tech would be the first person to call. The tech thinks the power to the appliance is not right and suggest they get an electrician . It all sounds perfectly normal to me.
 

Besoeker

Senior Member
Location
UK
Hey yal! So have a customer that has low power to their fridge. They had a tech come out and he determined that the fridge is fine, but the power at the receptacle is not. He measures 120v across both bottom and top, but once the fridge is plugged in it is underpowered, and the bottom face on the receptacle measures 7v-20v. I believe it is a dedicated circuit and will check out the wiring and panel tomorrow, but figured I would ask ahead of time for any ideas!
How can you determine if the fridge is OK if you can't supply it with the correct voltage?
 

sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
Thanks everyone! Turned out to be bad breaker contacts to the bus bar, it was loose as hell. So pretty simple after all.

Well that's what you think, I'm going with the tabs were broken off the recept. and he was reading induced voltage. ....too late?
 

tkb

Senior Member
Location
MA
although the refrigerator could be on an individual branch circuit, the overwhelming majority of them are wired onto one of the small appliance branch circuits to save money when building the house.

while the appliance Tech has been there, I would take what they say with a grain of salt the size of Rhode Island.

Though there are many ways to troubleshoot this, I would start finding out if the circuit and or the refrigerator are new, if there have been any recent modifications to electrical circuit, Etc. if it is an individual branch circuit, which will usually narrow down to three points... The refrigerator, the receptacle, or the connection to the breaker.

with an extension cord to the refrigerator off another circuit to eliminate it as a problem, and then a shop light with a 100-watt bulb in it plugged into the receptacle and observe what it does.

If the 120 volts measured at the outlet is not a phantom reading, it would take virtually a short circuit to create a 100 + voltage drop at the receptacle given the typical distances involved in houses. This would have certainly have tripped any ocpd.

I would not test the refrigerator again on the circuit until the problem is found... Last thing I want is to blow up somebody's brand new $3,000 refrigerator.

Where can I get one of these mythical 100 Watt bulbs? :lol:
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
That seems pretty plain to me. You have a duplex receptacle. when the refrig is plugged in to the top, there is easy access to the bottom, where the tech is reading 7-20V. Which does translate to a resistance in series with the refrigerator. To assume it is a loose wire may be jumping the gun. My first guess with just the information available is a bad breaker, mostly because it is easier to eliminate.

Circle gets the square. One check for armchair troubleshooting. Seriously though, go to the places that are easiest to get to and most likely to be the cause of the problem. In this case, the breaker was that spot.
 
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