Non sinusoidal wave circuit/ receptacle not working

[winnie]

You probably are connected across a switch leg instead of a hot and neutral.

The distorted waveform has vaguely sine shaped peaks with long absolutely flat '0' periods. It sure looks to me like you are measuring voltage in series with some sort of rectifying load. Maybe some 4 foot fixtures converted to LED or similar.

 

[Jpflex]

You probably are connected across a switch leg instead of a hot and neutral.

It sounds like you need to call an electrician. I suggest using an extension cord plugged into a known-properly-wired receptacle and a solenoid tester to check for real power between each cord slot and each bad-receptacle slot.

Did you check voltage at the recpt with a load plugged into the recpt.

My old saying is check what's easiest to check first. Make sure the hot and neutral really are.

Distortion from various types of loads is generally in the current waveform. This is reflected back as what is usually small voltage variations thru the impedance of the serving transformer. A good example is the "chopped" current waveforms of modern electronic dimmers.

View attachment 2567590

Mark

The waveform I uploaded was not with the vacuum cleaner plugged in but with the scope and DVOM leads into receptacle directly. Here is a picture of the waveform on a receptacle in adjacent rooms as it’s normal and a clean waveform

 

[Jpflex]

The distorted waveform has vaguely sine shaped peaks with long absolutely flat '0' periods. It sure looks to me like you are measuring voltage in series with some sort of rectifying load. Maybe some 4 foot fixtures converted to LED or similar.

I guess this is possible. I just found another junction box in the attic that had a cleaner signal and the receptacle now works.

However the entire room has this same bad waveform but other receptacles are powering on devices including vacuum cleaner so this was odd.

I wanted to check a and b phase at main panel but I couldn’t because I had other work

 

[Dsg319]

What about a simple bad connection somewhere?

I’ve had instances where you can read nominal voltage with a typical high impedance multi meter but when you add a load there’s a lot of voltage drop across the connection and not able to “turn on” said vacuum or other devices.

 

[Tulsa Electrician]

I guess this is possible. I just found another junction box in the attic that had a cleaner signal and the receptacle now works.

However the entire room has this same bad waveform but other receptacles are powering on devices including vacuum cleaner so this was odd.

I wanted to check a and b phase at main panel but I couldn’t because I had other work

Ok, now I'm interested in the wave form.
Check amp draw on circuit and see what on that. Then unplug or turn off and see if the wave changes to a normal value. Switch leg to an led maybe?

 

[ptonsparky]

With older wiring, especially K&T, start over from the beginning. Don't tap off any of it. Takes less time to run new than diagnose issues that aren't there.

 

[Jpflex]

Ok, now I'm interested in the wave form.
Check amp draw on circuit and see what on that. Then unplug or turn off and see if the wave changes to a normal value. Switch leg to a led maybe?

This is a good idea to see if a reactive load is distorting the wave but if you notice not only is the waveform on my fluke oscilloscope non sinusoidal but has low peak voltage and overall lower RMS voltage around 40 volts AC.

I do not know why my DVOM shows 125 volts AC

I wish I could do some more trouble shooting but I would have no way to justify this with the company and so for now I’ve move in to other projects.

When I get a chance to go back to the panel I will definitely scope a and b phase to neutral

 

[Jpflex]

What about a simple bad connection somewhere?

I’ve had instances where you can read nominal voltage with a typical high impedance multi meter but when you add a load there’s a lot of voltage drop across the connection and not able to “turn on” said vacuum or other devices.

This is exactly what I was thinking. If say I had one strand of wire from 12 AWG wire connecting circuit, I still may show 120 volts to receptacle but not have ampacity needed?

 

[LarryFine]

I do not know why my DVOM shows 125 volts AC

Because it uses too little current to expose a high-resistance connection or break.

 

[LarryFine]

To me, this is simple trouble-shooting. To use a high-impedance meter, re-create the problem with a load, then check for improper voltages.

Also do fall-of-potential checks by testing for voltage between points on the same conductor pathway that should not have any voltage between them, but do.

 

[Jpflex]

To me, this is simple trouble-shooting. To use a high-impedance meter, re-create the problem with a load, then check for improper voltages.

Also do fall-of-potential checks by testing for voltage between points on the same conductor pathway that should not have any voltage between them, but do.

Indeed. I would have done this but the wires are exothermic welded together and are taped together old school and it’s a pain to remove tape and reconnect

 

[ActionDave]

Odds are better than not the connections are soldered rather than welded, and yes that old tape is some tough stuff.

 

[winnie]

Indeed. I would have done this but the wires are exothermic welded together and are taped together old school and it’s a pain to remove tape and reconnect

Very unlikely that old school K+T was exothermic welded. Standard technique was to twist the wires together securely, and then dip the splice into a pot of molten solder, then tape.

It is a huge pain to remove the tape, and if the splice was subject to any heating then the old wire insulation is probably brittle.

Jon

 

[Speedskater]

This is exactly what I was thinking. If say I had one strand of wire from 12 AWG wire connecting circuit, I still may show 120 volts to receptacle but not have ampacity needed?

If the strand doesn't have the ampacity, it will act as a fuse and fail. But one strand would have a high resistance and a large voltage drop.

 

[Jpflex]

If the strand doesn't have the ampacity, it will act as a fuse and fail. But one strand would have a high resistance and a large voltage drop.

Not if the circuit is unloaded. If you put a high impedance (typically 10 mega ohm DVOM Meter) to check voltage at the receptacle, you may still be able to see 120 volts but not have ampacity for loads

 

[Dsg319]

It

Not if the circuit is unloaded. If you put a high impedance (typically 10 mega ohm DVOM Meter) to check voltage at the receptacle, you may still be able to see 120 volts but not have ampacity for loads

I think he’s saying also instead of the strand burning up because of current such as acting like a fuse it might be acting like a load in series with the vacuum ( think light bulb filiment ) and having a large voltage drop across it. Im not 100 percent I have this right in my head. But If it is in fact acting as a load in series to the vacuum that maybe would explain why the led would light up but nothing else. Enough power available for the led to function probably because it has a lower power consumption then the stray of copper acting as a load in series.

Just an idea. Someone correct me.

 

[Little Bill]

It

I think he’s saying also instead of the strand burning up because of current such as acting like a fuse it might be acting like a load in series with the vacuum ( think light bulb filiment ) and having a large voltage drop across it. Im not 100 percent I have this right in my head. But If it is in fact acting as a load in series to the vacuum that maybe would explain why the led would light up but nothing else. Enough power available for the led to function probably because it has a lower power consumption then the stray of copper acting as a load in series.

Just an idea. Someone correct me.

I've used plug-in testers many times that showed voltage and proper wiring. But when a load was plugged in, the voltage went away. That was due to bad or loose connection. I think that may be similar to what you're saying.