Thank you for the helpful info. I'm not an electrician, but am curious: why does a loose upstream neutral connection cause its voltage to float under load?
Because as you try to pass current thru the circuit, it wont flow so you lose the voltage connection. If it was a good connection, the bulb would come on and the 120V would stay solid. The connection was too lose to allow the current to flow but it had enough of a connection to "see" the 120V .... Im a lineman for an ISP and whether working on copper or fiber, they work the same way. I can shoot a 60mW light down a fiber and look at the other end about 3000 ft away and the light should be as BRIGHT as if i were looking at it directly, if the light is the same, then its good, but if its weak, then there is a kink in the fiber or a bad splice. Same as copper, it can test ok but try to pass electrical data across it, thats the actual test.
Now, the fun begins: finding the loose neutral. Carry on. I plug in a light with an extension cord, so I always see the lamp. First, I start thumping outlets with the palm of my hand. If the light flickers, I have found the culprit. It only sometimes works, but it is a good starting point.
You are reading voltage because you dont need a "solid" connection to read voltage across the wire. You just need enough continuity to see voltage between the 2 wires. Voltage is only half the story. The true test is that current flow test and when you put that bulb in, the current tried to flow but failed because you have a lose connection somewhere and that "lose" connection is not enough for the amount of current needed to pass thru. Kinda like a car battery, just because you see 12V does not mean the battery has the capacity to flow enough current to turn the starter / engine, as soon as you try to crank the motor, that 12V is GONE like your test did when you plugged the light in, then when you stopped cranking or pulled the bulb off, the voltage returned to 12V or 120V ... Same situation here, you got 120V but then tried to pass current and it dropped off because it can't due to a lose connection. As a lineman for an ISP we learned this very trick, just because you have continuity between 2 wires does not mean the current will flow. You don't need much continuity for that meter to see across it. That meter has a 9 volt battery and if the wires can support enough current flow to complete the circuit for 9V, you will then see the 120V across it. The true test is the current flow test. If it can pump current thru, then its a good circuit.
Steve, great video as always. Love the simplicity of using a nightlight to place a load on the circuit. Couple questions, if I may? You mentioned that, in case of loose/floating neutrals neutral would assume line potential. This was demonstrated by your measuring potential at neutral wrt ground using the VAC function on your meter. Does this not also imply some capacitive coupling between line & neutral? How otherwise could neutral assume line potential? In the case of capacitive coupling between line and neutral, I assume a dead short is prevented because a circuit with loose connections isn’t current-worthy?
It's about relative impedance. The upstream loose connection on the neutral line was of very high impedance. The impedance of the 4 watt bulb was relatively very low. This represents a voltage divider with the impedance of the bulb in series with the upstream loose connection. In a voltage divider, the highest impedance has the greatest share of the 120v across it - causing the voltage difference between ground and the compromised neutral point to be close to line voltage - and the remaining voltage (a few volts) across the bulb.
Thanks for your reply. I can see how placing a load on the circuit creates a voltage divider in series with the HiZ loose connection. I simply don’t yet comprehend how any voltage is applied to the neutral conductor. I will continue to focus on this until I understand. Appreciate you, Sir!
When talking about the neutral, everytime you said upstream, I was thinking downstream because I imagine current flowing from the circuit breaker to the outlet on the black (hot) wire and coming back to the panel from the outlet on white (neutral) wire. But we're talking about AC, so I guess upstream of the outlet is the panel.
Yes upstream is the panel ... As a lineman for an ISP we refer our cables as Feed Side and Field Side. Feed side is the Input and Field is the output to the customer. So in electrical in the home, Upstream would be the feed from the panel and downstream would be the output to the other outlets.
Be nice to see what the wires looked like causing the issue. Not just a analysis of the outlet with the meters
Noted for future reference. Thanks for the feedback.
Thank you for the helpful info. I'm not an electrician, but am curious: why does a loose upstream neutral connection cause its voltage to float under load?
Because as you try to pass current thru the circuit, it wont flow so you lose the voltage connection. If it was a good connection, the bulb would come on and the 120V would stay solid.
The connection was too lose to allow the current to flow but it had enough of a connection to "see" the 120V ....
Im a lineman for an ISP and whether working on copper or fiber, they work the same way.
I can shoot a 60mW light down a fiber and look at the other end about 3000 ft away and the light should be as BRIGHT as if i were looking at it directly, if the light is the same, then its good, but if its weak, then there is a kink in the fiber or a bad splice.
Same as copper, it can test ok but try to pass electrical data across it, thats the actual test.
@@ACommenterOnRUclips I appreciate the explanation - thanks!
Now, the fun begins: finding the loose neutral. Carry on. I plug in a light with an extension cord, so I always see the lamp. First, I start thumping outlets with the palm of my hand. If the light flickers, I have found the culprit. It only sometimes works, but it is a good starting point.
You are reading voltage because you dont need a "solid" connection to read voltage across the wire. You just need enough continuity to see voltage between the 2 wires. Voltage is only half the story.
The true test is that current flow test and when you put that bulb in, the current tried to flow but failed because you have a lose connection somewhere and that "lose" connection is not enough for the amount of current needed to pass thru.
Kinda like a car battery, just because you see 12V does not mean the battery has the capacity to flow enough current to turn the starter / engine, as soon as you try to crank the motor, that 12V is GONE like your test did when you plugged the light in, then when you stopped cranking or pulled the bulb off, the voltage returned to 12V or 120V ... Same situation here, you got 120V but then tried to pass current and it dropped off because it can't due to a lose connection.
As a lineman for an ISP we learned this very trick, just because you have continuity between 2 wires does not mean the current will flow. You don't need much continuity for that meter to see across it. That meter has a 9 volt battery and if the wires can support enough current flow to complete the circuit for 9V, you will then see the 120V across it.
The true test is the current flow test. If it can pump current thru, then its a good circuit.
Yup. Exactly the point of the video. Current flow causes the available voltage to be "dropped" across the upstream loose connection.
@@TheTechCircuitso I can do to fix the issue??
Steve, great video as always. Love the simplicity of using a nightlight to place a load on the circuit. Couple questions, if I may?
You mentioned that, in case of loose/floating neutrals neutral would assume line potential. This was demonstrated by your measuring potential at neutral wrt ground using the VAC function on your meter. Does this not also imply some capacitive coupling between line & neutral? How otherwise could neutral assume line potential?
In the case of capacitive coupling between line and neutral, I assume a dead short is prevented because a circuit with loose connections isn’t current-worthy?
I guess I just don’t quite understand how neutral would be “pulled up” to line potential due to a loose connection…
It's about relative impedance. The upstream loose connection on the neutral line was of very high impedance. The impedance of the 4 watt bulb was relatively very low. This represents a voltage divider with the impedance of the bulb in series with the upstream loose connection. In a voltage divider, the highest impedance has the greatest share of the 120v across it - causing the voltage difference between ground and the compromised neutral point to be close to line voltage - and the remaining voltage (a few volts) across the bulb.
Thanks for your reply. I can see how placing a load on the circuit creates a voltage divider in series with the HiZ loose connection. I simply don’t yet comprehend how any voltage is applied to the neutral conductor. I will continue to focus on this until I understand. Appreciate you, Sir!
When talking about the neutral, everytime you said upstream, I was thinking downstream because I imagine current flowing from the circuit breaker to the outlet on the black (hot) wire and coming back to the panel from the outlet on white (neutral) wire. But we're talking about AC, so I guess upstream of the outlet is the panel.
Yes upstream is the panel ...
As a lineman for an ISP we refer our cables as Feed Side and Field Side.
Feed side is the Input and Field is the output to the customer.
So in electrical in the home, Upstream would be the feed from the panel and downstream would be the output to the other outlets.