Open neutral mini lesson

Quick lesson on the effect of opening the neutral conductor in a 120/240 circuit.

[yechihast]

Closed neutral = lamps connected in parallel. Open neutral = lamps connected in series.

[griffmustard]

My interpretation of your demonstration is that without the neutral, you have 2 lamps in a 240V circuit with differing wattages, hence the reason why one lamp is brighter than the other. In series, if both lamps are (120W) for instance, then the voltage drop across both lamps would be equal, while the same amount of current is pushed through both of them. If however, one lamp is (120W) and the other is (60W), then the voltage drop across the (120W) would be 160V, while across the (60W) would be 80V. Again, the current (.75A) would be the same through both lamps. With the neutral intact, you now have a parallel circuit, with the same voltage (120V) across both lamps, but if the wattages are different, then you'll have different amounts of current going through each lamp. And the neutral is there to carry the imbalance amount of current back to the source.

[Stephen]

Suggestion: Add in the voltage drops across each bulb.

This is a typical 3 wire circuit illustration where you have 2 "hots" and a "common neutral." A neutral normally carries the unbalanced current in a 3 wire circuit. If you open the neutral the circuit becomes a series circuit. IF the circuit is unbalanced with, for example a 60 watt bulb on one side and a 100 watt bulb on the other, the neutral would carry 40 watts back to the transformer. IF the neutral is open then the current from each bulb will flow through the other to return to the transformer. There will be different voltage drops across each bulb because the resistance is different, and the smaller bulb will become brighter and eventually burn out. Both bulbs will then go out because there is no return as the circuit is open.

The demonstration is "Technically sound and correct." Anyone stating this is not correct does not understand what is taking place.

[apackwestbound]

Nice demo. It might have been helpful if you had put a volt meter on the neutral after you had opened (broken) the connection to further demonstrate the potential danger of this situation.

[MeeFeeTree]

both lams are at different values; when neutral breaks more voltage goes to smaller lame, and less to bigger lamp, if both lamps were equal breaking the neutral wouldn't effect them.

[OnTheGoKRO]

I have a issue… lol.

One day My light randomly stops working… (2 light fixtures to one switch! And other one works fine) …. So I disassemble the bulb fixture that isn’t working and test the wires….WIRES are getting power… but bulb isn’t working…SO…I go ahead and buy a new connection where the bulb screws in….
I Install new bulb connection and install new bulb … STILL NO light on….

So I check the power and IT has power and correct volt…. But the bulb still isn’t coming on?! Lol.
————————————-
-So the electric to the fixture is good
-The bulb connection is hot and good
- Electricity in the wires are good
- connections are tight….
-I replaced the switch just to be sure …
Idk what to do ….

?!
Since two fixtures are tied to 1 switch…. Maybe one of the wires to 1 of the fixtures tied to 1 switch maybe the neutral wire has become damaged over time?…….

Any help would be appreciated. Trying to help my dad here and I’m stuck haha

[MrTacolover]

Nice video, however it would have made it clearer if you mentioned that this only happens when the two bulbs share the same nuetral upline of the panel. With dedicated nuetrals for each circuit this wouldnt happen

[patcotsman]

I was going to comment about the brightness difference until I noticed that commentor Griff literly used the words I would have used. Sometimes I like to use extremes in a hypothetical case. For instance, one lamp might be 1000 watts, the other might be 10. The resistance of the 1000 watter would be so low as to be a virtual short to the 10 watt lamp, which would surely burn out. I didn;t try doing the math on this, as Griff did. All in all, a great demo.

[tedlahm]

If both bulbs are the same resistance and same wattage, how does the
circuit decided which one gets the MOST voltage ? Sharing the 240 volts in a SERIES CIRCUIT.

PS. if the loads were DIFFERENT, then only the lower current draw would continue to operate? The higher current draw would not be able to operate? thank you. KVL series circuits.

[christheother]

When this happens devices that were in parallel might end up being in series (as you demonstrate). In a house you might go around with a multimeter and measure odd voltages across lights etc. Lights might not appear work but when measured have lower than normal voltage across them. Very bad.

[urbannpa]

Thank you, Right to the point you explained my problem.

[jaredkay]

I liked the video to change the likes to the number 667...God bless.

[ammarbasrah]

If the three loop one neutral common and bad neutral what happen

[tsjuno]

this is so hard to explain to the young guys coming in. I'm going to have to make one. very nice

[ARNALDOPLACETAS]

Good explanation… I have the experience with some one els with 10 power outlets with computers connected… no one survive..😂

[Stefancy]

Current still flows through jumper after opening neutral that's why lights stay lit

[samanthagriffinv.]

Please explain if the neutral is at fault then how is the circuit complete

[tedlahm]

KVL does Kirchhoff voltage law apply? The two bulbs are in SERIES across 240
volts AC when you open the neutral? Classic example of a shared neutral?
Thank you.

[olaguna]

This is for anyone. Am I correct in saying the bulb with the higher resistance get brighter?

[billygraham]

This is very weird to me. Both black 120V and red 120V are connected to bulbs, but grounded to the same white. The ground is removed and so there is no ground (neutral), just two hots. One hot is supposed to then become a ground (neutral) and the other becomes a 240V? DOES THAT HAPPEN AUTOMATICALLY SOMEHOW???? PLEASE EXPLAIN THAT!!!