# Strangest defect I've encountered

Inspected about an 80-year old house today. It had some electrical issues. The oddest one was that I could not get the hall light to come on initially, but later I noticed that it was on dimly. Towards the end of the inspection, I was checking the oven which had been on for a while. It was just barely warm. I turned the knob up and out of the corner of my eye, I noticed it get brighter in the hallway. After playing around with the oven knob for a couple of minutes, I realized the hall light came on dimly when I turned the oven knob on. I could turn the hall light on brightly by turning the knob to “Broil”.

I’m not necessarily asking for an explanation of this. I just wanted to share this with ya’ll.

So to turn the Hall Light on, You need to set the Oven to Broil.

Is there a Problem with that?

No problem, you have to see what the Rock is cookin…

Sounds Like a neutral is loose in the panel .
Roy Cooke

that is a good one!

Very nice…

Thought the same when read about the hall light, but the oven made me think (since it was mentioned as having bearing on the problem) that something else is wrong. Since electric ovens typically use 240v, no neutral required(except for features: clocks, timers, lights, etc). Makes me also wonder if it’s a 120 service, which makes me lean back towards a floating neutral.

IMHO: Definiately defer to an electrician.

tom

How would a floating neutral create this condition?

Simple terms:

Voltage is the measure of potential between two points. This case what is called a ‘hot’ and a ‘neutral’. For case of argument we can assume a good path for electricity back to the source will mean that a neutral is zero volts, since no ‘back-pressure’ is created. When you loose a neutral in the panel going back to the service, you loose that great path back to the pole, and now electricity must ‘return’ via another path, often the grounding rod or grounded water piping. Since there is much resistance, this creates a sort of back-pressure. So very little electricity(amps) can flow. So lights(120 volt) dim, and electric toasters[120v] don’t heat up.

I tried to keep it simple for typing reasons, if something doesn’t make sense, feel free to ask, but it comes down to this, if the return path is broken, then no flow of electricity. However if there is a grounding path(ground rods,etc), electricity will continue to flow very slowly, since the earth is a path back to the electric source.

You can verify this on different levels. As a HI, you can visually inspect the service conductors, see if the cables are in good condition, good crimps at the POA. Look inside the panel, do all wires look properly terminated, and uncorroded? As an electrician, there are other opptions, amp meter on the grounding electrode conductor, votages accross bars, etc.

Once again IMHO: Defer to an electrician.

tom

Tony, Tony…

The service is 240 volts. When the oven did not get very hot, I thought it may only be getting 120 volts.

" I turned the knob up and out of the corner of my eye, I noticed it get brighter "

“When the oven did not get very hot, I thought it may only be getting 120 volts”

This is a textbook case of an open hot leg.

But a simple open hot leg doesn’t explain the effect on a hall light.

What if the oven and hall light were on the same circuit, the light downstream from the oven and the light had the switch on the neutral conductor instead of the hot.

Sure it does. If there was an open leg, none of the 120 loads on that bus would work. Then you turn on a 240 resistive load like an oven and the current passes thru the oven element and onto the dead bus. The voltage is limited by the resistance of the oven element, acting as a dimmer. I suspect there may have been more than the hall light not working. Mike may have had the oven warming up as he checked receptacles, which would have enough current to light up the little neon test lights. Also, the problem could be at a subpanel with only a few 120 loads.

brian winkle, that is some fine detective work! RIF.

tom

thanks Tom, I love troubleshooting more than anything…er…anything workwise anyway. When I get a call to install ceiling fans or something I schedule it out 7 to 10 days, but when it is a trouble call, I drop everything!

What is RIF?

Brian, could you simplify your explanation a little? I’m not understanding how current got to the hall light.
The hot leg is one of the ungrounded conductors at the main bus? It’s not connected so half the circuits have no power? How does power reach the light from the oven element?

Picture a panel with 120 to one side only. The other side is dead. Then take a 240 breaker, put a piece of wire from one terminal to the other, plug it onto the buses and turn it on. Now both buses will have 120. Now subsitute the short piece of wire for a 50’ circuit with an oven at the end. Same principle.

:idea: Thanks, Brian. :-;;