open/loose neutral?

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jemsvcs

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While troubleshooting a lighting circuit I got the following readings off of two SPST switches that were located within the same j-box:

These readings were taken with both switches open and the wiring is knob-and-tube and old romex.

Switch #1:

1. line terminal to load terminal - 117V
2. line terminal to line terminal of Switch #2 - 230V
3. line terminal to load terminal of Switch #2 - 34V
4. load terminal to load terminal of Switch #2 - 0V

Switch #2:

1. line terminal to load terminal of Switch #1 - 117V
2. line terminal to load terminal - 34V

Why the 34V on readings dealing with the load terminal/wire of Switch #2.

[ December 03, 2004, 06:46 PM: Message edited by: jemsvcs ]
 
Re: open/loose neutral?

You didn't say what problem you are having. Are the two switches from the same branch circuit? Is there a problem with both of them?

I hope you don't mind some advice:

It seems like you need to focus on the problem and try to come up with a theory as to what is wrong. Then try to decide what voltage readings will prove or disprove your theory. Taking voltage readings between every two points possible is a good way to get overwellmed.

That said, here is my theory: Switch 2 may be bad. It has 34 volts across it when open, and it should have 120 volts across it.

Steve
 
Re: open/loose neutral?

When you say "grounded terminal" do you mean the " grounding " terminal, that is, the green ground screw?

The 34 volts could be phantom voltage. I'm guessing that you are using a digital meter if you are getting readings that precise.

Read this thread for more info about digital meters versus wiggies.

I concur with Bob on that issue, using a digital meter can be very frustrating when simply testing for the presence of voltage.
 
Re: open/loose neutral?

Digital meter? Place small light across the points being tested, even a 4 or 7watt, that voltage most likely will drop to zero which is an indication that what you had actually had been measuring was voltage that was induced by an adjacent energized line conductor. Digital meters are great instruments and are extremely accurate. But they are also very sensitive, that is they are capable of measuring potential without actually loading the points being measure unlike the old analog meters, which is specified in ohms per volt. If an analog meter is available you may get a much lower voltage reading or maybe even zero.
 
Re: open/loose neutral?

When i say grounded terminal i mean the terminal where the grounded conductor is attached.

Yes...i was using a digital multimeter. But why would i pick up only 34V between both ungrounded terminals and the gounded terminal of Switch #2 when i get 117V between both ungrounded terminals and the grounded terminal of Switch #1?
 
Re: open/loose neutral?

Originally posted by jemsvcs: When i say grounded terminal i mean the terminal where the grounded conductor is attached.
Click to expand...
I think you might be getting terminology confused.

A "grounded conductor" implies a "neutral", a "grounding conductor" implies "bare or green earth conductor."

So do you mean what is commonly referred to as a neutral , or the grounding conductor?

You should never have a grounded conductor on a single pole switch. This would cause a dead short.

The 'other' terminal on a single pole switch is still part of the ungrounded circuit.

[ December 03, 2004, 01:51 PM: Message edited by: peter d ]
 
Re: open/loose neutral?

Yes...i was using a digital multimeter. But why would i pick up only 34V between both ungrounded terminals and the gounded terminal of Switch #2 when i get 117V between both ungrounded terminals and the grounded terminal of Switch #1?
Click to expand...
One possibility would be a burnt out light bulb on switch #2, and a good light bulb on switch #1. Could also be an open wire on switch #2.

Steve
 
Re: open/loose neutral?

Peter,

Sorry about the mix up...I thought about this for so long that I started to confuse myself :D

What I was trying to say...but not so well...was the load side of the switch instead of 'grounded'. So that should clear it up...unless they switched the neutral in this instance.

So, my original question still remains as to why i'm reading 34V between the line side of both switches and the load side of Switch #2.
 
Re: open/loose neutral?

A 100 watt light bulb is as useful as a meter for stuff like this.
 
Re: open/loose neutral?

The two switches are (obviously) on seperate circuits, different phases.

I'm trusting you have a short on the load side of switch #1, and that's what brought this on. You wouldn't get decent voltage if you tested a neutral that was being fed from a light bulb, right? That's spent power after the bulb. As in, if you were to hook several light bulbs in series (one wire, not two [parallel] like romex), each bulb in line would be dimmer than the last, until there was no power for the last bulb.

Normally you wouldn't test line to load on a switch--there shouldn't be anything meaningful to see. A switch is an intentional break in a wire. Standing on the highway, can you measure how fast the Earth is spinning?

So, if you hook a meter inline on a switch, the meter would detect the voltage that the bulb didn't use...34V. I might not have my terminology or theory right on the money, but it's functionally right.

You have a short on the switchleg for switch #1.
That's why either switch's line side will find a good neutral on the load side of switch #1, telling you that "Yes, You have 117 VAC."

Hope that helps.

Re-reading that, it was as clear as Nostradmus. Oh yeah. Needus anny alp, allcy me.
 
Re: open/loose neutral?

When you have a old house wired with knob&tube wiring, your switches are wired with the grounded(neutral) wire instead of the ungrounded(hot)wire.
It sounds like an open neutral on switch 2. when you use your meter to test, you are closing a circuit of an open neutral with a light bulb. this is why you get the 110v reading. When you test it the other way ,you get 34v which in most cases is an open neutral. Either wires got mixed up on the switches,or it's an open neutral somewhere on that circuit.
You mentioned that there was romex. If the basement was rewired your problem might be in one of the j-boxes. Last but not least,rewire. :p
 
Re: open/loose neutral?

Jem,

When you're dealing with Knob & Tube there is no equipment ground - just phase and neutral. If the old NMC cable doesn't have a ground wire inside the jacket - same situation.

Just a suggestion - take some inexpensive wire (i.e. telephone or alarm cable) and strap one end to something that's definitely grounded - like a water pipe. Pull off enough to reach the area where you're testing and cut and strip that end. Clip one lead of your meter (set to read AC voltage) to the phone wire and take your readings to each point at the switches again.

Having 230V at that junction box could be legit if there are two different phases switching lighting circuits. The 34 volts is a mystery unless you're reading to neutral through a bulb filament or some other load downstream
 
Re: open/loose neutral?

How can you measure voltage across two points if both points are grounded or ungrounded (same phase)? I would have to ask the same question as posted previously: What was the initial problem??
 
Re: open/loose neutral?

How can you measure voltage across two points if both points are grounded or ungrounded (same phase)? I would have to ask the same question as posted previously: What was the initial problem??
Click to expand...
line----->0 34V 0-----switchleg----bulb----neutral


the bulb reacts as a shoddy source of neutral
the meter completes the circuit, sorta.
test leads are on the zeroes in my cruddy diagram.
Make sense?
 
Re: open/loose neutral?

As in, if you were to hook several light bulbs in series (one wire, not two [parallel] like romex), each bulb in line would be dimmer than the last, until there was no power for the last bulb.
Click to expand...
If you hook several bulbs in series, (and they are all the same type of bulb) they will all burn with the same brightness. The last bulb doesn't get any less power than the first one (unless there is a lot of voltage drop in the wire feeding the last one).


So, if you hook a meter inline on a switch, the meter would detect the voltage that the bulb didn't use...34V.
Click to expand...
No, the voltage across any device in a series circuit depends on the resistance of that device. The device with the highest resistance gets the highest voltage. Voltmeters usually are not connected in series because of their high resistance. But, assuming the switch was closed, and a voltmeter were connected in series, the voltmeter would read the whole 120V, the lamp would stay off and would have 0 volts across it.

Steve
 
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