I have a programmable switch that requires a neutral line to work. The
switch boxes in this old house do not have a neutral line. I was told
this by an electrician.
However, my son has a newer house, which may have a neutral line. I have
an old Wiggy voltage tester. How can I test for a neutral line? How can
I tell the identify the line, the load, and the neutral (if there is
one)? I believe the ground will always be a bare wire, right?
The voltage between line and load would be the same as between line and
*Wrong. The resistance in the load could affect the voltage reading. On a
Wiggy it may show up as just the little light coming on, but not the
solenoid kicking in.
*Yes if there is no power on the load.
If there is only one two wire cable with ground going into the switch box,
the white wire is likely to be the line and the black would be the load. If
you have more than one cable in the box with the white wires spliced
together, then you are most likely to have a neutral.
Um, sort of correct. The voltage between line and load would only show a
voltage drop. The actual voltage present would not be measured. The voltage
drop reading should be very miniscule. If not, serious issues are at hand.
The difference between load side of line and neutral *might* be different than
between line and neutral at service entry. Voltage drop and conductor/termination
resistance comes into play with this. I don't recall the allowable percentage,
but somewhere along 5-10% max of premise voltage for circuit, or nominal voltage
rating of device being powered. Most devices have an acceptable voltage range.
However, anything approaching this in a residential setting is cause for concern
due to short runs not providing enough conductor resistance, therefore leading
one to suspect improper/corroded terminations in the circuit.
This is a generalization, of course.
On Friday, December 13, 2013 12:44:43 PM UTC-5, Irreverent Maximus wrote:
What's the difference between a "voltage drop" and "actual voltage present"?
I think you may be assuming he's talking about measuring the voltage with the
load connected to the line? I don't think that's the case. I took it to
mean that the load is disconnected from the line and the meter is hooked
between line and load. That is what you could do at a switch box going to
If you hook a voltmeter between the line and load and that is the
only path for current to the load, then you have a voltage divider
between the meter and the load. How much voltage you see is going
to depend on the resistance/impedance of the meter compared to the
load. With any reasonable load, most of the voltage is going to be
across the meter, because it's resistance is huge compared to the load.
If you had a 100W light bulb as the load, and an electronic VOM,
you'd see almost all the 120V across the meter.
If not, serious issues are at hand.
You might be right. I presumed that the load was in circuit. The drop between
line and load should be barely observable, if at all. The drop across the load
accounts for the wiring and the load. This is still small.
Oh, I forgot. The voltage drop between line and load is only the conductor. Think
of where you measurement points are. There is not a "load", but there is resistance.
Most meters will not show anything. The drop noticed is only the difference that one
might observe between voltage at the main versus that which would be observed say
between the circuit breaker and the neutral in the panel. Or, if one found a way
to intercept the line before the load while in the outlet box. A probe into a
wire nut, perchance.
On Fri, 13 Dec 2013 18:34:10 -0600, "Irreverent Maximus"
there is NO voltage drop. E=IxR. The voltage drop is E. The
resistance of the conductor is R. If the current is 0, it doesn't
matter WHAT the resistance is, there can be no voltage drop, so
whether the voltage is flowing directly to the switch, or through the
load to the switch, the voltmeter will read exactly the same.
My assertion is with a load connected. Maybe I did not explain it
correctly. The allowable drop for branch circuits is 2% (3% in some
A common practice for ferreting out issues with motor starters is to
measure the voltage across the input and output of each pole. Though,
this is primarily with poly-phase systems. Reading a voltage indicates
a termination/contact problem.
On Fri, 13 Dec 2013 20:15:07 -0600, "Irreverent Maximus"
electrical problems on a car. Check voltage drop from - battery post
to engine block with starter cranking to check integrety of the ground
circuit - then across every connection if there is a problem until the
high resistance is found - and the same on the positive (load) side.
Same thing in the charging system, lights, heater, etc.
On Friday, December 13, 2013 6:53:24 PM UTC-5, Irreverent Maximus wrote:
The problem is you can't just say the drop between line and load.
What does that even mean?
You have to define where the meter is actually connected. And in
the context presented here, ie investigating wires at a switch
box, the way I would think it means is between the line and the
wire going to the load, with the wires apart.
Otherwise, what is between line and load? Across the switch,
with the switch closed? In that case, you should see near zero.
Open the switch and you'll see near 120V.
I do believe I accounted for this. I was referencing someone else's
point on the subject. I suppose I could have gone into extreme detail,
but that really was not the point of the discussion.
In a pure trouble shooting scenario, all points of possible readings
would need be taken into account. One might be able to find a faulty
termination in a j-box in the attic. Tracing circuits is not fun,
but must be done at times.
On Thu, 12 Dec 2013 23:15:52 -0800, Jennifer Murphy
If the power switch is off. If it's on, the voltage would be 117
or so on a regular lightbulb/fan etc. circuit.
Make a drawing of all this and stare at for 5 or 10 minutes total.
Use the same technique for more complicated situations as you
progress. For my Toyota car, I've been staring at the manual for
about 20 hours so far, and I think I understand about all that I can.
If it were an American car, there woudl be more info and a better
manual and 10 hours might be enough.
I think Tony made a couple assumptions, but they make sense to me...
the one place in a house that I've used or wanted to use a "programmable
switch" was for the bathroom vent fan, to get all the steamy air out
after a hot shower, but e.g. with a regular switch you either turn it
off when you leave for work or else leave the fan running all day. What
you really want in that situation is a timer, where it will run for say
two hours after you turn it on then shut off.
*IF* that is the OP's situation, a spring timer is a perfectly good
solution and easier than repulling wire to use her device of choice. If
it's something else, probably not so much.
replace "roosters" with "cox" to reply.
On Thu, 12 Dec 2013 23:15:52 -0800, Jennifer Murphy
Not necessarily. There could be all sorts of things going on, like no
Not necessarily. In the above case, you'll often see a phantom
voltage between load and neutral (or ground). It's better to measure
between hot and ground, then hot an neutral. None of this is a very
good way to identify the neutral, though.
A mechanical timer is just a switch. It doesn't need a neutral. It
doesn't solve all of the problems that a programmable switch does but
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.