incorrect voltages on old wiring
I have an old house with a combination of knob and tube and various splices and additions. I found voltages of ~70 across conductors on some light fixtures and ~37v and 118v on these same conductors when measured against known ground. Also, ground plug was ~55v ?? on receptacle with no ground connected. I am guessing that something is incorrectly wired in series somewhere to give these “stepped voltages”. Any other ideas on what could be causing these non nominal voltages. It looks like I am going to be punching a lot of holes in the walls and rewiring. I just added a new 200 amp service and tied into the old wiring, planning on waiting for total gut/remodel to upgrade, but the old stuff is just too messed up to use on even a limited level.
Replies
check yer tester?
I think I'd be remodeling it REAL soon, and install just enough new circuts to work with, disconnect all else.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
I agree with Sphere.
Either you have a missing neutral on a 240 feed "someplace".
Or you have some things in series.
One thing to watch out for old wire is that they did not alway keep a clear distintiction between hot and neutral and the switch might have been in the neutral leg.
Then things like borrowing a hot from one box (circuit) and the neutral from another.
How did you connect the old wiring to the new 200 amp pannel.
One thing that you can try to get a long extension cord and plug it in to a receptacle right at the new pannel.
Then you can use a meter between the ground on extension cord and each part of the old wiring. Alway use that ground as a reference point.
but first start with measuring the neutral and 2 hots at the pannel. If they aren't zero, 115-125, and 115-125 then you have something wrong right there.
Then move a short distance into the old circuit and check ther and then move a little further downstream.
Edited 7/28/2004 8:59 pm ET by Bill Hartmann
The hot and neutral being switched somewhere is likely. This circuit has been spliced and tapped into repeatedly, as I discovered today after further investigation. I did use an extension cord off the new washer circuit to get a reference ground and I am only using the new circuits now. The voltages appeared to be close to fractions of 110, i.e. 55/55 or 37/70. I gutted most of the circuit tonight and it will be completely replaced. Could you explain how swapping the neutral or a missing neutral could produce different voltages? Thanks everybody for the inputs.
Reminds me of a couple hours I spent with a friend trying to sort out the the K&T wires in my kitchen lights. Turned out that all three lights were switched neutrals, and the hot for the system was a lone wire that entered the wall 8 ft from the switch. What we assumed were a hot and neutral was actually a pair of neutrals. End solution was a new run of 14-2 and surface mounted track lighting.
One rule I have is to never connect new Romex from the panel to existing K&T. Once you see a bunch of K&T in an attic or basement ceiling that looks like the tolley wires in the town square, it is pretty hard to add juice to the mess.
I do have one K&T circuit left, the first floor ceiling lights. We have replaced a few fixtures, and I use an extension cord connected to a known-polarity outlet to establish the hot and neutrals for the fixture.
Replacing K&T wiring is a decision you will never regret.
Bad connections, loose or missing neutrals when a neutral is shared, a loose neutral or connection in the panel or large voltage drop across a breaker are possible when you mentioned that this is K&T, knob and tube wiring, one thought came to mind.
Somewhere your hots and neutrals have been reversed. This can cause loads to be in series. This divides the voltage available to either load.
Neutrals and hots are very easy to confuse in the field on many K&T installations. Typically the wiring is tinned copper covered in vulcanized natural rubber and a woven covering, typically cotton, linen, sisal or some combination. The Hot will be dark-brown fibers woven into a lighter brown base. Neutrals being a natural off white again the same brown base.
Problem being that with dim lighting, dust and a little wear the dark brown looks lighter, making the lighter brown look off-white on the hot. The off-white threads look darker against the brown background and the brown is easy to mistake for the darker brown. Under lousy field conditions, poor lighting, tight space and 140F neutrals and grounds are hard to tell apart. Given a couple of loose connections and voltage feeding through a lightbulb or exhaust fan motor winding and even given a ground reference it can be an open question.
Great care has to be taken to get it right. Even experienced electricians get it wrong some times. Mostly it causes very few problems but it can greatly complicate troubleshooting and can cause nagging and intermittent issues that can go on for decades, literally.
Usually when you get a voltage below 100V it's because one wire isn't really connected and you're just picking up capacitive noise. Use something like a 6w night light bulb when testing, to avoid this confusion.
Very true with high impedance digital voltmeters. Less an issue with K&T as the wires tend to be a greater distance from each other and lees likely to have a ghost voltage. Still possible I guess.
This is another reason I prefer a solenoid type meter for most troubleshooting as it is immune to ghost voltages. You can, with a little experience also work in dim locations by feel alone and still get a good idea of relative voltages. IMHO one of these units is $20 well spent.
From: http://www.galesburgelectric.com/KLEIN_TOOLS_69115__Wiggy_Solenoid_Voltage_Tester-p-209.html
KLEIN TOOLS Wiggy¯ Solenoid Voltage Tester
Genuine Wiggy¯ solenoid voltage tester for 120V to 600V AC (50/60 Hz) or 120V to 600V DC current.
Locates blown fuses, grounds and system leaks quickly.
UL and CSA approved.
Large, easy-to-read voltage indicator scale and DC polarity indicator.
Operates without the use of batteries.
Compact design, with high-impact case and probe assemblies.
Sealed construction keeps out dust and dirt.
Probes have retractable protective sleeves that can be adjusted and locked to expose the appropriate tip length desired for any application.
Probes store conveniently in case, which can also serve as probe holder.
Test leads are 28" (711 mm) long (including probe module) and have strain-relief protection.
4Lorn1: A pair of Kleins a screwdriver and a Wiggy sticking out of a pair of jeans are pretty much the 'electrician's uniform' on construction sites around here. A Buck knife or Leatherman hanging off the belt on a rear quarter completes the picture.
See this is your 3ed post, so have no idea of your expertise, etc...
All previous comments are valid.
One item on the 70 V on the lights -- are the lights REALLY dimmer than in other places? If not, to repeat, check yer tester?
Just to roil the pot and "initiate a newbie", what is the brand and model number of your meter? You do have it set on ac vs dc fer sure?, etc. <G>
PS edit you posted as I was typing
the 55/55 is easy, series loads as stated by a previous poster, 37/70 I'd nave to think about, unless 3 loads in series, which is too easy, you'd notice not much running correctely. Any surge protectors already connected, the capacitance in some could give a voltage divider to produce 37/70 at no load.
Edited 7/28/2004 11:12 pm ET by JUNKHOUND