It’s agood thing I always turn off the lights before changing a bulb.
I attended a 2-day hands-on wiring class last weekend and bought a touch tester and a multimeter, then tried out my skills changing the switch to the garbage disposer. While confirming power on/power off to the receptacle with the touch tester, I discovered that the ground terminal was lighting up as hot. I’ve confirmed this with two different touch testers (a cheapie and a mid-price one), and also with the multimeter: 125V H-N, 0V H-G, and an inconstant voltage drop N-G (generally less than about 50-60V).
This is an old house with knob and tube wiring in some parts and Romex in others. The kitchen is NOT to code or anything approaching, but supposedly all of the dangerous stuff was found and fixed a year and a half ago, along with installing a new subpanel in the kitchen and one in the garage, and upgrading the service from 60A to 200A. The circuit breaker has *not* been tripping, and other than replacing one of the GFCIs a couple of weeks ago (wouldn’t reset) and the disposer switch on Saturday (bad contact with switch closed), everything has been working fine.
The 15A circuit in question contains the following: about 9 overhead light fixtures throughout the house; two GFCI duplex receptacles over the kitchen counter; a duplex receptacle under the sink for the dishwasher; another for the garbage disposer; a switch for the garbage disposer; and a pullchain sconce light fixture in the laundry room. I’m not sure if the front and back porch lights are on the circuit. There’s a mixture of 12ga and 14ga wiring in the kitchen, and the 14ga is kind of stiff. Some of the boxes are overstuffed, but I haven’t examined all of them yet. I’m not sure if the ceiling fixtures are knob and tube or Romex (haven’t been in the attic yet).
Lathe and plaster walls, and I’m not yet ready (financially, design-wise, time-wise, or emotionally) for a gut-remodel of the kitchen yet.
Obviously, the circuit is not grounded, because the breaker has not been tripping. OK, or maybe the breaker’s no good, but I think it far more likely that there’s no ground. Certainly the GD switch is not grounded — someone cut off both ends of the green wire between the switch and the receptacle.
Any suggestions for how to track down where the ground fault is? The lack of grounding is a whole ‘nother issue — I’m not sure if the main panel has a direct wire to ground. I know there is a grounding rod and the water main supply (galvanized pipe) is bound to it, but I haven’t seen any wire from the panel to a grounding rod. It’s on my list of things to check, along with crawling around in the attic to see what’s there.
The freaky thing is that my touch tester lights up and beeps within one inch of the pullchain (or any part of the fixture) in the laundry room whether the light is on or off, as well as near the bedroom ceiling fixture if the lights are on.
Thanks for any suggestions,
Rebeccah
Replies
Hi Rebeccah,
I am not an electrician, but from your post it sounds like the typical years old hodgepodge of additions to the wiring. The only thing I can think of right off is if some one reversed the neutral and hot in some of the older wiring where the wires look the same. I have done a fair amount of electrical work, but it is usually light trouble shooting, or new work.
Actually the reason I replied is to suggest that if you dont already have one, the 8 or 12 dollar receptacle testers are really handy for detecting whether a receptacle has been wired properly. You have probably seen them, they look like a plug with three lights on the front. The order the lights, light in tells you how the receptacle is wired. You can also get them with a built in gfci trip for testing gfci's.
webby
Edited 11/21/2005 5:23 pm ET by webby
Edited 11/21/2005 5:25 pm ET by webby
Hi, Webby.I thought about the possibility of reversed hot and neutral, but if that were the case, the *neutral* terminal would be hot. It's not. It's the ground terminal that's hot.I just diagrammed out what I know about how my kitchen is wired, and I bet I know what *might* be wrong.It's probably one of two things. My first thought was my front porch might might actually have a ground fault, since I've seen evidence of water in the wall there.The second thought is there might be a mistake in the wiring of the switched receptacle for the garbage disposer. I'm going to play around with wiring sketches a bit, then check how that receptacle is actually wired.
Since you're under the sink in an old house, use a water pipe as a "reference ground". Then you can tell for sure which wire is hot and which is neutral.You'll still have an ambiguous situation with any floating wires, though.
If ignorance is bliss why aren't more people
happy?
My water distribution system is a mix of galvanized (mostly) and copper; I'm told it might not actually be a reliable ground. My instructor recommended getting a grounding clamp and a long wire and connecting it directly to my grounding rod as a ground reference.My main concern is not so much determining "which is hot and which is neutral" in a specific box, but determining which box has the grounding problem.However, I just found some literature on the Fluke web site, and I'm much less worried about my bedroom fixtures coming up "hot" with my high-impedence tester -- apparently they can do that normally when they're turned on. Still doesn't completely explain the laundry room fixture showing "hot" even when turned off, really. I also understand your previous comment about induced voltage in unterminated wires better, now, and if I've got a loose ground wire, that *could* be the problem all by itself. But I need to find out for sure.
Not a reliable ground, true, but sufficient for measuring.You really need to get yourself the lightbulb tester. Not a neon light, but a 25W bulb in a "pigtail" socket. A decent hardware store should be able to set you up.Note that turned on/off doesn't make a lot of difference. The ground may be traveling some distance with the hot, before it gets to the switch. In fact, in most cases the switch is actually on a leg off to the side.(Which brings up a whole 'nother set of variations to think about.)
If ignorance is bliss why aren't more people
happy?
(Which brings up a whole 'nother set of variations to think about.)Yes, it does. In fact, the next box I open up will be the one for the switched receptacle. I have a hunch there may be something amiss, especially since the white wire on the switch wasn't taped black and someone cut off both ends of the grounding wire in the romex that connects the receptacle and the switch.I'll keep you (and my instructor) posted later. Thanks for the help, BTW.Rebeccah
Yeah, I've seen that "nuisance" ground wire snipped short against the jacket several times.IIRC, it's not required to tape the white wire black on a standard switch leg -- the fact that it's a switch leg is signal enough. The white from the switch should be wired to the black from the breaker in the fixture box. You wire the fixture to the breaker white and the switch black.
If ignorance is bliss why aren't more people
happy?
OK, I've opened up both the DW and the GD receptacle boxes to have a look, but it's night time and rather than test voltages on exposed wires when I'm tired, I'm just looking by flashlight with the breaker off. The garbage disposer receptacle is ungrounded (despite a 3-prong outlet), just like its switch, with the green wire cut off as the Romex enters the box. Otherwise, it appears to be wired correctly. Well, except that rather than 3 white wires being pigtailed together, two are under the two screws on the same side of the duplex device -- the tab is unbroken.The dishwasher receptacle at least has a grounding wire, but it was loose, so I've tightened it, and pushed the bare metal wire to a corner of the box away from the other wires. The metal box is not grounded (none of them seem to be), but I don't have any grounding screws at the moment. Again, rather than pigtailing, whoever came before made use of the two sets of wire connectors on the duplex device (one of the hots is a push-in or else is permanently connected to the back, the other hot and both neutral connectors are screws).So, other than the absence of a continuous ground, no obvious miswiring among the devices in the kitchen.Oh, and testing the voltage from hot slot to sink water supply pipe goes full scale; neutral to water pipe, 0; and ground to water pipe, less than 10 (but *not* 0). This was not on the wires themselves, though. I really was afraid if I started undoing the wires, they're so stiff I'd feel obliged to change them out for good ones when I put everything back together, and then I'd have to put the right receptacles, and if I do all that, I'd really like to wire the new dedicated receptacles back to the breaker like you're supposed to -- right now, I'm still to slow to do all of that at night when I have to work in the morning. Rebeccah
With a high-impedance tester (either meter or a neon tester) it's common for an unterminated wire to register "hot", usually in the 50V range. This is caused by capacitive pickup from adjacent "hot" wires.
To verify things use a low-impedance tester, either a "wiggy" (solenoid tester) or an incandescent lamp.
happy?
An "unterminated wire" -- means what, exactly?
And how do I tell if my tester is "high impedance" or "low impedance"? Certainly the cheapie tester was flickering in all kinds of places, but the more expensive one I got the next day (after my class instructor told me to throw the other one out) was unequivocal.
Hot slot:
bright glow and loud sustained beep.
Neutral slot:
nothing (except it pulses a faint glow every second
so you know it's functioning).
Grounding slot on affected circuit:
bright glow and loud sustained beep.
Grounding slot on unaffected circuit:
nothing.
Grounding slot on unaffected circuit with an appliance plugged into the adjacent receptacle on the duplex:
intermittent flashing with less loud beep
that coincides with the flash.
Hold up 1" from light fixture on affected circuit:
bright glow and loud prolonged beep.
You have a proximity tester there. This is not what you need in this situation.
If ignorance is bliss why aren't more people
happy?