K&T 'Ground' Carrying Half Voltage???

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  #1  
Old 07-23-13, 08:15 AM
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K&T 'Ground' Carrying Half Voltage???

In helping someone with a bathroom reno, I encountered a K&T cluster whereby several cables connected to a K&T (ungrounded of course) wire end, including the bathroom we're doing. All in a messy, outside the box jumble. I'm going to assume the house is half K&T still.

My 'hot or not' tester was giving a detection reading on hot & ground, and not on negative. So I tested with a digital multimeter. I'm getting full voltage readings on positive/negative (around 118). When I test pos/ground or neg/ground, I get 'half readings' of around 57 or 64 (higher with pos/ground than neg/ground).

I've confirmed similar readings at a couple receptacles attached to this circuit and elsewhere in the house. Some other receptacles in the house are giving normal readings (full voltage with pos/neg & pos/ground, no voltage on neg/ground).

I'm going to suggest the homeowner gets a hold of an electrician asap, but forgetting about that part for the time being, any insight as to what might be going on here, or any ideas as to further tests I should be performing or wiring adjustments to make to try to remedy the situation for now anyway? Are these normal readings for K&T?

Thanks for looking.
 
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Old 07-23-13, 08:29 AM
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Alternating current wiring does not have a positive or negative. You have ungrounded and grounded conductors and grounding conductors if more modern. These are commonly called hot, neutral and grounds.

I don't know about the CEC, but under the NEC ungrounded circuits should not be extended.
 
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Old 07-23-13, 08:36 AM
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Ah sorry, I was interchanging 'hot' with 'positive' and 'neutral' with 'negative.'

Maybe for now the best idea is just to run a new cable to the main panel while I have some access in the walls, rather then reusing the previous bathroom circuit.

Still wondering about the other readings however...
 
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Old 07-23-13, 08:43 AM
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I suspect phantom voltage if you used a digital meter. It disappears under load.
 
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Old 07-23-13, 08:45 AM
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When I test pos/ground or neg/ground, I get 'half readings' of around 57 or 64 (higher with pos/ground than neg/ground).
K&T systems weren't grounded but you said you have K&T so what ground?

My 'hot or not' tester was giving a detection reading on hot & ground,
A useless device for any real testing.

I tested with a digital multimeter... I get 'half readings' of around 57 or 64
Probably because you are using a digital meter that has too high an impedance to cancel induced voltage. Evan a cheap $8-$15 analog multimeter would probably give you a more accurate measurement.

Based on repeated use of incorrect terminology and what seems to be incorrect assumptions on what you have I'd you buy a book such as Wiring Simplified available on Amazon and in the electrical aisle of some building supplies stores and read up on the basics before doing more electrical work.
 
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Old 07-23-13, 09:15 AM
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Thanks for the responses thus far...

K&T systems weren't grounded but you said you have K&T so what ground?
I was referring to the bare wire (yes I realize a wire is just a wire & if it's not grounded it's not a ground) - I am unsure whether that wire might be connected to ground at some point on the circuit that I can't see, but I assume not - my concern is just finding that kind of significant voltage on a (supposedly) neutral/ground reading.

I'm relatively familiar with wiring concepts in a newer installation and have read the simplified code numerous times (despite my loose jargon in the initial post, sorry about that - I don't frequently discuss electrical concepts). Admittedly I'm not nearly as sure how to decipher these readings I'm getting from the K&T, and hence my concern for whether there is a serious problem here, or whether those readings are standard. As stated, I'm going to recommend they get an electrician to check it out.

For now I'm just going to run a new circuit for the bathroom, but if anyone does have any more insight on the readings I'm getting it'd be much appreciated.

Thanks again!
 
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Old 07-23-13, 11:51 AM
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my concern is just finding that kind of significant voltage on a (supposedly) neutral/ground reading.
The neutral is a current carrying conductor. Voltage readings on a neutral in the 50 to 60 volt range usually indicate a poor or failing neutral connection somewhere else in the system. As old as the wiring is, I am not surprised.
 
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Old 07-23-13, 01:37 PM
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OK thanks for the info - I just pulled a new cable to the panel and will run the bathroom entirely from that. I'll tell them to get someone else to check out the K&T.

Thanks again all for your help!
 
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Old 07-23-13, 03:39 PM
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Maybe for now the best idea is just to run a new cable to the main panel while I have some access in the walls, rather then reusing the previous bathroom circuit.
That's the best idea for now and the future. Will one 20A circuit handle all of the loads, or do you need more than one?

Originally Posted by pcboss
I don't know about the CEC, but under the NEC ungrounded circuits should not be extended.
Remember that this circuit is dedicated to use in the bathroom. No loads outside the bathroom may be connected to it.

I encountered a K&T cluster whereby several cables connected to a K&T (ungrounded of course)... I tested with a digital multimeter. I'm getting full voltage readings on positive/negative (around 118). When I test pos/ground or neg/ground, I get 'half readings' of around 57 or 64 (higher with pos/ground than neg/ground).
I'm curious. Ignoring your misuse of "positive" and "negative" for the moment, since the circuit has no grounding conductor, what did you use for the ground connection for your meter?

Wiring Simplified.
 
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Old 07-23-13, 04:20 PM
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Nash asked:
since the circuit has no grounding conductor, what did you use for the ground connection for your meter
I originally asked that also and his contradictory and unclear answer was:
I was referring to the bare wire (yes I realize a wire is just a wire & if it's not grounded it's not a ground) - I am unsure whether that wire might be connected to ground at some point on the circuit that I can't see, but I assume not
Almar there should be no bare wire if this is K&T. Can you post a picture of the wiring? http://www.doityourself.com/forum/li...-pictures.html
 
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Old 07-23-13, 04:45 PM
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Originally Posted by ray2047
I originally asked that also and his contradictory and unclear answer...
Thanks, Ray. I somehow missed that reply. Sorry 'bout that.

To that point:
I encountered a K&T cluster whereby several cables connected to a K&T (ungrounded of course) wire end, including the bathroom we're doing...

I was referring to the bare wire (yes I realize a wire is just a wire & if it's not grounded it's not a ground) - I am unsure whether that wire might be connected to ground at some point on the circuit that I can't see, but I assume not - my concern is just finding that kind of significant voltage on a (supposedly) neutral/ground reading.
"Ground" - the equipment grounding conductor - can only be established at the service entrance - in or just ahead of the panel. If one of the cables with a ground wire in that cluster is coming from the panel, then you should have ground present. It sounds from your description, though, like it's the K&T that's coming from the panel, so you don't have a ground there.

To make a ground available for testing, you can plug a 3-wire extension cord into a receptacle that you know to have a connection to ground and take the female end of the cord to the location where you need to test. You can use the ground slot in the extension cord as your test reference point for ground.
 
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Old 07-23-13, 06:04 PM
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You can use the ground slot in the extension cord as your test reference point for ground.
And you can use the narrow slot of the extension cord to check if the bare wire in the box is really a ground by measuring between the bare wire in the box and the narrow slot.
 
  #13  
Old 07-26-13, 08:45 AM
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Thanks for the further info/ideas on testing, particularly the extension cord idea


there should be no bare wire if this is K&T
Yes the bare wire I was referring to was in cables subsequently, but apparently still a long time ago (they were orange clothlike cables with sort of paper strand insulation in them) added on to the original K&T - the "ground" readings I was referring to were taken from receptacles attached to those newer cables.

I only saw the one junction which had the K&T wires connecting to the newer orange cables that included the bare wire (a jumbled mess, unboxed in the wall). The bare wires were not attached to anything but each other there, as obviously there was no corresponding wire from the two K&T wires utilized. I was unsure whether that circuit may have been connected to panel ground somewhere else (they weren't at the connection I could see). And I was particularly concerned with whether those bare wires may have been contacting something other than ground, which was why I was getting those voltage readings.

Anyway, I disconnected the old bathroom wiring from the jumbled mess & put the remainder of that mess in a box with an access plate, then ran the new circuit for the bathroom which will all run from a GFCI receptacle and be sufficient for the bathroom loads.

As noted before, I will recommend that they have an electrician look at the old wiring, but I will probably test it with the extension cord as well, once I get some more of the bathroom finished!

Thanks again for the help.
 
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Old 07-26-13, 09:08 AM
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Thank you for letting us know how it is going.

Just for information if someone connected new cables to existing K&T that was a NEC code violation because ungrounded wiring can not be extended. (Local code may vary.)
 
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Old 07-26-13, 01:21 PM
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Sounds like a plan.

One benefit going forward is that you will now have at least one receptacle in the house with a true ground that you can use for plugging the extension cord into for extending your test references. It might trip once in awhile, though, depending on what test you're doing.

Thanks for the further info/ideas on testing, particularly the extension cord idea
Pretty slick, isn't it? I can say that 'cause I got the idea from Ray.
 
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