Puzzle

Reply

  #1  
Old 12-28-04, 05:32 PM
papi's Avatar
Member
Thread Starter
Join Date: Jun 2002
Posts: 153
Difficult Puzzle

Apologies for long post[confusing ]Part of the house has K&T [3 hots 3 neutrals] some asbestos insulation wedged in between 2 hots and 2 neutrals and heating ducts was removed i had to disconected the 2 fuses to cut the power to those circuits for i could not run the furnace and have the live wires coocked .Today i opened the panel to disconect this two hots and two neutrals finding this situation:
1] I disconect the 2 hots that run closed to the heating ducts.
2]Leave the third hot[not running close to heat ducts] conected for some lights upstairs]
3]Disconect one of the neutrals of the 2[running close to heat ducts]
4]Neutral bar has two wires still conected
5]Not knowing wich of this two is the one that runs in the heat. ducts and want to disconect I tested for continuity disconecting both from the neutral bar this is what i got:
6] One wire 0 ohms the other 8 ohms
7With either neutral disconected and power back on , some lights and plugs had power ,others no power as expected, but one light in the Dinning Room and a light in Staircase [that were on another circuit]were ON but very dimm like if they were conected in serie [ half the voltage]and the DR switch controls BOTH lights and that never hapenned before
8]With both neutrals back in the panel and the third hot still conected neither the DR or Staircase lights work [some how it makes sense for i disconected the hot that feeds these lights ]
Ideas
 

Last edited by papi; 12-28-04 at 09:48 PM. Reason: adding info
Sponsored Links
  #2  
Old 12-29-04, 11:08 AM
Member
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
Papi,

I've not drawn out a circuit diagram, and doing so is the only way to properly solve your puzzle. However once I read your description, I have a really strong hunch as to what is going on. Draw out a diagram and I think you'll find:

A couple of your lights are cross circuited, connected from the 'hot' of one circuit to the 'neutral' of the other circuit. With the neutral disconnected from the panel, it can float to some intermediate voltage, and things can get powered between the 'neutral' and 'ground'.

The 8 ohms that you measured is probably from one circuit to another through a lamp.

You might also have a 'switched neutral' circuit. This is not code, and hasn't been for a very long time, but in the era of knob and tube, three way circuits were sometimes done where the neutral was connected to the switch. With this sort of connection, power on a floating neutral can go through the light to the properly connected neutral.

-Jon
 
  #3  
Old 12-29-04, 02:16 PM
papi's Avatar
Member
Thread Starter
Join Date: Jun 2002
Posts: 153
Jon thank you very much for taking the time to reply,i still need to disconect the neutral that runs in betwwen the heat. ducts [now without thermal insulation] for i believe it is a fire hazard,but if things are like you very well explain to me, im going to loose some outlets in the only K&T that is still conected and providing minimun light to staircase and two plugs upstairs.also i would have to find where this'' crossover'' is located.
Since i cant do a full rewiring of the house [ basement and kitchen are wired with NM] untill summer i have been trying to have a couple of new lines installed to deactivate the last K&T circuit but because of some other issues i cant make lots of holes on the plaster walls right now,im thinking of combining some NM conduit and some wiremold .If you have any suggestions they are much appreciated.Thanks a lot and BEST OF THE SEASSON
 
  #4  
Old 12-29-04, 02:27 PM
Member
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
Papi,

Try setting thing up so that you get that 8 ohm reading again, and then unscrew suspect bulbs until that reading goes away or changes. This will help you find the cross-circuited fixture.

Do you have any '3-way' switch circuits on the K+T?

-Jon
 
  #5  
Old 12-29-04, 11:21 PM
papi's Avatar
Member
Thread Starter
Join Date: Jun 2002
Posts: 153
Jon

The DR light switch and a three way [ staircase light] are in the same box]
With both neutrals connected neither light works[ both lights in the same circuit but hot removed from the panel now]
With one neutral conected,does not matter wich one, both lights work [ very dimmed] and are now controled by the single pole DR switch and three way switch[staircase light] does not work.
Should i check the wires in the switches to see if they are black or white? [switched neutral]
Should i loose one of the light bulbs in the DR or staircase and disconect one neutral at the time?
If i find where the cross is would that allow me to eliminate the neutral that runs in the heat.ducts and keep one K&T circuit ?
Thanks again .Regards papi
 
  #6  
Old 12-30-04, 03:51 AM
Member
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
papi,

Clearly if you figure out where the two circuits are linked, once you break the link you will be able to use the other circuit. But figuring out where they are linked is going to be a significant undertaking.

As I said before, you are going to have to spend time drawing out circuit diagrams and figuring out where the circuits are linked. I fiddled with it a bit and realized that there have to be several cross links; you will need to find each of them.

Checking in the boxes to look for white or black wires probably won't help; most K+T predates wire color coding, or the colors have all turned to various shades of black.

First try to find the crosslink.

Disconnect all of the supply leads to these circuits.

Next, try to measure voltage between these supply leads and each other, and between the leads and ground. You should use a low impedance voltage tester like an analog meter or a 'wiggy', because you could pick up induced voltage from another circuit. If you measure any real voltage at this point, then _stop_; you need to figure out which other circuit is feeding these wires.

Once you have determined that there is no voltage on these wires, you start measuring continuity.

First you will measure the resistance between the various supply leads, to try to find the cross link. You _should_ get infinite resistance between each hot and the other neutrals, and some resistance between each hot and its own neutral. Seeing some resistance between one hot and another neutral means a cross-circuit. Seeing continuity between one neutral and another means a joined neutral. If you measure a cross circuit, then try turning off lights or removing bulbs until the cross-circuit goes away. If you can find the cross circuit this way, then it will save a bit of work.

If the above doesn't work, then I think that you are going to have to spend some time 'ringing out' all of these circuits, to figure out for _each_ junction box which wire to which supply wire. This is not a small task, but is easily understood. What you need to do is disconnect all three circuits. Then using a continuity tester probe from each wire in each junction box back to each K+T wire back in the panel. By doing this you will be able to determine which wire goes to which hot or neutral.

Come up with a naming scheme, eg H1, H2, H3, N1, N2, N3 for the supply leads. For each junction box in turn, measure continuity between the wires in that box and the supply leads. Write up a table where you say 'in junction box 1, wire A goes to H1, wire B to N1, etc. If you measure a significant resistance between a supply lead and a particular wire, then that probably means that you have a connection _through_ a load, eg. if you are measuring the switched hot going to a lamp, you should see continuity with resistance to the neutral for that circuit.

Once you've done all of these measurements, it should be clear where the crosslink is, and you can get rid of it.

-Jon
 
  #7  
Old 12-30-04, 11:38 AM
papi's Avatar
Member
Thread Starter
Join Date: Jun 2002
Posts: 153
Jon many thanks again for your excellent and detailed explenations ,I have learn a LOT from them .I gonna try what you sugest ans see how far i can get.On the othe hand i have to balance time and effort invoved for there is a point where it would make more sense to run a temporary line maybe wiremold and or NM conduit to three or four plugs and lights and get rid of the K&T untill summer when i should be able to rewire the hole house
Thanks a lot for your time and interest i ll keep you informed
Regards papi
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes