Receptacles in series problem

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  #1  
Old 05-15-05, 09:52 AM
durian
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Receptacles in series problem

I am new to home wiring but have done my best to learn to wire things safely. I have already found things that the previous owner of my house did not do correctly.

In Brief
Voltage to one 15A circuit’s receptacles dropped to 96V. [The 15A breaker never tripped.] I’ve replaced the first 2 of them in the series. In each case, digital multitester shows 120V at the brass screw, but only 96V when tested through the outlet openings, with hot-and-ground test showing 18V.

How do I diagnose this problem?

Background Details
I have a 15A circuit that appears to be parallel, with one leg supplying the outlets to a room and the other supplying an overhead ceiling fan/light. I had a small 75W TV and 2 or 3 small kitchen appliances plugged into a bright orange heavy duty (13A/125V/1625W) extension cord that was plugged into one of the receptacles on this circuit. A short somewhere caused the whole receptacle leg of the circuit to lose voltage, so that each receptacle only had 96V when tested with digital mutitester thru the outlet openings.

I initially suspected the extension cord (which may have been damaged inside from tight crimping) or the TV, but both operate fine when plugged into a GFCI on separate circuit.

I have replaced the first two receptacles in the series. In each case, wires were short, and I had to add pigtails to the wires in the receptacle box to provide the 6” or 8” required. I used 14G wire for the pigtails, though the source wire appears to be 12G. In each box were 2 sets of hot/neutral/ground wires (black/white/bare) from what appears to be 12-2 NM cable. The boxes end up being pretty crowded, but the “leakage” of current or voltage occurs before the wires have been crammed back into the box, so it is not the overcrowded box that is causing the leakage.

The 96V voltage is insufficient to light even a small nightlight. The multitester has no problem reading 120V in other outlets throughout the house.

Grounding or Lack of It
The metal boxes for the receptacles in this series have no ground wire screwed to the box. Ground wire from the receptacle is connected to ground wires from line and load cables only. Is this safe? Is it maybe the source of my problem? Is it safe to add another ground wire and screw to the device box and connect this to the line/load/receptacle ground connector, even if the box itself isn’t grounded to anything?

More info
Initially I thought the problem was with the 2nd receptacle, where the extension cord had been plugged in. I added pigtails and replaced this receptacle, and voltage returned to 120V . . .until I plugged in the extension cord and the TV, which caused the circuit to lose power again, back down to 96V. So, I replaced the receptacle AGAIN, but this time it would not get up past 96V.

Next I tried to replace the first receptacle in the series with a GFCI. The reset button popped and could not be pressed down again. The instructions said this meant I wired it wrong, connecting the source/feed hot wire to the LOAD terminals instead of the LINE terminal, but this is not the case. I think that the circuit has the very type of current leakage that the GFCI is designed to test for, and that’s what’s keeping the GFCI tripped.
 
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  #2  
Old 05-15-05, 11:06 AM
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You have several problems and I think you need on-site help.

1. An extension cord, not matter how heavy, should not be used for kitchenm appliances. You mentioned a 13 amp rating, but small kitchen appliance could draw 13 amps EACH.

2. The measurement hot-to-ground 18V is probably extraneous, because you seemed to indicate there is no ground connector ( bare wire) in the box.

3. The 96 volt reading could be caused by current overload somewhere, a partial short somewhere, loose connections either in the hot side or the neutral side.

All in all, this circuit needs to have every connecor and every device checked out.
 
  #3  
Old 05-15-05, 04:42 PM
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Further comments:
  • Extension cord manufacturers are notoriously optimistic. I'd never want to put anywhere near 13-amps on an extension cord that the manufacturer rated for 13 amps.
  • Voltage drop reduces current, and makes it less likely for the breaker to trip. But, if your voltage drop was accurate (which it is not!), that much voltage drop would mean a bad connection somewhere. Bad connections mean heat, and heat means fire.
  • But your voltage measurement is not be valid. The fact that it cannot power a light proves that you are measuring "phantom voltage" (google that term). You have an open neutral. It often results from a bad backstab.
Sorry, but I only had time to read the first half of your post.
 
  #4  
Old 05-17-05, 01:40 PM
durian
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Thanks for your help. There are four receptacles in series on this circuit. I have replaced each of them and grounded each to the metal box, so that each middle-of-run box has four bare wires twisted with a (green) wire nut (incoming bare, outgoing bare, bare to device, bare to box). There are no backstabs. All connecting wire is now 12G, not 14G.

Still I get 120V when I put the contacts of the multitester to the brass screw and the metal box, but only 96V or less when I plug into the actual hot and neutral receptacle holes.

I have inspected all my wire connections and they all look fine, none loose or broken.

Now I'm wondering if there could be damage to a cable somewhere, one of the ones that run from box to box, in the wall. Any suggestions?
 
  #5  
Old 05-17-05, 01:49 PM
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Perhaps there is a junction box on this circuit? Have you checked the connections at the panel box?
 
  #6  
Old 05-17-05, 02:08 PM
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If you measure 120 volts across the Black and White wires at the Service-panel, and 95 volts with the meter DIRECTLY across the Black and White wires at a receptacle, then there is a voltage-drop of 120 - 95 = 25 volts in the circuit between the circuit-breaker and the receptacle.

The voltage-drop is a VD = I X R value, say 25 volts VD = 2 amps X 12 Ohms, presuming there is a resistance value of 12 Ohms in the wiring.If you triple the current the V-D is 6 X 12 = 72 volts.

I suggest you plug a kitchen-counter appliance such as a toaster into the receptacle, and measure the receptacle-voltage with the circuit conducting a larger current to determine if there is a an increase in the circuit V-D, remebering the V-D increase is directly proportional to the current (amps/ "I") increase.You must very accurately measure the circuit voltage at the "source", i.e., the panel, to establish a 'reference' or "standard" value.

Good Luck and Enjoy the Experience!!!!!!!!!!!!
 
  #7  
Old 05-17-05, 02:10 PM
durian
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Don't know where to look for junction box, all is behind drywall. Connections at panel work fine, seems to me, because this is parallel circuit, one leg for receptacles, one for overhead lighting. Overhead lighting works fine when power is on to that circuit.

How do I find junction box? And where do I look for the open neutral condition if all the connections in the receptacle boxes look solid?

I'm new to home wiring, so I may be making some unwarranted assumptions.
 
  #8  
Old 05-17-05, 04:10 PM
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It wouldn't be the first time a connection was found hidden inside a wall in a box or not.
 
  #9  
Old 05-18-05, 04:50 AM
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If I read the posts correctly, it sounds like :

(1) you are measuring 120V from hot to ground
(2) you are measuring 96V from hot to neutral

I agree with John, you have an open neutral.

Where do the separate legs for the overhead lights and the receptacles connect together? That would be the place to start....
 
  #10  
Old 05-18-05, 03:22 PM
durian
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Is there a way to find the junction box or split point in the circuit that does not involve ripping off all the drywall between panel and the room served by the circuit?

My conclusion that it is a parallel circuit is inference only. A single circuit controlls both the 4 receptacles in series and a switch that in turn controls an overhead light/ceiling fan. The switch does not affect behavior of the receptacles.

House was probably rewired as part of a major renovation that was done about 1997, before I bought the house.

Any advice would be appreciated. If there is a special tool used to trace wires behind the wall, then I'll buy it.
 
  #11  
Old 05-18-05, 04:38 PM
durian
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OKAY, I THINK I FOUND THE PROBLEM, BUT WHAT ARE THE IMPLICATIONS OF WHAT I FOUND?

In the beginning of this project I thought the problem was with the 2nd receptacle in the series of four. When working on that one I tightened the clamp that holds the incoming and outgoing cables in place, and I tightened it WAY TIGHT. (Both cables enter through knockouts in the top. A single screw tightens the clamp on both cables).

Today it occurred to me that maybe that was the source of the open neutral. I loosened the clamp screw and everything works!

But of course that got me thinking what had caused the open neutral in the first place. I'm thinking that my overtightening forced the metal clamp to bite through both the sheathing and the neutral's insulation, so that the metal clamp touched the copper of the neutral wire, in one or both of the cables. I don't know if I'm on the right track, but if I am it seems like it is not very safe. I.e. slight changes in the box over time could eventually allow the exposed part of the neutral wire to touch other metal.

Please tell me if you think I have diagnosed this correctly, and what to do about it to make it safe.

Thanks to all who have contributed and to all who will help with this question.
 
  #12  
Old 05-19-05, 08:49 AM
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If loosening the cable clamp fixed the problem, then you really need to do further analysis. I see two possible explanations:
  1. The clamp was so tight as to actually damage the cable. If so, you should replace both runs of cable (all the way from box to box). Since you said "WAY TIGHT", I would say that cable replacement is warranted, even if the cable doesn't look damaged.
  2. Loosening the clamp caused a poor connection in the box to become a little bit better connection. Remake all the connections in the box to make sure that they are most excellent.
 
  #13  
Old 05-19-05, 09:28 AM
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Is this a multi-wire, shared-neutral circuit? In other words, is this circuit powered by 2 breakers or a double-pole breaker, such that each half of each split-duplex receptacle is powered by a separate hot wire and the brass tab between the two outlets is broken off on the hot side?

If you do not have enough slack in the cable to pull through 6 extra inches of new cable, you need to do more investigaton.

You could just replace the whole cable to be safe, but that would be 'overkill' if John's right and there was just a loose connection in the box.

You could have an electrician in to do a 'megger test' to test the integrity of the insulation. You'll have to call and get a quote, but this could be as pricey as running a new cable.

You could check the resistance of the cables conductors with an ohmeter--with the circuit breaker(s) OFF, of course. Have a helper bend the cable back-and-forth where the clamp was tightened up. If the one of the conductors was damaged, you will read infinite resistance at some point.

Post back with your results.
 
  #14  
Old 05-20-05, 11:01 AM
durian
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I think John Nelson has diagnosed the problem corrrectly, that my overtightening damaged the cable and its contents.

I have never run cable behind a finished wall before. I'm thinking that all I need is some new Romex, electrical tape, and some sort of electrician's lubricant. Then I can tape the new cable to the damaged cable, lube up the tape joint and use the damaged cable as a fish tape to pull the new cable through. Am I missing anything here, or is it really this simple?

And, is there a brand of electricians lube that you recommend?
 
  #15  
Old 05-20-05, 11:35 AM
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If the original cable was installed while the wall was still unfinished, it will be stapled. Therefore, it will be impossible to use it to pull new cable through. So you'll likely need to abandon it.

Fishing cable through finished walls is an art. There are many tricks and the tricks appropriate to you depend on dozens of site factors. The first thing that comes to mind is to ask is there an accessible attic above, a crawl space or unfinished basement below?

It is very unfortunate that the inspector didn't notice this cable damage during the rough inspection. Most would have.
 
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