Broken feeder cable?

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  #1  
Old 03-08-12, 05:54 PM
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Broken feeder cable?

Garage running Underground feeder 4/4/4 AL from main panel off dual 80 amp breaker (240V).
Yesterday I found half the 240V garage panel was inoperative.
Tested lugs, one of the feeders is 120V, the other is at 80-90V.
Swapped the feeders at the 80 amp main to ensure it wasn't the breaker. Same results.
Tested at the 80 amp breaker at main panel, both legs 120V.
When I remove the 80-90V feeder off the 80 amp main panel breaker and test it at the garage it drops from 80-90 to 0.

Not many underground animals around here in SC and it's clay 24" deep.

It is however in an area that I have allowed some heavy vehicles to cross perpendicular over where the wire was buried less than 8 months prior. Including dualies with loads of firewood and a school bus many times.

Could this snap the wire? And would a broken wire now in contact with earth cause the 80-90V reading without tripping the breakers?
 

Last edited by Ninjaman; 03-08-12 at 06:25 PM.
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  #2  
Old 03-08-12, 07:53 PM
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4/4/4
I'm puzzled. Is this three conductor cable? It should be four. Sounds like you may need to replace the cable anyway to be up to code.
 
  #3  
Old 03-08-12, 08:03 PM
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You are correct. After researching what I needed for the run for 100amp service using alum to a new garage which also does not and will not have water or other cables run to including any shared with the house that the main panel runs, I figured on 4/4/4/6.

Upon getting permits I spoke with the local inspector, chesterfeild county SC and he informed me I HAD to (he was the one that would be rough and final insp) run 4/4/4. 2 hots and a neutral all run to the main panel. No ground run from garage to the main panel. And an 8' copper grounding rod at the garage with -6 copper run into the shared ground/neutral bar in the garage panel. And the strip to box grounding lug used to ground the strip to the box. With all GFCI outlets in the garage. So this is what I did. I found it odd but that is what they would pass.
 
  #4  
Old 03-08-12, 08:07 PM
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I doubt very much that the vehicles would damage your wire that is buried down 24" in clay. Also the earth us a rather poor conductor so I doubt contact with the ground would trip the breaker anyway. If current was flowing you should be able to measure it with a clamp on meter.


Just to make sure I have it all clear, With the wires not connected to the 80 amp breaker in the main panel, what is the voltage off the 80 amp breakers screws (set meter to at least 240v):
Hot to hot
Each hot to neutral
Each hot to ground

Turn off main breaker in garage. Turn on 80 amp breaker in Main panel. Take the same readings above in garage.

Turn off both the main breaker in garage AND the 80 amp breaker in the main panel. Now take a resistance (ohms) reading between each wire. (hot, hot, neutral) You should get nothing.

Your installation was approved by the AHJ so your fine. That is how it has been done until 2008. You may be on an older code then others.
 
  #5  
Old 03-08-12, 08:19 PM
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Yes, ground rod 8' all but 1' buried in clay with 6 copper to neutral/ground shared bar that is also grounded to box.

Will test more tomorrow.

For now:
GE box two rows of breakers. two 4 alum 120V hot feeds. One feed each side with feeds alternating breakers left right.
I noticed a flickering not starting fluorescent light and a GFCI also on that circuit tripped (orange) and would not reset. But other circuits worked.
After testing, I found with everything connected, one lug (feeder) at the garage panel has 120V while the bad feeder was at 80V.
Still everything flipped on ad connected, the main panel 80amp 240 breaker reads 120 on both legs.
I did switch the feeders on the 80am main legs just for kicks, this did not change anything.
With the 80V bad feeder removed from the 80amp main breaker testing at the garage panel drops from 80 to 0.

I find it hard to believe 24"+ down in clay that it would have split/broke. But I am at wits end, especially since one of the hot feeders and neutral are working great. I currently have the one bad feeder off the main breaker and am running the garage off the one good feeder.
 
  #6  
Old 03-08-12, 08:38 PM
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All it takes is for a small nick to allow water into an aluminum cable and soon the cable will fail.

The resistance of the earth can be too high to trip the breaker.

You might be able to find the breaker with a toner like Miss Utility uses.
 
  #7  
Old 03-08-12, 10:14 PM
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Four-wire feeders to outbuildings have ALWAYS been allowed by the NEC. If your inspection authority disapproved your original plan then perhaps they have a local amendment but that sounds extremely unlikely to me.

Also, #4 aluminum in a cable is limited to a maximum of 65 amperes so your 80 ampere circuit breaker is too large. 80 amperes is only allowable if the #4 aluminum conductor is not part of a cable and is in free air.

I strongly suspect that the 80 volts you are measuring is a phantom voltage. Are you using a digital voltmeter? Have you measured from hot to hot rather than from hot to neutral?
 
  #8  
Old 03-09-12, 06:03 AM
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All 8' of the rod should be in contact with the soil, not like the 7' you say you have.
 
  #9  
Old 03-09-12, 06:39 AM
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My Bad, I meant 2-2-4 USE-2 which [email protected] and [email protected]

The grounding rod is all but buried, maybe 4 inches sticking up to allow for the collar and copper ground wire to connect to it.

Using a digital meter. I will measure HOT/HOT if the rain stops today. And measure all the other ways Tolyn asked for. So far I only measured the legs of the main 80 amp both at 120V Hot to Neutral and both feeders at the garage panel to Neutral which are 120V and 80V

Thanks
 
  #10  
Old 03-09-12, 07:07 AM
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Does the breaker trip when the ground is wetter?
 
  #11  
Old 03-09-12, 09:00 AM
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Lots of rain in the last week and this week. Still no tripping of breakers.
 
  #12  
Old 03-09-12, 05:15 PM
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Did a little testing today. Bear with me, I had chemo yesterday and am a little wore out/tired today.

Here is what I got so far.

At the main panel 80amp breaker:
Feed wires disconnected from breaker
Breaker on
126V each leg tested to neutral
250V leg to leg

Suspect feed wire (still disconnected from breaker) to neutral 86K ohm - 300K ohm
Good feed wire (still disconnected from breaker) to neutral 5-6M Ohm

At garage panel:
Feed wires disconnected from panel but hooked to main breaker and breaker on
Good feed to neutral 124V
Suspect feed to neutral 68V
Good feed to suspect feed 190V

Suspect feed disconnected from main panel/breaker
Suspect feed to neutral no imp reading - open

So does this sound like the suspect feeder is broken underground?
 
  #13  
Old 03-10-12, 12:18 PM
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Sorry to hear your doing chemo. Good luck!

When you took your resistance reading (ohms) I suspect the breaker in the garage was on. It needs to be off. Otherwise you will be just reading through any load that is on the panel.

Also, when you took your voltage readings in the garage, you need to have the breaker on in the main panel but off in the garage. Again, otherwise you could be feeding through a 240 volt piece of equipment.

So, Turn off main breaker in garage (house breaker on) and take a voltage reading:
hot to hot
good feed to neutral
suspect feed to neutral

Then turn off both breakers (house and garage) and take an ohm reading between each wire.
hot to hot
good feed to neutral
suspect feed to neutral
 
  #14  
Old 03-10-12, 01:23 PM
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I wonder where you might get a megger. It would be interesting to see the ohm readings from a VOM of feeders to earth ground and followed by megging them.

At the MAIN panel w/feeders to sub panel connected, does that main breaker have the same voltage readings on both sides of the breaker (incoming & outgoing side of main)?
L1 to L2, then each to neutral and earth ground ??? As I've read through this thread, maybe I missed making sure you're not losing something across one phase of your main breaker.
 
  #15  
Old 03-10-12, 02:49 PM
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Both feeds and neutral disconnected from panels

Both feeds and neutral bound together at the main

Tested at the other end (garage)
Good feed to neutral .2 Ohms - feed and neutral continuity
bad feed to neutral 500 K Ohms - broken

She's broken.

Time to dig.
 
  #16  
Old 03-10-12, 03:12 PM
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Here is my issue:

With the wires disconnected, and isolated from the panels so there is no connection between the wire ends to anything, Your meter should read nothing between each wire, hot to hot, or either hot to neutral. If your are getting any type of ohm reading, then your wires have been damaged some how or you do not have them isolated.

If your going to start digging, this might help you pin point the location:

With a wire long enough to get where you need to search, connect one end to your neutral bar, and the other to one lead of your meter. Stick the other lead in the ground where you think the break is. You might get a voltage reading, and if you do, you can keep poking around until you find the highest voltage. That will be your break.

Just be careful not to get across the wire connected to the neutral bar and the ground because you could get poped.

Please let us know what you find.
 
  #17  
Old 03-10-12, 03:24 PM
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As stated, I disconnected all wires from both panels but then bound both feeds and neutral all together on the main panel end. All to each other.

Therefore, testing imp at the other end would show a break if there was no continuity.

The good feed to neutal showed continuity with .2ohms - thru itself up to the connection I made, back down the neutral.

The bad feed however showed not to have continuity thru itself and back down the neutral. 500K Ohms.
 
  #18  
Old 03-10-12, 03:28 PM
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I am going to try the Look for voltage in the ground test you mentioned. Should be interesting! thanks.
 
  #19  
Old 03-10-12, 03:59 PM
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THANKS, I think that worked.

Using digital meter I connected a long wire from the Neutral bar to the meter. I then used an 8" long metal screwdriver with a wire attached at the top going to the meter.

Poking all the way down where I thought it was broke I started finding 1 volt, got up to 2, then bam, 3 and 3.5 volts. Then started tapering off. Again and again I found the same spot working in all directions to make sure. Kept landing the highest voltage, 3.5V, in one spot. Marked it and will start digging soon.

It's a spot that I allow heavy vehicles to cross where the wire is buried. It's right where you can see tire tracks.
 
  #20  
Old 03-10-12, 05:05 PM
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It's a spot that I allow heavy vehicles to cross where the wire is buried.
May be time to consider sheathing that portion of the cable in Schedule 80 or RMC.
 

Last edited by ray2047; 03-10-12 at 06:32 PM.
  #21  
Old 03-10-12, 06:21 PM
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Sounds like your one your way.

Sorry if I caused any confusion, I misunderstood how you tested the wires. Makes sense now.

Let us know the outcome please.
 
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