Trouble with Warehouse Circuit

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Skelufteay

Skelufteay

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Denver, Colorado
I was asked for some advice on a potentially burned breaker, and am kind of stumped on what to do next. I have some experience in electrical troubleshooting with Solar, but building wiring is still a little new to me. So any advice you can give would be awesome (and I know enough not to shock myself or damage things).

History on building:
It is a warehouse (1.2k sqft) built in the 70's, originally used for storage, then modified to be a call center, and now it is a theatre with office. Due to all these changes, outlets have been added, exit signs have been added, and the circuit breaker is more or less unmarked and illogical (figuring out marking will be my next project).

A few months back, the office circuit was overloaded and the breaker tripped (a space heater was turned on the same time as the microwave or something like that). When we turned the breaker off, then on again, half of the outlets came back on, but one outlet and the exit signs did not (yes, I know they should be on a dedicated circuit but for whatever reason they are not). This strikes me as very odd, since (I believe) each breaker should only have one wire and all the devices are connected in series. From what I am gathering, I think there are two lines on the same breaker, as some outlets work but others do not.

What I have tried so far:

I tested the outlet that was not working (its a 4 plug box, made of two receptacles with 2 sets of 3 prongs each), for continuity (while breaker off).
  • The negative wire is continuous with the negative side of the outlet
  • The positive wire is continuous with the positive side of the outlet
  • The neg/pos/GND wires are continuous with the wires from one receptacle to the other (so i know that the lines between them are alright)
  • The negative to positive side of the receptacle do not have continuity (it beeps once then goes silent) ... to me this means the outlet has a short and needs to be replaced, as I checked other outlets in the same manner and they had continuity from neg to pos when metering the left/right holes.
    • After replacing both outlets in this box, the signs did not come back on, and the outlet is not working still. But the other outlets on the circuit are working.
    • (I am thinking someone in the building's history took the dedicated line of the exit signs and spliced in an outlet for the office, as it is one of the lines that runs from ceiling to ground on the exterior of the wall).

My plans for continued troubleshoot:
  • I did not see a GFI in the breaker panel, but will re-look and see.
  • test continuity of the lines from breaker to outlet to test lines to see if they are still good (is it best to take the GND and pos wire (then GND and Neg) and disconnect from outlet and breaker, join them on the outlet side and meter on the breaker side?)
  • Test for ground fault: Disconnect the circuit from its power source ? remove the terminals at the panel ? and disconnect the load (device, or devices if they?re lights) from the circuit. Turn all switches for that circuit to the ?on? position. Place the leads of the multimeter, set to the ohmmeter function, across the positive and negative sides of the circuit. A reading of infinite ohms means the circuit is good and the device is bad; a reading of less than infinity means there is a problem in the wiring.
  • Check the signs for blown fuses ... though they did run on backup battery while the power was out, but now those batteries are dead and the theatre needs them light for fire code, as you know. I guess the fuses could be on the incoming line of power, but allow for battery to operate when they blow.

Not sure what else to add, so if there is more information needed please let me know and I can find it out. Thank you for helping me with this!
 
Is the breaker a single pole breaker? With only one handle and one wire attached?
If so, then all of the devices should be in parallel (not series).
But if it is a two (or three) pole breaker, one pole may be failing to close.
As for fixing it, get an electrician rather than a EE on the job.
JMO.

Tapatalk!
 
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I can tell you are a Solar guy (no offense), because there's no Pos and Neg in AC. It's line and neutral. Just wanted to say it before someone else did.:p
 
You need to check for splices before the dead outlet. These splices could be in a junction box, receptacle box, or the receptacle itself could be used for the splice (ie, fed on one screw, feeds the next on the other screw or pokehole). My first guess would be a bad back-stabbed outlet that the dead one is fed from.

/mike
 
Skelufteay said:
all the devices are connected in series.
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meternerd said:
I can tell you are a Solar guy (no offense).
Click to expand...


You are not going to have devices wired in series in a typical AC circuit. Think about voltage drop and you will understand why.


Once you understand what you are dealing with go to the last device that is working and check that out. You should have both hot and neutral (return ). Then go to the first device that isn't working and you will be missing either the hot or neutral. There may be junction boxes between them or even just a burned wire someplace between.
 
growler said:
You are not going to have devices wired in series in a typical AC circuit.
Click to expand...
Correct but you will find them daisy chained which is what I think happened here. I suspect the over load heated a weak splice and it went open causing all downstream receptacles to de-energize.
 
meternerd said:
I always wonderd about that. Isn't a car wired grounded and ungrounded? Hmmmmm...........:?
Click to expand...

In general they are not "earth" grounded. Most for many years have had the negative bonded to the vehicle frame and even use the frame as current carrying conductor for many items.

Go back far enough like pre 1950 or maybe even 1940 and you find some that had the positive bonded to the vehicle frame. I'm not as certain about cars, but old farm machinery definitely had some "positive ground" equipment out there. and you had to watch for this when switching components or even when jump starting a machine.
 
dereckbc said:
Correct but you will find them daisy chained which is what I think happened here. I suspect the over load heated a weak splice and it went open causing all downstream receptacles to de-energize.
Click to expand...

They could be daisy chained and that would be typical for an office. This was a warehouse and would not have required very many receptacles to start with, who knows how they were added. There could be a junction box in a drop ceiling or attic and all the receptacles (one this circuit) feed out of that.

Since this is an exit light and a receptacle on the same circuit I would think that the receptacle is on the emergency light circuit and may not even be the same circuit as the other receptacles. His problem may be in another exit or emergency light j-box.

I have no idea where the break is, we would have to assume the place is wired correctly to start with and since there are receptacles on the emergency circuit I kind of doubt that.

I was just pointing out that daisy chained devices are still a parallel circuit and it's important to know this.
 
series in a one line diagram does not always (more like usually does not) equate to series wiring of the loads in the circuit:happyyes:
 
kwired said:
In general they are not "earth" grounded. Most for many years have had the negative bonded to the vehicle frame and even use the frame as current carrying conductor for many items.

Go back far enough like pre 1950 or maybe even 1940 and you find some that had the positive bonded to the vehicle frame. I'm not as certain about cars, but old farm machinery definitely had some "positive ground" equipment out there. and you had to watch for this when switching components or even when jump starting a machine.
Click to expand...

Guess I'm reverting back to my early days on a nuclear sub. They have ungrounded 120V systems, so that if you get smacked by a depth charge and the "line" conductor grounds, it won't trip the circuit. Have ground detectors all over. Ahhh...those were the days.:sick:
 
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