Breakers just wont trip

[Flex]

I am currently working at a Walmart doin renovations. Have been several accidental wire cut throughs, and even a few exposed live wires above the ceiling that have contacted metal, (my mc toss). On not one occasion has a breaker tripped. Why in the world wouldnt any of the breakers trip. The panels are fairly new Cutler Hammer.

 

[zog]

Do they have GF protection?

 

[Flex]

dont believe so

 

[iwire]

These are branch circuit breakers right?

And the runs are long right?

You likely had to much circuit impedance to trip the breaker in the instantaneous region, given time the thermal would have tripped.

 

[raider1]

I agree with Bob,

Most likely the length of the branch circuit is such that the impedance of the ground fault current path is high enough to limit the fault current to below the instantaneous trip threshold of the breaker.

Chris

 

[Flex]

i was thinkin that, so i tried shortin a recept maybe 100 ft away and still nothin. Not something i do regularly but im just stumped.

 

[zog]

What are the breaker catalog numbers?

 

[iwire]

i was thinkin that, so i tried shortin a recept maybe 100 ft away and still nothin. Not something i do regularly but im just stumped.

Not that you should be doing that but it was not a 'bolted fault' it was a fault that produced arcing correct?

The arcing adds impedance to the circuit.

 

[bphgravity]

...Have been several accidental wire cut throughs, and even a few exposed live wires above the ceiling that have contacted metal...

Sounds to me like incredibly unsafe working practices. I am surprised no one has been killed. Where?s an OSHA inspector when you need one??? Yikes...

 

[Sierrasparky]

I have seen A fellow worker get frustrated trying to locate the breaker to turn off a circuit before proceeding and decided to just short the darn thing out against all the others including the boss. Well Let me tell you he won't do that again.Well he found the breaker, it was the one with the big hole in it, sparks flew out of the breaker damaged a couple of others and the buss.

 

[hillbilly1]

Is it a 277 volt circuit? or 120 volt? Since you said you tried it on a receptacle 100' away, I would venture a guess that XO is not bonded to ground on the transformer feeding that panel.

 

[broadgage]

I have seen A fellow worker get frustrated trying to locate the breaker to turn off a circuit before proceeding and decided to just short the darn thing out against all the others including the boss. Well Let me tell you he won't do that again.Well he found the breaker, it was the one with the big hole in it, sparks flew out of the breaker damaged a couple of others and the buss.

I think that most would agree that attempting to trace or isolate a circuit by introducing a deliberate short to trip the breaker is unwise and best not done.

BUT is not the purpose of the MCB to protect against short circuit or overload ?
Should not the breaker trip without causing damage to itself or the panel or other surroundings.
What if the circuit was shorted due to accidental damage, or a defective appliance, surely the breaker should trip, and suffer no damage, and be able to be reset.
Damage to the breaker or to the panel/adjacent breakers suggests to me that it was defective, or that the available short circuit current was in excess of the interupting rating of the breaker.

 

[Flex]

I am curious if the steel in the building is bonded and how the mdp is bonded. Some of the other work I have seen is incredibly dangerous so who knows if they even knew what they were doing when the built the building. The breakers are type "BA" cutler hammers, neither 120v or 277v breakers are tripping.

 

[kwired]

When conductors are shorted do you get a fireworks show or just one pop or nothing at all?

Surely you will trip a breaker if faulting phase to phase or phase to neutral, the longer it takes the more severe voltage drop may be.

If your problem is phase to ground only then you have issues with system bonding jumper.

 

[zog]

If you want to know if the breaker works right or not you have to properly test it, no way of knowing by shorting it out if you are above the TCC trip point.

 

[K8MHZ]

The breakers are type "BA" cutler hammers, neither 120v or 277v breakers are tripping.

Cutler-Hammer 'never-trips'.

Here are my experiences with C-H breakers, cut from another thread:

I used 'C-H' to mean 'Cutler-Hammer'. I don't know if it was a BR or a CH style panel, it was a few years ago.

One of our local inspectors carries around a pen knife with the end melted off it. Not just a nick, but almost a half inch of blade is gone. When the inspector was an EC, he messed up and managed to short the hot and neutral of a 15 amp C-H circuit with his knife. The breaker did not trip and the knife fused between conductors until the blade finally melted off. He was about 15 feet from the breaker panel. Again, I don't know if it was a CH or BR style.

We used the bosses clamp on ammeter.

He was upstairs and I was in the basement putting breakers in an upgrade. When I flipped on one of the 15A breakers, all the lights in the basement dimmed out to nearly nothing. When I turned the breaker off, the lights came back to full brightness.

Since this was an old house, I suspected a bad connection. I figured that this would show up as a very low current. I had boss man come down and clamp the #14 conductor as I turned on the breaker. When he said "115.7", I said (almost as a reflex), 'not volts, amps'. He chuckled and said, "that IS amps".

I then clicked the breaker back off. We found a hot to neutral direct short in an outside light.

From this thread about C-H breakers melting.

http://forums.mikeholt.com/showthread.php/137189-Help!-Furnace-Breakers-Melting!!!

 

[augie47]

Assuming a "standard" Wally-World with a 480.277 service................Are we talking 277v circuits ? If so, are you sure there is an adequate service bond to building steel ?
120 v circuits.. same question on the transformer..is the secondary bonded to steel ?
If the bonds are good then I agree with Bob.

 

[hillbilly1]

Assuming a "standard" Wally-World with a 480.277 service................Are we talking 277v circuits ? If so, are you sure there is an adequate service bond to building steel ?
120 v circuits.. same question on the transformer..is the secondary bonded to steel ?
If the bonds are good then I agree with Bob.

I just run across A problem like that a couple of weeks ago in a orange box in West Virginia, the brillant electrical contractor that wired the store fastened the 600 Kcmil service conductors to the back of the CT cabinet with mineralac straps directly around each conductor. A couple of booms later, we were out there replacing the service conductors. When I was reconnecting the new service wires, I noticed the neutral/ground bond link disconnected on both MDP's!

 

[augie47]

I just run across A problem like that a couple of weeks ago in a orange box in West Virginia, the brillant electrical contractor that wired the store fastened the 600 Kcmil service conductors to the back of the CT cabinet with mineralac straps directly around each conductor. A couple of booms later, we were out there replacing the service conductors. When I was reconnecting the new service wires, I noticed the neutral/ground bond link disconnected on both MDP's!

eliminates those pesky nuisance trips caused by faults to ground

 

[skeshesh]

If you want to know if the breaker works right or not you have to properly test it, no way of knowing by shorting it out if you are above the TCC trip point.

This I have to agree with. The rest is speculation, although they are educated guesses. If I were to pick I'd guess check the N-G connection. Interesting stuff about C-H breaker also.