Old breakers not tripping

[NewOnMyOwn]

I came up in the union doing commercial work. A lot of times when doing demo we'd blow up circuits to trace them out using a cord and plug to a handi-box with a good switch to short it out. Or sometimes guys who like melted metal flying thru the air would just short the circuit out the old fashioned way.

My question is this: Many times the breakers would not trip, the lights would just dim. This would happen with a variety of panel manufacturers. My understanding is that in these buildings the homeruns are long enough and the splices might not be good enough to allow 20A+ to flow. Would that be a reasonable assessment in general? Or is it just bad breakers that don't trip?

 

[jaylectricity]

Federal Pacific breakers are notorious for not tripping on a short circuit.

I do a similar thing (although definitely illegal and mostly dangerous). Sometimes it is the mechanics of the breaker itself. Anytime I install ground fault or arc fault protection I teach the customers to use that test button. Not so much to make sure it is working properly, but because it exercises the device.

The same is probably true for many circuit breakers.

 

[iwire]

I came up in the union doing commercial work. A lot of times when doing demo we'd blow up circuits to trace them out using a cord and plug to a handi-box with a good switch to short it out. Or sometimes guys who like melted metal flying thru the air would just short the circuit out the old fashioned way.

You have to stop doing that.

My question is this: Many times the breakers would not trip, the lights would just dim. This would happen with a variety of panel manufacturers. My understanding is that in these buildings the homeruns are long enough and the splices might not be good enough to allow 20A+ to flow.

The impedance of the circuit has a direct effect on the trip time of the breaker.

The breakers we use are 'inverse time' breakers which means the larger the fault current the faster they will trip.

A 20 amp breaker may carry 25 amps forever, it might carry 35 amps for a few minutes and it certainly might carry 100 amps for a few seconds. I have seen a 30 amp breaker carry 150 amps for a few seconds.

Or is it just bad breakers that don't trip?

It's bad that you are shorting circuits to find them.

 

[hillbilly1]

Federal Pacifics definetly hard to trip, I don't know if they have thermal only trip mechanisms, without the magnetic trip, but on a short circuit almost impossible to trip. Low available fault current on long wire runs may be part of it, but never got many calls on one of those tripping.

 

[jwjrw]

The only time I will do that is if someone has done some creative wiring and I dont know what breaker and there is a need not to lose power if possible to computers or something.

 

[iwire]

The only time I will do that is if someone has done some creative wiring and I dont know what breaker and there is a need not to lose power if possible to computers or something.

Well ....

You never know when the feeder breaker will trip faster, it happens and then the computers are down and you end up looking like a moron.

The short circuit on one circuit can cause nasty spikes on on other circuits which could harm electronic equipment and you end up looking like a moron.

The breaker does not trip and you start a fire or just damage the conductors and you end up looking like a moron.


I suggest a circuit tracer.

 

[jwjrw]

Well ....

You never know when the feeder breaker will trip faster, it happens and then the computers are down and you end up looking like a moron.

The short circuit on one circuit can cause nasty spikes on on other circuits which could harm electronic equipment and you end up looking like a moron.

The breaker does not trip and you start a fire or just damage the conductors and you end up looking like a moron.


I suggest a circuit tracer.

Sound advice I have a really nice one, but with high ceilings and conduit ran all over that can be easier said than done. I am not implying this is something I would normally do but yes I know I have once maybe twice. I would never leave a circuit grounded out if it didnt trip immediatly.

 

[480sparky]

....I would never leave a circuit grounded out if it didnt trip immediatly.

So what do you do when the copper welds itself to the ground?

 

[jwjrw]

So what do you do when the copper welds itself to the ground?

Oh I short them with my defective set of klein linesmans with the cheap metal from china( actually I love my kleins )to whatever is nearby.....
Really Ive only done it once or twice.

 

[mxslick]

It never ceases to amaze me that every time this topic comes up, that there are folks who either see no problem with it or admit that they continue to do it.

People, wake up. There are several reasons why it is an incredibly stupid thing to intentionally short out a circuit because you're too lazy to trace it out.

• Breakers won't always trip for the reasons outlined in the other posts above;
• Available fault currents in some facilities have gone way up as utilities upgrade their infrastructure;
• There is a serious risk of molten metal setting something on fire or worse, ending up injuring someone;
• You can easily compromise the circuit in question and/or other circuits;
• You can easily scare or injure nearby people;
• You can often end up tripping a feeder or main breaker, then how stupid do you look?;
• And like Bob said, you WILL look like a moron.

If a circuit tracer is too much for your budget, get a cheap set of walkies and have your help cycle breakers until you find the circuit in question.

You can virtually ALWAYS prepare the occupants for the very brief outage to find a breaker..so in my mind, unless you're working a nuclear power plant, there is NO EXCUSE to not find the breaker!!

Any contractor working on my property or job site who employs that method will find themselves escorted to the door faster than they thought possible.

 

[NewOnMyOwn]

I went back and read the first post and see that I wasn't clear. My intentions in the first sentence was to say that this is something that I did years ago when I was coming up. Not today.

My curiosities aren't about blowing circuits up, they are about dead shorts not tripping the breaker, and the reasons why that happens. Whether it's more likely to do with non functioning breakers or just plain high resistance not allowing enough current to flow for long enough to trip the breaker.

 

[cpal]

I agree with Bob Bad Idea, and for those newer elctricians please don't be influenced to try it.

I had a crew that stabbed the ltg circuit under the phase lug to install kitchen appliances in apt buildings back in the 70's. Murry brkers.

Its a little nerve racking to hear a 24 unit building hum. when some one installing a switch lost the hot ro ground.

This is definetly bad Ju Ju.

don't work it hot and buy an ohm meter, circuit tracer , tone generator, etc.

 

[brian john]

Federal Pacific breakers are notorious for not tripping on a short circuit.

The same is probably true for many circuit breakers.

You have evidence other that hearsay regarding this statement.

 

[don_resqcapt19]

...
My curiosities aren't about blowing circuits up, they are about dead shorts not tripping the breaker, and the reasons why that happens. Whether it's more likely to do with non functioning breakers or just plain high resistance not allowing enough current to flow for long enough to trip the breaker.

Not all older branch circuit breakers have an instantaneous trip function and even where they do have such a function the trip point may be anywhere from 8 to 50 times the handle rating of the breaker. As others have pointed out that the impedance of the circuit will limit the current and, in the cases where there is an instantaneous trip function, the current flow may be much less that what is required to trip the device. In these cases the trip will be based on the inverse time curve and it may be a number of seconds before the device opens....of course it could just be that the breaker is no longer functional and it will not trip no matter how much current flows.

 

[LarryFine]

My curiosities aren't about blowing circuits up, they are about dead shorts not tripping the breaker, and the reasons why that happens. Whether it's more likely to do with non functioning breakers or just plain high resistance not allowing enough current to flow for long enough to trip the breaker.

Electrically speaking, it could be either one. Have you tried a clamp-on ammeter during the uninterrupted fault?

 

[LarryFine]

Federal Pacific breakers are notorious for not tripping on a short circuit.

The same is probably true for many circuit breakers.

You have evidence other that hearsay regarding this statement.

Which statement are you doubting?

 

[NewOnMyOwn]

Electrically speaking, it could be either one. Have you tried a clamp-on ammeter during the uninterrupted fault?

Nope, this was many years ago.

I just thought of it today because I was speaking to another electrician who was looking for some rare breakers he needed for a customer's panel. He would be happy to take whatever he could find, new or used. That got me thinking about the old breakers not tripping, and the possibilities of putting an old defective breaker into a new situation- how would you ever know for certain without having it tested?

 

[LarryFine]

... how would you ever know for certain without having it tested?

Bingo!

 

[zog]

Nope, this was many years ago.

I just thought of it today because I was speaking to another electrician who was looking for some rare breakers he needed for a customer's panel. He would be happy to take whatever he could find, new or used. That got me thinking about the old breakers not tripping, and the possibilities of putting an old defective breaker into a new situation- how would you ever know for certain without having it tested?

You don't. I needs to be tested. There are some pretty shady guys dealing breakers on the internet, you have to be very careful, if you buy a used breaker, install it, it fails and causes damages, guess who will be at fault? You either need to test them or ensure you are buying from a real dealer that reconditions them per PEARL certification standards and provides a complete test report with the breaker.

 

[NewOnMyOwn]

Good to know, thanks.

I thought it was more common for sparkies to have big collections of old, used, rare breakers for use when the need arises. But as you said, doing so could lead to a world of problems.