Testing elec breaker to verify trip

[s219]

I would replace the outlet with a GFI. Much better protection than a 15 amp breaker. There are testers available to plug in and test the breaker but not so cheap. A GFI tester will probably work. I have not tried it but it creates a short to test the GFI.

I don't think GFI would have done a thing in this case, since it really only detects a difference in current between what's flowing on the hot and what's flowing on the neutral. If they don't match to within a tolerance, it assumes current has been diverted to ground and trips.

 

[MarkF48]

The circuit breaker operates on a time/current curve. It's conceivable that the zinc penny may have initiated an arc when it first hit and the active arc was of a high enough resistance that the current was below a value that would have tripped the breaker instantaneously. The burnt outlet and the fact the light fell out when when the metal connection in the outlet lost their springiness due to heating lends the idea that there was arcing and heating going on, so perhaps the amps, while high, wasn't sustained long enough to trip the breaker.
I've a feeling that if the penny were real copper it may have bridged the prongs with little or no arc and tripped fairly quick.

A thought on "testing" the breaker (not for the faint hearted) ... if you have a hardware store that carries the old screw in fuses, buy a few rated at around 20-25 amps (maybe slo-blo). Screw them into a lamp fixture (one that you could consider sacrificial... not the wifes favorite lamp) that has a fairly heavy cord and beefy switch. Wearing safety glasses and work gloves, throw the lamp switch on . If the time/current curves are similar for the breaker and screw in fuse, the breaker should trip before the fuse blows. If the other way around the breaker may have an issue and replacement should be considered.

 

[buickanddeere]

The circuit breaker operates on a time/current curve. It's conceivable that the zinc penny may have initiated an arc when it first hit and the active arc was of a high enough resistance that the current was below a value that would have tripped the breaker instantaneously. The burnt outlet and the fact the light fell out when when the metal connection in the outlet lost their springiness due to heating lends the idea that there was arcing and heating going on, so perhaps the amps, while high, wasn't sustained long enough to trip the breaker.
I've a feeling that if the penny were real copper it may have bridged the prongs with little or no arc and tripped fairly quick.

A thought on "testing" the breaker (not for the faint hearted) ... if you have a hardware store that carries the old screw in fuses, buy a few rated at around 20-25 amps (maybe slo-blo). Screw them into a lamp fixture (one that you could consider sacrificial... not the wifes favorite lamp) that has a fairly heavy cord and beefy switch. Wearing safety glasses and work gloves, throw the lamp switch on . If the time/current curves are similar for the breaker and screw in fuse, the breaker should trip before the fuse blows. If the other way around the breaker may have an issue and replacement should be considered.

A 30amp fuse will be gone in milliseconds on a typical household 15amp breaker. The breaker would not even twitch.

 

[dstig1]

I agree that it should have tripped. I have seen the smallest things trip breakers. Had a similar event where the chuck key to a drill slipped and crossed the prongs while I was unplugging it. Couldn't repeat that if I tried. Instant trip. After arc gouging out the prongs a bit... I have turned the ground plug up on a lot of things, but I don't do it so much anymore. I find that it really stresses the ground pin on extension cords such that they end up coming loose and pulling out of the plug at some point. The weight of the cord pulls down and bends the ground pin a bit constantly, so it eventually comes out.

Regular breakers are dirt cheap - typically under $5. If you have any questions, change it. If it is an AFCI, I can see your hesitation as they run $35-40 or so...

 

[LD1]

I too am surprised it didn't trip.

Do you have an amp clamp?

Run a couple o hair dryers or similar to get over the amp ratinv of the breaker to see how long it takes to trip

 

[MarkF48]

A 30amp fuse will be gone in milliseconds on a typical household 15amp breaker. The breaker would not even twitch.

You do know that fuses do have time curves based on thermal melt times, don't you? One of the reasons I threw in the suggestion for slo-blo to extend the clearing time a bit further to give the circuit breaker a chance to clear if it can.

Typical fuse time curve characteristic....
http://wiki.diyfaq.org.uk/images/f/fc/Curve-BS3036.png

 

[buickanddeere]

You do know that fuses do have time curves based on thermal melt times, don't you? One of the reasons I threw in the suggestion for slo-blo to extend the clearing time a bit further to give the circuit breaker a chance to clear if it can.

Typical fuse time curve characteristic....
http://wiki.diyfaq.org.uk/images/f/fc/Curve-BS3036.png

Post a chart with the response curve of a typical consumer grade breaker. The P fuse and even a D fuse will be gone long before the breaker responds. I used to setup protective relays and test breakers for a living.

 

[MarkF48]

Post a chart with the response curve of a typical consumer grade breaker. The P fuse and even a D fuse will be gone long before the breaker responds. I used to setup protective relays and test breakers for a living.

I believe we have similar backgrounds Time curve for Square D QO 15 amp breaker attached.

 

[JRobyn]

I concur on using a hair dryer, or maybe a small space heater or both to intentionally SLIGHTLY overload the circuit briefly while using a clamp-on ammeter to test. I have a 15a bathroom branch circuit that we quickly learned would not simultaneously carry our 4-bulb vanity light and wife's hi-power hair dryer for more than about 1-2 minutes without triping the breaker.

Count me with those who are very surprised that the penny short did not trip your breaker!! In my experience, when I have accidentally put enough of a short across a circuit the breaker trip was almost instant with MUCH less arcing/burning/damage than you have. And I have done it plenty of times!! :duh::embarrassed:

It makes me glad that I spent more for Square D QO (quick open) breakers for the new house.

- Jay

 

[CobyRupert]

It's a thermal-magnetic breaker. Two distinct protective functions.

Testing the thermal trip aspects of the breaker by applying an overload condition (hair dryer, etc..) does nothing to test the (magnetic) short-circuit overcurrent protection function of the breaker. It is this function that failed. Not the thermal function.