# Why doesn't this breaker trip?



## Service Call (Jul 9, 2011)

What brand breaker?


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## Service Call (Jul 9, 2011)

And does it pull a constant 40 amps?


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## Fuma (Feb 4, 2016)

both were siemens



Service Call said:


> What brand breaker?


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## Fuma (Feb 4, 2016)

It is pulling a constant 40A



Service Call said:


> And does it pull a constant 40 amps?


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## don_resqcapt19 (Jul 18, 2010)

The UL standard will permit a 30 amp breaker to carry 40.2 amps forever without tripping.

Take a look at the time current curves for you breaker. If the breaker is installed in a non-heated area, make sure you apply the temperature adjustment.


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## joebanana (Dec 21, 2010)

Was the replacement a "new certified" breaker, or, one that's been kicking around for a while? Did you exercise it? Does it rattle when shook? (maybe it was dropped?) If it's on a #10awg. circuit, I'd be concerned, a #8awg, not so much. But still, see if you can find someone in your area that tests breakers, and certifies them.


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## joebanana (Dec 21, 2010)

don_resqcapt19 said:


> The UL standard will permit a 30 amp breaker to carry 40.2 amps forever without tripping.
> 
> Take a look at the time current curves for you breaker. If the breaker is installed in a non-heated area, make sure you apply the temperature adjustment.


Does that standard permit #10awg wire to draw 40a. forever without degrading?


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## don_resqcapt19 (Jul 18, 2010)

joebanana said:


> Does that standard permit #10awg wire to draw 40a. forever without degrading?


The #10 is considered protected by a 30 amp OCPD that meets the UL standards. The temperature of a #10 operating at 40 amps will not exceed 90°C.


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## joebanana (Dec 21, 2010)

don_resqcapt19 said:


> The #10 is considered protected by a 30 amp OCPD that meets the UL standards. The temperature of a #10 operating at 40 amps will not exceed 90°C.


Is that, "will not" or, "shall not"? Just wondering, too dang lazy to crack the book.


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## frenchelectrican (Mar 15, 2007)

joebanana said:


> Is that, "will not" or, "shall not"? Just wondering, too dang lazy to crack the book.


It worded will not.,, 

In most case useally for short term the tempture rise will not affect with 90*C conductors but with 60/75*C conductor it kinda on borderline..

That based on exposed everoment but buried in insluation like in attic or in inslualted walls then it can be a issue.. ( short term it don't hurt but long term yuh ... ) 

Merci. Marc


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## don_resqcapt19 (Jul 18, 2010)

joebanana said:


> Is that, "will not" or, "shall not"? Just wondering, too dang lazy to crack the book.


Will not...40 amps is the ampacity of #10 copper in the 90°C column.


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## donaldelectrician (Sep 30, 2010)

Fuma said:


> A while back I installed a 240v NEMA 14-30 dryer outlet on a 30A 2 pole breaker. I recently plugged in my new EV charger with a 14-30 to 14-50 adaptor. I expected the the 30amp breaker to trip because my EV charger is pulling 40amps, but it didn't. I then replaced the CB because I thought it could be faulty.
> 
> My CB still is not tripping when I pull 40amps from a 30amp receptacle. Could someone please tell me why this is and if i should be concerned?




As explained ... it should hold ... and most likely your unit is not pulling 40 amps all day or at all ... that is usually a Max Rating anyway ... Worst Case ... Chargers are running at a lower amperage ... usually .

Did you amp probe It ? Just asking ... Should of tried that before changing
the CB .



Don


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## frenchelectrican (Mar 15, 2007)

donaldelectrician said:


> As explained ... it should hold ... and most likely your unit is not pulling 40 amps all day ... that is usually a Max Rating anyway ...
> 
> Did you amp probe It ? Just asking ..
> 
> ...



Don., majorty of EV charger do run full speed at first hour or so then taper down as it need to be.

However that is the other issue is that the EV charger I am condersing that is a contituion load so I do not know if OP did check the rating ( even thru the nameplate stated 40 amp max ) so that is something ya have to think about it..


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## donaldelectrician (Sep 30, 2010)

frenchelectrican said:


> Don., majorty of EV charger do run full speed at first hour or so then taper down as it need to be.
> 
> However that is the other issue is that the EV charger I am condersing that is a contituion load so I do not know if OP did check the rating ( even thru the nameplate stated 40 amp max ) so that is something ya have to think about it..



Thanks for the info ... Well at least it will not be Continuous ...



Don


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## don_resqcapt19 (Jul 18, 2010)

donaldelectrician said:


> Thanks for the info ... Well at least it will not be Continuous ...
> Don


It might not actually be continuous, but we have to treat it as such.


> 625.41 Rating
> Electric vehicle supply equipment shall have sufficient rating to supply the load served.* Electric vehicle charging loads shall be considered to be continuous loads for the purposes of this article*. Where an automatic load management system is used,the maximum electric vehicle supply equipment load on a service and feeder shall be the maximum load permitted by the automatic load management system.


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## EM1 (Oct 25, 2014)

Even at a constant 40A load, that is only 1.33 times the breakers nameplate rating. At 40Amps it will trip....eventually, you might have a looooooong wait. Check out the attached link, most molded case breakers at twice rated current can take over a minute.

http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf


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## Service Call (Jul 9, 2011)

I find it odd that they manufacture such an adapter, if its not home made. I know they make them for rv's and boats, but you can chose your load with those. 

But to knowingly produce an item that allows you to put more load on a circuit then it was designed for, for extended periods of time, without any control, amazes me.


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## donaldelectrician (Sep 30, 2010)

EM1 said:


> Even at a constant 40A load, that is only 1.33 times the breakers nameplate rating. At 40Amps it will trip....eventually, you might have a looooooong wait. Check out the attached link, most molded case breakers at twice rated current can take over a minute.
> 
> http://static.schneider-electric.us...100-400 A Frame FA-LA/FA-FC-FH/0600DB0105.pdf



I used to know that chit ... The CB trips after so many minutes / hour at % of over load ... darn getting old . The short circuit pick ups are one thing but the OL Pick ups are another .


Don


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## emtnut (Mar 1, 2015)

Fuma said:


> A while back I installed a 240v NEMA 14-30 dryer outlet on a 30A 2 pole breaker. I recently plugged in my new EV charger with a 14-30 to 14-50 adaptor. I expected the the 30amp breaker to trip because my EV charger is pulling 40amps, but it didn't. I then replaced the CB because I thought it could be faulty.
> 
> My CB still is not tripping when I pull 40amps from a 30amp receptacle. Could someone please tell me why this is and if i should be concerned?


As to should you be concerned ? Yes! Your pulling 40A from a 30A circuit !
Your an Aircraft Electrician, would you do this on an AirBus circuit ?
I doubt your garage is at 37,000' ... but the principal is the same :jester:

Or do you guys take into account that the ambient air is -30 at 30,000' :laughing:


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