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#46365 12/19/04 05:47 PM
Joined: Mar 2002
Posts: 179
D
derater Offline OP
Member
A neighbor lady plugged in her vacumn and the
receptacle fried and the lights went out.
She's not an idiot so when she called I had her look at breakers; none off.Go over today
and as she said, but when I found and switched the 15a breaker the circuit held/lights on.They've tripped the bath circuit and the toggle went 'off'.Today this
one was in 'on' position.R/r'd the receptacle.They're older Murray bkrs.How common is this?

#46366 12/19/04 06:14 PM
Joined: Oct 2004
Posts: 806
Member
At least the breaker did trip, unlike our FPE/Zinsco friends. [Linked Image]

Sounds like the only problem is with the handle toggle mechanism, maybe a few manual operations would clear it up?

But since breakers aren't that expensive, I would have replaced it anyway.

I have had breakers fail to close or reset even out of the panel, just worn out I guess.


Stupid should be painful.
#46367 12/19/04 06:28 PM
Joined: Nov 2003
Posts: 127
S
Member
We had Murray breakers installed in my dad's house back in '67 or so to replace the fooze panel. I remember a few times where the CB's would rattle/buzz but not trip- there's also a good friend of the family that refers to them as "Murray Maytrip" breakers- are these a known problem? Perhaps...

Just my two cents' worth.


No wire bias here- I'm standing on neutral ground.
#46368 12/19/04 08:12 PM
Joined: Mar 2002
Posts: 179
D
derater Offline OP
Member
My point is that it interupted the current but the toggle remained in the on position.
When 'reset' it powered the circuit.In this vein I'd seen somewhere,(maybe here)about
'exercising' breakers, though I think the thread was industrial.

#46369 12/19/04 08:25 PM
Joined: Mar 2002
Posts: 179
D
derater Offline OP
Member
My point is that it interupted the current but the toggle remained in the on position.
When 'reset' it powered the circuit.In this vein I'd seen somewhere,(maybe here)about
'exercising' breakers, though I think the thread was industrial.

#46370 12/19/04 09:48 PM
Joined: Sep 2003
Posts: 650
W
Member
Remember that breakers are required to 'trip free', meaning that if you try to hold the breaker on, it is supposed to trip anyway.

This means that in some sense the trip mechanism disconnects from the handle. If the handle is a little bit sticky, then the breaker will trip but the handle won't move.

-Jon

#46371 12/19/04 10:34 PM
Joined: Apr 2002
Posts: 914
E
Member
This is why I never believe a home owner when they say "I checked and all the breakers are on". I can't count the number of times I've seen breakers that looked on, but were tripped.

#46372 12/19/04 10:47 PM
Joined: Dec 2000
Posts: 4,287
Member
Sometimes C/Bs trip but still appear to be turned on.
The ones that I've run into this the most on have been GE's.
If you go down the line in a panel and push the handles towards the on position, you can often find the one that's tripped.
It baffles even many electricians [Linked Image]

#46373 12/20/04 12:34 AM
Joined: Oct 2000
Posts: 2,721
Broom Pusher and
Member
Winnie's response regarding the Trip-Free abilities of commonly used MCCBs (Molded Case Circuit Breakers) is why these types of things occur often, with older and newer Breakers.

They have tripped as needed, due to an Over Load / Over Current scenario, only the Reset Handle was not thrown to an "Offset" position (Trip Position being either mid-way "Trip" position, slightly behind the "On" position, or to full Off position).

The tripped device will throw to Off very much easier than the Reset ones (devices in the "On" position being the reset ones).

There is another scenario where an overcurrent does not result in a visibly tripped device - and this in fact will not be tripped at all!
It's when the time-current trip charasteristics of the upstream device causes it to trip before the downstream one does (AKA: Non-Selective Coordination).
These scenarios are really fun (invert the term "Fun").
An example:
20 amp 3 Pole 240 VAC 10KAIC MCCB has ground fault - this device sees 2400 Amps for the fault level.
The panel is fed via a 100 amp 3 pole 240 VAC 10KAIC MCCB, which has exact same trip characteristics, and in fact at the +2000 Amp level, the two devices' current lines have already overlapped.
9 out of 10 times the 100/3 will trip only.

Last scenario involves exceeding the AIC of a device - barbequed breaker / welded closed contacting points - no way to trip this device (except to blow it up from a runaway fault or an arc)
[Linked Image]

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#46374 12/20/04 05:31 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
Scott I do not understand this comment.

Quote
Last scenario involves exceeding the AIC of a device -

Shouldn't all the devices be rated for the fault current available?

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

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