Circuit Breaker

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Esthy

Senior Member
Okay, one more time and hope I don’t get scolded, have compassion for the elderly! These configurations of the electric furnaces don’t make sense to me.

I keep finding too many of those smaller wires connected to those 60 amps breakers burned out. Those 60 amps breaker “act as disconnects” and are supply by 100 amps breaker from the service panel.

But there is no way that the 60 amps breaker will trip when there is an overcurrent on one of those smaller wires, usually the damage occurs at the female terminal connection, but many of those small wires don’t have the female terminal and are connected to the 60 breaker by the way of twisting the 3 or 4 wires and connecting in the breaker lug.

I know as I have been told that this is the furnace configuration, bla, bla, BUT if those wires keep burning out, it is because this is not the right configuration!

AND still it doesn't make sense to me, because 2 of those furnaces went already on fire.
 

GoldDigger

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Placerville, CA, USA
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Those smaller wires are installed by the factory.
They may also be high temperature wire types. (Which could still cause a problem with terminal temp rating if the NEC applied in the first place.
I wonder how many of the burned out wires are really because of high resistance push on terminals rather than resistance heating of the wires.
 

norcal

Senior Member
Those ITE/Siemens BQ breakers with 1/4" quick disconnect tabs are marked that they are not for general purpose use or something to that effect, for whatever it's worth. Prob. not much.:p
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
...
But there is no way that the 60 amps breaker will trip when there is an overcurrent on one of those smaller wires, usually the damage occurs at the female terminal connection, but many of those small wires don’t have the female terminal and are connected to the 60 breaker by the way of twisting the 3 or 4 wires and connecting in the breaker lug.

I know as I have been told that this is the furnace configuration, bla, bla, BUT if those wires keep burning out, it is because this is not the right configuration!

...
In my opinion the wires burning out have nothing to do with the size of the OCPD, and everything to do with the quality of the connection.

As far as the protection and the NEC, it does not apply. That is part of the equipment and the rules in the product standard that was used to list the product apply.
 

templdl

Senior Member
Location
Wisconsin
Intriguing. One would expect that the panel maker would have receiveda UL listing for their design.
When one considers either thermsl or short circuit protection it is hard t believe that that only thing the 60a rated breakers bring to the party is being a disconnect. The instantaneous or SC protection is based upon 60a which is often time at least 6000a. Protecting he wires from being overloaded would be dependent upon the load that each wire is feeding which is sort of like an 18ga lamp cord feeding actable lamp and feed from a 15 or 20a breaker. Can the breaker provide OL protection for a 18ga lamp cord? Not.
 

kwired

Electron manager
Location
NE Nebraska
Those ITE/Siemens BQ breakers with 1/4" quick disconnect tabs are marked that they are not for general purpose use or something to that effect, for whatever it's worth. Prob. not much.:p
Not as familiar with Siemens products as Square D products, but Those are likely just a "unit breaker" ordered with special lugs (the quick disconnect tabs). They are also available with typical set screw type lugs on both ends of the breaker. Internals of the unit are most likely same thing as any other breaker in same product line. I guess it depends on what you mean by general purpose use. They won't plug into a loadcenter, which may be seen as general use type for these and other "miniature" breaker types.



Intriguing. One would expect that the panel maker would have receiveda UL listing for their design.
When one considers either thermsl or short circuit protection it is hard t believe that that only thing the 60a rated breakers bring to the party is being a disconnect. The instantaneous or SC protection is based upon 60a which is often time at least 6000a. Protecting he wires from being overloaded would be dependent upon the load that each wire is feeding which is sort of like an 18ga lamp cord feeding actable lamp and feed from a 15 or 20a breaker. Can the breaker provide OL protection for a 18ga lamp cord? Not.
These breakers are supplying a fixed resistance load. There will never be an overload condition. If you have a 9.6 kW element connected to it, how is it ever going to draw more then 9.6kW without an increase in supply voltage or someone physically connecting more load to it?

They will respond to short circuits and ground faults though.

The failure the OP is seeing (and I see it often as well but usually at heating elements, control relays, high limit switches, etc more often then at the breaker, is a failed connection that heats up because of resistance in the connection. Same failure still happens with a bad connection even if trip setting of the breaker is 25 or 30 amps instead of the usual 60 amps often seen.
 

templdl

Senior Member
Location
Wisconsin
Not as familiar with Siemens products as Square D products, but Those are likely just a "unit breaker" ordered with special lugs (the quick disconnect tabs). They are also available with typical set screw type lugs on both ends of the breaker. Internals of the unit are most likely same thing as any other breaker in same product line. I guess it depends on what you mean by general purpose use. They won't plug into a loadcenter, which may be seen as general use type for these and other "miniature" breaker types.



These breakers are supplying a fixed resistance load. There will never be an overload condition. If you have a 9.6 kW element connected to it, how is it ever going to draw more then 9.6kW without an increase in supply voltage or someone physically connecting more load to it?

They will respond to short circuits and ground faults though.

The failure the OP is seeing (and I see it often as well but usually at heating elements, control relays, high limit switches, etc more often then at the breaker, is a failed connection that heats up because of resistance in the connection. Same failure still happens with a bad connection even if trip setting of the breaker is 25 or 30 amps instead of the usual 60 amps often seen.

There is a sacrifice with SS and GF protection with the higher instantaneous with a 60at breaker though. But then you can't have the best of both worlds an the trade off is that the fault current must be greater in order to trip the 60at breaker. But SS protection has been provided never the less.
 

GoldDigger

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Location
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There is a sacrifice with SS and GF protection with the higher instantaneous with a 60at breaker though. But then you can't have the best of both worlds an the trade off is that the fault current must be greater in order to trip the 60at breaker. But SS protection has been provided never the less.
SS = Short Sircuit?
 

kwired

Electron manager
Location
NE Nebraska
There is a sacrifice with SS and GF protection with the higher instantaneous with a 60at breaker though. But then you can't have the best of both worlds an the trade off is that the fault current must be greater in order to trip the 60at breaker. But SS protection has been provided never the less.
How much higher is instantaneous trip point for a 60 amp breaker vs a 25 or 30 amp breaker? How long does the fault need be in the circuit before it damages the conductor? Then you have to throw available fault current into the mix. Higher available current usually means faster trip time but you still need to remain under the AIC rating or you have other problems.
 

templdl

Senior Member
Location
Wisconsin
How much higher is instantaneous trip point for a 60 amp breaker vs a 25 or 30 amp breaker? How long does the fault need be in the circuit before it damages the conductor? Then you have to throw available fault current into the mix. Higher available current usually means faster trip time but you still need to remain under the AIC rating or you have other problems.

I would anticipate that the mag trip is anywhere from 10-20+ the rating of the breaker. This would mean the a 60at breaker would be double that of a 30at.
The the actual pickup is dependent upon the type of fault. An arcing could realling doesn't have any specific values and the fasult current may even be great at the time the arc is struch and as the sarcing propagates the impedance may increase and the current decreases. As then becomes the fact if the mag pickup of 30at breaker would sence the fault sooner that a 60at breaker.
With a bolted fault it !ay be potluck which one would trip should the fault current be of a significantly high magnitude.
Then bolted faults are very rare.
 

kwired

Electron manager
Location
NE Nebraska
Let's not forget the conductors/equipment being protected by the breaker in the OP is inside the appliance and is not premises wiring.
 

templdl

Senior Member
Location
Wisconsin
Let's not forget the conductors/equipment being protected by the breaker in the OP is inside the appliance and is not premises wiring.
I certainly don't disgree with you. Enclosed electrical equipment if it is UL listed had complied with the UL requirements for that listing even though we could pick it apart using theory. When it comes to circuit protection realistically there are sdo many variable it is almost like shooting at shadows. You just attempt to close the gap knowing that it is not an exact science as some think it may be.
 
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