Square D tandem breakers overload?

[powerplay]

On a Main Square D Panel, I was wondering if it is an good idea to use tandem breakers if the panel was rated for them. I had heard that using a tandem with one heavier load such as an washer, would cause a noticeable voltage drop with a lighting circuit sharing the same tandem breaker. Thanks again!

 

[dhalleron]

I have no data or research to back it up, but I've always felt that tandem breakers were prone to failure more than full sized ones.

Just like quick wiring a receptacle, they might be designed for that purpose, but I don't like them.

 

[gar]

110624-0931 EDT

On a QO-15 with a 12 A load I measured the total drop from bus to output terminal at 0.127 V. Much of this is in the thermal element. I do not want to open a breaker to get an internal connection to eliminate the the thermal element.

Instead just assume for round numbers that the bus to breaker drop was 0.1 V at 10 A, a high figure. Also assume that washer inrush current is 100 A, probably high. Then at most the mutual (common) impedance at the bus to breaker interface would produce a 1 V drop to the lighting circuit from motor inrush. Practically nobody can see this under normal conditions. There will be more drop from the pole transformer impedance in most residential applications.

I do not think this is a problem unless there is an overstressed spring contact on the QO contact to the bus.

Would I use a tandem breaker? No. The only reason to use one would be there was no other way.

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