Breaker did not trip

[edstevn]

I had a breaker that did not trip. There was a loose connectionin on a lug, the lug had a darkened color due to the arcing which produced heat. The question I have is why did the breaker not trip?

[jar546]

Is it a Federal Pacific Stab-Lok panel?

A loose lug on the breaker could have been a contributing factor.

Now the breaker needs to be replaced.

If it was a high amperage breaker, there could be enough heat to cause discoloration on the lugs but not trip due to lack of enough amperage sensed inside the breaker.

Many possibilities

[jimbo]

Was there a short circuit which SHOULD have caused the breaker to trip? A loose connection can arc under normal current draw. The breaker does not see this as a fault which it should trip/

[Thatguy]

A loose connection can only reduce the current in a circuit, so it's possible there really was not enough amperage to trip the breaker.
In this case power that is supposed to go into the load goes into heating the bad connection.

[edstevn]

It was not Federal Pacific Stab-Lok panel. It was in GE breaker panel.

[jwelectric]

only an arc fault would have tripped

[220/221]

Standard breakers trip when too much current flows thru them.

Arcing and burning can easily occur with current flow under it's rated max.

[Johnny C]

A faulty connection at the breaker terminal offers resistance to the flow of current thereby limiting the amount of current passing through the breaker. So the breaker doesn't trip due to high current. However, I have investigated instances where the heat generated by the bad connection caused the breaker to trip due to the transfer of heat from the fault into the heat sensing element in the circuit breaker.

[edstevn]

Thanks for your advice!

[Thatguy]

the lug had a darkened color due to the arcing which produced heat.

You might want to replace the breaker.
This is not my field, but I'd think whatever heat treatment, annealing, tempering, etc., the metal of the breaker connector received at the factory, it has certainly been erased.