Originally Posted by jcthorne
If you are pulling 21amps from that circuit, the 20amp breaker is already bad or is not a 20amp breaker protecting the circuit.
You are in a dangerous situation. You will not see or feel the hotspot in the circuit wiring in the house until the smoke comes out......
Its a 20amp circuit for a reason. Designed to allow 16amps continuous draw. You are way beyond its ampacity.
A 20 amp circuit will handle 20 amps 24 hours a day 365 days a year in a perfect world, the 16 amps you are quoting is a design specification, you do not want to have a known load running at 100% of the breaker rating all of the time. The breaker will temporarily hold an overload inversely proportionally to the load, the greater the overload, the quicker the breaker will trip. Ambient temperature of where the breaker is located also affects trip time, if it is in an airconditioned area, it will take longer to trip, if it is in a garage where the temperature is much higher, it will trip quicker. So the breaker is not necessarily bad. That being said, your second sentence, does hold some truth, a bad connection hidden in the walls, or a bad outlet can cause a fire because of heating just like the adapters the OP was using.