The 120 element trips a GFCI, because a GFCI DOES NOT really sense a SHORT. What it does is sense the imbalance between the White(Neutral) and HOT(black) wire. Which a SHORT does make happen. But in this case, the 120 element does not have a ground wire, just the Hot and Neutral. The Element IS inside a metal steel tube which is connected to the RV ground. When a Refer 120 element BLEEDS current(defective element) it will cause that imbalance of current and if ON a GFCI circuit will trip the GFCI. If NOT on a GFCI circuit, the 120 element will operate as designed, as that bleed is not enough to cause a Circuit Breaker trip as from a short. Doug