I'm curious what happens when a Silicon Carbide shelf touches an element which pops out of one side and touches a different element which pops out on the other side. It's essential to know what the potential down-side is - even though it doesn't seem likely.
So both elements when powered up are supplied with voltage from the same source and are operating to the same ground. Let's assume here something like 208 VAC. So the hot side first element has a voltage of 208 V above nominal ground. If the second element is powered also, it is also sitting at 208 V above ground. Since both elements are at the same potential above common ground, no current will flow. So nothing will happen (other than possible physical damage to the elements at the points of contact).
But let's say that the first element is powered up at the time, and the second element is on an "off" duty cycle (as in a zone control type kiln might be). Element 1 is at 208 V. Element 2 is at 0 V..... but.. and this is where the "but" come in... it dependes on how the contactors for the specific kiln break the circuit. If they completly break both poles of the supply circuit, then there is no path to ground again even though the is no potential on element 2. It is "floating". What then happens is that if there is a path to ground from that second element ... then current will flow. BUT the amount will be determined by the total resistive and reactive resistance of BOTH the elelments from the source on element 1, plus the shelf, plus the element 2 to to bount of w hatever ground is "made".
I don't have resistance numbers for the Advancer material. I bet it is high. Most glo-bar type kilns use 440V to power them.
Worst case is likely that the kiln's breaker should blow if the current gets too high.
I think in almost all, if not all, cases, lacking a human being getting their body in the way to run current to ground, it is not going to cause any issues. Plus you'd have to work at having a proper sized shelf set in such a way that even elements "popping" out of the grooves would contact two separate elements at the same time. If it was cocked to one side..... then it'd be further from the other. If it was the correct size shelf to start with, there'd be good clearance from the banks of elements....... the kiln would have to be in really bad repair to have that situation develop then....which would be "operator error" to let it get to that level of disrepair.
BTW.... I would have thought the local breaker on your kiln should have blown, not the main somewhere else.