23 Feb 07 10:55
Just to clarify, you said that there are "two 120 volt relocatable power taps (both with surge protectors)daisy chained together and powered via an extention cord connected to a 2500 watt generator".
Can I assume that these are two surge suppressor multi-taps, with multiple 120V 3-W plug connections, similar to what would be used for a computer station, where you would plug in the CPU, monitor, printer, etc? One is plugged into the other, which is plugged into an extension cord, which has its ground plug cut off, and is plugged into a generator?
You then state "I initailly suspected that the MOV's from the power tap connected to the generator may have failed and caused the fire". Are these the MOV's in the first power tap which is connected to the extension cord plugged into the generator?
"then I found arcing on an extension cord that connected a second power tap number to the first power tap. " Is this another extension cord between the two power taps?
As for your questions, if the above assumptions are correct:
A1 I can't see any issue with one surge suppressor multi-tap plugged into another. The length of the conductor to each suppressor and the clamping voltage would have to be taken into account to determine which would work first, though.
A2 The open ground removes the reference point for the voltage across the MOV, and the connection for the discharge of voltage if the MOV would go to low resistance (clamp) if there were a voltage spike above its rating. It's possible that the coupling capacitance of the cable provided enough of a ground reference to allow the MOV to clamp, but there was nowhere for the energy to go since the ground connection was missing.
A3 The only issue I see here is the unlikelyhood of a voltage spike happening at all from the generator as a source.
A4 Assuming that there was a voltage spike in the cable system on the line conductor, since the ground was removed, the only place to discharge would be to the neutral. This would cause some arcing, given that the spike was above the insulation rating of the system.