Hi Folks!
I hope I am not asking something that has been answered here previously. I could not find a definitive answer, but I am not the best searcher-of-things sometimes.
My questions concern proper fuse type, sizing & placement for a Variac.
I have a variable transformer. I believe it is really an inductor, as opposed to a true transformer. But, I may be wrong.
It is Variac brand Type 100-R. The rating plate states 230 volts 2kVA Max current 9 amps.
It is to be connected through the isolation transformer which powers my bench. The unit will be tapped to supply 0-140vac secondary. Preliminary bench testing confirmed 120vac pri = 0 to 140vac sec (At 230 primary, 0-291vac sec). I plan to use nominal 120vac primary so I can plug into an existing GFI protected receptacle (from the iso trans).
Primary Fuse:
For a normal control transformer, I would size the primary fuse for up to 125% of 9amps (NEC 450.3(b) FN-1 (Guess my trade?)
Is 9 amp slow acting fuse proper for the primary? Since there is no laminated coil involved, I would expect the inrush be much smaller than on a normal transformer. Note, however, that loads will not always be 'ramped up' to full voltage. Sometimes I'll energize the load at the pre-selected voltage.
If I used "next standard fuse size" to 125% of 9amps, which would be 11.5 amps, is the winding still protected?
Secondary Fuse:
Single or multi-tap secondaries are easy to size.
But, since the device's output voltage is variable, properly sizing a secondary fuse becomes a challenge. Am I correct that I should protect from the primary side only?
I sure appreciate any ideas & thoughts you all have about properly protecting this device. Thanks Again!
Paul
I hope I am not asking something that has been answered here previously. I could not find a definitive answer, but I am not the best searcher-of-things sometimes.
My questions concern proper fuse type, sizing & placement for a Variac.
I have a variable transformer. I believe it is really an inductor, as opposed to a true transformer. But, I may be wrong.
It is Variac brand Type 100-R. The rating plate states 230 volts 2kVA Max current 9 amps.
It is to be connected through the isolation transformer which powers my bench. The unit will be tapped to supply 0-140vac secondary. Preliminary bench testing confirmed 120vac pri = 0 to 140vac sec (At 230 primary, 0-291vac sec). I plan to use nominal 120vac primary so I can plug into an existing GFI protected receptacle (from the iso trans).
Primary Fuse:
For a normal control transformer, I would size the primary fuse for up to 125% of 9amps (NEC 450.3(b) FN-1 (Guess my trade?)
Is 9 amp slow acting fuse proper for the primary? Since there is no laminated coil involved, I would expect the inrush be much smaller than on a normal transformer. Note, however, that loads will not always be 'ramped up' to full voltage. Sometimes I'll energize the load at the pre-selected voltage.
If I used "next standard fuse size" to 125% of 9amps, which would be 11.5 amps, is the winding still protected?
Secondary Fuse:
Single or multi-tap secondaries are easy to size.
But, since the device's output voltage is variable, properly sizing a secondary fuse becomes a challenge. Am I correct that I should protect from the primary side only?
I sure appreciate any ideas & thoughts you all have about properly protecting this device. Thanks Again!
Paul