Outlier,
For what it's worth had the 120V branch circuit that feeds the variac been protected by an AFCI,(Arc Fault Circuit Interrupter), breaker the breaker would have tripped open when the variac started series arcing. I am just not sure if under normal operation of the variac a slight arcing of the wiper brush contacting the bared autotransformer coil as the variac was ramped up or down might cause the AFCI breaker to trip open.
You could have an electrician install an AFCI breaker in the electrical panel that feeds the branch circuit and find out when you get the new variac.
Note, depending how old the electrical panel is and manufacture of will determine if the electrical panel manufactured breaker will fit the model/style/series of your panel.
AFCI breakers have been in use since 1999. As per the 2014 NEC code all newly installed 120V 15 and 20 amp branch circuits used for lighting and receptacles in habitable areas of a residential dwelling unit shall be AFCI protected. It should be said the AHJ, (Authority Having Jurisdiction), has the final say where they must be used.
http://www.afcisafety.org/qa.html
.
For what it's worth had the 120V branch circuit that feeds the variac been protected by an AFCI,(Arc Fault Circuit Interrupter), breaker the breaker would have tripped open when the variac started series arcing. I am just not sure if under normal operation of the variac a slight arcing of the wiper brush contacting the bared autotransformer coil as the variac was ramped up or down might cause the AFCI breaker to trip open.
You could have an electrician install an AFCI breaker in the electrical panel that feeds the branch circuit and find out when you get the new variac.
Note, depending how old the electrical panel is and manufacture of will determine if the electrical panel manufactured breaker will fit the model/style/series of your panel.
AFCI breakers have been in use since 1999. As per the 2014 NEC code all newly installed 120V 15 and 20 amp branch circuits used for lighting and receptacles in habitable areas of a residential dwelling unit shall be AFCI protected. It should be said the AHJ, (Authority Having Jurisdiction), has the final say where they must be used.
http://www.afcisafety.org/qa.html
.