Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 65 of 72
PART 1: CIRCUIT BREAKER MINIMUM FRAME SIZE SELECTION GUIDE
There are three classes of duty cycle to consider:
A HIGH duty cycle application is seam welding. For HIGH DUTY CYCLE applications,
the circuit breaker size should be:
CIRCUIT BREAKER SIZE (amps) = TRANSFORMER NAMEPLATE KVA x 2
A MEDIUM duty cycle application is defined as 7 spot welds or more in any 30-second
time interval. This corresponds to a duty cycle of more than 5%. Robot applications,
manually operated welders, or multi-transformer cascading controls usually fall into
this category. For MEDIUM DUTY CYCLE applications, the circuit breaker size should
be:
CIRCUIT BREAKER SIZE (amps) = TRANSFORMER NAMEPLATE KVA X 1.6
A LOW duty cycle application is defined as 6 or fewer spot-welds in any 30-second
time interval. This corresponds to a duty cycle of 5% or less. Welders on fixtures or
hard automation usually fall into this category. For LOW DUTY CYCLE applications,
the circuit breaker size should be:
CIRCUIT BREAKER SIZE (amps) = TRANSFORMER NAMEPLATE KVA X 1.3
The result of the calculation of PART 1 sets the MINIMUM acceptable circuit breaker
frame size, based on average current considerations. Depending upon the results of
the computation for the required magnetic trip setting (PART 2), a larger circuit
breaker may be required.