Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 66 of 72
PART 2: MAGNETIC TRIP RANGE SELECTION.
The selection of magnetic trip range is determined by maximum peak current draw,
not duty cycle or average current. In order to compute maximum peak current draw,
maximum welding current, type of welding machine, and number of welds made
simultaneously need to be known. The following generalizations are biased toward
worst-case; they will usually indicate a need for a higher magnetic trip range than
what is actually needed. These generalizations should be used ONLY if better data is
not available.
The basic formula for selecting the required magnetic trip setting is:
MTS = WC * NSW * MF
Where:
MTS = Magnetic trip setting
WC = Welding current per weld; assume 18,000 amps for steel, and 40,000
amps for aluminum
NSW = Number of simultaneous weld loops. Usually, this is equal to the
number of weld spots. Where series welding is used, each pair of weld spots counts
as one.
MF = Machine factor; 0.084 for a hanging gun station, 0.042 for a machine or
fixture welder, 0.021 for an integral transformer welding gun.
EXAMPLE:
Assume that four welds on a steel automobile body are made simultaneously in a
fixture-type welding machine. Using these assumptions:
WC = 18,000 amps (for steel)
NSW = 4 (4 welds made simultaneously)
MF = 0.042 (for a fixture welder)
The required magnetic trip setting would be:
MTS = 18,000 * 4 * 0.042 = 3042 amps
If the required magnetic trip setting is higher than what is available on a circuit
breaker frame size selected according to the first part of this write-up, a larger
circuit breaker is required. The circuit breaker size should be selected according to
EITHER average current or peak current considerations, whichever is higher.