Specifications

MedWeld 3000 Catalog Revision 8
July 2002 Page 69 of 72
PART 2: ISOLATION CONTACTOR CURRENT RATING SELECTION BASED ON TRANSFORMER CONNECTION.
CASE 1: (simplest)
If just one single-phase transformer is connected to an isolation contactor, the
required isolation contactor current rating is the value of average current calculated
for that transformer from Part 1.
CASE 2:
If two or more transformers are connected in parallel on the same two poles of an
isolation contactor and are welding simultaneously, the required isolation contactor
current rating is simply the sum of the average currents calculated for each
transformer (from Part 1).
For example if three 50 KVA welding transformers, welding simultaneously in a fixture
application are connected to the same two poles of an isolation contactor, the
required current rating for the isolation contactor is:
65 + 65 + 65 = 195 amperes.
CASE 3:
If two or more transformers are connected in parallel on the same two poles of an
isolation contactor and ARE NOT welding simultaneously (cascade operation), the
required isolation contactor current rating is equal to the average current for the
largest transformer (from Part 1) times the square root of the number of
transformers.
For example, if a 100 KVA and a 75 KVA transformer are connected in parallel to the
same two poles of an isolation contactor and are operated in cascade in a fixture
welding application, the required current rating for the isolation contactor is:
130 * sqrt(2) = 184 amperes.