At 07:29 AM 9/3/2009, Aaron wrote: >I have 3 resistance heaters. One is rated for 880 watts at 220 VAC and >the other two are each rated for 400 watts at 220 VAC. I am trying to >calculate the theoretical currents for each phase if I wire the heaters >in a delta configuration across a 3 phase supply. Can anybody point help? Easy. Lets call the 3 phase supply lines A, B, C. Find the current through each heater when connected across the supply. Call those currents Iab, Iac, Ibc where Iab is the current of the load connected from lines A to B. Note that 220Vac is NOT a standard voltage in North America - its 208Vac. That will reduce the heater current (and output power) from your rated 220Vac. You are going to have to figure out the resistance of each heater (Eg. R= (220V)^2 / 800W), then figure out the current at 208Vac. Or: find the current at 220V, then divide that by the ratio of 220V / 208V. Whichever is easier for you. Add Iab to Iac, then divide that result by 2, then multiply that by SqRoot (3) (about 1.73). That amount is the current in conductor A. In other words, (Iab + Iac) * 0.866 . Add Iab to Ibc, then divide that result by 2, then multiply that by SqRoot (3) (about 1.73). That amount is the current in conductor B. In other words, (Iab + Ibc) * 0.866 . Add Iac to Ibc, then divide that result by 2, then multiply that by SqRoot (3) (about 1.73). That amount is the current in conductor C. In other words, (Iac + Ibc) * 0.866 . I hope this helps. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist