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RESISTANCE 47
oils, as in Fig. 11, or else get a rheostat of the required capacity, so that the amperage will not overheat the coils « >r grids.
(62) It is more efficient to work your rheostats below rather than above capacity. The general results will be better and the rheostats will last twice, or more than twice as long.
Testing for Ground
(63) If a test lamp is used to test for a ground between resistance elements and the rheostat casing, conned one test lamp lead to opposite polarity of the one leading to the rheostat; leave current switched on but turn off the light source. Touch the casing or metal frame with the end of the other test lamp wire. If the lamp lights or there is a spark when you remove the wire, then there is a live connection between the rheostat frame and the resistance elements. If the lamp burns brightly there is a heavy ground. If it burns but dimly or not at all, if a spark is emitted when the connection is broken, then the leak has high resistance. If the lamp does not light nor spark, then there is no "ground. "
Testing for Grounded Coil or Grid
Testing for grounded coil or grid is a tedious job. First, remove the casing, then do whatever may be necessary to release the first coil or grid. It varies with different types of rheostat, but there should be little difficulty in finding the right way to do it.
Remove the first coil or grid and test with a magneto and bell. A battery and bell may be used instead of the magneto. A better method is to apply a test lamp after energizing the partly disassembled rheostat with voltage. If the ground still exists — the bell rings or the lamp lights — remove successive grids or coils until the test shows up clear. Obviously the previous element is at fault and repairs should be made at that point. In reassembling the rheostat be careful to get all coils or grids thoroughly insulated from the frame. * Fig. 13 is the diagrammatic representation of a rheo