In event the KVA rating is not known, the HP rating may be used to arrive at a sufficiently accurate value for practical purposes, Dry machines in good condition will have an insulation resistance value considerably higher than that obtained from the formula. A megohmmeter offers the simplest method of measuring this resistance as it gives a direct reading, but the voltmeter method can be used providing a proper direct-current source is available. DIELECTRIC TESTS After the windings have been thoroughly dried out, and insulation resistance readings are satisfactory, 2 high potential test may be applied to determine the dielectric strength of the insulation. New windings should successfully withstand a high potential test of twice normal voltage plus 1900. Old windings, of course, will not stand such a test: but it may reasonably be assumed that they might withstand 1-1/2 times normal voltage for one minute. <igh potential tests should not be applied repeatedly, as frequent application of high potential tends to weaken the insulation. After a dielectric test, insulation resistance readings should again be taken to ascertain whether or not the insulation has been damaged by the high potential. A periodic insulation resistance check is advisable, especially on large machinery. 4 record of such readings should be kept. Consist- ent readings will indicate continuing satisfactory condition of the insulation. Declining reading will provide advance warning of troubles which may be corrected before breakdown occurs, FaRICDIC GLEANING If top performance is to be expected from the machine, it must be kept clean. The frequency and extent of the cleanings will, of course, 3-36