STANDARDIZATION HI /./-.N / //// i / 23 



236 The Kit I.AIIUN under test should be in normal condition as to dry- 

 ness and the temperature should when possible be that reached ia normal 

 Njrvt <- 



237 \ i-i'i i IONAL CONDITIONS AND PRECAUTIONS FOR CLASS 2. The following 



:u and precaution*, in addition to the foregoing, apply to tests 

 of apparatus included in Class 2. 



238 SUDDEN INCREMENT or '1 > OLTAGE on the apparatus under teat 

 should be avoided, particularly at high voltages and with apparatus having 

 considerable capacity, as a momentarily excessive rise In testing voltage 

 will result. 



239 Si OLTAGE of the circuit supplying the 



>* the test should be avoided as they are likely to set up 



240 <>.\* in . :ig the test voltage are es- 

 sential in or urtou* high frems ir banco* from 



1 by a small water rheostat. 



:ig may occur, causing high-frr< turhancet which should be 



ully av*: 



241 TKANHFORMBR < c transformers, the low- voltage 



.ibly be connected to the core and to the ground when 

 the high-voltage test i> bring made, in he stress from 



low-voltage D h would otherwise result through condenser 



action. The various terminals of each winding of the high-tension trans- 

 former should be c -get her during the test in order 

 to prevent undue stress on the insulation between turns or sections of the 

 winding in case the high-voltage test causes a break-down. 



(O METHODS FOR MBAI-KIM. int. n \GB. 



242 FOR MK\M KIM. no ii \iB, two instruments ar in common 

 use. (1) the spark gap and .It meter. 



243 1 '. so that it will break down with a 

 certain pred< and is connected in parallel with the in- 

 sulal ige applied to the insu. 



n the break-down voltage of the spark gap. A given 

 setting of the spark gap is a measure of one definite voltage, and. as its 

 operatic- upon t: vim value of the voltage wave. 



rm and is a limit on the maximum stress to which 

 the The spark gap is not conveniently adapted 



low voltages. 



244 >;ap may be set for th 



v apparatus adjusted to give a voltage at 



The spark gap should then be 



adj 'age. and the auxiliary apparatus 



>gc of the former breakdown, which 



be the assumed voltage for the test. This voltage is to be maintained 

 for the required interval. 



246 T new sewing needles, supported 



axially at the ends of 'or* which are each at least twice the 



f the ga; should be no extraneous body near the gap 



. radius <: 'able of approximate striking dis- 



This table should be used in connection 



with tests n. c spark-gap methods. 



246 A N \ I M K of about one-half ohm per volt should be 

 inserted in series with each terminal of the gap so as to keep the discharge 

 current between the limits of one-quarter ampere and 2 amperes. The pur- 

 pose of the resistance is to limit the current in order to prevent the surges 

 which might otherwise occur at the time of break-down. 



247 J. The VOLTMETER gives a direct reading, and the different values of the 

 voltage can be read during the application and duration of the test, 

 suitable for all voltages, and does not introduce disturbances into the test 



-.lit. 



248 In VOLTMETER MEASUREMENTS, the voltmeter should, in general, derive 

 its voltage from the high-tension testing circuit either directly or through 



