THE TRANSFORMER 



305 



ratio of 20 : 1 might be used in connection with a voltmeter 

 having a range of 125 volts. Such a transformer is called a 

 potential transformer; it generally has a full-load capacity of 

 only a few watts, i.e., just sufficient to operate the volt-meter. 

 In using potential transformers it must be remembered 

 that they will not be accurate if more than the rated load 



FIG. 196. A Small Electric Welding Transformer. The transformer 

 proper is located beneath the work holders. Thomson Electric 

 Welding Co. 



is taken from them; also, they cannot be used as step-up 

 transformers if accurate results are required, a transformer 

 1 uiving a ratio of 60 : 1 stepping down might have a ratio 

 of 1 : 57 when used as a step-up transformer. 



The current transformer is used when very heavy alter- 



