498 



REGULATIONS FOR WIRING 



[Cn. XIII 



fire by the wires coming in contact with inflammable material, the 

 wires are carefully insulated so that the current is kept in the circuit 

 and not allowed to escape by taking short cuts or by going to the 

 ground. Two things are necessary for this: (i) The naked wires 

 must in no case touch each other at any point, for that would make 

 a short circuit. (2) The naked wires must not touch anything 

 which is a conductor. 



The wires are insulated by covering them with a coating of 

 rubber, asbestos, silk, etc., that is, some substance which will 



FIG. 267. AN ELECTRIC CIRCUIT WITH A DOUBLE GROUND. 

 C D The two poles of the dynamo. 

 G Generator (dynamo). 

 B 1 A conductor extending from the circuit near the pole C to the ground 



<'). 



B s A conductor near the pole D extending to the ground (g 2 ). 



In this case the current will short-circuit, passing from the point B 1 to g l and 

 from g 1 to g', B 2 and back to the dynamo at the pole D instead of passing 

 through the arc lamp (A ) and the rheostat (R). The single ground is dangerous 

 only in that there is liable to be formed a second ground from some other part 

 of the circuit. 



g 1 , g 2 The earth into which the conductors, B 1 , B 3 extend. 



A Arc lamp. 



R Rheostat. 



not serve as a conductor. Where the wire must be uncovered, as 

 at switches, etc., some solid substance like porcelain, slate, hard 

 rubber, glass or some other non-conducting substance is used, for 

 the naked wires to rest against. 



REGULATIONS FOR WIRING: PRECAUTIONS 

 691. National Electric Code. To make the wiring and con- 

 nections of electric apparatus good and safe in every respect, the 

 electrical engineers, architects and fire underwriters have formu- 



