OVER-VOLTAGE PROTECTION 



611 



its discharge rate is materially lowered. Where warm climatic 

 conditions prevail the arrester should be in as cool a place as pos- 

 sible and protected from the direct rays of the sun (Fig. 390). 

 A high initial temperature will reduce the available heat storage 

 capacity of an arrester and its ability to care for long continuous 

 discharges. A high operating temperature also increases the rate 

 of dissolution of the films which would necessitate more frequent 

 charging. In some cases it may be found advisable to charge 

 two or more times a day. When operating under conditions of 

 high temperature any failure to periodically charge the arrester 



FIG. 390. Outdoor Lightning Arrester Installation Showing Protecting Shield 



against Sun. 



increases the liability of damage from a heavy charging cur- 

 rent. 



Only arresters of the outdoor type, with special bushings and 

 covers, should be installed out of doors. Care must be taken to 

 see that the bushings and covers are correctly assembled to be 

 water-tight. The arresters may be mounted either on a platform 

 between poles or on a platform near the ground and surrounded 

 by a fence. The position of the arresters should preferably be 

 such that their operation can be observed by the station attendant. 

 While installing arresters out of doors care must be taken not to 

 let the wooden and fiber parts of the cone stack become wet in 

 case of rain and to keep dust from the cones and electrolyte. 



