XPost: sci.electronics.design, sci.electronics.misc, sci.electronics.repair   
   From: diverse@tcp.co.uk   
      
   On 17/02/2014 07:50, Jeff Liebermann wrote:   
   > On Sun, 16 Feb 2014 22:23:31 -0800, Mike Cook    
   > wrote:   
   >   
   >> A small 1/2 hp induction motor is turned on and off with a motor-rated   
   toggle   
   >> switch connected to a 208V 20A branch circuit. No other protection   
   installed.   
   >>   
   >>   
   >> Obviously not enough protection so I'm planning to add a slow-blow 9A fuse   
   >> (rating of the motor) to keep it safe.   
   >>   
   >> Any objections?   
   >   
   > Any reason that you didn't bother to disclose all the important motor   
   > characteristics and details?  Single phase or 3 phase?  1725 rpm or   
   > something else?  The nameplate of your 1/2 hp motor should specify the   
   > operating current at 208v.  What is the nameplate operating current?   
   > Extra credit for the maker and model number.   
   >   
   > The problem is that starting current can be 3 to 4 times the nameplate   
   > oprating current.  Your common 9A slow blow cartridge fuse isn't going   
   > to work if your motor operates at about 4A.   
   >   
   > You have some choices.  Try plugging into this calculator and pick the   
   > fuse type (non-time delay, dual element time delay, instant trip, or   
   > inverse time trip) that you find appropriate.   
   >    
   >   
      
   And does the motor have to start-up fully loaded   
      
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