[BC] Transmitter Safety

[DHultsman5 at aol.com]

In a message dated 5/2/2008 12:51:47 PM Central Daylight Time,  
glaenzer at verizon.net writes:

Hello  Dave;

I don't think the NEC addresses anything inside the  cabinet.

Gary




Gary they may not address it directly but my recollection is that the  
mention was deriving any voltage referenced to ground.   It was  cheaper to put in 
another single phase service to the crystal heaters since they  needed to on 
all the time.  However if an FM exciter need 110 VAC to  operate by the terms of 
the rules you were required to use a stepdown  transmformer from 220 VAC to 
120 VAC at which point you could ground one side of  the secondary.
 
In the Collins 831 Series transmitters there was a step-down transformer  for 
the exciter.  In the 816R series there is a transformer to run the  tuning 
motors and the small blower on the harmonic filter which are 115 VAC  items.
 
One of the problems with UL approval is that the have to have a sample of a  
product to destroy. Which is OK of an electric iron or hair dryer that your 
are  going make a coupole of million.  But  transmitters and other  inductrial 
items are high priced, low volume items since they are not consumer  
orientated.  
 
Probably one of the best things UL did was the making manufacturers of the  
old 5 tube AC/DC radios use plastic cabinets of in the case of metal cabinets 
is  isolators within the cabinets.  This was before the days of polarized plugs 
 and many a housewife has plugged the radio in the kitchen the wrong way and 
been  shocked since the chassis could be the hot side of the AC.
 
Dave 



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