A small controls transformer in the RTU unit? Protection requirements.

Cartoon1

Cartoon1

Senior Member
Location
Florida
Occupation
Electrical Engineer
Hello All,
I have an RTU unit that is rated for 480V main lennox. We are adding an ionization device on it that requires 24VAC and the load is only .41A or 10 watts. The lennox is providing a small transformer rated 480V primary to 24VAC secondary rated for 75 VA somewhere inside the unit and it has a protection 3.5AMP circuit breaker (on secondary). The transformer catalog number 42w94, model LB-74930.

My question is: wouldn't i also need a primary fused on this transformer? and if so what should it be? and what type?

Thank you,
 
FYI, NEC 725.127 and 450 are your references. If the transformer was fed from a power and lighting circuit it could be protected at a 20A max breaker, since this is not your situation then article 450 dictates your requirements which include primary protection. Sorry if I don't specifically answer you, teach a man to fish and all.:)
 
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