Single phase xfmr

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hhsting

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I have 10kva 277V to 120V single phase transformer. The primary breaker is 45A. I have phase wire, neutral wire and equipment grounding conductor wire primary side.

However at the secondary side their is no breaker provided. Would it need breaker on secondary side or not?
 
hhsting said:
I have 10kva 277V to 120V single phase transformer. The primary breaker is 45A. I have phase wire, neutral wire and equipment grounding conductor wire primary side.

However at the secondary side their is no breaker provided. Would it need breaker on secondary side or not?
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That would depend on what size the conductors are on the secondary side.
 
Post #1 I like to add that transformer is part of isolation panel in ambulatory setting. It is an isolation transformer. Would that change the answer?
 
hhsting said:
Post #1 I like to add that transformer is part of isolation panel in ambulatory setting. It is an isolation transformer. Would that change the answer?
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An isolated power system in a health care facility would be a listed system. I don't believe it would have a grounded conductor (neutral).
 
As David says, an Isolated Power System in a hospital would be a listed system (at least in modern times) so when the primary is fed your done.

Roger
 
hhsting said:
Post #1 I like to add that transformer is part of isolation panel in ambulatory setting. It is an isolation transformer. Would that change the answer?
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Not certain for the application, but general rules permit protecting the secondary of a two wire - two wire transformer with the primary as long as it is sized per voltage ratio and conductors are sized to that ration as well. Your 45 amps for 10 KVA is right about 125% of the kVA rating, and should be acceptable from that aspect presuming the secondary conductors are sized for 10 kVA @ 120 volts which should be about 83 amps.
 
david luchini said:
An isolated power system in a health care facility would be a listed system. I don't believe it would have a grounded conductor (neutral).
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Primary breaker, transformer and secondary panel are all part of an all in one manufacturer provided isolated power system panel. I dont have manufacturer datasheet or part number but plans show from switchboard their is fdr bkr 45A with phase, neutral and EGC going to primary 45A bkr.
 
kwired said:
Your 45 amps for 10 KVA is right about 125% of the kVA rating, and should be acceptable from that aspect presuming the secondary conductors are sized for 10 kVA @ 120 volts which should be about 83 amps.
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I think you mean the conductors should be sized for 104Amps
 
hhsting said:
Primary breaker, transformer and secondary panel are all part of an all in one manufacturer provided isolated power system panel. I dont have manufacturer datasheet or part number but plans show from switchboard their is fdr bkr 45A with phase, neutral and EGC going to primary 45A bkr.
Click to expand...

As Roger mentioned, you bring you circuit to the primary...you don't have to worry about the secondary.
 
hhsting said:
Primary breaker, transformer and secondary panel are all part of an all in one manufacturer provided isolated power system panel. I dont have manufacturer datasheet or part number but plans show from switchboard their is fdr bkr 45A with phase, neutral and EGC going to primary 45A bkr.
Click to expand...

And that's it, you don't need anything else. If you were to modify the assembly you would be voiding the listing. The system will have to be commissioned after installation, this includes equipotential, leakage current, LIM operation, alarm levels, etc...

Roger
 
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