Xfrmr secondary protection

2phase

Member
Location
Ky
Occupation
Electrician
I am familiar that the code says xfrmr secondaries don't have to be protected, i have found that code reference. What i am looking for is a definite answer to is 'can secondaries go right to a load without protection?' Someone wired up a 480v to 110v xfrmr with the secondaries SO cabled into a 4square with a couple of duplexes. I dont think the 20A fuses in front of the primary will blow if there is a fault on the secondary. Any help?
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
In general, transformers and their secondary conductors can be primary only protected if you can meet the requirements of 240.21(C)(1). While you don't say the size of the transformer, it is unlikely this will work in your situation. Obviously in your case a 20 amp primary will be way over sized for a 120 volt 20 amp receptacle on the secondary.
Also this transformer will require proper grounding and bonding on the secondary. And the SO cord is a no go.
 

2phase

Member
Location
Ky
Occupation
Electrician
In general, transformers and their secondary conductors can be primary only protected if you can meet the requirements of 240.21(C)(1). While you don't say the size of the transformer, it is unlikely this will work in your situation. Obviously in your case a 20 amp primary will be way over sized for a 120 volt 20 amp receptacle on the secondary.
Also this transformer will require proper grounding and bonding on the secondary. And the SO cord is a no go.
Thanks for the reply. You're right on the primary protection definitely. However, without being savvy on calculations i opted to fight my case with the verbage "a single load", by using a 4sq with 2 duplexes, this set up is being used as a portable temp 120 power source, not a single load with calculations being made for protection. I pressed the issue with management and they conceded. The code is bare minimum i reminded them. We can always do more. Thanks again.
 
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