Electrician Talk banner
1 - 17 of 17 Posts

·
Registered
Joined
·
2,062 Posts
Discussion Starter · #1 ·
Ive got a 480 feed to a 480/208-120 transformer. It's fed off a 200 amp existing 480 brkr. Out of the transformer I'm feeding a 120/208 panel with a 400 amp main breaker. The 480 breaker is located about 225 ft away from the transformer but yet within sight of. It's a warehouse. My question is do I need to put in a 300 amp over current protection on the secondary side of the transformer? We are on the '08 code if that makes a difference.
 

·
Registered
Joined
·
11,429 Posts
Ive got a 480 feed to a 480/208-120 transformer. It's fed off a 200 amp existing 480 brkr. Out of the transformer I'm feeding a 120/208 panel with a 400 amp main breaker. The 480 breaker is located about 225 ft away from the transformer but yet within sight of. It's a warehouse. My question is do I need to put in a 300 amp over current protection on the secondary side of the transformer? We are on the '08 code if that makes a difference.
so your 400A panel is now a 300A panel. Within site, as defined by the NEC means no more than 50 feet away and within site (see section 100- Definitions; 'In Site From')
 

·
Registered
Joined
·
8,050 Posts
Your disconnect for the transformer primary is allowed to be in a remote location as long as it can be locked open. If this was my install and I had to be cost conscious I'd set it up just with what you got. Not sure where 300 amp anything came into your equation though. If your secondary has a 400 amp main and your transformer is 112 kva then you're all set
 

·
Registered
Joined
·
2,062 Posts
Discussion Starter · #6 ·
ponyboy said:
Your disconnect for the transformer primary is allowed to be in a remote location as long as it can be locked open. If this was my install and I had to be cost conscious I'd set it up just with what you got. Not sure where 300 amp anything came into your equation though. If your secondary has a 400 amp main and your transformer is 112 kva then you're all set
Maybe my math was wrong. I thought 112.5 Kva at 208 was only good for something like 290 amps. If I'm wrong then that's ok by me.
 

·
Registered
Joined
·
8,050 Posts
Service Call said:
Maybe my math was wrong. I thought 112.5 Kva at 208 was only good for something like 290 amps. If I'm wrong then that's ok by me.
You are correct. I was thinking of a 150. I can't remember the last 112.5 I did, they are useless to me.

That being said I'd look into refitting your secondary panel to a MLO maybe
 

·
Registered
Joined
·
3,838 Posts
While the 400 amp OCPD in the panel is compliant for the protection of the transformer secondary, the secondary conductors must have an ampacity of at least 400 amps. You are not permitted to use 240.4(B) for this application. In other words, you need to install 600kcmil copper, not 500kcmil for the secondary conductors.
 

·
Registered
Joined
·
6 Posts
While the 400 amp OCPD in the panel is compliant for the protection of the transformer secondary, the secondary conductors must have an ampacity of at least 400 amps. You are not permitted to use 240.4(B) for this application. In other words, you need to install 600kcmil copper, not 500kcmil for the secondary conductors.
The secondary conductors also must be protected within 25' unless this meets the "supervised installation" requirements.
 
1 - 17 of 17 Posts
Top