Supervised Location of Installed Transformer

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WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
Long story short, I just finished working on a TI restaurant renovation project. All appliances are 208V 3Ø, landlord shell drawings indicated landlord would provide power to space. Found out later in the project (after architect finished design) that we were expected to house the step down delta transformer in our space. Per code without changing rated walls and enclosing the transformer in its own space, a 112.5KVA xfmr was needed. Loads are fine as they are around 200A demand. 112.5KVA outputs roughly 312A, I specified A 400A panel w/ 300A MCB. Contractor referenced the code book and said OCPD could be 400A per NEC.

The only location we could find to put this transformer was in a corner of the store managers office.

My question to you guys is clarification on the NFPA 70E 450.3(A) code.

What defines a supervised location?
In my opinion a supervised location is a locked area that only maintenance personal or licensed electrical worker can access. Is this up to the building official to decide one way or another?

If considered supervised, the secondary OCPD of the transformer can be sized for 250% of its rated current. Otherwise the “any location” installation allows secondary OCPD to be max 125% of xfmr amperage (390A or less). I went with the safer approach and made sure the secondary OCPD was 300A or 350A. I'm just curious for future projects. Thanks in advance!
 

don_resqcapt19

Moderator
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Location
Illinois
Occupation
retired electrician
The primary voltage is over 1000 volts?
I would not consider any restaurant a supervised location.
If the primary is less than 1000 volts, you need to be looking at Table 450.3(B). 250% primary protection is permitted as long as the secondary protection does not exceed 125%.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The primary voltage is over 1000 volts?
I would not consider any restaurant a supervised location.
If the primary is less than 1000 volts, you need to be looking at Table 450.3(B). 250% primary protection is permitted as long as the secondary protection does not exceed 125%.
Don, is this from NFPA 70E?

My question to you guys is clarification on the NFPA 70E 450.3(A) code.
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
The primary voltage is over 1000 volts?
I would not consider any restaurant a supervised location.
If the primary is less than 1000 volts, you need to be looking at Table 450.3(B). 250% primary protection is permitted as long as the secondary protection does not exceed 125%.
Oh wow good catch. Primary is 480V. So supervised location isn't even part of the equation. Primary OCPD is at 130% and design for secondary OCPD is just under 100%. Design is still complying with code. Thanks again for your inputs.
 
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