Transformer Primary and Secondary Protection

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kshah

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Location
Irvine, CA
Hi All,

I have a situation on a project that is currently in construction. The design calls out for a new 30kVA step-down transformer (480V - 208/120V) to be installed. The transformer is planned to be installed in an electrical room with a new branch circuit panelboard at 208/120V with a main breaker installed next to the transformer. The transformer is being fed from a 480V distribution board which is located about 50' away. Due to space restrictions within the electrical room, there is a proposed relocation for the branch panelboard. There is space in the adjacent room to place the panelboard, which will be serving said room. Now you have the transformer in the electrical room and the panelboard in the adjacent space over 25' away and the 480V distribution panel in a different room about 50' away.

My question is regarding the required primary and secondary overcurrent protection needed. Based on my review of NEC 240.21 and 450.3, I believe that i would need to provide an overcurrent protection device on the primary side of the transformer AND the secondary side of the transformer within the electrical room. Thus, I would see an enclosed circuit breaker mounted to the left and right of the transformer in the electrical room. Is this correct? I appreciate any help.
 
augie47

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The transformer primary overcurrent protection can be located any distance from the transformer as they receive their protection at the point of origin.
The secondary conductors need to comply with 240.21(C) as they are unprotected until they have OCP.
 
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K

kshah

Member
Location
Irvine, CA
WOW! You guys are great, and quick!

I'm a bit slow, so sorry if I am not getting this right away.

If I understand the responses correctly and after reading 408.46 (2008), I would only require a OCPD on the secondary side of the transformer.

I think i was confused with providing disconnecting means and OCPD for the primary. In the case that the transformer needed service and the primary needed to be de-energized, a disconnect at the primary would be useful, but its not required by the NEC. The transformer is protected by the OCPD at the 480V distribution board. Do I have this right?
 
VUGear

VUGear

Member
Location
I-40, TN
Pierre C Belarge said:
The disconnecting means is not required to be within sight of the transformer.
Click to expand...
Except that there are a few AHJs that require a service disconnect (without OCP) on the primary side of the transformer if remote from its source. A plans reviewer made me do it in FL recently and I couldn't talk him out of it.
 
raider1

raider1

Senior Member
Staff member
Location
Logan, Utah
VUGear said:
Except that there are a few AHJs that require a service disconnect (without OCP) on the primary side of the transformer if remote from its source. A plans reviewer made me do it in FL recently and I couldn't talk him out of it.
Click to expand...

Did they give you a code section to back it up?

Chris
 
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