We Have A 200 Amp 480 Volt 3 Phase Buss Plug That Feeds A 112 Kva 480 Primary 208/120 Secondary 3 Phase 4 Wire Transformer, Which Supplies A 225 Amp 3 Phase 4 Wire Main Lug Only 42 Circuit Distribution Panel. What Is The Correct Fuse Size For Overcurrent Protection On The Primary? The Primary Wire Size Is 2/0, The Secondary Wire Size Is 250 Mcm. Since The Panel Is Main Lug Only The Overcurrent Protection Is On The Primary Side Of The Transformer. Currently We Have It Fused At 175 Amps.
Correct Over Current Protection
- Thread starter GWITT
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davidr43229
Senior Member
- Location
- Columbus, Oh
Your FLA is 134.87. NEC 450.3 calls out for 125% or next size larger, or 167% of next size smaller. The wire sizes come from NEC 310.16 On the primary, even though you did not call out a temp rating of the wire, you are fine.
Dave
Dave
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
Where is the secondary side protection?
-Jon
-Jon
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- New Jersey
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- Journeyman Electrician
davidr43229 said:
He's only fine on the primary since he intends to leave the violation of no OCPD for the secondary conductors.
davidr43229
Senior Member
- Location
- Columbus, Oh
Wholeheartedly agreed, which the origional poster made no mention of.
125% or the next size larger.
Dave
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
MPD gave you very good references in the NEC as how to protect the secondary conductors and panel.
Based on your OP, the panel will need an overcurrent device protecting it, not a MLO panel.
Art 450 is for protection of the primary and secondary windings of the transformer.
Based on your OP, the panel will need an overcurrent device protecting it, not a MLO panel.
Art 450 is for protection of the primary and secondary windings of the transformer.
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