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XMER PRIMARY&SECONDARY PROTECTION
- Thread starter llrodriguez
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Re: XMER PRIMARY&SECONDARY PROTECTION
in 240.21(c)1 first paragraph, you will have overcurrent protection on the secondary side. Just because the transformer section(450) does not require it, you end up with it from the overcurrent section(240).
EXACTLY MY POINT. SHE NEEDS OVERCURRENT PROTECTION ON THE SECONDARY SIDE OF THE TRANSFORMER. Where it needs to be installed and what size it can be are different questions. Unless you have one of the transformers mentionedOriginally posted by jim dungar:
If Linda has several panelboards with main breakers which are located within 25ft of cable of the transformer, then a single secondary device is not required per 240.21(C)(3). In this instance, the sum of the ratings of the panelboard mains can not exceed the output rating of the transformer
....
240.4(F) does require conductors on the multi-voltage secondary of a transformer to have overcurrent protection. 240.21 lists the requirements for the location and sizing of this required protection. A grouping of panelboard main devices would meet 240.4(F) if they are located per 240.21(C).
in 240.21(c)1 first paragraph, you will have overcurrent protection on the secondary side. Just because the transformer section(450) does not require it, you end up with it from the overcurrent section(240).
Re: XMER PRIMARY&SECONDARY PROTECTION
so you can size the primary ocp larger than 125%Originally posted by llrodriguez:
If secondary protection of a xmer less than 600 v is never required, then when would you ever apply method 2 primary/secondary protection of Table 450.3(B)??
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Re: XMER PRIMARY&SECONDARY PROTECTION
Linda, method 2 is for when you do provide secondary protection, then you can change the size of the primary protection.
jschultz, the correct answer is transformers do not need protection - stop looking in 450, conductors do need protection start looking in 240.
One example: Industrial application, 75KVA 480V primary to 208Y/120 secondary transformer, output rated for 208A, conduit, ambient, and terminations per 75C column.
Per 240.4(F) conductors need protection. 240.21 says the protection does not need to be at the begining of the conductors. 240.21(C)(3) will allow (3) 25' long feeders of 350kcmil (310A max.) to (3) wall mounted 100A main breaker panelboards.
[ April 21, 2004, 09:07 AM: Message edited by: jim dungar ]
Linda, method 2 is for when you do provide secondary protection, then you can change the size of the primary protection.
jschultz, the correct answer is transformers do not need protection - stop looking in 450, conductors do need protection start looking in 240.
One example: Industrial application, 75KVA 480V primary to 208Y/120 secondary transformer, output rated for 208A, conduit, ambient, and terminations per 75C column.
Per 240.4(F) conductors need protection. 240.21 says the protection does not need to be at the begining of the conductors. 240.21(C)(3) will allow (3) 25' long feeders of 350kcmil (310A max.) to (3) wall mounted 100A main breaker panelboards.
[ April 21, 2004, 09:07 AM: Message edited by: jim dungar ]
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