I have a question regarding 240.21(B)(3). I have a setup where the total length of the primary plus secondary conductor is over 25'. As a matter of fact the primary cable and the secondary cable are each over 25' in length. The transformer is a 225 kVA 480-208/120 volt, 3ph, 4w dry type. My supply is from a fused bus plug and the panel fed by the transformer has a 600 A MCB. My question is do I need to provide overcurrent protection at the transformer on the primary side or secondary side, or maybe both? :-? Thanks for your help.
Transformer Tap
- Thread starter hersched
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lowryder88h
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- Massachusetts
transformer
transformer
See 450.3 and table 450.3(B) also 408.36 (D)
transformer
See 450.3 and table 450.3(B) also 408.36 (D)
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I think you may want to start reading the code at 240.21(C).
If your primary conductors have the correct overcurrent protection that also provides transformer primary protection - table 450.3(b) then you do not have a "tap" on the primary.
240.21(C) gives you a choice of tap lengths and requirements for your secondary conductors. It would appear that the 225kva transformer has adequate secondary protection by virtue of the 600 amp MCB at the panelboard. You just need to determine your secondary conductor length and make sure you conform to the applicable provisions found in 240.21(C).
If your primary conductors have the correct overcurrent protection that also provides transformer primary protection - table 450.3(b) then you do not have a "tap" on the primary.
240.21(C) gives you a choice of tap lengths and requirements for your secondary conductors. It would appear that the 225kva transformer has adequate secondary protection by virtue of the 600 amp MCB at the panelboard. You just need to determine your secondary conductor length and make sure you conform to the applicable provisions found in 240.21(C).
pete m. said:
If I'm reading this correctly it looks like I need to add overcurrent protection on the secondary.
240.21(C)(1) doesn't apply as I have a 3-phase delta-wye transformer
(2) doesn't apply as my secondary conductors are over 10' long.
(3) doesn't apply as it is not a industrial application
(4) doesn't apply as it is not outdoors
(5) doesn't apply as my primary and secondary conductors are over 25'
(6) doesn't apply for same reason as (5).
Am I correct?
To put it simply, you will need to have secondary conductor protection that will comply with one of the requirements found in 240.21(c) and that would be dependent on length of conductor. 240.21(C)(6) will, most likely, give you the greatest flexibility (keeping in mind that (C)(6) only deals with secondary conductor length). Unfortunately I don't know of any code provision that will allow secondary conductors at 70 feet in length for the installation that you have described.
Pete
Pete
Pierre C Belarge
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- Westchester County, New York
You should probably take a look at 408.36(D).
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