25 foot tap rule

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steve.s

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Rockton IL
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Hello I'm new to the forum here. I have a question regarding the 25 foot tap rule I have fused disconnect mounted right on my transformer on the line side do I also need on a disconnect on the load side go to my 208 panel that is over 25ft away?
Thanks for any input on this, let me know if you need any more info.

Regards Steve
 
See 240.21(C) for transformer secondary rules, but generally your panel main will suffice on a 25ft secondary.
 
Your transformer requires secondary overcurrent protection and so does the panel. If they're within 25' of each other a main OCPD in the panel will be sufficient as Augie stated. More than 25' and you'll need an OCPD within 25' of the transformer.
 
It's not technically a tap as you have described. Instead, this circuit classifies as transformer secondary conductors governed by 240.21(C). The rules to transformer secondaries are analogous to the rules for taps in 240.21(B), but it is a different classification.

The primary OCPD can only protect the secondary conductors indirectly, if it is a certain topology that qualifies. Anything with a WYE or centertap doesn't qualify. It has to do with whether or not there is a possibility that overcurrent could redistribute among the phases as it is carried across the transformer windings and go "unnoticed" by the primary OCPD. If overcurrents are guaranteed to line up winding-to-winding, the primary can indirectly protect the secondary. A hypothetical 200A OCPD at 480V would effectively act as a
 
steve.s said:
It is a WYE transformer so I do need the other disconnect.
Thank you for all the help
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If the transformer is protected on the line side by an OCPD rated no more than 125% of the primary current, the transformer secondary winding does not require overcurrent protection.

However, the transformer secondary conductors need protection per one of the rules in 240.21(C).
 
Just to prevent a misunderstanding in the future in the event you have something other than a wye secondary, 408.36 requires panels be protected by a main either integral with the panel or ahead of the panel.
 
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