# Fused disconnect or straight blade disconnect on line side of transformer



## namffuak (Dec 11, 2010)

I'm creating a field guide for some of our younger apprentices on step down transformer installation and it got me thinking about what style of disconnects we install ahead of the transformers. For example, let's say we have a 480/277V service feeding a facility and we need to install a new 208/120V panel board in a different part of a facility from the 480V MDP. It would make sense to set the transformer next to the new panel board to minimize the length of wire you would have to run off of the secondary. So we run our 480V line side into a disconnect which feeds the transformer and then into the OCPD in the new panel board. My question is this:
I've only every seen/installed fused disconnects on the primary side. Is this necessary? Could it be non-fused? What is common practice in your neck of the woods? Thanks for your feedback.


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## B-Nabs (Jun 4, 2014)

Canadian answer: as long as the OCPD protecting the conductors going to the primary satisfies the rules for transformer protection, an unfused disconnect would be perfectly fine.

Sent from my SM-G920W8 using Tapatalk


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## telsa (May 22, 2015)

That's a disconnect that would never get any use, a complete waste.

The style: feeder conductors protected by C/B in the 480Y277 panel -- which has provision for lock-out.

Once installed, it's rare for such a dry-type transformer to ever be shut down.

It's solid state, and over engineered, to boot. (NEMA standards)

And there is always a fused disconnect// C/B (tap rules) protecting the secondaries...


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## Pete m. (Nov 19, 2011)

What I typically see and have installed is exactly as telsa stated.

An overcurrent device at the MDP that is lock-able in accordance with 110.25 and the labeling required by 450.14.

Pete


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## ELECTRICK2 (Feb 21, 2015)

B-Nabs said:


> Canadian answer: as long as the OCPD protecting the conductors going to the primary satisfies the rules for transformer protection, an unfused disconnect would be perfectly fine.
> 
> Sent from my SM-G920W8 using Tapatalk


Is any disconnect required in Canada?
As long as you can lock out at the other end, what's the point of a disconnect, fused or not?


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## micromind (Aug 11, 2007)

telsa said:


> That's a disconnect that would never get any use, a complete waste.
> 
> The style: feeder conductors protected by C/B in the 480Y277 panel -- which has provision for lock-out.


Same here; once in a while an engineer will be stupid enough to spec a disconnect, but it's rare.


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## namffuak (Dec 11, 2010)

*Thanks guys*

I really appreciate your feedback. Very grateful for the transfer of knowledge. Good stuff.


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