Disconnects with Transformers

[jonny1982]

Does anyone know the code for, say I have a 277/480 panel and I need a 120/208 panel about 10 feet away from it. I would come out of the 277/480 panel, into a step down transformer and then into the 120/208 panel. The transformer, and both panels are all within 15 feet of each other. Do I need disconnects? If the 120/208 panel is main breaker and not main lug, could this count as the disconnect since it is right there? And could the breaker in the 277/480 panel count as the line disconnect?

Thanks

 

[arcsnsparks98]

I dont have a copy of the NEC in front of me but I am almost positive that you are allowed 10' on your transformer. That being the distance from the 480/277 panel with no disconnect.

 

[Smart $]

We could go with all the Code jargon but the end result is your premise is correct as long as you use appropriate equipment sizes and rating.

 

[jonny1982]

I dont have a copy of the NEC in front of me but I am almost positive that you are allowed 10' on your transformer. That being the distance from the 480/277 panel with no disconnect.

Do I need a disconnect for the load as well (120/208 panel)? Do you know where it says this in the code?

Thanks

 

[jonny1982]

We could go with all the Code jargon but the end result is your premise is correct as long as you use appropriate equipment sizes and rating.

So your saying no disconnects are required as long as I use the proper breakers?

Thanks

 

[arcsnsparks98]

Do I need a disconnect for the load as well (120/208 panel)? Do you know where it says this in the code?

Thanks

The breaker for the transformer is the disconnect for the 120/208 panel.

 

[jonny1982]

The breaker for the transformer is the disconnect for the 120/208 panel.

Thank-you. Do you know which article this is in the NEC?

thanks

 

[Smart $]

So your saying no disconnects are required as long as I use the proper breakers?

Thanks

Yep.

The 480/277V panel breaker serves as primary protection and the main breaker in the 208/120V panel serves as both the secondary and panelboard protection.

 

[jonny1982]

Yep.

The 480/277V panel breaker serves as primary protection and the main breaker in the 208/120V panel serves as both the secondary and panelboard protection.

Thanks! Do you know where this is listed in the NEC?

 

[Smart $]

Thanks! Do you know where this is listed in the NEC?

Just off the top of my head, Table 450.3 for transformer protection, 240.21(C) for transformer secondary conductors length, protection, other stip's..., and don't recall the exact section for panelboard protection, but it's in Article 408.

 

[arcsnsparks98]

The 10' i quoted earlier is for a tap with no OCP. 450.13 says disconnect within sight so you will be fine. As smart$ said, size your primary conductors and OCP off of table 430.3(B ).