# Sizing fused disc fot 112.5 transformer primary 240v delta



## rickeyrick (Jan 5, 2016)

Need information on sizing primary side of transformer 112.5 240 3 phase disconnect


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## WEGI (Dec 27, 2015)

Hey Rickeyrick,.
Take a look at the attached from Mike Holt, It'll lead you through step by step on the sizing of primary secondary conductors and any protection required along with a bunch of other info that you are going to need.
Hope this helps.

https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/TransformerInstallation~20020516.htm


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## rickeyrick (Jan 5, 2016)

So if I'm feeding 120/240 v 3 phase delta to the 112.5 primary whats the fuse size for the primary disconnect for the 112.5 transformer.


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## don_resqcapt19 (Jul 18, 2010)

rickeyrick said:


> So if I'm feeding 120/240 v 3 phase delta to the 112.5 primary whats the fuse size for the primary disconnect for the 112.5 transformer.


Find the primary current and apply the rules in Table 450.3(B).


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## WEGI (Dec 27, 2015)

The way the math seems to me is:
112500/(240 x 1.732)= 112500/415.68=270.64amps
270.64 x 125% + 338.30
Next size up = 350amps


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## WEGI (Dec 27, 2015)

Should read 270.64 amps X 125% =338.30 amps


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