Fuse Cutout Switch

Status
Not open for further replies.
Keri_WW

Keri_WW

Senior Member
I need help sizing a fuse cutout switch for a pole mounted transformer. The lines are 12.47 kV, the transformer is 7.2 kV to 277 single phase. I was planning on 15E, because I believe that is a pretty standard size. I saw in a catalog smaller sizes, so I just wanted to double check.

Thanks,
Keri :grin::grin:
 
Don't I need an E-rated fuse? The smallest I can find from Gould Shawmut is 5E and the smallest from LittelFuse is 10E, so I am not sure what the industry standard is...?
 
Keri_WW said:
Hah, forgive me for leaving that crucial piece of information out! 10kVA. Thanks for the chart jghrist. So if I read it correctly, I need a 2H?
Click to expand...
That's right.

I'm more familiar with utility applications of medium voltage cutouts, but the only E rated fuses used by utilities are S&C type E which are a power fuse and would be used if the available fault current was higher than the cutout rating (usually 10 kA Asym, but check with the cutout manufacturer). These are not used in a fused cutout but are cartridge type fuses. Cutouts use fuse links.
 
Keri_WW said:
Hah, forgive me for leaving that crucial piece of information out! 10kVA. Thanks for the chart jghrist. So if I read it correctly, I need a 2H?
Click to expand...
yes, or a 2 amp Kearney QA or Type 200

add: or X or D link
 
Last edited:
The utility I used to work for used either a 3H or a 2T fuse for a 10 kVA overhead transformer. I suspect there are several sizes that would work depending on how fast you want it to blow.
 
It also depends on whether you are protecting the transformer or the line. We protect the line and use a 15 T fuse for a 10 kVA transformer. if you want to have some fun, do the calculations on that fuse. A T rated fuse for a 100 ampere cutout will hold 150% indefinitely. Will a shorted transformer at the terminals take out the fuse? :)
 
I've attached my two examples. The first is going to a 500 kVA pad mount transformer (12.47 kV to 480 V). The second is the aforementioned 10 kVA transformer.
 
Status
Not open for further replies.
Top