I have a 125VDC Panel (225A Main, 10 KAIC) being fed from a 125 VDC Battery Bank (60 cell, 280 Amp Hour). The Battery Bank is in a room adjacent to the Panel it is feeding. Conductor size is 2 - #4/0 conductor. Per NEC code article 480.5, I am required to have a fused disconnect switch readily accessible at the battery bank. I need to size the disconnect switch and fuse for the battery bank. I plan to use a cutler hammer Type DH Heavy duty safety switch (industrial application), 250 V DC, Fuse class H with 200 A fuse, 2 pole in a Nema 1 enclosure. Ampacity of the #4/0 cable is 230A at 75 deg C. Will the 200A fuse work for this application? The next standard size fuse is 400A but that won't protect the conductos. Any suggestions and comments are welcome. Thanks!!!
Fused Disconect for 125 VDC Battery Bank
- Thread starter pdemapan
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SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
I think the more important issue here may be the available short circuit current. It should be evaluated to be sure it does not exceed any of the interrupting ratings.
Is this for a UPS or control circuits ?? What is the expected load ?
Is this for a UPS or control circuits ?? What is the expected load ?
unfortunately, I don't know the expected load other than the main is 225 A with 10 KA interrupting capacity. As of now, i'm using the 225 A main and ampacity of the cable to size the disconnect. Should I really be sizing it based on the size of the battery? I'm confused and can't seem to find enough resources right now. Any response will be greatly appreciated.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
Do you know what the load is ?
UPS ?
Control Circuits ?
Solar Application ?
UPS ?
Control Circuits ?
Solar Application ?
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
My first thought too.
I'd wager a 280AH battery bank could eat a 10K breaker and come back for seconds.
The fuse will be an essential element in limiting the fault current to something sane.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
If you have already purchased the switch DC rated class K fuses looks like a better choice if you cannot determine that the SC amps is under 10K. They come in ratings between 50K to 200K and are supposed to be interchangable with class H.
- Location
- Illinois
- Occupation
- retired electrician
The next disconnect size is 400 amps, but 225, 250, 300 and 350 are standard fuse sizes and these fuses fit in the 400 amp disconnect.
Power Tech
Senior Member
- Location
- Lebec, California
Why don't you go with a 225A disconnect breaker.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Sounds like one could do welding with this supply.
ELA
Senior Member
- Occupation
- Electrical Test Engineer
Do you know the part number of the batteries being used?
If so you could look up what the short circuit current might be or calculate an approximation from the internal resistances and open circuit voltage of the cells.
This could tell you if the interrupting rating is a potential issue.
What is the maximum load you expect on the batteries? I would think you might want to tend towards a fuse with a lower amperage rating to help protect the battery bank from an excessive load.
If so you could look up what the short circuit current might be or calculate an approximation from the internal resistances and open circuit voltage of the cells.
This could tell you if the interrupting rating is a potential issue.
What is the maximum load you expect on the batteries? I would think you might want to tend towards a fuse with a lower amperage rating to help protect the battery bank from an excessive load.
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