UPS Wire Size

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pacificjohn

New member
Hello,

Wire size selection for 50 KVA 40 KW 3 Phase UPS.
and safety consierations
System:
1. UPS input is PF .95
2. Full Double Conversion System.
2.1 input is a full-wave delta DC Rectifer.
3. Worst case continious load is 125 Amps per leg.
4. PDP is EMT through concrete floor, popup next to rear of UPS
4.1 Rear of UPS is walk way with 3 ft clearence to PDP panels.
5. Battery Cabinet is ajacent to UPS
5.1 Battery Backup is for 30 min., DC current is 195 amps, 200 amp shunt trip circuit breaker, wired to UPS EPO

A. Plan is to use pull box on rear floor of UPS, using termainal block inside for lug connection, using multi strand SOOW or Single wires. Less than 30' to PDP for AC in AC out.
A.1 What size of pull box and wire size does code require for AC in AC out DC in out.
B. Is EPO required near exit for system shut down?
Thanks
John
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
480V or 208V???

The manufactuer usually has a table that lists the wire sizes for inputs and outputs. They usually wind up being a lot larger than one would initially think. I think they take load current + charging current into account, and probably overload capacity of the UPS, and maybe even derating the wire for harmonics.

Anyhow, I would try and find a manufacturers table for sizing the wire.
 

tkb

Senior Member
Location
MA
Don't forget about the battery recharge on the input.
That is why the manufacturer recomends a larger input than bypass.
 

brian john

Senior Member
Location
Leesburg, VA
To sum it up, an often overlooked aspect of installing UPS's systems is the installation manual, and it seem's most electrician's ignore this valuable guide.
 

adelle

Member
What are you using SOOW wire for? I believe this is cord stock and would not be listed for internal wiring. MTW is used internally or THHN in conduit between cabinets.

Also check the voltage rating of the battery cables. For example the APC Silcon series requires 1kv rated wire. The battery is wired +/-384v with a center tap ground so you have 768 volts between the + & - leads in the same conduit. Standard 600v THHN is no good here.

I concur, READ THE INSTALLATION MANUAL. Also, is this job speced by a PE? Many juristictions won't permit a hardwired 3 phase class UPS without PE sealed plans.
 
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