We need to run power to a jib crane where the hoist motor is 480v. We only have 208v in the building. We are trying to giving the GC a quote for a step up transformer. The crane suppler is telling us to size everything for 30amps at 480v. The electrical supplier is telling us that we need to supply a transformer good enough to cover the Lock Rotor Amps on the hoist motor or we will have a severe voltage drop upon start up. The FLA is 12 amps. How do I find the LRA?
Oh, and the cut sheet is for a European made motor. I can't read it! lol
Thanks
Fortunately the cut sheet is in English even if the format is not what you are used to. Translate "," to "." in numbers though.
SWAGs:
1. The specified fuse (time delay) for 480V operation is 20Amps. That indicates to me that although the operating current (FLA, also close to I
A on this sheet) will be less than 20A the starting current will be much higher than 20A.
2. The starting current and the LRA will be in the same ballpark, although with a different duration depending on how heavily loaded the motor is at startup.
3 In the table row for DCPro-25 (two pole) at 480 volts, the "normal" current, I
N, is shown as 8.7 Amps. The heading of the last table tells us that the starting current is symbolized by I
A. Then going back to the first table, we find that the ratio of I
A to I
N is 4.95.
Therefore, I
A is equal to 8.7 times 4.95, or 43A. Enough higher than 30 to cause me mild concern.