3 phase induction motor amperage

Thread Starter

madmax0r

Joined Oct 1, 2013
4
Quick question,


Is the full load amperage on a 3 phase motor nameplate the "combined three phase amps" or the single phase, per phase current to determine wire size per phase?



Thanks in advance, Im new to this forum and wasn't sure where this topic would go so I put it in physics. Hopefully thats the right spot.



-BH
 

Thread Starter

madmax0r

Joined Oct 1, 2013
4
I find it very odd that that is rarely specified.. Is it normally only stated if it is 3 phase amps? Any derivative of the horsepower or kilowattage would be a 3 phase amperage... it seems like it should be specified either way..
 

MaxHeadRoom

Joined Jul 18, 2013
19,492
The plate usually specifies FLA (Full Load Amps), this is the value you would expect if you were to measure any phase at full load current.
The current in the three conductors occurs over 1 electrical rotation of 360°, 120° apart.
Max.
 

Thread Starter

madmax0r

Joined Oct 1, 2013
4
thanks again max, I suppose it all becomes obvious once you understand the mechanics behind the math well enough. some of the more complex things like calculating power factor lag still gets me a bit twisted up sometimes. The not knowing weather or not it is combined amperage or phase amperage has been a major point of confusion when I'm calculating something 3 phase.
 

t_n_k

Joined Mar 6, 2009
5,447
thanks again max, I suppose it all becomes obvious once you understand the mechanics behind the math well enough. some of the more complex things like calculating power factor lag still gets me a bit twisted up sometimes. The not knowing weather or not it is combined amperage or phase amperage has been a major point of confusion when I'm calculating something 3 phase.
There's no inconsistency in assigning the per phase current rating. The convention applies across all components in 3-phase system. Adding the currents over all three phases would be of little use anyway since as you indicate the per phase current rating directly impacts the selection of interconnecting cable conductor size.
 
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