Three phase and IBM

Tony Duell ard at p850ug1.demon.co.uk
Sat Mar 19 14:47:02 CDT 2011


> 
> Brian Knittel wrote:
>  > I need to know how to determine if the setup needs to be wye or delta.
> 
> Check the power plug or cable.  If the equipment has a neutral (not 
> ground!) lead, it needs wye.  Otherwise it needs delta.
                                ^^^^^^^^^^^^^^^^^^^^^^^^^
Isn't it more corret to say 'Otherwise the load is delta-connected and 
can be conneted ot a delta-connected supply. You could also conenct it to 
a star (Wye) supply of the appropriate phase to phase voltage by ignoring 
the neutral ocnnection of the supply'.

Most computer systems that need 3 phase mains are star (Wye) connected, 
simply because you can connect single-phase loads (of which there are 
likely to be many) from one phase conductor to neutral. 


> 
> That usually means that a four-lead power cable (three phases and 
> ground) for delta, and five-lead (three phases, neutral, and ground) for 
> wye.  However, some old equipment doesn't have a ground lead, in which 
> case it is three for delta, four for wye.
> 
> If the equipment contains any three-phase synchronous motors, you have 
> to get the phases in the right sequence; if they are reversed, the 
> motors run backwards.  That can affect blowers, and the spindle motors 
> of disk drives.

Murphy's law ensures that you will get this wrong the first time. If at 
all possible, make sure that whatever the motor is drivbing will not be 
damaged if it runs backwards 9remove drive belts, etc if necessary) and 
poer up briefly to see which way it turns. 

-tony



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