AC Motor SSR Ctrl û Voltage - Isolation Questions

[Haldir]

Three Questions:
1) In industrial controls in the U.S., when using 3-phase is it more common to use 208 or 220 VAC per delta phase?
2) If a few intermittently operating 1 hp motors are tapped off of one phase of a 3-phase system, is it a go idea to install a transformer between the motors and the main line of power for isolation purposes? Namely because the control systems (PLCs, etc.) are getting their power from a different phase, but they have a common line.
3) In the past we have used five SCR Drives to run the aforementioned motors. Since only one motor actually needs directional/speed control, is it bad design practice to use AC induction motors operated by SSR’s (Power-IO H Family SSR’s) for the four motors that do not need directional/speed control?

 

[NorthSlope]

1. If you're playing in the US of A use 208Y / 120. Not some odd-ball voltage rating.
2. Probably not necessary. Any motor small enough to be a single phase load should NOT affect the controls unless you'rew on an incredibly soft system.
3. YES it is bad practice. You're spending somebody's money where it doesn't have to be spent and SCR drives in use throw all sorts of harmonic junk back on the A-C system.

 

[Mike2468]

Yes, using expensive SCR based motor control is overkill for many applications. For these applications, a simple on/off SSR motor starter such as the Power-io unit is all that you need. We noticed a large decrease in electrical noise when we replaced the SCR motor control with the SSR motor starters. We also saw a decrease in electrical noise compared to a few mechanical starters that we replaced at the same time.