Circuit Breaker Sizing

[mpilliod]

I've been looking over the technical documentation for Yaskawa and I'm no less confused than when I began. They give guidelines for sizing breakers if you are only running a single drive. They then show a multiple drive configuration with single breakers for power and control but without a formula to arrive at the correct value. Their multiple drive configuration is similar to Centroid's. Their tech support then tells me that this should never be done and that they each need a breaker, even though their own documentation shows it.....

I have (4) 750 watt sigma 7 drives and I'm going to run them on single phase 240v. According to their docs, Current capacity is 8.7 amps main and 0.2 for the control. They then list 34 amps each for the main and control for inrush current. 68 amps.. Really?

Main circuit should hold for 5 sec at 3X capacity, and for 20ms at inrush. If I put one breaker on the main and one on the control for all 4 drives, what value would that be? Also is that a 1077, 508, or 489? Curve B, C, D???

Do you add them together, or do you assume that they are less demanding as they wont' all be driving at full bore simultaneously???

Also, the filter they recommend is a Japanese brand that isn't sold in the US. Has anyone used TDK brand? I'm looking at the RSEN series 20 amp.

Thanks!

[Centroid_Tech2]

Although you're right that you most likely won't be running all drives full power, the circuit breaker(s) should be sized to the potential sum of the connected loads. The use of a UL 489 D curve circuit breaker should take care of the inrush current. Something like the Eaton FAZ-D40-2-NA sold by AutomationDirect for the main motor power and the FAZ-D2-2-NA for the control power would work.

[CRM]

following for future reference...

[jhenise]

I had pretty much the same questions trying to size a breaker to run 3-4 Yaskawa 0.85 kW amplifiers.
The info here makes sense. The D-curve breakers seem to fit Yaskawa Specs...

nice reference on breaker curves
https://www.c3controls.com/wp-content/u ... Curves.pdf

Still is it better to protect 4 amplifiers with 4 breakers? obviously a single large breaker can deliver much more current to a given amplifier if they are in parallel off of that breaker but perhaps this is communally done. Its is annoying to have to use too many breakers for cost and wiring cabinet space / complexity.

A follow up question regarding multiple servo drives on a single contactor:
In the schematic shipped with my Centroid Oak board it shows three contractors uses to switch the power to three Yaskawa Servo amplifiers. The actuation circuit for the three contactors comes from the E-stop they are either all on or all off acting in parallel essentially, and the three legs of the three phase that they are switching are paralleled into the contactors... Why not just use one contractor to power up all three servo amplifiers?
it does look like they use some of the extra contacts on the three contractors to switch other things... perhaps that is why?

[cncsnw]

A separate breaker for each drive is nicer for both protection and for troubleshooting.

When space was critically limited, I have used one circuit breaker for multiple drives. Generally just adding the rated input currents (in your case, 8.7A per drive) has been sufficient, even with C-curve breakers. The 40A D-curve breaker would be more than enough.

The line power breaker should be UL489, because it is providing power to a "motor controller".

The logic power breaker can be UL1077 if you want, because it is only protecting control circuits.

With SigmaV and Sigma7 drives, I prefer to use a safety relay (e.g. Dold BH5928 series) controlling the CN8 inhibit circuit, rather than using one or more emergency stop contactors to interrupt line power. That is what the CN8 circuit is for. Repeatedly interrupting line power is hard on the rectifier components.