MCC vs Drives/Control Enclosure

Hello!

What are your thoughts on a packaged MCC solution such as Allen-Bradley's Centerline series which can contain any combination of starter buckets, VFD's, PLC's, and HMI's versus just putting together a control and drives enlcosure?

Anything new I have done from the ground up in the last 10 years has always been in a standard floorstanding enclosure.

I have noticed in industries such as petro-chemical, power, and wastewater they are still putting in new complete MCC solutions.

Why?

TIA,

Greg

I would guess for arc flash rating.

There are plenty of issues on both sides of that coin, depending on whether you are looking at single free standing or wall mount drives vs multiple drives in one box, the size of the drives, the complexity of the machine, etc. etc.

The issue of being able to disconnect and isolate one VFD without having to shut them all down does play into the Arc Flash protection issue for sure and favors MCC format, as does individual LO/TO capability. Then because UL845 listing includes factory heat rise testing, buying in an MCC ensures that the drives meet those requirements.

But if for example the VFDs are on a machine that, if one motor must be shut down the entire machine must be shut down anyway, then that tends to favor a control panel concept because it is generally less expensive. Mounting the panel outdoors and/or if air conditioning is necessary, again favors a control panel concept.

Free standing or wall mount VFDs increases the cost of running feeder circuits/conduits to each drive as opposed to a common MCC bus to feed them, but are likely necessary above 200HP anyway (because of UL845 issues and heat rise).

There are lots of other issues as well, including SCCR labeling, etc. etc., so it really is something that is tackled on a case by case basis. No single answer will cover all potential issues.

It depends on what you are doing. If you are supplying a machine, then it generally comes with all starters and VFDs included in a panel on the machine or for installation close by.

For most non-OEM situations, the power distribution and control is better suited to MCCs. Significant process plants will use several MCCs in different locations. MCCs do a lot better job of managing power distribution and improving safety.

While you can put PLCs in the MCC, I rarely do it. A-B used to push DeviceNet MCCs and I have used a lot of them. Now they prefer Ethernet/IP MCCs and so do I. If the MCC is networked, there is very little need for a PLC rack in an MCC compartment. Even if I do end up using normal IO for an MCC (different brands), it will be a remote rack in an MCC compartment. The PLC processor will be somewhere more accessible.

Arc flash awareness has driven a lot of changes in the way we do things. Nowadays I am very reluctant to design a panel with 480vac and controls together. My PLC panels are usually separate and are completely 24vdc (no ppe required to work on them).