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Here's what I've observed so far:

All three contain circuit breakers. All three supply power to motors, although switchgear and PDC-fed motors are obviously higher-voltage, larger motors.

Switchgears are higher voltage than PDCs, and supply power to the transformers which feed the PDCs.

PDCs are higher voltage than MCCs, and supply power to MCCs. From what I've seen, PDC housings contain the transformer that feeds the PDC. (Is this always the case?)

Are there any other important differences/details that I've missed?

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  • \$\begingroup\$ Correction: All three can feed motors directly. \$\endgroup\$ – Taraz Mar 13 '14 at 22:12
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Kind of old and I apologize for resurrecting a "zombie thread", but I don't think the entire question was answered and I happen to know this very well.

"Switchgear" (SWG) and "Switchboards" (SWB) (two different things) are for power distribution, meaning they take in primary or secondary voltages at a site and distribute it to other equipment. In general, SwitchGEAR is HV (above 25kV) and MV (1kV-25kV) and involves equipment that contains very high energy "cells" that, if something goes wrong, will isolate and contain the damage to that one cell so as to not shut down an entire facility or area. SwitchBOARDS are typically down stream of SWG and are the distribution point for OTHER loads, such as transformers, Panelboards (PBD) and Motor Control Centers (MCC). There are different ANSI and UL standards for SWG vs SWB, mainly because the intent is for SWG to "hold in" and take the abuse of a fault for a relatively long time while waiting for some other device further down stream (SWB, PBD or MCC) to act on it to clear the fault. So the SWG is the "last line of defense", but would have the widest reaching effects if it is the thing that must clear the fault.

Motor Control Centers are basically the same as SWB construction (they grew out of that industry in the 1950s), but are generally used to provide power to motors, not general loads. They are different from SWBs in that you have 'cells" (called "buckets") that contain the control equipment so that in theory, you can disconnect power from one bucket and allow the rest of the machinery powered by that MCC to continue to run. You cannot do that with a typical SWB, if you had to remove one breaker or switch, you have to kill power to the entire SWB. There are exceptions to this rule, but conceptually, this is what it boils down to.

A Power Distribution Center (PDC) is basically just the name for a factory-built structure, a portable building, designed to HOUSE equipment such as SWG, SWBs, Transformers, PBDs, MCCs and/or other controls or instrumentation, in any combination or configuration the end user desires. There is no standard definition of what goes INTO a PDC, but there are several standards as to how they are built, depending on where they are going and what they are housing. Some must be built to withstand explosions, such as in a refinery hazardous area, some must be able to withstand extremes of weather such as high winds, crushing snow, marine salt spray etc.

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This is barely an answer but more of a help to understand what the op means in some of his words - I'm English and these terms are probably a little different over here.

"Switchgear"? I think you may mean switchboard as in the following: -

enter image description here

Hopefully this may account for "power distribution centre" - I'm assuming you might mean Panelboard or do you mean a PDC at a generating plant? Clearly MDC is motor distribution centre. This document furnished the drawing.

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  • \$\begingroup\$ MCCs are usually 600V or 480V. PDCs have a higher voltage coming in to the transformer (e.g. 13.8 kV or 4.16 kV). Switchgears dstribute the higher voltage to the PDC transformers (and lower voltage switchgears, if applicable). It looks like a switchboard is not the same as a switchgear (electrical-engineering-portal.com/download-center/…). \$\endgroup\$ – Taraz Mar 13 '14 at 23:03
  • \$\begingroup\$ @user228546 I'm just trying to help you improve your question dude. Like I said my answer isn't really an answer. \$\endgroup\$ – Andy aka Mar 13 '14 at 23:40
  • \$\begingroup\$ Thanks for trying. Sorry, I didn't mean to be snarky. \$\endgroup\$ – Taraz Mar 14 '14 at 0:58
  • \$\begingroup\$ no probs dude. Consider amending your question to make it more accessible - that's all I'm hinting at. I'll prob delete my ramblings tomorrow so don't rely on them ! \$\endgroup\$ – Andy aka Mar 14 '14 at 1:02
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I haven't heard of a "PDC" in my part of the world.

In my experience, "switchboard" refers to a board which contains circuit breakers only, with no motor contactors.

"MCC" - motor control centre - refers to a board which includes motor contactors.

Note the distinction between circuit breakers and contactors.

  • Circuit breakers are only expected to operate when isolating a circuit/performing manual switching, say a few times a day, or clearing a fault in anger, say once a year.
  • Contactors are expected to operate frequently, multiple times per hour, when starting or stopping a motor.

Hence, an MCC is a board that can be used to control motors (frequent starting and stopping) using contactors.

A switchboard isn't intended for motor control, only power reticulation. (If a switchboard feeds a motor 'directly', you will find there is a contactor somewhere else that is doing the control.)

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I think @Andy-aka has a very good answer, I just wanted to follow up on this.

(note this mainly applies to industrial scale power distribution, not to residential)

Typically a switchboard is the primary power distribution device in a building. This feeds larger loads directly, as well as feeding panel boards and motor controllers which can further distribute power. Switchboards are typically larger and accessible from both sides (front and back) while panel boards are only supposed to be accessible from the front.

so in summary, we have 3 types of panels:

switchboard - Higher voltage and current, with more space inside and accessible from both front and back

panelboard (AKA loadcenter) - these are fed from a switchboard and distribute electricity to end user loads. typically lower current and voltage. Only accessible from front. prior to NEC 2008, there was a distinction between power panel boards and lighting and appliance panel boards (namely the 42 circuit rule among others) but now these just differ primarily in shape. This is the "circuit breaker panel" that is installed in most residential homes.

motor control center - is partially a panelboard, but also contains contactors and VFDs to drive motors. May also contain some control circuitry to control the motors as well.

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