What is LV Switchgear/MCC/Panelboard etc.?

[SolarPrestige]

Hello everyone,

Might seem like a too basic question, but comes down to being new to doing arc-flash calculations. I am looking at IEEE 1584 and where it states that there are classes known as LV switchgear, LV MCCs and panelboards. Just concentrating on low voltage with this. This standard is North American oriented, and to me in the IEC part of the world, I work with mainly switchboards, MCCs, and distribution boards (DB). Switchgear to me is the parts that go into these types of panels systems to make an assembly. The question is, what does 1584 means by the terms it uses? This is to avoid making a mistake in selecting the wrong type.

Further, I also see ETAP bus selection is adding a thing called a switchrack into the mix and it also includes switchboard, but is this my type of switchboard? So, in ETAP I have Other/MCC/Switchgear/Switchboard/Switchrack/Panelboard/Cable Bus/Open Air to chose from for a bus type. I guess "Other" isn't a concern, and open air sounds like not in a panel, free mounted. Cable bus is presumably a bus-duct distributor. The others, I can't decide between them.

Any help appreciated.

Greg

 

[Gr8blu]

For 1584:
Switchgear: The make-or-break contacts (breakers, electrical disconnects, fuses, etc.) and the "cabinet" that surrounds these to prevent inadvertent access to the live points. These are usually part of a larger assembly - but not always.

MCC (acronym for "motor control center"): An assembly to control some or all electric motors in a central location. It consists of multiple enclosed sections having a common power bus and with each section containing a combination starter, which in turn consists of motor starter, fuses or circuit breaker, and power disconnect. A motor control center can also include push buttons, indicator lights, variable-frequency drives, programmable logic controllers, and metering equipment. It may be combined with the electrical service entrance for the building.

Distribution board: the point at which an incoming-power supply divides into separate circuits, each of which is controlled and protected by the fuses or switchgear of the switchboard.

Panel board: The (US) National Electrical Code defines a panelboard as a single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front (Article 1 00-Definitions).

Switchrack: Custom-engineered and custom-built with the entire assembly pre-wired to customer specifications, switchracks are designed for single-phase and three-phase low voltage power and can be outfitted with motor controls, circuit breakers, panelboards and other components.


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[xnuke]

Eaton has some tutorials on some of these items that might be helpful:
LV Panelboards, Switchboards, and Switchgear
MCCs are much like switchgear except the cubicles/cells/buckets contain motor control circuitry and equipment.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SolarPrestige]

Thanks for that link to the Eaton tutorial. It makes panelboards and switchgear a little easier to understand. Still classifications that are generally confusing to me, particularly what the difference is for a switchboard, but then switchboard is not used in IEEE-1584, so maybe it doesn't matter that I get what this is.

To me, the following is the equivalence for what I would call these types.

Panelboard = Distribution Board (DB)
Switchgear = Main Switchboard (MSB) since it appears at the head of an installation

MCC is the same usage for me as Gr8blu described (but note, not part of that Eaton tutorial).


Is is that "switchgear" contains cells or buckets for each outgoing circuit? The next level down, "switchboard" doesn't, so you might for example open a panel door and have many CB's or whatever in the same space? Then an MCC is like switchgear and requires each outgoing circuit to be in its own cell/bucket (thanks xnuke for that description).

A switchrack sounds like it can be a large assembly. It's a mixed bag of types and can be small or large?

 

[dpc]

For arc-flash calculations, the equipment type categories have an effect on the default enclosure size and the assumed arc gap - and of course whether this is in an enclosure or open air. You should select whichever category most closely matches the actual equipment regardless of the precise terminology. In most software packages, the gap and enclosure size can be modified for a specific bus as well.

 

[eeprom]

From the point of view of arc flash, the difference between these devices has to do with protective device isolation, and the physical size of the compartment. Both of these parameters have an effect on arc flash evaluation.

A panelboard is a bus that has breakers bolted to it. Panelboards often feed branch loads, but sometimes they supply feeders. Mostly branches. The breakers are all together in the same enclosure. If there is an arc on any breaker, all the breakers can easily be affected. Most importantly, the main breaker (usually in a panelboard) is also right there. So an arc on the downstream side of a load breaker can escalate to the high side of the main breaker. This is called flashover, and is in reference to PD isolation. A panelboard, if it has a main breaker, it is not isolated. The size of a panelboard is usually fairly shallow with a decent sized foot print. If an arc blast occurs in a panel, not all of the blast is necessarily directed at a person standing at the panel.

LV switchgear is a bus that has breakers fastened to it by sockets. Most of the time, LV switchgear is used for distribution of feeder circuits, not branch circuits. The breakers are all in separate enclosures (cubes). An arc occurring in one cube is very unlikely to propagate to another cube. In the case of LV switchgear, the PD is almost always considered isolated. Also, the LV cubes are usually fairly large, but they are deep. If an arc flash occurs in a cube, the blast will be directed towards anyone in front of the panel.

An MCC is just like LV switchgear except it's smaller and it's meant for branch circuits (mostly). Each circuit is in a small cube or "bucket". The main breaker is always in it's own bucket. In terms of PD isolation, an MCC main is usually considered isolated, but not always. I generally consider MCC mains as isolated. The buckets in an MCC are fairly small and deep. An arc flash occuring in any bucket is going to be directed directly in the face of the person working in the bucket.

I hope that helps.

 

[SolarPrestige]

More terminology that needs to be defined. A FEEDER will hook up another electrical panel? A BRANCH means connected to loads like lighting and power sockets, and motors if it originates at an MCC?
I understand feeder and use this the same way. A circuit that supplies a downstream electrical panel of any type really, but where further control and branching/feeding occurs. A branch circuit sounds like what I call a final circuit, it terminates at a load or loads.
What I can see in Etap, there is only one difference amongst Switchgear, Switchboard and Switchrack options. So I am thinking that these are included for people that like to use one of the terms over the other two, as otherwise they seem to be identical. The difference I see is that a Switchboard has Enclosure Isolation defaulting to OFF and the other two it is ON.
I must point out that I am working with IEEE 1584 : 2002. I don’t have the 2018 version and maybe there are differences that ETAP has included for working with that later version.

Anyway, I appreciate the advice you are all giving.

 

[davidbeach]

A feeder runs between OCPDs while a branch runs from an OCPD to a load.

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