Confused about the term "(Exposed) Live part"

[zemingduan]

I'm so confused about the term "live part or the exposed live part" when determine working space and distance in according to NEC 2017 110.26(A)(1), 110.31 & 110.34(A).

I see the definition of live and exposed live part in NEC, but I am still confused. What is the insight of which equipment/conductors is considered as "live or exposed live part" ?

If a disconnect switch is supplied from a feeder rather a service conductors, which means you can deenergize this switch through supply side disconnect, is it still considered as live part? For example, a 100A elevator non-fused disconnect switch next to the elevator motor supplied from a fused disconnect switch in electrical room, is the non-fused disconnect switch live or exposed live part?

Is a service rated meter bank with 800A MCB supplied from service conductors live or exposed live part?

Is a 2.4 KV outdoor safety switch with handle to shut it off in school campus supplied from MV feeder from a main switchgear considered as live part or exposed live part?

Is an enclosed transformer(not utility transformer) considered as live or exposed live part? I think I doesn't requires testing or inspection when it is energized. Thus it's not a live part.

Very appreciate you guys helping me to understand this.

 

[don_resqcapt19]

Other than the transformer, in my opinion, all of those items are covered by the workspace rules in 110.26 and 110.34. Some will even include the transformer.

 

[petersonra]

IMO it is an exposed and energized part if it has power connected to it and there is any way, regardless of how convoluted, that a part of a person's body could become energized. If it is guarded so you can't get at it (like it is inside of a box), it might be energized but not exposed.

I mostly agree with Don that all the items listed require work space. My personal opinion is the transformer does too, but a lot of electricians find it convenient to claim otherwise.

 

[Dell3c]

Transformers also, YES..

 

[Carultch]

Think of exposed as meaning "expose-able", such that even equipment that is normally covered by a dead front, can have exposed live parts during maintenance. If there is any need to work on it energized, the rules of 110.26 and 110.34 apply. Even measuring your voltages is energized work. You may want to plan more space than 110.34 requires, to anticipate space for the "hot stick" to service the equipment. I.e. a fiberglass rod that is used for keeping your distance from medium voltage equipment, while working on it energized.

110.34 is the medium voltage counterpart to 110.26
110.31 is for parts behind a fence that are permanently exposed, and is for protecting the general public from accidental contact. By contrast, 110.34 is for medium voltage equipment that is normally behind a dead front, and the space required is for the maintenance personnel to do their work. Where 110.34 applies, but 110.31 does not apply, a metal fence would be considered Condition 2.

 

[zemingduan]

Think of exposed as meaning "expose-able", such that even equipment that is normally covered by a dead front, can have exposed live parts during maintenance. If there is any need to work on it energized, the rules of 110.26 and 110.34 apply. Even measuring your voltages is energized work. You may want to plan more space than 110.34 requires, to anticipate space for the "hot stick" to service the equipment. I.e. a fiberglass rod that is used for keeping your distance from medium voltage equipment, while working on it energized.

110.34 is the medium voltage counterpart to 110.26
110.31 is for parts behind a fence that are permanently exposed, and is for protecting the general public from accidental contact. By contrast, 110.34 is for medium voltage equipment that is normally behind a dead front, and the space required is for the maintenance personnel to do their work. Where 110.34 applies, but 110.31 does not apply, a metal fence would be considered Condition 2.

Carultch thanks for the explanations. It helps a lot. From my understanding, an outdoor 2.4KV enclosed switchgear equipment, like the equipment on the wall in picture below, doesn't need to be 10' away from the fence. I think it is enclosed equipment as described in 110.31(D). Is it correct? You can see from the picture, the right most switch on the wall is definitely less than 10' from the fence.

 

[don_resqcapt19]

Carultch thanks for the explanations. It helps a lot. From my understanding, an outdoor 2.4KV enclosed switchgear equipment, like the equipment on the wall in picture below, doesn't need to be 10' away from the fence. I think it is enclosed equipment as described in 110.31(D). Is it correct? You can see from the picture, the right most switch on the wall is definitely less than 10' from the fence.
View attachment 2556686

The equipment in that picture only needs to comply with 110.34.

110.31 applies where the enclosure for the live parts is the vault, room or fence. Once you are inside that "enclosure" you can reach out and touch the live parts without having to open any type of enclosure.

If this was over 1000 volts, it would be an example of where 110.31 applies. It would also apply in applications that are similar to utility substations.

 

[steve66]

Carultch thanks for the explanations. It helps a lot. From my understanding, an outdoor 2.4KV enclosed switchgear equipment, like the equipment on the wall in picture below, doesn't need to be 10' away from the fence. I think it is enclosed equipment as described in 110.31(D). Is it correct? You can see from the picture, the right most switch on the wall is definitely less than 10' from the fence.
View attachment 2556686

The working clearance depth is usually measured from the front of the equipment, which is normally where you find a removable cover, or a door.

The sides of those switches are part of the box that the switch is in. They aren't removable, so the working clearance only applies to someone standing in front of the switch. So for a 480V switch, they would need a 30" wide space in front of the switch, 3 to 4 ' deep depending on what is behind that person (insulated wall, grounded wall, or other live equipment).

The side of the switch could be right against a wall.

And I'm not sure where 10' came from, unless those switches are > 600V.

 

[zemingduan]

The working clearance depth is usually measured from the front of the equipment, which is normally where you find a removable cover, or a door.

The sides of those switches are part of the box that the switch is in. They aren't removable, so the working clearance only applies to someone standing in front of the switch. So for a 480V switch, they would need a 30" wide space in front of the switch, 3 to 4 ' deep depending on what is behind that person (insulated wall, grounded wall, or other live equipment).

The side of the switch could be right against a wall.

And I'm not sure where 10' came from, unless those switches are > 600V.

Steve the 10' came from 2017 NEC 110.31 paragraph 2 and the table 110.31 for volt between 1001-13799V. I think Don answer the questions perfectly. When you do this sort of electrical installation like Don states, the fence shall be 10' away from the live parts. Table 110.31 doesn't apply to the enclosed switches in my picture.

110.31 applies where the enclosure for the live parts is the vault, room or fence. Once you are inside that "enclosure" you can reach out and touch the live parts without having to open any type of enclosure.

The working clearance you states are described in NEC 110.34(for equipment >1000V) & 110.26(A)(1) (for equipment <=1000V). It applies to those switches.