Disconnects Line/Load from Top

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fifty60

Senior Member
Location
USA
Does NFPA 70 dictate that the line conductors must enter from the top terminals of the disconnect? I know NFPA 79 goes into detail about the physical placement of a disconnect inside of a sub panel, but my question is regarding where the line conductors can actually enter the disconnect. Can the line conductors be connected to the bottom terminals of the disconnect?
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Does NFPA 70 dictate that the line conductors must enter from the top terminals of the disconnect? I know NFPA 79 goes into detail about the physical placement of a disconnect inside of a sub panel, but my question is regarding where the line conductors can actually enter the disconnect. Can the line conductors be connected to the bottom terminals of the disconnect?

If I understand your question correctly, this is more of a listing and manufacturer's requirement issue than and NFPA 70 one. Listed disconnects today are constructed so that when they are in the off position there are no exposed live parts. If the line side conductors are hooked up to the bottom terminals of a top feed disconnect, then it would be a violation of the listing.
 

Carultch

Senior Member
Location
Massachusetts
Does NFPA 70 dictate that the line conductors must enter from the top terminals of the disconnect? I know NFPA 79 goes into detail about the physical placement of a disconnect inside of a sub panel, but my question is regarding where the line conductors can actually enter the disconnect. Can the line conductors be connected to the bottom terminals of the disconnect?

Operationally, there is no difference in the current flow for the line and load terminals.

But for safety, a listed disconnect is built to minimize the exposed live parts in the OFF position. The disconnect is built such that you de-energize the blade and the load terminals, and the inevitably live line terminals are hidden by a line shield.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
there is no requirement for where the conductors enter.

however, if the terminals on the device being used as a disconnecting means are labeled (such as line and load) then you have to respect those markings and connect accordingly.

MCCB are commonly made that are allowed to be reverse fed. They have no line/load markings on the terminals. MCCB that cannot be reverse fed have line and load markings on the respective terminals.
 

tx2step

Senior Member
And if it's a fused disconnect, if you feed power to the bottom (load) lugs, the fuses will be energized if you have to change a blown fuse...not good, especially if it's the service disconnect.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Several years ago we did a large store that had the line coming into the bottom of the panels and the load out of the top. The MCB and the rest of the 'guts' were installed 'upside down'. The line / load markings were printed both ways, right side up and up side down.

Hundreds of stores were built like this with no issues.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Several years ago we did a large store that had the line coming into the bottom of the panels and the load out of the top. The MCB and the rest of the 'guts' were installed 'upside down'. The line / load markings were printed both ways, right side up and up side down.

Hundreds of stores were built like this with no issues.

240.81 would appear to prohibit the practice of installing a CB upside down.
 

iwire

Moderator
Staff member
Location
Massachusetts
there is no requirement for where the conductors enter.

however, if the terminals on the device being used as a disconnecting means are labeled (such as line and load) then you have to respect those markings and connect accordingly.

MCCB are commonly made that are allowed to be reverse fed. They have no line/load markings on the terminals. MCCB that cannot be reverse fed have line and load markings on the respective terminals.

Well put.
 
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