tap OCPD for panels

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electricalperson

Senior Member
Location
massachusetts
we are installing a 200 amp 120/208v panel. in the trough theres 500 mcm conductors that are protected by a 400 amp fused disconnect. the boss said we dont need any OCPD for the subpanel. the panel is a MLO. i cant find this anywhere in the code. i am sure the panel needs a breaker or at least a fused 200 amp disconnect. can anyone explain this to me?
 

charlie

Senior Member
Location
Indianapolis
. . . The boss said we don't need any OCPD for the subpanel. . .
240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (H). Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

This is a tap and the tap rules do apply. The underlining and large text are by me. Bottom line, you have to have a single overcurrent device except for a 10' tap and all of the rules are followed. :)
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
In addition to 240.21 noted by Charlie there is the following:
408.36 Overcurrent Protection.
In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
You have a few options, install 200 amp fuses in the disconnect, install a 200 OCPD for the 200 amp panel or use a panel rated for 400 amps with 500 kcmil conductors.
 

charlie

Senior Member
Location
Indianapolis
In addition to 240.21 . . .
That is interesting Gus. I was thinking about only the conductor protection and not equipment protection. That is the way a lot of people get into trouble with the 240.21(C) tap rules where a transformer is involved. They comply with 240.21 and fail to comply with the 450.3 requirements.
icon11.gif
:)
 

electricalperson

Senior Member
Location
massachusetts
i was checking out the tap rules of article 240 and the panelboard rules. i could not find anything that said a sub panel can be installed without a 200 amp for example OCPD. i personally believe a panel needs breakers or fuses. i cant really think of anything that wouldnt require breakers or fuses. i know the 10 foot tap rule doesnt require it but whatever it connects too might. this sound correct?
 

hurk27

Senior Member
i was checking out the tap rules of article 240 and the panelboard rules. i could not find anything that said a sub panel can be installed without a 200 amp for example OCPD. i personally believe a panel needs breakers or fuses. i cant really think of anything that wouldnt require breakers or fuses. i know the 10 foot tap rule doesnt require it but whatever it connects too might. this sound correct?

Power panel boards use to not have to have OCPD's protecting it if either didn't have a neutral to it, or if it did, and it had less then 10% of breakers 30 amp or less, something like that, but I'm not sure if this was changed in the 2008?
 

cripple

Senior Member
Section 240.21(B) has the requirements for installation of feed tap which is what you have described. This requirement does permit conductor (feeders) to be tapped without overcurrent protection at the tap.
240.21(B)(1) does permit the tap conductor to be terminated to MLO panel, if the tap conductors does not exceed 10 ft and the tap conductors comply with all of requirements.
(1) The ampacity of the tap conductors is
a. Not less than the combined calculated loads on the circuits supplied by the tap conductors, and
b. Not less than the rating of the device supplied by the tap conductors or not less than the rating of the overcurrent protective device at the termination of the tap conductors.
(2) The tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.
(3) Except at the point of connection to the feeder, the tap conductors are enclosed in a raceway, which shall extend from the tap to the enclosure of an enclosed switchboard, panelboard, or control devices, or to the back of an open switchboard.
(4) For field installations where the tap conductors leave the enclosure or vault in which the tap is made, the rating of the overcurrent device on the line side of the tap conductors shall not exceed 10 times the ampacity of the tap conductor.
The (2) taps not over 25 ft, (3)taps supplying a transformer [Primary Plus Secondary Not over 25 ft Long], (4) taps over 25 ft, and (5) outside taps of unlimited length are required the terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Almost every tap rule now requires the conductors to terminate in a single OCPD or if there are multiple devices the sum of the handle ratings cannot exceed the rating of the conductors. For the majority of intallations this means panelboards need a main device, somewhere upstream.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If referencing the 10ft tap rule there are conditions and one of the conditions does not require an overcurrent device. Ir referencing the 25ft tap rule, an overcurrent device will be required.

Pierre, Would you think that other than service panels, 408.36 (as reworded in '08) would apply with the 10ft tap rule also.
 

electricalperson

Senior Member
Location
massachusetts
240.21 B 1 (10 foot tap rule) has an FPN that points too 408.36

408.36 requires OCPD not greater than the rating of the panelboard. i believe when you tap even if the conductors are under 10 feet you need OCP when you feed a panel with the tap.

i believe this installation is a violation of the NEC. at least i done a good job at doing it
 
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