single buss dual feed

[jcassity]

not attempting to sound stupid in any way here so I will just simply ask the question.

I can not find it in my 2011 NEC anywhere but I remember stumbling upon it a few years ago in older version but forgot to book mark it.

Where in the NEC is the discussion or language brought about stating you can not feed a single buss with two separate OCP's?

example,
dual 300A ocp's feeding a 600A buss.

these dual 300A ocp's are not ganged either.

thanks everyone,, I personally would never do this but now that I am faced with the actual real world, I should be able to cite the NEC code and cant.... still "word" searching my 2011 NEC now.

much appreciated!

scott
304 772 3411

 

[petersonra]

unless it is a listed factory assembly, you cannot put OCPD in parallel.

240.8

however, if they are being fed from two different sources they are not in parallel.

 

[augie47]

Fairly commonplace in some of our larger industrial facilities.
They actually feed 800 amp buss off (2) 800 amp breakers from different switchgear.
Overload is prevented by a computer link between the two switchgear. Fairly elaborate system.
(FWIW, each switchgear is fed by a different main distribution system...fairly fail-safe as far as assurance of available power)

 

[fmtjfw]

not attempting to sound stupid in any way here so I will just simply ask the question.

I can not find it in my 2011 NEC anywhere but I remember stumbling upon it a few years ago in older version but forgot to book mark it.

Where in the NEC is the discussion or language brought about stating you can not feed a single buss with two separate OCP's?

example,
dual 300A ocp's feeding a 600A buss.

these dual 300A ocp's are not ganged either.

thanks everyone,, I personally would never do this but now that I am faced with the actual real world, I should be able to cite the NEC code and cant.... still "word" searching my 2011 NEC now.

much appreciated!

scott
304 772 3411

On the other hand, ponder these code sections. 2011 & 2014:

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.

Exception No. 1: Individual protection shall not be required for a panelboard used as service equipment with multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panelboard assembly. Gets rid of old split bus design.

Exception No. 2: Individual protection shall not be required for a panelboard protected on its supply side by two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A panelboard constructed or wired under this exception shall not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker shall be considered as two or three overcurrent devices, respectively.
This apparently allows a 400A/320A service with two 200A CBs feed a 400A MLO panel with each feeder connected to the load side a CB and terminated on the panels main lugs.

Exception No. 3: For existing panelboards, individual protection shall not be required for a panelboard used as service equipment for an individual residential occupancy.