SCCR Requirements for Power Distribution Blocks

[mikerick]

Can somebody tell me where exactly in NEC it says that you have to have a SCCR rating for power distribution blocks?
Per NEC 110.10, I understand that any ?circuit protective device? must have an SCCR rating higher than that which is available, but how about something that is not a ?circuit protective device?? For example, we have a wire way for a backboard, and in that wire way there are lugs or power distribution blocks. Do these lugs or distribution blocks have to have an SCCR higher than that available? Section 110.10 would not seem to apply, since this is not an OCPD. Similarly, how about an enclosure that has only a power distribution block in it; it is not an Industrial Control Panel by definitions, nor is it an OCPD; so does it require an SCCR rating higher than what is available?

 

[petersonra]

please read 110.10 again.

 

[jim dungar]

110.9 is about AIC and protective devices.
110.10 is about SCCR and other components.

 

[kwired]

AIC is "interrupt rating" and applies to switches, breakers, fuses, anything that is intended to interrupt current, and is a rating that typically means the device can safely interrupt current levels up to its rating without damaging the device, kind of sort of anyway

SCCR is a "withstand rating" and applies to other items not intended to interrupt current, but still need to be able to withstand a certain level of fault current. For instance the bus bars in a piece of equipment may need additional bracing above certain fault levels before they can have a higher SCCR rating.

Since power distribution blocks are not current interrupting type of device they only need to be able to withstand fault current not greater than whatever rating they may have.

 

[D!NNy]

I am not quite sure what NEC is referring to but please see my analysis and correct me if i am wrong.

Some people are recommending that if PD is having high SCCR and kAIC rating than available then anything down stream of it are not required to be rated for either kAIC or SCCR rating since all the PD or Non PD will be protected by upstream PD so that all the down stream components will never see that high fault current.

For instance see my oneline attached: if there is fault at location 2, all the PD inside the MCC are 65kAIC and 65kASC rated, downstream elements like distribution block and VFD's are not required to be rated for available fault current which is 25-30kASC.

But my concern is if the PD-'B' in MCC clears the available fault in 3 cycles the distribution block has to be rated to with stand for the fault current for 3 cycles at least if not it will melt before the PD 'B' clears the fault.

I understand why all the components in the MCC are rated for the kAIC or kASC: bcoz if there is fault at location 2 then you want to trip the breaker B not the A. so PD 'B' be rated for the available kAIC and kASC.


Thanks

 

[D!NNy]

Also most of the distribution blocks are rated for 14kASC or 10kASC (but this must be specified with the duration). or all the electrical equipment with kASC rating has to have time current characteristics curves (TCC's) similar to cables......?

See the attached coordination if the cable is capable of withstanding for the fault current for 0.1 seconds @73.894kASC and 4.99 seconds at 10.472kASC then why not for the distribution block which is more rigid than cable ( which holds the same cable).


Please suggest if i am thinking in the wrong way????
Thanks

 

[D!NNy]

here are attachments for SC calcs and coordination

 

[D!NNy]

sry for the resolution

 

[petersonra]

Equipment that does not interrupt fault currents is required to be able to withstand whatever the maximum level of fault current there is that the piece of equipment might see.

Equipment that does interrupt fault current (such as circuit breakers and fuses) has to be able to interrupt whatever maximum level of fault current it might see.

The farther downstream you go, typically the less fault current is available because of the extra impedance in the wiring.

 

[mikerick]

Equipment that does not interrupt fault currents is required to be able to withstand whatever the maximum level of fault current there is that the piece of equipment might see.

I don't see power distribution blocks specifically mentioned in NEC 110.10. So correct me if I am wrong, including the power distribution blocks in the requirements of 110.10 is based on interpretation of the code?

 

[don_resqcapt19]

I don't see power distribution blocks specifically mentioned in NEC 110.10. So correct me if I am wrong, including the power distribution blocks in the requirements of 110.10 is based on interpretation of the code?

The list in 110.10 is of the things that are used to protect the equipment. A power distribution block is equipment.