Using a busbar on motor ocpd's

[Jsantangelo]

I have 100-amp fuses in my systems main disconnect. These are connected to a PDB and from the PDB to a busbar connecting 5 OCPD's at 10-amps each. Can I use #6AWG conductors from the PDB to the busbar or do I need to add a 50-amp OPCD between the PDB and busbar?

 

[petersonra]

Is the bus bar listed as a tap conductor?

 

[Jsantangelo]

Yes.

 

[don_resqcapt19]

Is the bus bar listed as a tap conductor?

So conductors need a special listing to be used as a tap conductor? As long as the ampacity of the busbar complies with the requirements for tap conductor ampacity I see no issue.

 

[wwhitney]

As long as the ampacity of the busbar complies with the requirements for tap conductor ampacity I see no issue.

This would require the use of the 10' tap rule, yes? It permits the ampacity of the tap conductors (#6 AWG wire) to be "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors". So if the busbar is rated 50A and is in the equipment that contains the 5x 10A OCPD, then the tap conductors would only need to be rated 50A?

Where as the 25' tap rule requires that "the tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors." The busbar plus 5x 10A OCPD would not meet this description.

Cheers, Wayne

 

[don_resqcapt19]

This would require the use of the 10' tap rule, yes? It permits the ampacity of the tap conductors (#6 AWG wire) to be "Not less than the rating of the equipment containing an overcurrent device(s) supplied by the tap conductors". So if the busbar is rated 50A and is in the equipment that contains the 5x 10A OCPD, then the tap conductors would only need to be rated 50A?

Where as the 25' tap rule requires that "the tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors." The busbar plus 5x 10A OCPD would not meet this description.

Cheers, Wayne

Actually the busbar cannot be a tap conductor in this installation. I did not look at it correctly. The busbar needs to be rated at 100 amps or protected at its ampacity. The taps would be the conductors between the busbar and the 10 amp OCPDs.

 

[don_resqcapt19]

I have 100-amp fuses in my systems main disconnect. These are connected to a PDB and from the PDB to a busbar connecting 5 OCPD's at 10-amps each. Can I use #6AWG conductors from the PDB to the busbar or do I need to add a 50-amp OPCD between the PDB and busbar?

These conductors need to be protected at their ampacity. If the upstream OCPD is 100 amps, then 6 AWG is too small.

 

[wwhitney]

The busbar needs to be rated at 100 amps or protected at its ampacity.

Because presumably 408.36 applies? Seems like if the busbar/equipment is rated 50A, #6 AWG would comply with 240.21(B)(1)(1)(b), but you'd have a 408.36 violation.

That leaves the question of whether an MLO panelboard with a 100A rated busbar and containing only 5x 10A OCPD can be considered as "rated" at 50A for the purposes of complying with 240.21(B)(1)(1)(b).

If not, how is the plural option in "rating of the equipment containing an overcurrent device(s)" portion of 240.21(B)(1)(1)(b) ever applicable? What sort of equipment can contain two or more overcurrent devices without being subject to 408.36?

Cheers, Wayne

 

[don_resqcapt19]

Because presumably 408.36 applies? Seems like if the busbar/equipment is rated 50A, #6 AWG would comply with 240.21(B)(1)(1)(b), but you'd have a 408.36 violation.

That leaves the question of whether an MLO panelboard with a 100A rated busbar and containing only 5x 10A OCPD can be considered as "rated" at 50A for the purposes of complying with 240.21(B)(1)(1)(b).

If not, how is the plural option in "rating of the equipment containing an overcurrent device(s)" portion of 240.21(B)(1)(1)(b) ever applicable? What sort of equipment can contain two or more overcurrent devices without being subject to 408.36?

Cheers, Wayne

I am reading this as a 100 amp OCPD is the power source. I see this as the 100 amp circuit feeding a Power Distribution Block, a conductor from the PDB to the busbar, and then taps to the busbar or panel containing five 10 amp OCPDs. I have no idea of the rating of the PDB or the busbar or if the busbar is part of a panelboard.

 

[wwhitney]

I am reading this as . . .

That's not quite how I read the OP, so some clarification from them would be welcome.

BTW, for complying with 240.21(B)'s requirements that discuss how the tap conductors "terminate", would you consider a 1 to 1 splice (1 conductor in, 1 conductor out) that changes the conductor material (Al vs Cu), size, or even type (wire vs busbar) to be terminating of a conductor? Or could the tap conductors contain such splice, as long as the overall length and final termination comply with the requirements?

Cheers, Wayne

 

[don_resqcapt19]

That's not quite how I read the OP, so some clarification from them would be welcome.

BTW, for complying with 240.21(B)'s requirements that discuss how the tap conductors "terminate", would you consider a 1 to 1 splice (1 conductor in, 1 conductor out) that changes the conductor material (Al vs Cu), size, or even type (wire vs busbar) to be terminating of a conductor? Or could the tap conductors contain such splice, as long as the overall length and final termination comply with the requirements?

Cheers, Wayne

I see the tap conductor as being from the source to the OCPD. I see no issue with splices or conductor type changes as long as the ampacity of the lowest ampacity conductor and the total length complies with the tap rules.