LOAD DIVERSITY REDCUE BREAKER SIZE

[ohmhead]

Well heres my question if you have more than three conductors in a raceway lets say the current in each conductor is 3 amps there connected to 20 amp breakers in panel . How does this effect size of the breaker at 20 amps with a low demand of 3 amps per conductor would you use a smaller breaker or would load diversity the demand factor of the load keep the breaker at 20 amps .

explain load diversity lets say at 50 percent of the breaker size is there a rule to reduce the size of the breaker .

Meaning if the conductors pulled less current then could you install more conductors in a raceway and reduce breaker size to protect them .

 

[petersonra]

Well heres my question if you have more than three conductors in a raceway lets say the current in each conductor is 3 amps there connected to 20 amp breakers in panel . How does this effect size of the breaker at 20 amps with a low demand of 3 amps per conductor would you use a smaller breaker or would load diversity the demand factor of the load keep the breaker at 20 amps .

explain load diversity lets say at 50 percent of the breaker size is there a rule to reduce the size of the breaker .

Meaning if the conductors pulled less current then could you install more conductors in a raceway and reduce breaker size to protect them .

Its possible that reducing the size of the breaker might help you with the derating issue. The breaker is there to protect the conductors. It does not care about the load.

I don't think there is any diversity or demand factor involved in counting up the number of current carrying conductors.

 

[ohmhead]

Question a protective overcurrent device a breaker or breakers all lighting branch circuits loaded at 3 amps if i had 10 circuits in one conduit and each circuit was attached to 10 single 120v/ 20 amp breakers . How would you calculate load diversity or would you ? Is it safe to have these each on 20 amp breakers lets say they were continuous duty 3 hours on. How do you calculate the ambient temp of these conductors we know the insulation is good for the breaker size of 20 amps . But by installing these in one conduit and all are at 3 amps fully loaded . Would this exceed the temp rating of the single conductor of the group would it effect the breaker trip time ?
What would be a NEC code issue with this install ?

 

[fmtjfw]

In the general case I do not believe load diversity can be used (over and above what is already built into the tables and rules).

Note that normally 9 current carrying conductors 12AWG THHN insulation in a single raceway can be protected by 20A OCPDs (and 20 CCC 12AWG THHN by 15A OCPDs).

With 120V non multiwire circuits that gives you 4 hots each 20A or 10 hots each 15A.
With 120/240V multiwire circuits that gives you 8 hots each 20A or 20 hots each 15A.
With 120/208V multiwire circuits that gives you 9 hots each 20A or 20 hots each 15A.

Under engineering supervision you can use Table B.310.15(B)(2)(11) and the accompanying equations. Doing this under engineering supervision would probably cost more that the larger wire or additional raceways. With 50% diversity, that could get you up to 85 CCC 12AWG THHN with 20A OCPDs.

 

[ActionDave]

Question a protective overcurrent device a breaker or breakers all lighting branch circuits loaded at 3 amps if i had 10 circuits in one conduit and each circuit was attached to 10 single 120v/ 20 amp breakers . How would you calculate load diversity or would you ? Is it safe to have these each on 20 amp breakers lets say they were continuous duty 3 hours on. How do you calculate the ambient temp of these conductors we know the insulation is good for the breaker size of 20 amps . But by installing these in one conduit and all are at 3 amps fully loaded . Would this exceed the temp rating of the single conductor of the group would it effect the breaker trip time ?
What would be a NEC code issue with this install ?

The issue you have is not the size of the breaker, but the size of the wire you are attaching to it.

The fact that the the load is only 3A on each circuit matters not. The only thing that matters is the number of current carrying conductors in the conduit. Ten 20A circuits in one pipe means one thing, derate by fifty percent.