15 current carrying conductors

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Dang old king

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I have a conduit run that is 50' long that holds 15 current carrying conductors.
They are 5(five) three phase motor feeds to 5 refridgerant compressors.
The motors FLA is 3 amps Ea.
The conductors are all 14 THHN AWG on 15 amp HACR breakers
Do I have to derate the conductors ?
 
You do have to derate the conductors, but your derated value would be sufficient for your motor branch circuit size.
 
Dang old king said:
I have a conduit run that is 50' long that holds 15 current carrying conductors.
They are 5(five) three phase motor feeds to 5 refridgerant compressors.
The motors FLA is 3 amps Ea.
The conductors are all 14 THHN AWG on 15 amp HACR breakers
Do I have to derate the conductors ?
Click to expand...

Yes, but you should be fine even after derating for Table 310.15(B)(3)(a) at 50%.
 
infinity said:
Does someone have the calculation?
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I answered before calculating but was comfortable when I saw the FLA.
After posting, out of curiosity thinking he might eb good for the whole 15 amps, I did check and under the '08 Code, with THHN and no other adjustment factors.. 25 x .5 = 12.5
 
iwire said:
Isn't the FLA is meaningless, wouldn't the conductors have to be rated for the OCPD?

Or is it different for motors?
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Yes the value of a motor load is known and you size the conductor to that.
That's why you're allowed to round up to the next standard size ocp device
 
Dang old king said:
Yes the value of a motor load is known and you size the conductor to that.
That's why you're allowed to round up to the next standard size ocp device
Click to expand...

Can you point out the code that says this?


Becuse if I am wiring lighting which would be a fixed load the derated ampacity of the conductors still has to exceed the rating of the OCPD.
 
If each motor had it's conductor in in separate raceways you would size the conductor at 125% and determine the maximum OCPD size from the tables in Article 430. If you put all of the conductors in one raceway, the maximum OCPD for each motor would not change but the conductor ampacity would still need to meet the 125% after applying derating.
 
iwire said:
Becuse if I am wiring lighting which would be a fixed load the derated ampacity of the conductors still has to exceed the rating of the OCPD.
Click to expand...

I don't think that is correct. If you had twenty lighting circuits with 10A (continuous) load on each (40 ccc's), 210.19(A) requires that the conductors have an ampacity not less than the maximum load to be served. So 40 #14 THHN derated to 40% would be 25A*0.4=10A. So #14 THHN would be OK for the load.

240.4 requires that the conductors be protected at their ampacity, except that 240.4(B) allows the next standard size up. 15A would be the next standard size up c/b from 10A, so 15A c/b's can protect the #14 conductors with an ampacity of 10.
 
david luchini said:
I don't think that is correct. If you had twenty lighting circuits with 10A (continuous) load on each (40 ccc's), 210.19(A) requires that the conductors have an ampacity not less than the maximum load to be served. So 40 #14 THHN derated to 40% would be 25A*0.4=10A. So #14 THHN would be OK for the load.

240.4 requires that the conductors be protected at their ampacity, except that 240.4(B) allows the next standard size up. 15A would be the next standard size up c/b from 10A, so 15A c/b's can protect the #14 conductors with an ampacity of 10.
Click to expand...

In your example would a 10 amp continuous load need to add in the 25% factor or did you mean that the actual load on each circuit is 8 amps?
 
infinity said:
In your example would a 10 amp continuous load need to add in the 25% factor or did you mean that the actual load on each circuit is 8 amps?
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No, 10A actual load on each circuit. The 25% factor is used for determining the minimum conductor size before any adjustment factors. The final adjusted/corrected ampacity would only need to be 10A for the 10A load.
 
david luchini said:
I don't think that is correct. If you had twenty lighting circuits with 10A (continuous) load on each (40 ccc's), 210.19(A) requires that the conductors have an ampacity not less than the maximum load to be served. So 40 #14 THHN derated to 40% would be 25A*0.4=10A. So #14 THHN would be OK for the load.

240.4 requires that the conductors be protected at their ampacity, except that 240.4(B) allows the next standard size up. 15A would be the next standard size up c/b from 10A, so 15A c/b's can protect the #14 conductors with an ampacity of 10.
Click to expand...

OK, I worded my post poorly, let me put it another way.

I have lighting circuits with 8 amps of load each, my deraeted wire 12 AWG ampacity is 10 amps.

I cannot use a 20 amp breaker on that circuit even though the load is not above the rating of the conductor even though we know the load is 'fixed'.

This seems to be what the OP is suggesting with motors.
 
iwire said:
I have lighting circuits with 8 amps of load each, my deraeted wire 12 AWG ampacity is 10 amps.

I cannot use a 20 amp breaker on that circuit even though the load is not above the rating of the conductor even though we know the load is 'fixed'.

This seems to be what the OP is suggesting with motors.
Click to expand...

I agree. I didn't quite read that into the OP, but I was looking more at the next standard device up he posted in post #9. Perhaps that is what he meant.
 
My logic may be flawed....
but 430.22 says the conductor ampacity shall be 125% of the motor FLA (Table)
In the case of motors the overload protection is not dependent on the circuit GFSC device supplying the branch circuit.
240.21 says overcurrent protection shall be provided at the source but has an exception for motors.
With your lighting circuit the conductor is required to be protected at it's ampacity at the source.
In the motor circuit the conductor is protected by the overload device which could be at the motor itself. The conductor is protected from GFSC at it's source
 
augie47 said:
My logic may be flawed....
but 430.22 says the conductor ampacity shall be 125% of the motor FLA (Table)
In the case of motors the overload protection is not dependent on the circuit GFSC device supplying the branch circuit.
240.21 says overcurrent protection shall be provided at the source but has an exception for motors.
With your lighting circuit the conductor is required to be protected at it's ampacity at the source.
In the motor circuit the conductor is protected by the overload device which could be at the motor itself. The conductor is protected from GFSC at it's source
Click to expand...

Gus, I think you're logic is flawed regarding the lighting circuit. 240.4 requires conductors to be protected at their ampacity unless otherwise permitted in 240.4(A) thru (G). 240.4(B) would permit a lighting circuit conductor with an ampacity of 10 to be protected by a 15A c/b rather than at it's ampacity (assuming the load on the circuit was not more than 10A.)

240.4(G) permits motor circuit conductors to be protected at other than their ampacity (as directed in Art. 430.)

240.21 doesn't provide an exception for motor circuit conductors to have overcurrent protection at their source, except for motor tap conductors per 240.21(F).
 
I think 240.4(D) would cover most lighting circuits. Other than covered in 240.4(E) and (G), overcurrent for conductirs #18 thru # 10
is pretty well specified.
 
augie47 said:
I think 240.4(D) would cover most lighting circuits. Other than covered in 240.4(E) and (G), overcurrent for conductirs #18 thru # 10 is pretty well specified.
Click to expand...

Yes, 240.4(D) would cover most lighting circuits...of course 240.4(B) would apply as well.

#14 AWG lighting circuit conductors with an ampacity of 10 protected by a 15A c/b would meet the requirements of both 240.4(B) and 240.4(D).
 
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