Inspector wants to disallow this interpretation.

[DonaldSparkyDog]

I was sizing a feeder to a 170 ton chiller based on the nameplate data of the chiller. MCA=343, I sized 2x2"w/3ea 2/0 thwn, MOCPD=450amps, I sized a 450amp breaker. The inspector says the feeder size must be large enough to be protected by the breaker. I think this is a motor feeder and the breaker can be sized larger than the wire ampacity but can not locate those verbs in the NEC.

 

[Dennis Alwon]

Look at 440.22-- not sure if a chiller falls under 440. otherwise 430.52

 

[infinity]

The MCA is used to size the conductors. The OCPD can be larger than the conductor ampacity.

 

[OTT2]

Looks to me as if you are following the labeling in the chiller 110.3(B). IMHO you are in compliance with the NEC.

 

[DonaldSparkyDog]

Yes

Yes

Yes the MCA is Min Circuit Ampacity and MOCPD is Max Overcurrent Protection Device, but the inspector, AKA AHJ, is stating that the NEC does not specifically allow in words anywhere a conductor is allowed to be connected to a breaker or other ocpd that is larger than the calculated ampacity of that conductor.

 

[DonaldSparkyDog]

His statement is that if a feeder is connected to x size ocpd then size the wire to that or the wire could overheat. I have never had an inspector as AR as this guy, he will allow it if I can find the verbage allowing it, not infering it.

 

[iwire]

AHJ, is stating that the NEC does not specifically allow in words anywhere a conductor is allowed to be connected to a breaker or other ocpd that is larger than the calculated ampacity of that conductor.

If that is what the inspector said that is a shame as there are numerous sections of the NEC that allow it.

In your case I would point out 240.4(G).

 

[OTT2]

Yes the MCA is Min Circuit Ampacity and MOCPD is Max Overcurrent Protection Device, but the inspector, AKA AHJ, is stating that the NEC does not specifically allow in words anywhere a conductor is allowed to be connected to a breaker or other ocpd that is larger than the calculated ampacity of that conductor.

Table 430.52 would be a perfect example where OCP can far exceed conductor ampacity.

 

[jim dungar]

Briefly,
240.4(G) allows for 'special' conductor protection.
440.22(A) allows for protection at 175 to 225% of equipment current.
440.35 says to size conductors based on the equipment "minimum circuit ampacity"(MCA).

 

[DonaldSparkyDog]

All good answers.

All good answers.

Thanks for all the good answers but he sticks to article 310-15(B) 1-6 and says that is the only allowable ampacity for conductors and in that article there is no reference to ocpd larger than the ampacity of the conductor. All the other mentioned articles only indicate the min size of conductor not the ocpd of that conductor except GF or Short Circuit protection, not running protection. I know, the heater elements and or CT's with relays would provide for that protection, but it's like pulling eye teeth with some people they have got to see it in written form before it can be tru.

 

[infinity]

Thanks for all the good answers but he sticks to article 310-15(B) 1-6 and says that is the only allowable ampacity for conductors and in that article there is no reference to ocpd larger than the ampacity of the conductor. All the other mentioned articles only indicate the min size of conductor not the ocpd of that conductor except GF or Short Circuit protection, not running protection. I know, the heater elements and or CT's with relays would provide for that protection, but it's like pulling eye teeth with some people they have got to see it in written form before it can be tru.

Sometimes inspectors need to spend some time in a refresher course. I'd hate to see this guy design a circuit with an instantaneous trip circuit breaker.

 

[david luchini]

Thanks for all the good answers but he sticks to article 310-15(B) 1-6 and says that is the only allowable ampacity for conductors and in that article there is no reference to ocpd larger than the ampacity of the conductor.

There is nothing in 310-15(B) 1-6 that has a reference to ocpd smaller than the ampacity of the conductors or equal to the ampacity of the conductors, either. 310-15(B) doesn't have anything to do with overcurrent protection of conductors. As others have pointed out, that is in article 240.

 

[jim dungar]

Thanks for all the good answers but he sticks to article 310-15(B) 1-6 and says that is the only allowable ampacity for conductors and in that article there is no reference to ocpd larger than the ampacity of the conductor. All the other mentioned articles only indicate the min size of conductor not the ocpd of that conductor except GF or Short Circuit protection, not running protection. I know, the heater elements and or CT's with relays would provide for that protection, but it's like pulling eye teeth with some people they have got to see it in written form before it can be tru.

Someone does not know how to read the NEC.
310-15(B) says absolutely nothing about protecting conductors, it is only about determining ampacity. Read the scope in 310.1, it does not mention protection.
Article 240 is about the protection of conductors.

 

[Rockyd]

At the bottom of the ampacity charts is a note directing to 240.4(D). Does this inspector realize he is not allowed to "selective" code enforcement? Does he get the fact that we are concerned at this point, this is about ground fault, and short circuit protection? After much observation over the years, I can tell you that Barney Fife lives in numerous townes and cities around America!

 

[DonaldSparkyDog]

Going all in.

Going all in.

Looks like it's time to go all in and contact the Chief Electrical Inspector on this one. I'll let you know what happens when I P.O. this inspector.

 

[mikeames]

Thanks for all the good answers but he sticks to article 310-15(B) 1-6 and says that is the only allowable ampacity for conductors and in that article there is no reference to ocpd larger than the ampacity of the conductor.

So this inspector is picking and choosing what parts of the code he wants to follow an dturning a blind eye to the other parts. Does he not realize that other parts of the code trump or are to be used in conjuntion with various sections?

 

[stew]

First of all 240. 4 directs you to the specific code section for air conditioning equipment which is 440. 440.4 (B) says the manufacture must list on the nameplate the "minimum supply circuit conductor ampacity". This is of course what tells us what wire size we need. 310.16 just tells us how much current a specific conductor can take and has no bearing whatsoever in making the ampacity determination. 440.6 say that the required ampacity of the conductors Shall be determined according to 440.6(A) and 440. 6(B). this is where they show you how the MCA is determined and just like any othe mutimotor driven device, which this is, its 125% of the largest motor and the sum of the nameplates of all the others, in this instance the fan motor(s). You might ask him why the manufacturer shows the MCA if it isnt going to be used for anything and maybe he can also show you the formula thatt he thinks is in 310.16 to develop the MCA? My bet is you will need to go at least one step higher or get someone in his office that is more familiar with HVAC than he is.

 

[stew]

and I missed stating article 430 35 which one of the earlier posters did as well which tells us what to do for this equipment. I belive you meant 2 ea 2/0 cu or were you talking al?

 

[infinity]

and I missed stating article 430 35 which one of the earlier posters did as well which tells us what to do for this equipment. I belive you meant 2 ea 2/0 cu or were you talking al?

I would guess that he meant copper, 175 amps each @ 75? C. (175 * 2 = 350 amps)

 

[DonaldSparkyDog]

Copper

Copper

Yes it would be CU wire at 75deg C Thwn 480 volt 3ph 3w 75feet from Main Switchgear.