240.4 Protection of Conductors

[kkeen]

All,
Article 240.4(B) appears to permit the use of an overcurrent device rated higher than the rated ampacity of the conductor as long as the listed conditions are met. For simplicity sake, I'm trying to determine if the NEC permits conductors properly derated to somewhere above 25 amps and somewhere below 30 amps to be used for an individual branch circuit supplying a single L6-30R receptacle. The installer has pulled eight current carrying conductors with temperature ratings higher (90C) than specified for terminations (60C) for ampacity adjustments and corrections (110.14(C)). The overcurrent protection device is a 30 amp molded case circuit breaker (non-adjustable).

Second part, doesn't this make the wire a fuse?

Any thoughts are appreciated.

 

[don_resqcapt19]

As long as the circuit feeds a single receptacle and the load is less then the derated ampacity of the conductor you can use the next larger standard size OCPD. As far as making it a fuse, that will not happen, the 30 amp OCPD will protect the wire. I am assuming that the conductors are #10.

 

[iwire]

The installer has pulled eight current carrying conductors with temperature ratings higher (90C) than specified for terminations (60C) for ampacity adjustments and corrections (110.14(C)).

Just curious why you figure 60 C terminations?

Most terminations are listed 75C even on circuits under 100 amps.

I agree with Don about the rest.

 

[Stubbie]

I'm curious.... what is the cord and plug load being served?

Stubbie

 

[kkeen]

Bob,

I haven't been able to confirm the termination rating of the receptacles yet, so am assuming 60 C as worst case (100.14(C)(a)(1)). I have a cut sheet (Bryant Tech-Spec L6-30R catalog number 70630R) but it doesn't specifically state the termination rating. It does mentions UL 498 and Federal Specification WC596 though. Is this a clue?

Thanks for your help, I really appreciate it.

 

[kkeen]

Stubbie,

The load being served is a data center rack.

KKeen