Gary, Regarding whether the ground conductor should or should not be also derated along with the power conductors;-- it depends. I believe that the NEC derating rules apply to individual conductors or to two or more in a cable or bundle. I have always conservatively interpreted this to mean that if the green/yellow wire is bundled alongside other wires, then you apply the appropriate derating formula for how-ever many wires in the bundle. The NEC term for power conductors is "flexible cords and cables" (used externally from the equipment) whereas "fixture wire" is for wires (which also could carry power) internal to the equipment. Check out Table 400-5(A) for Allowable Ampacity for Flexible Cords and Cables. Also check out 400-5 for derating formula and explanation whether or not the third Neutral conductor can be considered a current-carrying conductor.
Tania Grant, [email protected] <mailto:[email protected]> Lucent Technologies, Communications Applications Group ---------- From: Gary McInturff [SMTP:[email protected]] Sent: Friday, March 10, 2000 3:37 PM To: '[email protected]'; '[email protected]' Subject: derating of conductors. Ran across a new wrinkle on this issue. The NEC in section page70-162 and table 310-17 does describe derating of ampacity capacity for conductors with temperature That is for normally current carrying conductors. - hot and neutral. How about for grounding and bonding conductors? I see section 250-95 basically says that the ground wire shall be the same size as the feed wires. It also says that if the feed wires are adjusted in diameter for voltage drop the equipment ground conductors shall be adjusted proportionally - but no reference (here at least) for temperature. I am wondering if the fact that the ground wire is not intended to be a normal current path but rather a short term 'emergency cutoff mechanism', if you will. As such it won't have current flowing along it long enough to be adversely affected by a higher than 30 degree ambient and therefore required to be derated for ambient. Make sense to anybody. Gary PS I also have a question for a non-member. He is wondering if anyone has a source for shielded power supply cords? I am also thinking that Europe hates those things because many countries many not have a grounded outlet, or that outlet is so far from earth ground that there is a significant impedance along that path. You can respond directly to [email protected] <mailto:[email protected]> ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
