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jkosan

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do I have to adjust size of current carrying conductors located in same conduit, longer than 24", more than three conductors, if these will be never use at the same time. Example heating and air-conditioning
 
electrical engineer

electrical engineer

do I have to adjust size of current carrying conductors located in the same conduit, longer than 24", more than three conductors, if these will be never used at the same time. for example : heating and air-conditioning.
Thank you for prompt respond.
Jerry Kosan
 
Article 220 recognizes the larger of the two loads between heating and air-conditioning and allows the smaller of the two to be omitted from the calculated load. So, in my opinion, I think it would be reasonable to assume that 310.15(B)(2)(A) would not apply to this instance. If, and only if, it were in an arrangement as you described where there would not be the chance to have more than three conductors carrying current at any given time in the raceway.

Pete
 
IMO, if you will only have 3 conductors carrying current at the same time, you only have "3 current carrying conductors". So my answer would be no, you don't have to derate.

However, if I remember right, this has been debated here before, and I don't think everyone agreed.

Steve
 
steve66 said:
However, if I remember right, this has been debated here before, and I don't think everyone agreed.
Click to expand...

Shocked am I. Shocked, that you could suggest such a thing.;)
 
Never ever assume heat and air wont run at same time.On purpose no, but i have seen relays stick.If we use the logic that some are not used while others are we would never settle this.It says current carrying conductors and that is what they are.Nothing says how often or how long or what conditions.
 
charlie b said:
Shocked am I. Shocked, that you could suggest such a thing.;)
Click to expand...


My mistake Charlie. As I recall it now, everyone agreed with me:D

Jim must have changed his mind, since he is now being "difficult" ;)

I will agree that in some cases air conditioning and heating might run at the same time. But if you truly know you will have only 3 wires carrying current at any one time, I still don't think you have to derate.
 
Jim W in Tampa said:
Never ever assume heat and air won?t run at same time. On purpose no, but I have seen relays stick.
Click to expand...
We don?t have to design and construct our systems to be immune to single failures. If a code violation (i.e., ?failure to derate for multiple conductors?) would only exist if a relay were to fail, then I submit that you don?t have to derate.

But let?s be clear. Suppose you wish to avoid derating by claiming two components will not both be operating at the same time, so that there are only three current-carrying conductors in the conduit. One example is heat and A/C. Another example is pump 1 and pump 2. I would want to see an interlock to prevent simultaneous operation. You can?t rely on, ?well of course nobody would be so foolish as to run both the heater and the air conditioner.?
 
I thought there used to be an exception for equipment that was "interlocked" so it won't run at the same time, but I don't see it in the 2005. Maybe I'm thinking of something else.

I'll also agree with your last statement. You can't rely on someone not running them at the same time. In some cases, you might even want to run the AC along with the heater to reduce humidity. (That's what the defrost setting on a car's heater does.)

Steve
 
Normal split unit AC/HEAT for house.In heat mode only air handler needs power (unless heat pump).In cooling mode air handler fan needs to run at same time as compressor.So just how can we not derate ?
 
Jim:

In that case I would agree you would have to derate. However, in a case where the air would not run with the heat, I wouldn't derate.

Steve
 
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