NEC Table 9 Alternating-Current Resistance

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Ingenieur

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K8MHZ said:
That's not the point. The point, at least to me, is the verbiage used. I'll use an online calculator and call it a day. The question was about the formula in post #1. Not real life.
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what makes you think an online calculator uses different numbers/methods?
that is real life, no measureable difference
 
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Ingenieur

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K8MHZ said:
I don't care if it does or not. You are evading the issue, and that issue is about the 'R' in the OP's first post. I think he made a valid observation.
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the point is there is no adjustment required because of the physics of the system

you do not use R, you use Z (for AC systems)
 
K8MHZ

K8MHZ

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GoldDigger said:
Because the effective inductance of the cable will be different if the current is unbalanced?
It should not change the skin effect term of the resistive component much though.
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The point is, three conductors and three phase are specified for a reason. The OP wants to use Table 9 as specified in the VD equation he posted, but has more than three conductors.

So, that being said, Table 9 doesn't apply. Since Table 9 doesn't apply, and the OP's equation specifies R to be taken from Table 9, the OP's VD equation can't apply. That's his dilemma. He either needs to use a different formula or just fudge it and call Table 9 close enough.
 
iwire

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Ingenieur

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K8MHZ said:
Then why are three wires specified?
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3 ph in conduit at 60 Hz (most typical application)
those may be measured values since calculating the value may not be accurate or representative
those are the test conditions

what will change Xl based on conductor count?
 
iwire

iwire

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K8MHZ said:
That's not the point. The point, at least to me, is the verbiage used. I'll use an online calculator and call it a day. The question was about the formula in post #1. Not real life. And someone thinks it matters, or it wouldn't be explicit as to 'three phase, three wires'. Why not just call it 60 Hz AC if it doesn't matter?
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And the point to me is the NEC does not tell us how to do voltage drop calculations so how can chapter 9 be looked at as right or wrong?
 
K8MHZ

K8MHZ

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Ingenieur said:
3 ph in conduit at 60 Hz (most typical application)
those may be measured values since calculating the value may not be accurate or representative
those are the test conditions

what will change Xl based on conductor count?
Click to expand...

What will change if I don't have three phase? Table 9 shows nothing about that.

Using Table 9 outside its parameters, no matter how much sense it seems to make, is fudging it if you are instructed to use it. I take it the OP doesn't want to fudge it, or he wouldn't have posted his question.
 
iwire

iwire

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K8MHZ said:
I know the OP didn't get his formula from the NEC, it just references the NEC.
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Exactly, so why would we expect the table in the NEC be written to acomadate this outside reference? :huh:

That was my point, it's like complaining my Chevys door won't fit my Ford.
 
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