CABLE IMPEDANCE IN EASYPOWER AND SKM

You seem to be hung up on the role of ambient temperature in the determination of conductor resistance. Obviously conductor temperature is affected by the ambient temperature. BUT - when the CONDUCTOR temperature is explicitly DEFINED as a data input, as it is in both SKM and Easypower, then that is the conductor temperature used to determine the resistance, regardless of what you specify for the ambient temperature. How could it be otherwise?

How would it work if you explicitly specified a conductor temperature of 75 deg C, but then you changed the ambient temperature data and the software adjusted the conductor temperature to something else? This would not be workable.

It's been an interesting discussion, but I don't think I have much more to add.
 
D. Castor said:
You seem to be hung up on the role of ambient temperature in the determination of conductor resistance. Obviously conductor temperature is affected by the ambient temperature. BUT - when the CONDUCTOR temperature is explicitly DEFINED as a data input, as it is in both SKM and Easypower, then that is the conductor temperature used to determine the resistance, regardless of what you specify for the ambient temperature. How could it be otherwise?

How would it work if you explicitly specified a conductor temperature of 75 deg C, but then you changed the ambient temperature data and the software adjusted the conductor temperature to something else? This would not be workable.

It's been an interesting discussion, but I don't think I have much more to add.
Click to expand...
"hung up on"
How about concern about what is actually happening, or NOT happening regarding the actual temp of the conductor when the calc is run.

"Obviously conductor temperature is affected by the ambient temperature. BUT - when the CONDUCTOR temperature is explicitly DEFINED as a data input, as it is in both SKM and Easypower"
My view of leaving the user to alter the field temp is unbelievably FLAWED. How to get the correct number by hand?
Any actual users of either package please come forward and state how you handle this.
My money is on 95% are using WHATEVER the default is.

"How could it be otherwise?"
Have a base value of R defined at a stated ambient and starting value of X amps, or percentage of rated amps, or even 100% per the NEC tables.
Then allow the user to adjust ambient if needed and operational amps and the software can then make appropriate calcs to adjust R.
If the user is working in high ambient temps, it is their job to adjust for max amp rating prior to input.

In post 29 you stated...
"In SKM, you can select whatever conductor temperature you want. You can have one temperature for SC calcs and a different conductor temperature for Load Flow. It's very easy to change in SKM. In EasyPower it's not as convenient, but can be done."

How in this NOT a software design flaw.
This allows an entry that could result in the conductor being operated outside of its max rating....flawed logic.
Users just paid $xxxx.xx for this package and they have to hand calc a non-linear relationship to get a new FIELD temperature.
We need to hear from actual users and state how they are doing this.
 
Notice that SKM allows you to enter an impedance tolerance. For short circuit calculations, you'll want to be at the low end of the tolerance, corresponding to low operating temperature of the conductors. For voltage drop calculations, the opposite - higher temperature = higher impedance.
 
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