IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
(OP)
Hi Folks,
I think I may have found an inconsistency in IEEE 242-2001 between the equations Section 9.5.2.4 and Table 9-6.
I hope that I am making a mistake somewhere, and y'all will be able to help point out my error.
Edit: I believe if you follow just the equation for any value of K other than 1, the equation results are way off. For values of k<1, you could overestimate the amount of current the cables could handle by a factor of 2 or more.
Based on the standard, values in table 9-6 are calculated based on the equation shown in 9.5.2.4:
However, if you plug in the values as indicated the results returned do not equal that of the table.
For example, take first line of table 9-6 calculated for EPR-XLP with Te=130, Tn=90,and To=40
From the table:
But, if you change the equation to divide by k instead of multiply by k then it appears to work.
From Equation as corrected:
Does the corrected equation work for y'all?
Did I miss somewhere in the section where is says the inverse of K should be used?
I attached my spreadsheet where I ran my tests.
Thanks,
Chris
I think I may have found an inconsistency in IEEE 242-2001 between the equations Section 9.5.2.4 and Table 9-6.
I hope that I am making a mistake somewhere, and y'all will be able to help point out my error.
Edit: I believe if you follow just the equation for any value of K other than 1, the equation results are way off. For values of k<1, you could overestimate the amount of current the cables could handle by a factor of 2 or more.
Based on the standard, values in table 9-6 are calculated based on the equation shown in 9.5.2.4:
Ie/In % = SQRT(((Te-To)/(Tn-To)-e(-Θ*K))/(1-e(-Θ*K))*((230+Tn)/(230+Te)))*100
Where:Ie is emergency operating current rating,
In is normal current rating,
Te is conductor emergency operating temperature,
Tn is conductor normal operating temperature,
To is ambient temperature,
K is a constant, dependent on cable size and installation type (see Table 9-5 in IEEE 242-2001),
230 is zero-resistance temperature value (234 for copper, 228 for aluminum),
e is base for natural logarithms.
In is normal current rating,
Te is conductor emergency operating temperature,
Tn is conductor normal operating temperature,
To is ambient temperature,
K is a constant, dependent on cable size and installation type (see Table 9-5 in IEEE 242-2001),
230 is zero-resistance temperature value (234 for copper, 228 for aluminum),
e is base for natural logarithms.
However, if you plug in the values as indicated the results returned do not equal that of the table.
For example, take first line of table 9-6 calculated for EPR-XLP with Te=130, Tn=90,and To=40
From the table:
k=0.5, %=1136
k=1.0, %=1602
k=1.5, %=1963
k=2.5, %=2533
From Equation as written:k=1.0, %=1602
k=1.5, %=1963
k=2.5, %=2533
k=0.5, %=2265.49
k=1.0, %=1603.885
k=1.5, %=1311.5
k=2.5, %=1018.061
k=1.0, %=1603.885
k=1.5, %=1311.5
k=2.5, %=1018.061
But, if you change the equation to divide by k instead of multiply by k then it appears to work.
Ie/In % = SQRT(((Te-To)/(Tn-To)-e(-Θ/K))/(1-e(-Θ/K))*((230+Tn)/(230+Te)))*100
From Equation as corrected:
k=0.5, %=1136.859
k=1.0, %=1603.885
k=1.5, %=1962.765
k=2.5, %=2532.281
k=1.0, %=1603.885
k=1.5, %=1962.765
k=2.5, %=2532.281
Does the corrected equation work for y'all?
Did I miss somewhere in the section where is says the inverse of K should be used?
I attached my spreadsheet where I ran my tests.
Thanks,
Chris






RE: IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
RE: IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
There maybe other approximation errors,but in case it wasn't clear, the results of the equation as listed cause much higher errors than 10%.
For k=0.5, the equation as written results in overestimating the allowable current by a factor of 2. So 200% error.
I.e. for a cable with a rating of 100 amps, the table estimates it could handle 1136 amps, but the equation says it could handle 2266.
So if you followed only the equation, you would would be overloading the hypothitcal 100 amp cable by over 1000 amps.
RE: IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
RE: IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?
I was so confused trying to get my spreadsheet to work😀
RE: IEEE 242-2001 - Intermediate Cable Overload Capacity - Equation 9.5.2.4 inconsistent with Table 9-6?