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3C+ N Impedances

3C+ N Impedances

3C+ N Impedances

(OP)
I have values for 3C Rw90 cable , is there simple method to calculte impedances ( Positive & Zero) for 3C+N ?
2) if I have positive impedances , what s the relation between Z+ and Z0?
3) How about 3C+N + a bre ground wire

I wish it was a simple program out there with all these information, I didn''t need to look around all the time to get this data!!
 

RE: 3C+ N Impedances

There is no simple formula to calculate impedances of conductors in raceway. The values depend on the geometry, which is impossible to predict with an analytical approach.

For typical values, see the reference in thread238-241284: X and R Values  

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: 3C+ N Impedances

(OP)
From SKM software which calcultes Impedances based on
IEEE 141 for
500 MCM Cable
in EMT
Z+= 0.0276+J0.0373
Z0=0.0438+J0.0999
per 1000ft/ohm
Insulation type : PVC
Insulation class: THHN

Nexans Cable Manufacturer

500 MCM Cable
in EMT
Z+= 0.0219+J0.0270
Z0=0.1844+J0.0326
per 1000ft/ohm
Insulation type : XLPE

There is big difference in Z0 values , I am wondering if anyone has experience calculating this values?

 

RE: 3C+ N Impedances

As ahleman says, there is no simple formula.  Particularly for zero-sequence.  More particularly for zero-sequence in ferrous conduit.

The manufacturer's data may not be considering a ground wire within the EMT.
 

RE: 3C+ N Impedances

(OP)
So..How do you perform your engineering studies which requires accurate data such as Arc flash analysis!!!
Does everybody design an excel spread sheet with formulas and calculate these values?

RE: 3C+ N Impedances

Various tables are available, such as in the IEEE Red Book that provide the necessary data.

In most cases, the analysis software being used will have this data in its database.   

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

RE: 3C+ N Impedances

(OP)
dpc.. Thats the concern in my post. Software based on IEEE Red book suggests data which is very different from manufacturer data.As an  expert which one you would trust?
do you calculate cable impedances using available formulas?
SKM suggests impedances , but it greatly varies with Nexcan's suggested values!!!  

RE: 3C+ N Impedances

Quote:

So..How do you perform your engineering studies which requires accurate data such as Arc flash analysis!!!
Arc flash analysis for NFPA-70E or IEEE-1584 is done with 3Ø faults.  As you have observed, there is a lot more agreement on positive-sequence cable impedances.  In most cases, transformer impedances will dominate the total impedance and small differences in cable impedance values will result in even smaller differences in calculated fault currents.
 

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