Area of Copper Shield Tape of Cable for Resistance Calculation

[etb90]

Dear all,

I really need help.anyone know any standard (BS/IEC/etc) that specify the calculation copper tape shield area for metallic screen resistance.

Your prompt reply is really appreciated.

Thanks

 

[cuky2000]

The shield resistance of helically applied Cu tape is calculated by determining the effective shield resistance in accordance with ICEA P-45-432 and then adjusting for temperature.

Notice that the skin effect of Cu tape is negligible because of small thickness. Usually the dc resistance of tape shield at 25⁰C in ohms per 1000 feet.

Below is an excerpt with various information from ICEA, and cable manufacturers in the USA including the tape resistance.

.....

 

[7anoter4]

IEC 60502-2/2005
10.2 Requirements
The dimensional, physical and electrical requirements of the metallic screen shall be
determined by national regulations and/or standards.
Usually the IEC Standard cable manufacturers present the screen area and the screen short-circuit withstand current in their catalogue.
If you intend to follow IEC 60287 calculation way you need Rs indeed. No IEC Standard indicates how to calculate.
In my calculation I used the ICEA P-45-482 as presented by cuky2000 calculating the tape width from the formula:
For Helically applied flat tape ,overlapped.[new cable, good contact ]
usually the tape winding angle is between 60 to 70 degrees.
W = 100 / (100 - OVL) .π . dm . Cos(70 / 180 * π)
A = 4 * THK * dm * Sqr(100 / 2 / (100 - OVL))[mm^2]
OVERLAP [%]=; OVL
SHIELD DIA[MM]="; dm
SHIELD THICKNESS[MM]="; THK
The French Standard HN-33-S-52-for instance- presents a formula for screen resistivity :
ρ1=R1.π.(d-T1).T1/2L
and from here:
R1=2.ρ1.L/[π.(d-T1).T1] where:
R1=measured resistance
L=the distance between the measured points[the length in m]
d=insulated core diameter[m]
T1=screen average thickness [m]

 

[7anoter4]

It is possible. If we consider the tapes lapped around the insulated core
as a cylinder then A it is a cross section area of the tube but S it is the
tapes cross-section area.
In my calculation I took overlap 50%, dm=50 mm, tape thick 10 mils[0.245 mm]
and the winding angle 67.8.Then I got A=34.74 and S=29.23 mm

 

[etb90]

Thank you for your reply 7anoter4.

Is thats means its allowable to use less area to determine the maximum metallic screen resistance and declare higher value for short circuit calculation.

Example: Declare area of copper tape for short circuit is 34.5sqmm (including overlap) and area to determine maximum metallic resistance 29.24sqmm (without overlap). This will give higher maximum value of metallic resistance which is 0.5998ohm/km and use this value as max value for measurement instead of using declare value for short circuit, we get lower value of max metallic screen resistance which is 0.508ohm/km.

If it allowable which standard to use as reference.

Is there any relation between both of it (metallic screen resistance and short circuit) during the installation/application of cable.

Please enlighten me.

Your prompt reply is highly appreciated.

Thank you.

 

[dpc]

It would be far simpler to just ask the manufacturers for this data. They have it.

 

[etb90]

what if manufacturer give different value like above. is that acceptable?

 

[dpc]

I guess that depends on your goal and your confidence in your calculations. Manufacturers can measure the resistance.

 

[etb90]

is there any standard that specify the resistance shall be based on effective area that we used to calculated short circuit?