Spacer cable ampacity 2

[Mbrooke]

In a nut shell dozens of 34.5kv sub-transmission feeders being converted over to SP for reliability and easement constraints. Typical max feeder loadings are 600, 800 and 1,200amps and each circuit rating will be sized accordingly.


What is the typical industry standard in sizing covered conductors?

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet270

 

[cuky2000]

For cable manufacturing specifications the following industry standard are used:
[ul]
[li]ICEA[/li]
[li]ASTM B230, B231, B232, B398, B399, B400[/li]
[/ul]
Should be noted that the National Electrical Safety Code (NESC / IEEE Std C2) treat covered conductors (CC) as bare conductors, with the only difference that tighter conductor spacing are allowed.

 

[Mbrooke]

Good to know, but Southwire limits the temp to about 75*C without much else said. With AAC and ACSR we usually go 125% of the listed rating, but in truth we generally know little about how the actual temp plays out.

 

[7anoter4]

In my opinion, NEC Table 310.15(B)(21) recommends ampacity for low voltage covered cable only and it is 16-25% more than the manufacturer recommendations.
I think also ,ANSI/ICEA S-70-547 does not indicate the ampacity and it is referring to cable construction only.
You may calculate the ampacity following usual procedure [Neher and McGrath or IEEE 835/94]. The manufacturer could [or should] calculate this in your benefit.

 

[Mbrooke]

How conservative is McGrath? In my experience the final ampacity is much lower than it actually could be. But I give big thanks to table 310.15 (B) (21), I think I might use that. Let me crunch the numbers and see how it plays out.

 

[7anoter4]

Even manufacturer recommends installation as an uninsulated conductor.
You cannot use it as a MV cable in no way.
The ampacity calculated as per 738/2006 and 735/94 depends less on the covering thickness and more on conductor diameter-if the concentric stranded or compacted-on conductor type- if it is ACSR or AAC for instance-on sun rays angle and wind angle. More or less NEC is close to calculation results.
While no installation official instructions are available, in my opinion NEC is the convenient indications (if the manufacturer does not recommend less).

 

[Mbrooke]

If using the NEC, would 310.15 (B) (21) or 310.60 be a better fit? It seems 310.15 works best, but is only rated for conductors 2000 volts and under. However 310.60 appears to apply to full shielded cables.

 

[7anoter4]

You are right. Since Table 310.15(B)21 is dedicated for single [isolated] cable and
usually-see for instance “Insulated and covered conductor systems for Low and medium voltage over head distribution lines by H.K.Agarwal (Supreme & Co), P.Barua (Supreme & Co.):
"They are twisted together to form a bundle as there is no requirement of phase to phase clearance. Individual cores are separated only at dead ends, supports, joints and tap-offs."
then is likely Table 310.60(C)(68). Calculated is close to this table also.

 

[jghrist]

The covered cable that the OP is referring to is spaced, not twisted together.

 

[Mbrooke]

This is what spacer cable looks like. I am aware that it is rare in some parts of the world and the US, so no biggy.

https://c1.staticflickr.com/3/2899/14660261542_775fc1f110_b.jpg

http://www.utilityproducts.com/content/dam/up/online-articles/2012/12/Hendrix1.jpg

http://sicaesa.com/resources/Hendrix+1.jpg

 

[7anoter4]

Thank you jghrist and mbrooke for your information. If the clearance between cables it is more than 2 diameters, in air, the cable is considered as single. So table 310.15(B)21 is closer. For 46 kV a derating factor of 0.95 it could be required. Since the solar radiation depends on latitude, season and day hour and the air temperature and speed is very difficult to appreciate it so a derating factor of 0.95 will be always required.