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#90150 - 11/01/04 09:22 AM Siamese Cable Fill Calculation
mustangelectric Offline
Member

Registered: 02/08/04
Posts: 496
Loc: Bentonville, AR
Hi,
I am still trying to pin down the number of Siamese cables I can get in a 2 inch schedule 40 PVC and 2" EMT.

Here is what I have come up with thanks to the previous thread.

SIAMESE CONDUIT FILL CALUCLATION BASED ON 40% FILL

Siamese Cable/Combo (RG59 & 1 Pair #22 AWG 1/2" Diameter)

1/2"=0.50"
Pi R(squared)=(.50*.50)*3.14159=
.785" area.

40% of 2" EMT = 1.342"
1.342"/.785"=1.7 cables

40% of 2" Schedule 40=1.316"
1.316"/.785"= 1.6 cables

I measured the actual cable and it is 1/2".

this does not jive with the follwoing calculations done at Belden cables site:
http://bwccat.belden.com/ecat/images/ConCap.htm

something smells fishy..

Thanks for any replies..

-regards

Mustang

[This message has been edited by mustangelectric (edited 11-01-2004).]
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2014 / 2011 NEC & Related Books and Study Guides
#90151 - 11/01/04 11:19 AM Re: Siamese Cable Fill Calculation
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
The first thing I notice is you are squaring the diameter, not the radius.
They are getting around this by using 3.14/4 (.785) instead of pi.
Try it using .25 for the radius, squaring that and multiplying it by 3.14
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#90152 - 11/01/04 11:38 AM Re: Siamese Cable Fill Calculation
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
If I was being lazy or didn't have a calculator I would look at table 5, pick a conductor the size of my cable (in your case 2/0 TFE,PFA,PFAH,Z is close enough for guv'mint work at .508), then use the conduit fill table in annex C.
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#90153 - 11/01/04 11:48 AM Re: Siamese Cable Fill Calculation
mustangelectric Offline
Member

Registered: 02/08/04
Posts: 496
Loc: Bentonville, AR
Hi,
Thanks for the reply. I did that already but I know that there are different calcs for straight runs or runs with conduit bends and maybe some other factors I am not quite sure on when dealing with this type of cable.

The calculation I did was from a recent thread in the forum on the same subject.

I will look at the calculation again.

I am not sure if it is right.

Thanks

Greg

[This message has been edited by mustangelectric (edited 11-01-2004).]
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#90154 - 11/01/04 02:53 PM Re: Siamese Cable Fill Calculation
Ryan_J Offline
Moderator

Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
Mustang:

1/2" diameter cable has a radius of .25"

.25*.25=.0625
.0625*3.14=0.196

So, 0.196 is your cable's area.
At 40% your EMT has an area of 1.342
1.342/0.196=

6.8 cables allowed in the EMT.
6.7 cables allowed in the RNC.
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Ryan Jackson,
Salt Lake City

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#90155 - 11/01/04 04:59 PM Re: Siamese Cable Fill Calculation
mustangelectric Offline
Member

Registered: 02/08/04
Posts: 496
Loc: Bentonville, AR
Hi,
Thanks for the replies. I see the error and appreciate the correction.

What is the difference in the calculation for the Siamese RG59 in a conduit with 3 90's? anybody know?

How do you calculate the Jam Ratio?

thanks again,

Mustang

[This message has been edited by mustangelectric (edited 11-01-2004).]
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#90156 - 11/01/04 05:27 PM Re: Siamese Cable Fill Calculation
Ryan_J Offline
Moderator

Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
The jam ratio is the inside diameter of the raceway divided by the outside diameter of the conductor. This value should be 2.8 to 3.2 according to industry representatives.

[This message has been edited by Ryan_J (edited 11-01-2004).]
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Ryan Jackson,
Salt Lake City

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#90157 - 11/02/04 06:07 AM Re: Siamese Cable Fill Calculation
mustangelectric Offline
Member

Registered: 02/08/04
Posts: 496
Loc: Bentonville, AR
Thanks for the great replies..very useful information..

-regards

Mustang
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