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#136650 - 04/20/03 02:04 PM Derating needed?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
I found this photo on a website promoting an electrical engineering company. Do you think this installation of theirs needs derating? [Linked Image]

[Linked Image]


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#136651 - 04/20/03 09:02 PM Re: Derating needed?  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
C-H,
They're Data cables aren't they?. [Linked Image]


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#136652 - 04/21/03 11:02 AM Re: Derating needed?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Eh, could be. Didn't think of that...


#136653 - 04/22/03 02:07 AM Re: Derating needed?  
Trumpy  Offline


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Joined: Jul 2002
Posts: 8,211
SI,New Zealand
C-H,
Sorry to pour cold water on your idea, mate.
But the question does beg asking, even if those cables are carrying relatively low currents, do they heat up to some extent?.
Given that they are so tightly bundled and all cables exhibit electrical resistance along thier length.
And it looks like those particular cables are running for a fair stretch!.
There's nothing like a neatly bundled and tied cable installation, though. [Linked Image]

[This message has been edited by Trumpy (edited 04-22-2003).]


Let's face it, these days if you're not young, you're old - Red Green grin

#136654 - 04/22/03 02:27 PM Re: Derating needed?  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Well, either my idea or the wiring needed cold water poured on it. [Linked Image]

[This message has been edited by C-H (edited 04-22-2003).]


#136655 - 04/22/03 03:19 PM Re: Derating needed?  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
That definitely looks like bundled data/TelCo cables.

As for heat dissipation, if we take a typical telephone cable the conductors might have a resistance somewhere in the region of 28 ohms per 1000 ft.

At a loop current of 100mA (which is toward the high side anyway), I^2*R comes to 0.28W over 1000 ft., or 0.56W allowing for the both sides of the loop.

That's 560 microwatts per foot for each operating circuit. Put away the fork -- You're not going to toast marshmallows on those cables! [Linked Image]



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