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#136650 - 04/20/03 11:04 AM Derating needed?
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
I found this photo on a website promoting an electrical engineering company. Do you think this installation of theirs needs derating?


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#136651 - 04/20/03 06:02 PM Re: Derating needed?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
C-H,
They're Data cables aren't they?.
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#136652 - 04/21/03 08:02 AM Re: Derating needed?
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Eh, could be. Didn't think of that...

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#136653 - 04/21/03 11:07 PM Re: Derating needed?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: 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.

[This message has been edited by Trumpy (edited 04-22-2003).]
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#136654 - 04/22/03 11:27 AM Re: Derating needed?
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Well, either my idea or the wiring needed cold water poured on it.

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

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#136655 - 04/22/03 12:19 PM Re: Derating needed?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: 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!

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