ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#136650 - 04/20/03 11:04 AM Derating needed?
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
Loc: Stockholm, Sweden
I found this photo on a website promoting an electrical engineering company. Do you think this installation of theirs needs derating?

Top
Test Equipment:
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
#136651 - 04/20/03 06:02 PM Re: Derating needed?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
C-H,
They're Data cables aren't they?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
Top
#136652 - 04/21/03 08:02 AM Re: Derating needed?
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
Loc: Stockholm, Sweden
Eh, could be. Didn't think of that...
Top
#136653 - 04/21/03 11:07 PM Re: Derating needed?
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
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).]
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
Top
#136654 - 04/22/03 11:27 AM Re: Derating needed?
C-H Offline
Member
Registered: 09/17/02
Posts: 1497
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).]
Top
#136655 - 04/22/03 12:19 PM Re: Derating needed?
pauluk Offline
Member
Registered: 08/11/01
Posts: 7520
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!
Top

Member Spotlight
Member Since: 02/23/13
Posts: 204
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 109 Guests and 8 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
Scotto, Freecrowder, clee512, Jdscott2005, FAIZAN

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals