RE: cable amp ratings - answers to wrong questions

["Roger Stockton" <rstockton@delta-q.com>]

> -----Original Message-----
> From: Victor Tikhonov [mailto:vtikhono@lsil.com] 
> Sent: May 30, 2002 12:20 PM
> To: ev@listproc.sjsu.edu
> Subject: cable amp ratings - answers to wrong questions
> 
> 
> The trouble with all the current ratings found in these books 
> is that it's pointless. 

[snip]

> So, who do you think writing these references books?

The Insulated Cable Engineering Association <http://www.icea.net/> or a
similar professional organisation, not the hired help at Home Depot
<GRIN>, helpful though they usually are.

If you want the exact information you are looking for, you'll probably
have to browse the ICEA site and purchase the appropriate document.  If
you are satisfied with information that gives you a reasonable comfort
factor with using a particular cable somewhat beyond its normal ratings,
then perhaps the information you can find by searching on "welding
cable" on General Cable's website is sufficient (look at the technical
information links associated with any of the products that comes up in
your search, especially "Installation and Engineering Information").

For instance, the table of recommended welding cable ampacities is based
on a 4V drop, 60% duty cycle, and a copper temp of 60C in a 40C ambient.
With these assumptions in mind:

#4: 150ft@100A or 100ft@150A
#2: 250ft@100A or 100ft@200A
#1: 300ft@100A or 100ft@250A
1/0:400ft@100A or 100ft@350A

(the distance is the maximum total circuit length).  This provides
information about cable resistance (4V drop in the specified length at
the specified current) and heating (20C rise in conductor temp at the
specified current and duty cycle).

Another table provides ampacity information for 90C conductor temp in a
40C ambient for 0-2000V:

                   Current
gauge  single conductor  2-conductor
-----  ----------------  -----------
 8          83              72
 6         109              95
 4         145             127
 3         167             145
 2         192             167
 1         223             191
1/0        258             217
2/0        298             250
3/0        345             286
4/0        400             328

Note that these ampacities are for welding cable with 90C rated
insulation, and the ampacity correction factors for 90C insulated cable
is provided as:

          ampacity
ambient  correction
(deg. C)   factor
-------- ----------
 10         1.26
 20         1.18
 30         1.10
 40         1.00
 50         0.90

Hopefully this information is enough for you to convince yourself if
what you want to do is likely to be OK or certain to be unsafe.  If not,
I'm sure you can get the original documents that this info was
extracted/condensed from through the ICEA... for a price.

Cheers,

Roger.