cable amp ratings - answers to wrong questions

[Victor Tikhonov <vtikhono@lsil.com>]

The trouble with all the current ratings found in these books is that
it's pointless. 

What means  max current for #4 is 95A? At 96A it blows up?

All it means that at above 95A the temp is more than rated value
manufacturer chooses as safe one. And safe rated value listed by 
most manufacturers is dictated by liability reasons, not technical. 
So if I'm willing to go over this rated temp (especially for a few
seconds while accelerating), 100A, 150A and may be 200A is ok 
*for my application* for 95A "rated" cable.

This all has to be calculated based on voltage drop, power dissipation
and insulation property allowing the heat to escape. Then variables
like if it's in the open air or bundled and buried under carpet
come to play. So, just looking up info in household reference books
is almost useless.

Other day I went to home depot to get a wire to run 240 to other side
of my garage there ai plug my EV. For fun I asked what wire size 
would I need for 40A load. Sales woman said #6. I asked, can I use
thinner #8? No, it's rated for 30A she said. So, I asked, what exactly
happens if I run 40A through #8 wire?

Reply was "we were told to inform the customers that this is unsafe
and they are not suppose to do it".

Me: I understand this position, but this wasn't my question.
THe question was what happens to the wire.

She: I don't know and not doing to tell you that "nothing happens" -
if you burn down your house, you'll come back after me.


So, who do you think writing these references books?

Victor



Mark Hanson wrote:
> 
> My Howard Sams book of Electronic Tables shows:
> #4 is .2485 ohms per 1000' 95A max
> #2 is .1563 ohms per 1000' 150A max
> #1 is .1239 ohms per 1000' 190A max
> 1/0 is .09825 ohms per 1000' 260A max
> 2/0 is .07793 ohms per 1000' 300A max
> 
> So number 2 cable is fine for a 120V 2000-3000lb vehicle with a ADC 8 or 9"
> motor. The motor to controller cables need to be twice as thick 2/0 (2X
> amps) and be as short as possible for back emf spiking and I2R losses at
> pulsed current. The motor and power cables must be ty-wrapped together if
> you like listening to AM.
> 
> -----Original Message-----
> From: Victor Tikhonov [mailto:vtikhono@lsil.com]
> Sent: Tuesday, May 28, 2002 9:41 PM
> To: ev
> Subject: Welding cable amp ratings
> 
> Listers,
> 
> Does anyone know a (web) source for reliable info about a welding
> cable current handling capability? Net search didn't yields anything
> meaningful to me. I want to know the voltage drop on X feet
> per Y amps (whatever data available) for standard gauge sizes,
> (gauge 4, 2, 1 and 1/0 will be enough).
> 
> Thanks in advance for leads.
> 
> Victor
> '91 ACRX