What do you think will happen? I think it will burn up the insulation on
the wire.



"Dave J" wrote in message
...
I have a subpanel that is about 80 feet away from the main panel. It
uses 6 gauge copper THHN wires conducting 220V current, in a 3/4"
raceway. What will happen if I upgrade the breakers to 100 A and try
to use close to 100A of 220V. Thanks, Dave J.

On Mon, 10 Oct 2005 11:33:07 -0400, John Grabowski wrote:
What do you think will happen? I think it will burn up the insulation on
the wire.

Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor
would produce 7.5 watts of power total, a negligible amount.

http://www.bnoack.com/index.html?htt...esistance.html

Is my calculation wrong?

Dave J



"Dave J" wrote in message
...
I have a subpanel that is about 80 feet away from the main panel. It
uses 6 gauge copper THHN wires conducting 220V current, in a 3/4"
raceway. What will happen if I upgrade the breakers to 100 A and try
to use close to 100A of 220V. Thanks, Dave J.




--

"Dave J" wrote in message
...
On Mon, 10 Oct 2005 11:33:07 -0400, John Grabowski
wrote:
What do you think will happen? I think it will burn up the
insulation on
the wire.

Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance
equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor
would produce 7.5 watts of power total, a negligible amount.


http://www.bnoack.com/index.html?htt...ata/wire-resis
tance.html

Is my calculation wrong?

Dave J

Power is current SQUARED times resistance...

Dave J wrote:
On Mon, 10 Oct 2005 11:33:07 -0400, John Grabowski wrote:

What do you think will happen? I think it will burn up the insulation on
the wire.


Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor
would produce 7.5 watts of power total, a negligible amount.

http://www.bnoack.com/index.html?htt...esistance.html

Is my calculation wrong?

P=I^2*R




Dave J

Dave J wrote:
Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor
would produce 7.5

VOLTS dropped across the wire. 7.5 volts times 100 amps gives 750 watts
dissipated in the wire.



watts of power total, a negligible amount.


--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

VOLTS dropped across the wire. 7.5 volts times 100 amps gives 750
watts dissipated in the wire.

750 watts over 80 feet of wire isn't so bad.

NEC lists the ampacity of 6 gauge wire as 55 amps or 70 amps depending
on
environment and raceway. 100 amps is certainly not up to code but
probably
won't cause an instant fire!

Upgrading to a larger wire size may well require a larger raceway, too.

Tim.

In article , (Dave J) wrote:

Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor

**typo** (you clearly meant "0.075 ohm")

would produce 7.5 watts of power total, a negligible amount.

Is my calculation wrong?

Yes, and very badly so.

Voltage = current times resistance.
Power = current SQUARED times resistance. So you're low by a factor of 100.




Dave J



"Dave J" wrote in message
...
I have a subpanel that is about 80 feet away from the main panel. It
uses 6 gauge copper THHN wires conducting 220V current, in a 3/4"
raceway. What will happen if I upgrade the breakers to 100 A and try
to use close to 100A of 220V. Thanks, Dave J.





--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

"Dave J" wrote in message
...
On Mon, 10 Oct 2005 11:33:07 -0400, John Grabowski
wrote:
What do you think will happen? I think it will burn up the insulation on
the wire.

Not likely. Resistance of 6 gauge wire is 0.47 ohms per 1,000
feet. I have 160 feet (going both ways), which makes resistance equal
to 160*0.47/1000 = 0.075 ohm. At 100 amps, a 0.047 ohm resistor
would produce 7.5 watts of power total, a negligible amount.

http://www.bnoack.com/index.html?htt...esistance.html

Is my calculation wrong?

Dave J


Yep! Wrong. Two things. My wire tables show 0.39 Ohms per thousand. Also,
the formula for power consumed in a resistor is I *squared* times the
resistance. Hence, 100 x 100 x 0.39 x 160/1000 = 624 Watts *total*, or
624/80 = 7.8 Watts *per foot* of conduit.


"Dave J" wrote in message
...
I have a subpanel that is about 80 feet away from the main panel. It
uses 6 gauge copper THHN wires conducting 220V current, in a 3/4"
raceway. What will happen if I upgrade the breakers to 100 A and try
to use close to 100A of 220V. Thanks, Dave J.




--

wrote:
VOLTS dropped across the wire. 7.5 volts times 100 amps gives 750
watts dissipated in the wire.


750 watts over 80 feet of wire isn't so bad.

NEC lists the ampacity of 6 gauge wire as 55 amps or 70 amps depending
on
environment and raceway. 100 amps is certainly not up to code but
probably
won't cause an instant fire!

Upgrading to a larger wire size may well require a larger raceway, too.

Tim.


He can pull three number four AWG THHN /THWN conductors in the 3/4 inch
raceway. Since the ampacity of #4 AWG is 85 Amperes he is permitted to
install a ninety ampere breaker.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison