Greetings could someone post an anwser to the group for the following:

I have a home that is about 20 years old. The sub-panel in the
basement is a 100 AMP panel. I have an aluminum wire that runs from
the panel to a new airconditiong unit I had installed recently. The
wire reads:
SE Cable Style U Type XHHW CDRS 600V 3 CDRS 6 AL (UL) 1983

I currently have a 40 AMP breaker installed that keeps tripping after
the AC unit cycles on and off a few times. The AC guy that installed
it said to put in a 50 AMP breaker but I can't find the information to
see if this wire can take that size breaker. If someone can help me
find the info or if you know for sure that a 50 AMP breaker is OK,
could you please let me know?

PS The AC unit says it can take a max breaker of 60 AMP.

Thanks

Joe

Check out table 310.16. in the National Electrical Code. If all of the
terminals are rated for 75 degrees Celsius, than you can install a 50 amp
circuit breaker. The electrician probably should have run a 60 amp line
since that is what the nameplate says is the maximum. You might want to put
an ammeter on the line to see how much current the unit is actually drawing.



"Joey_Bitchn'" wrote in message
...
Greetings could someone post an anwser to the group for the following:

I have a home that is about 20 years old. The sub-panel in the
basement is a 100 AMP panel. I have an aluminum wire that runs from
the panel to a new airconditiong unit I had installed recently. The
wire reads:
SE Cable Style U Type XHHW CDRS 600V 3 CDRS 6 AL (UL) 1983

I currently have a 40 AMP breaker installed that keeps tripping after
the AC unit cycles on and off a few times. The AC guy that installed
it said to put in a 50 AMP breaker but I can't find the information to
see if this wire can take that size breaker. If someone can help me
find the info or if you know for sure that a 50 AMP breaker is OK,
could you please let me know?

PS The AC unit says it can take a max breaker of 60 AMP.

Thanks

Joe

"Joey_Bitchn'" wrote in message
...
Greetings could someone post an anwser to the group for the following:

I have a home that is about 20 years old. The sub-panel in the
basement is a 100 AMP panel. I have an aluminum wire that runs from
the panel to a new airconditiong unit I had installed recently. The
wire reads:
SE Cable Style U Type XHHW CDRS 600V 3 CDRS 6 AL (UL) 1983

I currently have a 40 AMP breaker installed that keeps tripping after
the AC unit cycles on and off a few times. The AC guy that installed
it said to put in a 50 AMP breaker but I can't find the information to
see if this wire can take that size breaker. If someone can help me
find the info or if you know for sure that a 50 AMP breaker is OK,
could you please let me know?

PS The AC unit says it can take a max breaker of 60 AMP.

Thanks

Joe

This is Turtle.

Joey , i know just about all # 6 AL. good wire like you yhave here will run good
on 50 amp breakers on them. Now one thing you did not say and that was how long
of a run was the #6 Wire as to distance fromn the breaker to the hvac units.
Untill you give this info. i can not say the wire would be OK or not. So for now
No it will not work till you give the wire distance to concider.

TURTLE

Turtle,
The length of the wire is about 30 feet on the conservative side. I
didn't get a chance to check the draw on the circuit though. I'll try
getting that tomorrow assuming I can figure out how to do it
correctly.
Thanks for the help
Joe

This is Turtle.

Joey , i know just about all # 6 AL. good wire like you yhave here will run good
on 50 amp breakers on them. Now one thing you did not say and that was how long
of a run was the #6 Wire as to distance fromn the breaker to the hvac units.
Untill you give this info. i can not say the wire would be OK or not. So for now
No it will not work till you give the wire distance to concider.

TURTLE

"Joey_Bitchn'" wrote in message
...
Turtle,
The length of the wire is about 30 feet on the conservative side. I
didn't get a chance to check the draw on the circuit though. I'll try
getting that tomorrow assuming I can figure out how to do it
correctly.
Thanks for the help
Joe

This is Turtle.

The Ugly Book says you have up to about 50 feet or a little more for the 50 amp
ability and 50 amp breaker. Your well under with 30 feet.

TURTLE

TURTLE wrote:
"Joey_Bitchn'" wrote in message
...

Turtle,
The length of the wire is about 30 feet on the conservative side. I
didn't get a chance to check the draw on the circuit though. I'll try
getting that tomorrow assuming I can figure out how to do it
correctly.
Thanks for the help
Joe


This is Turtle.

The Ugly Book says you have up to about 50 feet or a little more for the 50 amp
ability and 50 amp breaker. Your well under with 30 feet.

TURTLE



This is odd, could you explain that to me? I am an automotive systems
engineer and I design the wiring for automobiles. The length of wire
has nothing to do with the fuse rating. The device on the end of the
wire also has nothing to do with the fuse rating.

Well ok, some devices can terminate a few different sizes of wire, and
this is a physical thing, nothing to do with current amount but with
diameter, etc.

So why does wire length matter for breaker size in a home?

--
Respectfully,


CL Gilbert

On 08/03/05 03:19 pm CL (dnoyeB) Gilbert tossed the following
ingredients into the ever-growing pot of cybersoup:

The Ugly Book says you have up to about 50 feet or a little more for
the 50 amp ability and 50 amp breaker. Your well under with 30 feet.

This is odd, could you explain that to me? I am an automotive systems
engineer and I design the wiring for automobiles. The length of wire
has nothing to do with the fuse rating. The device on the end of the
wire also has nothing to do with the fuse rating.

Well ok, some devices can terminate a few different sizes of wire, and
this is a physical thing, nothing to do with current amount but with
diameter, etc.

So why does wire length matter for breaker size in a home?

I assume that he means that a longer wire will result in a larger
voltage drop, so one would use a larger wire to reduce the resistance
and the voltage drop -- and a correspondingly higher-rated breaker to go
with the larger wire.

Perce

I assume that he means that a longer wire will result in a larger
voltage drop, so one would use a larger wire to reduce the resistance
and the voltage drop -- and a correspondingly higher-rated breaker to go
with the larger wire.

This is my understanding as well, and I've seen it in practice. Running
a 16A compressor on a 30A circuit done in 10/2 wire for 60 feet saw too
much drop across it to power the compressor in the winter. Bringing the
compressor within 6 feet of the box solved that problem.

Nathan

According to CL (dnoyeB) Gilbert :
This is odd, could you explain that to me? I am an automotive systems
engineer and I design the wiring for automobiles. The length of wire
has nothing to do with the fuse rating. The device on the end of the
wire also has nothing to do with the fuse rating.

Well ok, some devices can terminate a few different sizes of wire, and
this is a physical thing, nothing to do with current amount but with
diameter, etc.

So why does wire length matter for breaker size in a home?

It doesn't matter directly, but there are some indirect effects.

First of all, and this applies to your engineering, the fuse/breaker
should be no larger than the current carrying capacity of the wire.

Second of all, in AC power wiring, devices are tested and approved
for connection to a maximum circuit ampacity. So, you can't put a
15A 120V device on a 60A circuit.

And thirdly, which is where wire length comes into play: certain
devices (especially A/Cs and other large motor-powered devices) have
very large startup surges. The wiring has to be large enough so
that coupled with wire length, there isn't excessive voltage drop to
the device. The more the voltage drops, the more the startup surge
is prolonged. Coupled with the fact that breakers and fuses have
time-delay factors built in, it's entirely possible for a large
startup motor load (like a central A/C) to trip a breaker on 100' of
wire when it wouldn't trip the breaker on 10' of the _same_ wire.

Often the wire size has to be a size or two larger than the ampacity
would dictate to reduce voltage drop. With A/Cs and certain other
loads, not only the wire sometimes has to be larger than you'd expect
(with long runs), the breaker has to be somewhat larger than the
steady-state draw of the A/C would suggest.

Central A/Cs often have somewhat oversize wires and breakers, with
a fuse local to the device closer to the A/C's continuous draw.

--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

"CL (dnoyeB) Gilbert" wrote in message
...
TURTLE wrote:
"Joey_Bitchn'" wrote in message
...

Turtle,
The length of the wire is about 30 feet on the conservative side. I
didn't get a chance to check the draw on the circuit though. I'll try
getting that tomorrow assuming I can figure out how to do it
correctly.
Thanks for the help
Joe


This is Turtle.

The Ugly Book says you have up to about 50 feet or a little more for the 50
amp ability and 50 amp breaker. Your well under with 30 feet.

TURTLE

This is odd, could you explain that to me? I am an automotive systems
engineer and I design the wiring for automobiles. The length of wire has
nothing to do with the fuse rating. The device on the end of the wire also
has nothing to do with the fuse rating.

Well ok, some devices can terminate a few different sizes of wire, and this is
a physical thing, nothing to do with current amount but with diameter, etc.

So why does wire length matter for breaker size in a home?

--
Respectfully,


CL Gilbert


This is Turtle.

In the World of Electricians we have a simi-rule book called a Ugly Book which
will tell use what size wire, load size, and breaker size that matches a load
and keeps the voltage drop to less than 2% of Voltage. If you have 120 volts
service. You don't want more than 2% or 2.4 volt drop caused by the wirte size
being too small for the ampcity. The fastest way to burn up a hvac system is to
run it on low voltage.

TURTLE

Turtle

I installed the 50 AMP Breaker and so far so good.I've had the A/C on
all day. The wires aren't even warm. The A/C unit read 37.5 AMP
minimum so I guess that with the 40 AMP breaker the initial voltage
drop over a few on/off cycles was enough for the relay not to
re-engage.
Thanks for the tip. If you lived in Fallbrook, Calif. I'd buy you
lunch for saving me the call to an electrician :-)

Cheers!
Joe

"Joey_Bitchn'" wrote in message
...
Turtle

I installed the 50 AMP Breaker and so far so good.I've had the A/C on
all day. The wires aren't even warm. The A/C unit read 37.5 AMP
minimum so I guess that with the 40 AMP breaker the initial voltage
drop over a few on/off cycles was enough for the relay not to
re-engage.
Thanks for the tip. If you lived in Fallbrook, Calif. I'd buy you
lunch for saving me the call to an electrician :-)

Cheers!
Joe

This is Turtle.

Your Elkcome.

The most you can put on a 40 amp breaker is 32 amps. The most you can put on a
50 amp breaker is 40 amps without running it hot . So your good on the 50 amp
breaker and a 37.5 amp load.

TURTLE

Chris Lewis wrote:

According to CL (dnoyeB) Gilbert :

This is odd, could you explain that to me? I am an automotive systems
engineer and I design the wiring for automobiles. The length of wire
has nothing to do with the fuse rating. The device on the end of the
wire also has nothing to do with the fuse rating.



Well ok, some devices can terminate a few different sizes of wire, and
this is a physical thing, nothing to do with current amount but with
diameter, etc.



So why does wire length matter for breaker size in a home?


It doesn't matter directly, but there are some indirect effects.

First of all, and this applies to your engineering, the fuse/breaker
should be no larger than the current carrying capacity of the wire.

Rules change a little for motor circuits. In general the wire has to
have a rating 125% of the motor rating. Because of the high starting
current of motors, time delay fuses/circuit breakers can have a rating
of 175% of the motor rating; this is for short circuit protection. For
overload protection motor starters with a narrow range overload trip
unit or thermal trip units in the motor are used. For low duty-cycle
welders the fuse can be much larger than the wire rating. (Don't use
higher ratings if you don't know what code requirements are and what you
are doing.)

Second of all, in AC power wiring, devices are tested and approved
for connection to a maximum circuit ampacity. So, you can't put a
15A 120V device on a 60A circuit.

Home A/C units will be marked with a maximum overcurrent device size. If
it says maximum fuse size, the device must be a fuse.

And thirdly, which is where wire length comes into play: certain
devices (especially A/Cs and other large motor-powered devices) have
very large startup surges. The wiring has to be large enough so
that coupled with wire length, there isn't excessive voltage drop to
the device. The more the voltage drops, the more the startup surge
is prolonged. Coupled with the fact that breakers and fuses have
time-delay factors built in, it's entirely possible for a large
startup motor load (like a central A/C) to trip a breaker on 100' of
wire when it wouldn't trip the breaker on 10' of the _same_ wire.

Often the wire size has to be a size or two larger than the ampacity
would dictate to reduce voltage drop. With A/Cs and certain other
loads, not only the wire sometimes has to be larger than you'd expect
(with long runs), the breaker has to be somewhat larger than the
steady-state draw of the A/C would suggest.

Central A/Cs often have somewhat oversize wires and breakers, with
a fuse local to the device closer to the A/C's continuous draw.