c/b and conductor sizing


  #1  
Old 03-10-07, 09:15 AM
H
Member
Thread Starter
Join Date: Mar 2007
Posts: 76
Received 0 Votes on 0 Posts
c/b and conductor sizing

I'm helping my sis with some repairs to her house in Tennessee, circa 1937. I looked at the breaker panel this am and said uh oh several times. First issue is the c/b and wire size to the heating/cooling unit. The circuit starts at the panel with a 60 amp/2pole breaker and ALUMINUM WIRE [it looks like it's #6 wire] which goes to a junction box in the basement [panel is also in the basement, the aluminum wire section is roughly 15 feet] where it changes to #8 copper wire and then goes to a disconnect box at the outdoor package unit. In the disconnect at the unit there is a 40 amp/2 pole circuit breaker and then a length of liquidtite to the unit. The nameplate on the unit indicates a minimum circuit ampacity of 30.9 amps and a maximum circuit ampacity of 50 amps. [the heat is gas] It appears that the house previously had a split system that was replaced with the package unit. The distance from the breaker panel to the outdoor unit is about 50 feet. I'm thinking that the #8 wire that runs from the junction box to the 40 amp c/b outside is improperly protected because of the 60 amp breaker upstream from that section of the circuit. I believe the best remedy is to replace the c/b in the panel with a 40 amp/2pole HACR breaker and also replace the aluminum wire that runs from the breaker panel to the junction box with #8 copper. Thanks in advance for your comments/suggestions. btw- heating/cooling is my normal line of work which is why I paid close attention to that circuit. I was very unhappy to see the aluminum wire. Thanks again.
 
  #2  
Old 03-10-07, 09:39 AM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,454
Received 0 Votes on 0 Posts
Why are you unhappy to see the aluminum? Larger AL (#8 and up) wire is NOT the problem that smaller wire is. Replace it if it makes you feel better but #6AL is perfectly safe.
A/C units follow different codes than other circuits, so the 60 amp breaker is very likely sized within code.
 
  #3  
Old 03-10-07, 11:38 AM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,162
Received 1 Vote on 1 Post
depending on the insulation type of the aluminum, it may be rated for the amperage. THHN aluminum is rated for 60 amps.

If a 40 amp breaker will handle the unit, go ahead and change the breaker in the panel to a 40 and all will be well.

I wouldn't be worried about the aluminum wire other than to be sure ther terminations are good and clean.

I disagree with petey on the upsizing of the breaker to cover the inrush current since the possibly oversized breaker is not on a branch circuit but a feeder. The branch circuit protection is the one allowed to be oversized.

It reality it doesn;t truly affect your situation because the feeder only feeds the AC unit but that is what it is.
 
  #4  
Old 03-10-07, 11:54 AM
H
Member
Thread Starter
Join Date: Mar 2007
Posts: 76
Received 0 Votes on 0 Posts
Thanks for your replies. The only thing I don't like about the aluminum wire is that alumimum has been responsible for many fires and is now not allowed in many areas. I don't think the aluminyum cable is THHN. It looks old and has a fabric kind of outer sheath. I haven't been able to read a marking on it. The maximum circuit ampacity listed on the unit nameplate is 50 amps. That, plus the fact that wire size changes to a smaller size at the jb is why I think the breaker in the panel is oversized. As for inrush current, a HACR breaker is designed to cover that. I'd feel the best if I replace the alumium wire and the breaker in the panel. It's a short run and easy to get to. Thanks again.
 
  #5  
Old 03-10-07, 12:05 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,162
Received 1 Vote on 1 Post
the problem with aluminum wire is when it was used to feed individual devices such as receps and switches.

As long as the lugs the wire is terminated in are rated for al, you are OK.

I won;t argue about you changing the wire since it's yours,not mine, just trying to ease your mind a bit about it being there.

also, since you have a 40 amp breaker at the disconnect, the circuit that feeds the unit is a 40 amo circuit.

as well, it is normal for aluminum wire to be larger than a copper conductor in the same circuit. Aluminum is never rated as high ampacity as copper so you have to use a larger aluminum conductor to achieve the same ampacity as when using copper.
 
  #6  
Old 03-10-07, 12:51 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,454
Received 0 Votes on 0 Posts
As nap said, the AL wire that is a problem is smaller (#10 and under). Larger AL conductors are NOT the same issue.



"I disagree with petey on the upsizing of the breaker to cover the inrush current since the possibly oversized breaker is not on a branch circuit but a feeder."

How do you figure? Just because there is a breaker at the unit? This is simply a disconnect. That does NOT make this a feeder.
If it were a fused disconnect would you feel the same way???
 
  #7  
Old 03-10-07, 01:06 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,162
Received 1 Vote on 1 Post
"I disagree with petey on the upsizing of the breaker to cover the inrush current since the possibly oversized breaker is not on a branch circuit but a feeder."

How do you figure? Just because there is a breaker at the unit? This is simply a disconnect. That does NOT make this a feeder.
If it were a fused disconnect would you feel the same way???
===============================

a branch circuit is defined as the wiring from the last OCPD to the appliance (actually; outlet , but in this case there is no outlet per se so it would be to the appliance). That makes the wiring from the panel to the last OCPD a feeder and not subject to the oversized breaker rules of the HVAC and motor exceptions. In this siutaion it is truly irrelevent because the only thing on that circuit is the AC. Merely a technicality.

and yes, I would feel the same way of the final OCPD were fuses. It doesn;t change anything.

Now if the disconnect at the AC were not an OCPD and simply a disconnect, that would make the entire run a branch circuit.
 
  #8  
Old 03-10-07, 01:34 PM
Speedy Petey's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Nov 2003
Posts: 2,454
Received 0 Votes on 0 Posts
I do agree it's a technicality.
Agree to disagree.

What's funny is I rarely use those sections of the code for motors, A/C units and welders in a residential setting. And I never use them if the circuit feeds a receptacle.
 
  #9  
Old 03-10-07, 01:48 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,162
Received 1 Vote on 1 Post
cool beans
 
  #10  
Old 03-10-07, 07:09 PM
H
Member
Thread Starter
Join Date: Mar 2007
Posts: 76
Received 0 Votes on 0 Posts
Thanks guys. I understand that aluminum wire has to be larger than copper to get the same rating. My main concern is that wire changes sizes in between the 60 amp breaker in the panel and the 40 amp breaker at the unit at the unit. Also, the maximum ampacity for this unit is 50 amps.

Here's the circuit: 60 amp c/b-------#6 AL---junction box-----#8 copper------40 amp c/b-----#8 copper-----heat/cool unit.

What protects the section of #8 copper in between the junction box and the 40 amp breaker [it has a 60 amp breaker upstream of it. Will that section handle 60 amps with no problem?]? Or is something wrong with my thinking?
Based on what I've seen in this house so far, I'm afriad to open the j/b to see how they spliced the AL to the copper. Once again, thank you all VERY MUCH for your help.
 
  #11  
Old 03-10-07, 07:58 PM
nap's Avatar
nap
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,162
Received 1 Vote on 1 Post
again, depending on the insulation it differs.

THWN #8 copper is good for 50 amps.

As you can see between the discussion between petey and myself, the technical correctness would be to put a 40 or 50 amp breaker on the feeder but in all reality the 40amp breaker is going to limit the draw from the appliance to that 40 amps. The only time the 60 amp breaker would be tripped is in a shot circuit condition or of you tapped that circuit for something else.

If there were no breaker at the appliance, you would be limited to a 50 amp breaker by the appliance nameplate.If a max OCPD wasn;t listed, the 60 amp breaker would be fine.

So, to make things correct, replace the breaker with a 40 or 50 amp breaker. I would definately check the copper/aluminum joint to be sure they used a correct method. A split bolt that accepts cu and al would be about the only thing available at the time this was done. A polaris connector rated for cu/al connections is available now if you need to correct the joints. That is the one place I would be concerned with the aluminum wire. Other than that, I wouldn't be concerned.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: