Breaker is not 90 degree certified
#1
03-16-05, 08:16 PM
Breaker is not 90 degree certified
I am adding a subpanel right next to my main breaker box. I am running 100 amp service to the subpanel off a branch breaker in my main panel. I purchased and installed (last night) 2-2-2-4 90 degree rated aluminum wire (XHHW-2) which allows both 110 Volt wires plus separate ground and neutral wires. This wire is rated for 100 Amp service. The 100 Amp breaker, however, is not rated for 90 degree wire, only 75. I looked at the breaker manufacturer's website, and it states: "All molded case breakers require 60/75 degree Centigrade Wire. 90 degree wire can be used but must be oversized to meet the 75 degree wire copper thickness."
I also referenced "Wiring Simplified" by Park Publishing (they sell it at Home Depot), which states, "Column C [in the wire amperage chart] covers conductors with high-temperature insulation (90 degree C). Although these wires are very common today, the termination rules tend to limit the usable current in these wires to the amounts in Columns A and B as noted." Column A & B have the 60 and 75 degree amperage ratings in the table.
My guess is that I will not ever exceed the 100 amps on the subpanel (at least while I am in the house), but I would hate to think that years from now when I sell the house that it would burn to the ground because of this. It sounds very much like maybe I should replace the wire. Thoughts?
I also referenced "Wiring Simplified" by Park Publishing (they sell it at Home Depot), which states, "Column C [in the wire amperage chart] covers conductors with high-temperature insulation (90 degree C). Although these wires are very common today, the termination rules tend to limit the usable current in these wires to the amounts in Columns A and B as noted." Column A & B have the 60 and 75 degree amperage ratings in the table.
My guess is that I will not ever exceed the 100 amps on the subpanel (at least while I am in the house), but I would hate to think that years from now when I sell the house that it would burn to the ground because of this. It sounds very much like maybe I should replace the wire. Thoughts?
#2
03-16-05, 08:25 PM
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Nobody makes any 90-degree terminations for residential use. The best you can ever do is 75 degree terminations, which means that wire can never be used above its 75-degree ampacity. Officially, #2 aluminum is only good for 90 amps at 75 degrees when used to feed a subpanel. However, for reasons I don't understand, inspectors routinely allow it to be used for 100 amps. Check with your inspector to see if that is his position.
#3
03-16-05, 08:46 PM
Re: Breaker is not 90 degree certified
It sounds like the easiest thing to do, especially since I don't anticipate ever loading this circuit with 100 amps, is to return that breaker in favor of a 90 Amp breaker. They didn't carry this at the store where I got the 100 amp breaker, but I am sure I can find it at a local electrical supply house. I will call around tomorrow and see who has it in stock.
The table I was referring to is based upon the 2002 NEC and does list the 2 gauge aluminum at 90 amps.
Thanks so much for your prompt reply.
Bruce
The table I was referring to is based upon the 2002 NEC and does list the 2 gauge aluminum at 90 amps.
Thanks so much for your prompt reply.
Bruce
#4
03-16-05, 08:49 PM
Breaker not 90 degree certified--Add on question
The other thing that I was wondering about was the termination of the neutral wire in the main breaker box. The wire is 2 gauge, which was too large to fit into one of the ground bar holes, so I split the strands and screwed them down into 2 adjecent holes (3 in 1, 4 in the other). I suspect this would raise eyebrows in an inspector's eyes, yes? What other options are there?
Thanks in advance.
Bruce
Thanks in advance.
Bruce
#5
03-16-05, 08:54 PM
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Buy a special neutral lug. It has two feet which fit in two holes in the neutral bar, and then has one larger hole for your #2 neutral.
#6
03-16-05, 09:39 PM
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Originally Posted by BruceW
"All molded case breakers require 60/75 degree Centigrade Wire. 90 degree wire can be used but must be oversized to meet the 75 degree wire copper thickness."
The insulation temperature is what determines the amperage. Infact 90deg wire has a higher ampacity than 75deg. Why is it then they are saying the better wire must be larger for the same amperage. I love manufacturers which mis-interpret the code.
Many inspectors allow 310.15(B)(6) to be used for sub-panel amperages. They consider the wire going to a sub-panel a feeder. And I agree. This let's us use #2al XHHW to feed a 100 amp sub-panel.
This sentence is the key IMO:
"..., the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch circuit panelboard(s)"
A sub-panel is a lighting and appliance branch circuit panelboard.
#7
03-17-05, 09:47 AM
Good Point Speedy Petey. I think we all know what they meant to say, and we all know that they didn't say what they meant to say. 
The manufacturer was Cutler Hammer.
I made a few calls, but cannot seem to get a good answer on whether inspectors would give the 100 amp breaker a
or 
, so I called around and found the 90 amp breaker. I am going to pick it up now along with the neutral lug.
Thanks everyone for your guidance on this one.
The manufacturer was Cutler Hammer.I made a few calls, but cannot seem to get a good answer on whether inspectors would give the 100 amp breaker a
or , so I called around and found the 90 amp breaker. I am going to pick it up now along with the neutral lug.Thanks everyone for your guidance on this one.
