100% Rated Breaker and Assembly

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minesh21

Senior Member
Location
CA USA
Hi,

I have a 800A Square D I-Line panelboard (480V, 3P) that will have a 100% rated MCB. The conductors will be (2) sets of 600 kcmil to utilize the full 800 amps. The wire will be 90 degree C but sized per the 75 degree C column in the NEC. Do the lug landings need to be rated for 90 degree C as well? I read that the entire assembly must be rated for 100% continuous use, but I'm unsure on temperature rating of the lug landings.

Thanks,

Minesh
 

Smart $

Esteemed Member
Location
Ohio
The lugs only have to be rated 75°C.

The only difference in wire sizing is using 100% of continuous rather than 125%... and that is only for determining the minimum wire size. Everything else is the same, including derating from the 90°C column. The circuit ampacity cannot exceed the 75°C value nor can the calculated load exceed the derated ampacity.

If the breaker is furnished with lugs and listed for 100% operation, you are good to go (provided panelboard and enclosure are also listed for 100% operation). If you change out lugs, you will have to verify the replacements maintain the 100% listing.
 

minesh21

Senior Member
Location
CA USA
The lugs only have to be rated 75°C.

The only difference in wire sizing is using 100% of continuous rather than 125%... and that is only for determining the minimum wire size. Everything else is the same, including derating from the 90°C column. The circuit ampacity cannot exceed the 75°C value nor can the calculated load exceed the derated ampacity.

If the breaker is furnished with lugs and listed for 100% operation, you are good to go (provided panelboard and enclosure are also listed for 100% operation). If you change out lugs, you will have to verify the replacements maintain the 100% listing.

What if we verify that the lugs are rated for 90 degree C? Can we size the wire for the 90 degree C column with a 100% rated breaker? 500 KCMIL gets you 430A at 90 degree C so parallel sets would work for a 800A 100% rated breaker.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
What if we verify that the lugs are rated for 90 degree C? Can we size the wire for the 90 degree C column with a 100% rated breaker? 500 KCMIL gets you 430A at 90 degree C so parallel sets would work for a 800A 100% rated breaker.

Only if the breaker is rated at 90 degrees C.

Chris
 

templdl

Senior Member
Location
Wisconsin
What if we verify that the lugs are rated for 90 degree C? Can we size the wire for the 90 degree C column with a 100% rated breaker? 500 KCMIL gets you 430A at 90 degree C so parallel sets would work for a 800A 100% rated breaker.

If you want the facts consult with the manufacture. I highly doubt if they are because the breaker itself must be tested to be within a specific temperature rise which is based upon 75degC.
The breakers is listed for 100% application based upon 100%+100%, the wire size ampacity must carry that computed load based upon the 76degC column but the cable must be rated 90deC in order to do so. The breaker is tested in the UL lab with 3'(?) of line and load cable to assure that the breaker does not exceed its temperasture rise. REMEMBER that the cable acts as a heat sink and should not add to the heating of the breaker but takes away heat.
Also the breaker must be installed in a minor and/or enclosure suited for 100% application.
You may have noticed that 100% rated breakers have electronic trip units.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Only if the breaker is rated at 90 degrees C.

There is no UL489 listing for molded case circuit breaker terminations sized above 75C. Electricians need to stop offering this up as some type of possibility, because it does not exist.
Conductors sized at 90C must be terminated prior to getting to a breaker or switch. Insulation rating requirements and conductor sizing may be separate issues (e.g. 90C insulation to fixtures).
 

raider1

Senior Member
Staff member
Location
Logan, Utah
There is no UL489 listing for molded case circuit breaker terminations sized above 75C. Electricians need to stop offering this up as some type of possibility, because it does not exist.
Conductors sized at 90C must be terminated prior to getting to a breaker or switch. Insulation rating requirements and conductor sizing may be separate issues (e.g. 90C insulation to fixtures).

Agreed

Chris
 

minesh21

Senior Member
Location
CA USA
If you want the facts consult with the manufacture. I highly doubt if they are because the breaker itself must be tested to be within a specific temperature rise which is based upon 75degC.
The breakers is listed for 100% application based upon 100%+100%, the wire size ampacity must carry that computed load based upon the 76degC column but the cable must be rated 90deC in order to do so. The breaker is tested in the UL lab with 3'(?) of line and load cable to assure that the breaker does not exceed its temperasture rise. REMEMBER that the cable acts as a heat sink and should not add to the heating of the breaker but takes away heat.
Also the breaker must be installed in a minor and/or enclosure suited for 100% application.
You may have noticed that 100% rated breakers have electronic trip units.

Thanks. I have a client that keeps pushing back saying we need 90 degree C lugs for the breaker. I am trying to get the manufacturer to provide documentation to prove what you have said above (because they don't believe me).
 

ron

Senior Member
Thanks. I have a client that keeps pushing back saying we need 90 degree C lugs for the breaker. I am trying to get the manufacturer to provide documentation to prove what you have said above (because they don't believe me).

Depending on the manufacturer, they might have literature on their website.
http://www.schneider-electric.us/si...ang=en&id=FA175147&locale=en_US&redirect=true

http://www2.schneider-electric.com/...7/en_US/Wire Terminations 0110DB9901R2-02.pdf
 

templdl

Senior Member
Location
Wisconsin
What if we verify that the lugs are rated for 90 degree C? Can we size the wire for the 90 degree C column with a 100% rated breaker? 500 KCMIL gets you 430A at 90 degree C so parallel sets would work for a 800A 100% rated breaker.
I don't believe that you will find 90degC rated lugs.
If you do specify a 100% rasted breaker the enclosure and assembly must the listed for applying the breaker at 100%. Then, to actually apply the breasker'at100% the cable is sized for 100% of the continuous load and 100% of the non continuous load. The cable size should be seized per the 75degC column of NEC table 310-16 but have a 90degC min rated insulation.
As such the we are ampacity is sized based upon 75degC and not 90degC so standard terminals are allowed.
Remember that the intent of using a 100% tasted breaker is to save on cable cost. In not needing to size the cable for 125% of the continuous load there is the opportunity to downsize the cable size. You may also be able to downsize the breaker frame. Another consideration is if derating the wire may be an issue. When you use a 90deg rated wire already I may be a benifit when considering derating factors. As such you should evaluate if using a 100% rated breaker is even benificial or not
Keep in mind that a 100% rated breaker is no better than one that is applied at 80% of its rating. That 80% is the result of sizing the wire based upon 125% of the continuous load and the breasker's applier to protect the cable which results is the breaker actually being applied at 80% of its rating. The is no real difference between the breakers only the labels and the way that they are allowed to be applied.
The 100% rating is as the result of the breaker being specifically tested for 100% and labeled as such by UL.
 

minesh21

Senior Member
Location
CA USA

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
My takeaway from the PDF (first link, page 4) is that the 90 degree C equipment rating is for over 600V only. Everything under 600V is rated for 75 degree C even though the 90 degree C lugs may be used.

That is correct.
 

kwired

Electron manager
Location
NE Nebraska
And you can find fused disconnects and maybe even breakers with lugs attached that are stand alone 90 degree lugs, but the complete assembly is still only rated 75C.
 
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