83% rule
- Thread starter pedro1200
- Start date
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Yes.
It can be applied as outlined in 310.15(B)(7), and the applicable systems (residential services or main feeders or other feeders sized the same as a main feeder) are limited to ratings between 100A and 400A.
Cheers, Wayne
It can be applied as outlined in 310.15(B)(7), and the applicable systems (residential services or main feeders or other feeders sized the same as a main feeder) are limited to ratings between 100A and 400A.
Cheers, Wayne
In a case like if service or feeder are below 100a but 100a rated conductor are installed can you do the 83%
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Yes, if the conductor is rated 83A or more (e.g. #4 Cu 75C or #2 Al 75C), you can install it protected at 100A, and if your residential load calc comes out to 100A or less (optional load calc is usually the lower option), then you are good to go.
Cheers, Wayne
Mike holts calculation book shows the conductor being sized to 75 degrees terminals even though the calculation after the 83% allowance brought you under 100a. Do usually side the conductor to the terminal with the value before the 83% is applied?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
more info is needed. If the calculated load is over 83 amps (83% of 100) then you can use a 100 amp overcurrent protective device.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Not sure I unders question. In the graphic you posted the service is 110 amps with the 83% rule the conductor protected by the 110 amp OCPD needs to be a minimum of 91 amps. With 75 °C terminals the #3 AWG is rated at 100 amps or more than the minimum of 91 amps.
The question was that in this scenario the 75 degree termination is sized to 75 degrees column and not 60 because it was given in the question, correct? Normally in other circumstances it would be 60 degrees column. After the 83% allowance you are below 100a
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Look at the code section Mike has in the note at the bottom. Since the OCPD is 110 amps the terminals must be rated for 75°C.
Thank you that was my question do use the 110 or 83% of 110 for the termination. I got it
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You start with the size of the OCPD and multiply by 83%. That is the minimum conductor size. Since it's 110 amps for the OCPD the terminals are 75°C so you can use the 75°C ampacity of the conductor according to the note in the graphic.
Got it
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Look at 110.14( B ) Over 100 amps the terminals are 75C
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Correct, as a test question the terminals at 110 amps are good for 75°C. In the real world even OCPD'S of 100 amps and less would have 75° C terminals.
That just cleared everything up
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Mike Holt's test questions will often have situations where he doesn't tell you the temp of the terminals. You have to remember that 100 amps and under you must use 60C even though in reality most equipment is rated 75C. The older panels sometimes lose their info label so if you cannot determine if the panel has 75C then you must use the 60C for 100 1mps and less
- Location
- New Jersey
- Occupation
- Journeyman Electrician
This 60° C nonsense should be removed from the code as it is obsolete and replaced with an IN stating that older equipment might have 60° C terminals.
- Location
- Illinois
- Occupation
- retired electrician
He does that because that is how most of the licensing tests work.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
No, we can't touch the archaic language in 110.14(C)! It is some of the oldest text in the code, and must be venerated as such! It should be protected by UNESCO!