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Bowhunter

Member
I'm having a hard time getting my head around the example D4(a) in the 2008 or the 2011 code book.
When sizing the feeder conductors every time I go to figure the proper size conductor and refer to 215.2(A) (1) It says: the conductor size, before the application of any adjustment or correction factors, it shall have an allowable ampacity not less than the non-continuous load plus 125% of the continuous load.
It seems pretty clear to me or does it? It does not say anything about actual load, calculated load, real load, or computed load. It says the non-continuous plus 125% of the continuous load.

I have all the literature from Jim Pauley on the subject from 1995. James Stalcup's articles. In fact I think the example in the code book was from James Stalcup. I also have Mike Holt's articles. And I use Tom Henry"s calculation book plus all these gentleman's articles on continuous loads. I've been teaching the N.E.C. for the past 15 years. Often time's I seem to think I understand the proper sizing of these conductors and it seems real clear to me, then I think that can't be right.

Anyway, is it just me or should there be some informational notes on types of loads in sections: 210.19 (A) (1) Branch circuit conductors, 210.20 (A) Overcurrent Protection for Branch Circuits,
215.2 (A) (1) Feeder Conductors, and 215.3 Overcurrent Protection for Feeders?

Then of coarse I do the math for the adjustment and correction factors starting in the 90 degree column but when I'm done and explain that the total ampacity has to carry the ampacity of the actual load and not the calculated load in the 75 degree column it becomes so confusing.

Thanks for letting me vent. If anyone has a fairly easy explination for properly sizing conductors for non-continuous loads plus 125% of the continuous loads please let me know.:?

jumper

Senior Member
in short, anything that runs 3 hours or more is sized at 125%, ie: commercial lighting, hvac, constant motors, etc; and everything else at 100%.

ritelec

Senior Member
Then of coarse I do the math for the adjustment and correction factors starting in the 90 degree column but when I'm done and explain that the total ampacity has to carry the ampacity of the actual load and not the calculated load in the 75 degree column it becomes so confusing.
or 60 degree... 100 amp and under

in short, anything that runs 3 hours or more is sized at 125%, ie: commercial lighting, hvac, constant motors, etc; and everything else at 100%.
Notice the word "commercial".....

In residential I've always applied the 125% to loads I would consider running at 3 hrs. or more..........however, just found out recently, the only "continuos" loads in a residence would be electric water heater and
I believe it was electric heat.

augie47

Moderator
Staff member
Note the definition of Continuous Load in Art 100. It states "the maximum current", so a piece of equipment that may be switched ON for 3 hours or more with a load that cycles or changes (such as most heating applications) is not necessarily continuous.

jumper

Senior Member
In residential I've always applied the 125% to loads I would consider running at 3 hrs. or more..........however, just found out recently, the only "continuos" loads in a residence would be electric water heater and
I believe it was electric heat.
The 125% for continuous is for branch circuit sizing not feeder/service concerning WH and electric heat.

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L (120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.

424.3 Branch Circuits.

(B) Branch-Circuit Sizing. Fixed electric space-heating
equipment and motors shall be considered continuous load.

ritelec

Senior Member
Mucho Thanks Fellas

Mucho Thanks Fellas

Thanks Jumper!

Ya know, I've let alot of this stuff fall by the way side over the past few years.

I've been picking up alot of info from this forum over the past several weeks and just wanted to that you all.

Rich

Smart \$

Esteemed Member
...
It seems pretty clear to me or does it? It does not say anything about actual load, calculated load, real load, or computed load. It says the non-continuous plus 125% of the continuous load.

...
210.19(A)(1) and 215.2(A)(1) are referring to calculated loads, as determined by Article 220 requirements. While examples in Annex D show continuous, non-continuous loads amidst the calculations, they are for compliance with the aforementioned sections only. Article 220 has no stipulation regarding non-continuous plus 125% continuous load.

General determination of minimum conductor size is threefold. 110.14(C), 210.19(A)(1) or 215.2(A)(1), and 310.15. The largest minimum wire size determined by each of these three sections is the minimum required (i.e. the section resulting in the largest conductor of the three supercedes the other two).

:blink: hmmm.... I think I got that right

Bowhunter

Member
To make it even more puzzling in the definitions in article 100 it says in the definition of ampacity: the current in amperes, that a conductor can carry continuously under the conditions of use without exceeding its tempeature rating. So all the conductors in Table 310.16 (2008) Code at 86 degrees F are already rated for continuous loads.

jumper

Senior Member
To make it even more puzzling in the definitions in article 100 it says in the definition of ampacity: the current in amperes, that a conductor can carry continuously under the conditions of use without exceeding its tempeature rating. So all the conductors in Table 310.16 (2008) Code at 86 degrees F are already rated for continuous loads.
conditions of use is part of final ampacity .

continuous = 80%

non continuous=100%

mixed= combination of both

jumper

Senior Member
I stole this from dennis alwon from an old thread

Basically the branch circuit conductors must be capable of carrying the load of the circuit. If part of the circuit is non continuous and the other continuous then it must carry the load equivalent for both.

Say you have 2 loads of 10 amps and 5 amps. The 5 amps is continuous so we must add the 10 amps plus 125% of the 5 amps. 10 + 6.25= 16.25. The conductor must be sized for the 16.25 amp load not 15 amps.

Smart \$

Esteemed Member
To make it even more puzzling in the definitions in article 100 it says in the definition of ampacity: the current in amperes, that a conductor can carry continuously under the conditions of use without exceeding its tempeature rating. So all the conductors in Table 310.16 (2008) Code at 86 degrees F are already rated for continuous loads.
True.

However, the concept behind the extra 25% is so the conductor does not operate continuously at the borderline condition. Also, in determining ampacity we anticipate certain conditions of usage. In hindsight, we are not always accurate in that assessment. Experience proves a little padding provides some extra assurance. Its easier and less costly than replacing conductors and equipment.... and perhaps even save a life.

jumper

Senior Member
True.

However, the concept behind the extra 25% is so the conductor does not operate continuously at the borderline condition. Also, in determining ampacity we anticipate certain conditions of usage. In hindsight, we are not always accurate in that assessment. Experience proves a little padding provides some extra assurance. Its easier and less costly than replacing conductors and equipment.... and perhaps even save a life.
Nice job sir.:thumbsup:

Bowhunter

Member
Thanks, Smart \$. That's the way Ive been sizing conductors and that's the way I will continue sizing them.

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