# NEC - when to use Continuous Load rating (X125%)



## indy-engineer

I'm referring to the posting for NEC Level of Difficulty where someone put up some sample NEC-type questions. I understand to multiply continuous load by 125% and non-continuous load by 100%, but how do you know when to use which. Is it related to lighting load?

Please help. I might get 3 or 4 questions right if I can understand this concept. I'm a second-timer and I took a loss on most of the NEC questions in April.

Thanks for anything!!


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## shellbell500

not sure i understand your question - i would imagine that the problems would tell you which of the load was continuous vs. not? this will be my first time on the test so correct me if i'm wrong. as far as i know you always multiply the continuous by 125% and the non-cont. by 100%, unless you are sizing conductors and you have to, i think, apply the demand factors on 100% of the load, not 125%, and compare the conductor sizes and choose the larger of the two. hmm - confusing.


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## chicago

On a somewhat unrelated topic at hand, can someone give me last minute feedback on the most typical Articles/Tables/terminology seen on the PE exams for the NEC 2005?

Here's what I have:

*Tabbed:*

Table 310.16 Ampacity

Table 430.250 Motor FLC

Chapter 9 Table 9

Art. 250 Grounding/Bonding

Art. 220 Branch ckt. loads

*Keywords: *

derate, demand factor, standard or next size up for fuses/CB's, adjustment/correction factor, continous/non-continous loads, GFC, overcurrent protection, separate overload,

*General rule of thumbs:*

125%*ampacity, P=S (power) where pf=1, 600V, 115% (motors-service factor), 135% capacitors, 250% FLC (CB's), 3x starting current, 6x starting current

Let me know if I'm missing anything significant.


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## SteveR

Isn't a load considered continuous if it will carry its maximum current for 3hrs or more?


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## jdd18vm

Basically continuous loads are defined as any load where the maximum current is expected for 3 or more hours. Mainly, but not exclusively Lighting. See the definitions Article 100. This is my first time too but from all the examples I've seen Lighting would be the continuous. Stop here if your satisfied 

Generally its a three step process: Calc load, size wire, select overcurrent

For a combined load: Calc your load as %125 any continuous plus %100 of the remaining loads, apply any demands.

That gives you your min size for the conductor. Look up in table, likely table 310-16 for the insulation (THHN THWN) given. Apply and derating factor like more than 3 conductors.

Overcurrent protection varies. Again generally the calculated number you got above, if it doesn't match a standard size, the next higher may be used.

For Motors depending on the device (ie non-time delay fuse) they call for, the percentage varies see Table 430.52

Remember on a single motor you have to use the Ampacity given in tables 430.248 and/or 430-250 not any Ampacity they may state in the problem.

For Motor Overloads use motor nameplate (or given ampacity) and Service factor. See Section 430.31 and 430.32

More than you need to know but these were all in the NCEES

Good Luck guys!

ps Shell yes i finally got 102


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## jdd18vm

chicago said:


> On a somewhat unrelated topic at hand, can someone give me last minute feedback on the most typical Articles/Tables/terminology seen on the PE exams for the NEC 2005?
> Here's what I have:
> 
> *Tabbed:*
> 
> Table 310.16 Ampacity
> 
> Table 430.250 Motor FLC
> 
> Chapter 9 Table 9
> 
> Art. 250 Grounding/Bonding
> 
> Art. 220 Branch ckt. loads
> 
> *Keywords: *
> 
> derate, demand factor, standard or next size up for fuses/CB's, adjustment/correction factor, continous/non-continous loads, GFC, overcurrent protection, separate overload,
> 
> *General rule of thumbs:*
> 
> 125%*ampacity, P=S (power) where pf=1, 600V, 115% (motors-service factor), 135% capacitors, 250% FLC (CB's), 3x starting current, 6x starting current
> 
> Let me know if I'm missing anything significant.


Of course Im with you Chi, first time. But all Ive read, you look like you have it well done! "the other board" sample exam got into some residential stuff there are good example calcs in Annex D might help.


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## indy-engineer

That's perfect and I'm satisfied. Thanks for the reply!!!


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