NEC Section 220.40

[xptpcrewx]

Engineers accustomed to objective elegance in mathematics, may not get more subjective and hidden meaning, between the lines of the National Code of Exceptions (NEC).

I don't see a reason/benefit to "encrypt" meaning in such a simple requirement. I understand the requirement, it's the wording which is arguable crap. I was also an electrician before I was an engineer, so I don't see the relevance of the statement.

 

[xptpcrewx]

Perhaps this will help you xptpcrewx. Look at the reason this is in there. We want to make sure that the wires can carry the load (amperage) that is going to be applied to them without overheating and burning up, period. So the bottom line is the ampacity of the conductors isn't allowed to be less than the actual amperage of the circuit (technically with a fudge factor). It is determined that one can safely reduce the "calculated maximum amperage" on the wires by anticipating nonconcurrent loads of many different items. So we are allowed to calculate the load by adding up all of the items and then reducing that load by applying demand factors, a s others said, because not all stoves are going to have all burners on at the same time, even if 80% of the people are cooking, each burner cycles on and off irregularly and with 100 burners total, 80 of them being used, half of them cycling 50% of the time, half cycling 75% of the time, they will not all be on at the same time. Hence demand.

Thanks. I get demand factors, the reason for them, how to apply them, etc. The OP is more about the specific wording that doesn't register well with me. The confusion is the word "calculated load" because it inherently includes the demand factor so it reads redundant.

 

[xptpcrewx]

By substitution of the word "calculated load". This is how I was originally reading it.

220.40 General. The [(sum of the loads on the branch circuits) X (applicable demand factors permitted)] of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.

Seems redundant... but "calculated load" isn't defined anywhere, so I suppose it's kind of a definition in of itself

 

[ramsy]

I don't see a reason/benefit to "encrypt" meaning in such a simple requirement. I understand the requirement, it's the wording which is arguable crap. I was also an electrician before I was an engineer, so I don't see the relevance of the statement.

Not accustomed to this crap, yet you were an electrician before?

 

[wwhitney]

Seems redundant... but "calculated load" isn't defined anywhere, so I suppose it's kind of a definition in of itself

Yes, indeed. Think of it as a restriction on how you calculate the load: however you do it, it shall not be less that this formula.

Cheers, Wayne

 

[xptpcrewx]

Not accustomed to this crap, yet you were an electrician before?

Who says I am not accustomed? PI's are submitted all the time to correct the crap, and sometimes the revision is even more crap.

 

[xptpcrewx]

Yes, indeed. Think of it as a restriction on how you calculate the load: however you do it, it shall not be less that this formula.

Cheers, Wayne

Key phrase in bold. Thanks.

 

[bwat]

By substitution of the word "calculated load". This is how I was originally reading it.

220.40 General. The [(sum of the loads on the branch circuits) X (applicable demand factors permitted)] of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.

Seems redundant... but "calculated load" isn't defined anywhere, so I suppose it's kind of a definition in of itself

It wasn’t until this post that I understood why you were thinking it was worded it strangely.

 

[Strathead]

By substitution of the word "calculated load". This is how I was originally reading it.

220.40 General. The [(sum of the loads on the branch circuits) X (applicable demand factors permitted)] of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, as determined by Part II of this article, after any applicable demand factors permitted by Part III or IV or required by Part V have been applied.

Seems redundant... but "calculated load" isn't defined anywhere, so I suppose it's kind of a definition in of itself

Not necessarily. This section applies to branch panels along with distribution panels. As such for distribution panel, the sum of the loads (now here is the rub where we need to be qualified to do this... the "loads" can't include any demand factors) would be the first step, and then the demand factors are applied, because the demand factors on this panel are based on all of the downstream loads. For example, two panels may have 20kva of receptacle load load, each panel feeders will use 10kva plus 5 kva per table 220.44, but the distribution panel will use 20kva for the panel loads, sum them up and then use 10kva plus 15kva per table 220.44.