Annex D3

[erickench]

As I look at this example problem in Annex D3 I come across a note at the end:

In the example, 125% of the actual connected lighting load (8500 VA x 1.25 = 10,625 VA) is less than 125% of the load from Table 220.12, so the minimum lighting load from Table 220.12 is used in the calculation. Had the actual lighting load been greater than the value calculated from Table 220.12, 125% of the actual connected lighting load would have been used.

Looking at the example itself you would see that the 125% factor is not applied to the continuous load as per Table 220.12 and is subsequently added to the noncontinuous load. But Mike Holt and James Stallcup both say that the 125% factor is applied regardless of whether the actual connected load or the Table 220.12 calculation is greater. Does anyone care to comment on this?

 

[david luchini]

Looking at the example itself you would see that the 125% factor is not applied to the continuous load as per Table 220.12 and is subsequently added to the noncontinuous load. But Mike Holt and James Stallcup both say that the 125% factor is applied regardless of whether the actual connected load or the Table 220.12 calculation is greater. Does anyone care to comment on this?

The example does apply 125% to the lighting load as calculated from T220.12...

Minimum Size Feeder
Subtotal noncontinuous load........ 12,200VA
Subtotal continuous load @125% 20,250VA
Total.............................................32,450VA

The note about 125% of actual connected load vs. 125% of minimum lighting load from T220.12 is poorly written. 125% is irrelevant to that discussion. What is important is whether the actual connected load or the minimum lighting load (that is to say 100% of connected load vs. 100% of T220.12 minimum load) is larger.

 

[erickench]

The example does apply 125% to the lighting load as calculated from T220.12...

I'm looking at the 2014 NEC. Where do you see the 125% applied? I don't see it.

 

[david luchini]

At the end of the example...

Minimum Size Feeder (or Service) Overcurrent Protection
[see 215.3 or 230.90]
Subtotal noncontinuous loads...................................... 12,200 VA
Subtotal continuous load at 125% (16,200 VA ? 1.25) 20,250 VA
............................................................................Total 32,450 VA
32,450 VA ? 240 V = 135 A
The next higher standard size is 150 A (see 240.6).

Minimum Size Feeders (or Service Conductors) Required
[see 215.2, 230.42(A)]
For 120/240 V, 3-wire system, 32,450 VA ? 240 V = 135 A
Service or feeder conductor is 1/0 Cu in accordance with 215.3 and Table 310.15(B)(16) (with 75?C terminations).

 

[erickench]

Are we looking at the same example D3 in Annex D? This is what I'm reading:

A store 50 ft by 60 ft, or 3000 ft² has 30 ft of show window. There are a total of 80 duplex receptacles. The service is 120/240 V, single phase 3-wire service, Actual connected lighting load is 8500 VA.

Noncontinuous Loads
Receptacle Load [see 220.44]
80 receptacles at 180 VA 14,400 VA
10,000 VA at 100% 10,000 VA
14,400 VA - 10,000 VA at 50% 2,200 VA

Subtotal 12,200 VA

Continuous Loads
General Lighting
3000 ft² at 3 VA/ft² 9,000 VA
Show Window Lighting Load
30 ft at 200 VA/ft² [see 220.24(G) 6,000 VA
Outside Sign Circuit [see 220.14(F)] 1,200 VA

Subtotal 16,200 VA
Subtotal from noncontinuous 12,200 VA

Total noncontinuous loads +
continuous loads = 28,400 VA

 

[Smart $]

Are we looking at the same example D3 in Annex D? ...

Everything quoted is same as 2011 NEC. Proceed further into the example....

Minimum Size Feeder (or Service) Overcurrent Protection [see 215.3 or 230.90]
Subtotal noncontinuous loads	12,200 VA
Subtotal continuous load at 125% (16,200 VA ? 1.25)	20,250 VA
Total​	32,450 VA

 

[david luchini]

Are we looking at the same example D3 in Annex D?

As Smart$ pointed out, you have to read the example all the way to the end.

The 125% factor is not applied in calculating the load. The total load is the non-continuous load (12,200VA) plus the continuous load (16,200VA) = 28,400VA total load.

The 125% factor is applied (at the end of the example) to figure minimum feeder conductor and OCPD size: 12,200 + 16,200*1.25=32,450VA.

 

[erickench]

The note is clear. The 125% is only applied when the actual load is greater than the Table 220.12 calculated load. I'm getting the feeling that the 125% may already be included in Table 220.12. In this case the VA/ft² is 3 VA/ft². The actual unit load would be .8 x 3 = 2.4 VA/ft².

 

[Smart $]

The note is clear. The 125% is only applied when the actual load is greater than the Table 220.12 calculated load. I'm getting the feeling that the 125% may already be included in Table 220.12. In this case the VA/ft² is 3 VA/ft². The actual unit load would be .8 x 3 = 2.4 VA/ft².

The note is misleading, especially if that is how you are interpretting it.

Article 220 load calculations DO NOT include a general 125% factor for continuous loads. The requirement for 125% of continuous load factoring is in Articles 215 and 230, for feeder and service conductors and overcurrent protection, respectively. That's why it's in the service or feeder conductor and overcurrent protection part of the determination.

Also, as David mentioned earlier, it matters not whether the actual connected lighting load is compared to the minimum table lighting load either at 100% of both or 125% of both. The calculation must be made using the larger of the two. But it would be easier to just compare at 100%, and definitely less confusing than comparing at 125% at that stage of the determination.

 

[jumper]

IMO that note should be rewritten using "100%" as per 220 calculations or moved down to Minimum Size Feeder and OCPD part, where the 125% factor is actually used.

As it stands, the placement and/or wording seems to continually cause confusion.

 

[erickench]

If you all look at the example the continuous and noncontinuous loads are added without the 125% factor included. I think what happened is that when these unit load values were determined it was taken into account that all the occupancies listed in Table 220.12 were continuous lighting loads. The only exception would be dwellings because the receptacle load is included in the calculation. Then again floor and table lamps could be plugged into these dwelling receptacles.

 

[Smart $]

If you all look at the example the continuous and noncontinuous loads are added without the 125% factor included. I think what happened is that when these unit load values were determined it was taken into account that all the occupancies listed in Table 220.12 were continuous lighting loads. The only exception would be dwellings because the receptacle load is included in the calculation. Then again floor and table lamps could be plugged into these dwelling receptacles.

As I and others keep saying, Article 220 load calculations do not factor continuous loads at 125%. However, they are kept separated so you can apply 125% during the service or feeder conductor and ocp determination...