Duplex Standard & Optinal Load calc.

[FastSparky]

I'm not sure on why my awnsers not matching perhapse it's the rounding up at the end for my AMPs.
So im going to give an example and am REALLY hoping someone can work it out for me, im not needing all the ref. pages just love to have it worked trew so i can look and see where im going wrong.

A Duplex W/ 120/240 V. 1 Phase service 800 sq. ft. W/

1 -7 kw range
1- 5 amp garbage disposal
1- 11 amp dish washer
1- 3 kw hot water heater
1- 15 kw heater
1- 21 amp 240v. A/C
The question wants to know both in a standard and an optinal service load in amps.

The 4 awnsers givin for standard are 223 , 211, 242 , 252 AMPS.

The 4 awnsers givin for optinal are 109, 200, 223, 240 AMPS.

Thanks for the help FS.

 

[charlie b]

Re: Duplex Standard & Optinal Load calc.

How about posting your solution first?

Also, just to clarify, I presume you meant 800 square foot for each of the two units?

 

[FastSparky]

Re: Duplex Standard & Optinal Load calc.

Thats just it it was asked the exact way im asking it so i dont know if its 1 or 2 ( 800 sq. ft ) units

 

[gndrod]

Re: Duplex Standard & Optinal Load calc.

hi fastsparky, is the 15kw space heating with 3 or less controls 220.82(C)(5) or 100% continuous load 220.82(C)(3)thermal storage heating? This needs to be discerned for [220.82(C)(?)] largest heating & A/C optional load determination. rbj, Seattle

 

[gndrod]

Re: Duplex Standard & Optinal Load calc.

fastsparky, this may be a trick question because the kitchen SA's are not listed. The G.D. and DW are the clue there. In either case, the answers using the SA's do not match either std or optional choices given. Obviously the clothes dryer and washer are on a multi dwelling house circuit or the laundromat down the street. Re-check your input for us. Tx, rbj, Seattle

spelling

[ February 08, 2006, 01:12 AM: Message edited by: gndrod ]

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

See 220.53 for a demand factor to apply to the HWH, the DW, and the disposal.

Also, the heater and AC won't both run, so use the larger load. Add in your lighting load for SF, and your laundry circuit. (The SA circuits are already included in the lighting load).

I get 251 amps for the standard method.

Warning: I don't do much residential, so I may not have the right answer.

[ February 08, 2006, 09:25 AM: Message edited by: steve66 ]

 

[FastSparky]

Re: Duplex Standard & Optinal Load calc.

LOL I was thinking it was just me but nice to see it stumped you also ground rod .

They didnt add up for me either and i tried nummuros ways to add up the duplex.

So then im like well mabey im just not rounding up to the right amps. But by looking at the anwnsers givin it dosnt seem as if its the case.

Which puts me back to the question at had to see if others that do know how to type it all out can and will so that I may see where different applications might make it click in my brain hehe.

Thanks guys FS.

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

I was going to post my solution, but I found at least two mistakes.

1) The SA circuits do need to be added. That's 4*1500VA.
2) The range gets a demand factor of 80%.
3) Not sure if both units can share a laundry circuit. So either 1500 or 3000 VA for laundry.

Steve

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

OK, I worked it again for the standard calculation. If you don't add any laundry circuits (which is allowed if the owner isn't going to allow washers and dryers), use the demand factors mentioned above, you should get one of the answers listed.

Steve

 

[FastSparky]

Re: Duplex Standard & Optinal Load calc.

This is what i came up w/ on STANDARD method :

800x2x3= 4800
1500x4 = 6000
W/ laundry 1500x2= 3000
-------
13800 - 3000= 3000
-3000
--------
10800 -- 35%= 3780
------
6780
15kw x 2 @ 100% = 30000


3000 x 2 = 6000
600 x 2 = 1200
1320 x 2 = 2640
------
9840 x 75% = 7380

7 kw x 2 = 14000 @ 65%= 9100
------
53260
devided by 240
------
w/ my caluculator i get 221.9
rounding up to the answer *223AMPS
Please if any one can check and add reply thanks FS.

 

[FastSparky]

Re: Duplex Standard & Optinal Load calc.

Now for Optional this is what I got


800 x 2 x 3 = 4800
3000 x 2 = 6000
1500 x 2 = 3000

Range 100 % x 2 @ 7 kw = 14000
GD 600 x 2 = 1200
DW 1320 x 2 = 2640
HwH 3000 x 2 = 6000
--------
37640
-10000 10000
-------
27640
@ 40% 11056

21056
Heat 15 kw x 2 = 30000 @ 65 % = 19500
------
40556
devided by 240v

with my calculator 168.98AMP
Which dosnt even come close to 1 of the 4 awnsers 190 , 200 , 223, 240 so again can someone double check my work and see whats up / also am i to round up to the closest matching service feeders in amps ( if so then it should be 175 amps table 310.15 B 6 ) Thanks yet again FS.

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

For the standard load: I forgot the 35% demand for lighting loads, but I don't think that applies to the SA circuits.

Here is how I see it:

For range, heat and SA:

(7KW * 0.8 + 15KW +1.5KW * 2) * 2 units = 47.2KW

For lighting:

800 * 3 * 2 units = 4800 ; 3000 + 1800 * 0.35 = 3.63KW

For appliances fastened in place:

{(11A + 5A) *120V + 3KW}* 0.75 * 2 units = 7.38KW

Adding them gives 47.2 + 3.63 + 7.38 = 58.21KW

58.21KW/240V = 242.54 Amps which should be rounded up to 243 amps, but is very close to the 242 amps listed. (Maybe the person who worked out the answer rounded off some off the answers to some of the intermediate steps.)

Steve

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

BTW: If you forget the 35% demand for lighting loads (like I did) you get the 252 amp answer. They are being very sneaky with the wrong answers they choose.

 

[haskindm]

Re: Duplex Standard & Optinal Load calc.

Small appliance circuits and laundry circuits are allowed to be added to lighting load and derated in the standard calculation per 220.52 (A) & (B).
Is the question asking for the "service load" in amperage, or is it asking for the minimum service size? There is a difference.
The 7KW ranges are under 8.75 kw so you would use 65% demand from column "B" of 250.55.
Since there are 2 dishwashers and 2 garbage disposals you have a total of four appliances fastened in place so 220.53 allows you to derate them to 75%.
The trick to this question is that there is NO OPTIONAL CALCULATION FOR A DUPLEX UNIT. A multifamily dwelling is considered 3 or more units. 220.85 (2005 Code) allows you to use the optional calculation for "Two dwelling units" if you "pretend" that there are three dwelling units. If the total load for 3 units is less than the calculated load using the standard calculation (Part III), then you may use the lesser of the two calculated loads.
Nothing is ever easy.

 

[FastSparky]

Re: Duplex Standard & Optinal Load calc.

I am going trew and looking at the past arcives in load calcutation and i found this for my help http://www.mikeholt.com/cgi-bin/codeforum/ultimatebb.cgi?ubb=get_topic;f=6;t=000298
Thanks C.B. for everything
Hope this is my ticket outta this mess FS.

[ February 09, 2006, 11:25 AM: Message edited by: FastSparky ]

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

Posted by Haskindm:

Small appliance circuits and laundry circuits are allowed to be added to lighting load and derated in the standard calculation per 220.52 (A) & (B).

I see that you are correct. I should of read farther.

The 7KW ranges are under 8.75 kw so you would use 65% demand from column "B" of 250.55.

What was I thinking? I didn't realize we had 2 ranges.

I don't know where Charlie B. got the demand factors he used. They look like they are from the table for non-dwelling units.

Steve

 

[steve66]

Re: Duplex Standard & Optinal Load calc.

I'll try this once more:

7000 * 2 * 0.65 = 9100 W (ranges)
4920 * 2 * 0.75 = 7380 W (appliances fastened IP)
15000 * 2 = 30000 W (heaters)
1500 * 4 + 1500 * 2 + 800 * 3 * 2 = 13800 W (SA circuits, 2 laundry ckts, and lighting load)

For the lighting load, we use 100% of the first 3000W, and 35% of the rest:

3000+ 10800 * 0.35 = 6780 W

9100 + 7380 + 30000 + 6780 = 53260 W

53260/240 = 222 Amps. So I would say 223 amps is the correct answer.

Steve

 

[gndrod]

Re: Duplex Standard & Optinal Load calc.

haskindm,
I read right past 220.85. Thanks for your keen observation. I noticed an absence of a largest motor requirement, in this case the disposer for adding 25% of 1200 va into the total sum. I am looking at Annex D example D1(b) which gives a one family dwelling figure for unbalanced circuit loading. Would this be applicable considering a two family off of the main and does this factor into determining the versus three unit low figure calculation?
rbj, Seattle

[ February 09, 2006, 08:37 PM: Message edited by: gndrod ]