Multifamily Dwelling 220.61...

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1793

1793

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Louisville, Kentucky
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Inspector
I'm working on a project and I have to calculate the Service for an Apartment Complex with 5 units. If someone would look at the worksheet I have I would appreciate it.

I am confused on the neutral calculations with regard to the 5 electric dryers, Table 220.54 and how to apply Article 220.61(B).

Thanks, and I look forward to your help

 
For all of the dryers, you can use a value of 70% for the neutral load. So for the individual unit, you should have 5000 * .7 (= 3500 VA) instead of .85. This unit only have one dryer, so you can't use the .85 factor.

For the entire service (all units combined), you have two factors to apply -- .85 because of 5 or more, and 0.7 because the neutral is 70% of the ungrounded calculation. So,

The overall service dryer load value is 5 * 5000 * .85 (= 21,250 VA)
The neutral load on the overall service from the dryers is 5 * 5000 * .85 * .7 (= 14,875 VA)

Is this a real example, or a test question? I don't see any cooking equipment, and this same 0.7 factor can be used on ranges, cooktop, and ovens.
 
Not a test question

Not a test question

The cooking equipment is gas. No central A/C either.

This is not a test question. I have been asked to work up a price to take the existing 3 apartments and 2 that will be after renovation all on separate meters. Currently this entire building has a 100 amp service.

I will go back and look at the book and worksheet again.

Mark, thanks for the explanation, I was not sure when to apply the 85% portion to the neutral calculation based on the text of 220.61(B).
 
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Revised worksheet

Revised worksheet

Here is a revised worksheet. Any input is welcomed and am I on the right track?

Should a 200 amp Service work for this Apartment Complex?

 
Hi Norb,
Are you sure of each unit?s electrical load? Are there any fastened-in-place appliances (water heater, garbage disposer, dishwasher, etc.)? Is there a wall or window air conditioner? If there are any motors, you must add to the calculation 25 percent of the motor with the highest full load current.
You need to recalculate the service/feeder. You cannot multiply the results of one unit by the number of units. The total general lighting load for each unit in your calculation is 6675 volt-amperes. Multiply this by the number of units. Then take 100 percent of the first 3000, and 35 percent of the remainder (13,631 VA). You can apply a demand factor of 85 percent to the five electric clothes dryers (21,250 VA) If these are absolutely the only loads, the minimum service is 145 amperes.
Charles
 
Charles R. Miller said:
Hi Norb,
Are you sure of each unit’s electrical load? Are there any fastened-in-place appliances (water heater, garbage disposer, dishwasher, etc.)? Is there a wall or window air conditioner? If there are any motors, you must add to the calculation 25 percent of the motor with the highest full load current.
You need to recalculate the service/feeder. You cannot multiply the results of one unit by the number of units. The total general lighting load for each unit in your calculation is 6675 volt-amperes. Multiply this by the number of units. Then take 100 percent of the first 3000, and 35 percent of the remainder (13,631 VA). You can apply a demand factor of 85 percent to the five electric clothes dryers (21,250 VA) If these are absolutely the only loads, the minimum service is 145 amperes.
Charles
Click to expand...

There is a furnace for each unit, gas. No disposer or D/W.

I have been using Annex D for this project and I see where I picked-up the wrong Total 6,675.

As I see it, in the example I can only use the 85% for the Dryers when I calculate for the neutral. Have I missed something?

I see my Service Total as 161 Amps, again based on the example in Annex D

Here is another worksheet. ( I don't know any other way to present this, if anyone can offer a better way, I'm all ears & eyes ).

 
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Norb,
I believe you can apply 220.83 to the total load (that includes space heating and upgraded vent whole house motors if added) because this is a remod adding 2 more units. Also, will a house meter be required for F/A and common loads? Optional calculations [220.82] can still be applied. Each Tennant feeder disconnect must be 60 A minimum, but like Charles mentioned, the overall Service requires a standard method calculation for table 310.16 conductor sizing.

I am a little slow and didn't catch your reply. I guess the gas heaters are wall radiants? (No furnace motor.)
 
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1793 said:
There is a furnace for each unit, gas. No disposer or D/W.

As I see it, in the example I can only use the 85% for the Dryers when I calculate for the neutral. Have I missed something?
Click to expand...

Does the furnace have a blower fan? If so, you need to include that, plus it will be your largest motor.

What example in the Annex leads you to believe that you can only use the .85 factor (there must be 50 examples in that annex). The .7 and .85 are different factors. The .85 is one you apply to the total load when you have 5 dryers. The 0.7 is the neutral factor that is applied to the modified total load. There seem to be multiple examples that back this up for both ranges and dryers.
 
Example D4(a)

Example D4(a)

suemarkp said:
Does the furnace have a blower fan? If so, you need to include that, plus it will be your largest motor.

What example in the Annex leads you to believe that you can only use the .85 factor (there must be 50 examples in that annex). The .7 and .85 are different factors. The .85 is one you apply to the total load when you have 5 dryers. The 0.7 is the neutral factor that is applied to the modified total load. There seem to be multiple examples that back this up for both ranges and dryers.
Click to expand...

I started at Example D4(a) pages 70-720 and 70-721.

I'm only interested in the standard calculation for service feeder and neutral. I have not looked at the "Further Demand Factor". :confused:
 
In that example, I only see ranges. These are similar to dryers, except there is a deman factor for only one range whease you need 5 dryers to get a demand factor. They assumed a 12 KW range, and this goes into the feeder calculation a 8 KVA. This is like the 0.85 factor, except you must use 1.0 with only one dryer. When the calculated the neutral load fro that one unit, the 0.7 factor was applied to the 8 KVA.

The demand load for all 20 ranges for the whole building is 35 KVA. A factor of 0.7 was then applied this when calculating the neutral load. Dryers are similar, but instead of using the range table you use the dryer table. That is where the 0.85 factor comes into play (5 dryers * nameplate *.85). That value is used in your service calculation for the whole building, and a 0.7 factor is used on that value when calculating the neutral load.
 
suemarkp said:
In that example, I only see ranges. These are similar to dryers, except there is a deman factor for only one range whease you need 5 dryers to get a demand factor. They assumed a 12 KW range, and this goes into the feeder calculation a 8 KVA. This is like the 0.85 factor, except you must use 1.0 with only one dryer. When the calculated the neutral load fro that one unit, the 0.7 factor was applied to the 8 KVA.

The demand load for all 20 ranges for the whole building is 35 KVA. A factor of 0.7 was then applied this when calculating the neutral load. Dryers are similar, but instead of using the range table you use the dryer table. That is where the 0.85 factor comes into play (5 dryers * nameplate *.85). That value is used in your service calculation for the whole building, and a 0.7 factor is used on that value when calculating the neutral load.
Click to expand...

Lets think about this one more time. I'm trying to learn here so I do appreciate any and all help. The orange lines are the new additions.

I have included a Misc. of 1,500 for Furnace and such. This exercise is for me to learn how to calculate a Service for this job. I know that specifics are needed but with I have at hand this is the best I can do, I'm shooting a little high I know.

 
The #'s look good, So you need 60A(230.79(D)) for each unit w/175A min Service. Are there no House loads? Hallway lighting, Smoke Alarms, Exterior Lighting, etc? These are all in addition to your Unit Loads.

Tom
 
House loads

House loads

Davis9 said:
The #'s look good, So you need 60A(230.79(D)) for each unit w/175A min Service. Are there no House loads? Hallway lighting, Smoke Alarms, Exterior Lighting, etc? These are all in addition to your Unit Loads.

Tom
Click to expand...

As it looks now the only thing will be a couple of hall lights and smokes. I figured these nominal.
 
As do HVAC loads. If that 1500 "misc" VA is meant to account for the furnace blower, it needs to be 100% nameplate + 25%. The 35% lighting demand factor can not be applied to HVAC circuits or to other appliances fastened in place (except lights).

1500 VA is a little steep for a furnace blower. If I had to guess, I'd call it 720 VA + 25% (largest motor) which is a new total of 960 VA.

Hopefully you can scratch by with a 200A service.
 
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