Standard Calculation for Dwelling Unit

[Electricalhelp]

I have a 1500 sq ft Apartment with 120/208V/1P Service.

I am trying to use to the standard method to calculate the load and was curious if I did the right steps.

But I was wondering if there is any factors I can use for the Ejector Pump or Air Conditional System to lower the load

I put a Laundry Load of 1500 VA, so can I remove the Washer and Dryer as well.

Do I need to increase the Small Appliance since there is a Fridge, Microwave and Hood?

 

[Tulsa Electrician]

To start
You can delete washer since you have laundry in there already.
You will need to move, dryer and range gas unit loads from the demand calc.
Maybe look at name plate for A/C

From your description you have a multifamily dwelling

 

[Electricalhelp]

To start
You can delete washer since you have laundry in there already.
You will need to move, dryer and range gas unit loads from the demand calc.
Maybe look at name plate for A/C

From your description you have a multifamily dwelling

Thank you for the help.
Can I ask why we need to move the dryer and Range after the demand calculation. Do you know what section I overlooked.
It is a multifamily dwelling but there is only 2 Units. So I can't use Table 220.84 Demand Factor since there is no factor for 2 Units.
Also this place was a existing dwelling unit but for 1 family. But now its a 2 unit apartment, so can I use Section 220.83?

 

[Tulsa Electrician]

The appliances can not be added to the demand portion.

 

[Tulsa Electrician]

220.52
(A) and (B) can be added to general lighting.
220.53 appliance load under four 100%
Note: other than electric rage,dryer,
220.53 can not be added to general lighting and it's demand per table 220.42.

 

[Tulsa Electrician]

You may want to look at optional
Ac larger than heat.
Yah you can all toghter.
First 10 kva @100%
Remainder at 40%
And compare to your standard after you adjust your numbers.

See 220.82

 

[Electricalhelp]

Standard Method: 91 Amp
Optional Method: 108 Amp

I thought Optional Method would usually have a lower calculated load

 

[Tulsa Electrician]

There is an error in calc on the optional method.

 

[wwhitney]

So with a 120/208 3-wire supply, how are you supposed to convert the load calc VA into amps? Because if all of the loads are 120V 2-wire, then you'd convert by dividing by 120V * 2. While if all of the loads are 208V 2-wire, you'd convert by dividing by 208V. Yet typically there is a mix.

And if you are supposed to track the mix through the calculation, how do you do that for the "10 kVA @ 100%, rest at 40%" computation for 220.82(B)? E.g. suppose the general loads before that factor add up to 10 kVA of 120V loads and 10 kVA of 208V loads. The total load after the factor is 14 kVA, but how much of that should be considered 120V loads vs 208V loads?

Cheers, Wayne

 

[Dennis Alwon]

Here is an example of what you would have. I added a few things and have electric range and dryer.

 

[Electricalhelp]

There is an error in calc on the optional method.

Sorry but I can't seem to find the error in my optional method.

 

[Tulsa Electrician]

You are correct. I took another look this morning and I was the one that was incorrect.
I based the statement on rounding the final number. It came out to .5 in this case you can round up not drop it. NEC: 220.5 (B)

22360/208=107.5
Sorry

You ask in your question.

"But I was wondering if there is any factors I can use for the Ejector Pump or Air Conditional System to lower the load."
Do you have the name plate of the AC unit. That may help reduce the load. To me it seams high for 1500 SF house.
Now for some fun I see you like spreed sheets. On the AC load you can use name plate or other information to get you there. I always prefer name plate however we seldom get that information in time. What one can do is use some basic math. In your example you used 12000 VA or 57.69 amps. It seam high for a new multifamily unit. If it is name plate well that is what you use. If was a guess well there may be a better way. sometimes in the field we have to take an educated guess due to the HVAC contractor being vague. For your spreed sheet you can use Amps=BTU/((SEERx.875)x Volts). Base your BTU on 20 per sq ft. Use a seer rating based on new equipment and stats energy code. For this we can use 14 SEER. Then we can use a zone area. The number below are for Zone 1&2 (hot)

Single Phase

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
Btu	37500​	3.125​	14.71743​	18.39678​	3826.531​	3.826531​
SEER	14​	​
Volts	208​

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
BTU	37500​	3.125​	14.71743​	18.39678​	3826.531​	3.826531​
SEER	14​	3.5​	16.48352​	20.6044​	4285.714​	4.285714​
Volts	208​

A side note: Using this calculation to compare to name plate for a 208/230 name plate use 197 for volts.

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
BTU	37500​	3.125​	15.53921​	19.42401​	3826.531​	3.826531​
SEER	14​	3.5​	17.40392​	21.75489​	4285.714​	4.285714​
Volts	197​

A side note: using this calculation to compare to name plate for a 208/230 name plate use 197 for volts.

I would say you could cut your AC VA load in half unless its name plate. 6000/208=28.85 x 1.25 =35.31 #8, 40 amp breaker@60c

"Do I need to increase the Small Appliance since there is a Fridge, Microwave and Hood?"
I do not see this in your calculations. If added to your standard calc using 220.53 you could use 75% for four or more.

Using all available information will yield a good answer.

Again Sorry about the .5

 

[farmantenna]

your AC number is way high. No way is a 1500 sq apt going to be more than 18 amp MCA at 208/240.

 

[farmantenna]

You are correct. I took another look this morning and I was the one that was incorrect.
I based the statement on rounding the final number. It came out to .5 in this case you can round up not drop it. NEC: 220.5 (B)

22360/208=107.5
Sorry

You ask in your question.

"But I was wondering if there is any factors I can use for the Ejector Pump or Air Conditional System to lower the load."
Do you have the name plate of the AC unit. That may help reduce the load. To me it seams high for 1500 SF house.
Now for some fun I see you like spreed sheets. On the AC load you can use name plate or other information to get you there. I always prefer name plate however we seldom get that information in time. What one can do is use some basic math. In your example you used 12000 VA or 57.69 amps. It seam high for a new multifamily unit. If it is name plate well that is what you use. If was a guess well there may be a better way. sometimes in the field we have to take an educated guess due to the HVAC contractor being vague. For your spreed sheet you can use Amps=BTU/((SEERx.875)x Volts). Base your BTU on 20 per sq ft. Use a seer rating based on new equipment and stats energy code. For this we can use 14 SEER. Then we can use a zone area. The number below are for Zone 1&2 (hot)

Single Phase

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
Btu	37500​	3.125​	14.71743​	18.39678​	3826.531​	3.826531​
SEER	14​	​
Volts	208​

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
BTU	37500​	3.125​	14.71743​	18.39678​	3826.531​	3.826531​
SEER	14​	3.5​	16.48352​	20.6044​	4285.714​	4.285714​
Volts	208​

A side note: Using this calculation to compare to name plate for a 208/230 name plate use 197 for volts.

House sq ft	1500​			MCA​
Zone	1.25​	Ton​	Amps​	Amps x 1.25​	VA​	KVA​
BTU	37500​	3.125​	15.53921​	19.42401​	3826.531​	3.826531​
SEER	14​	3.5​	17.40392​	21.75489​	4285.714​	4.285714​
Volts	197​

A side note: using this calculation to compare to name plate for a 208/230 name plate use 197 for volts.

I would say you could cut your AC VA load in half unless its name plate. 6000/208=28.85 x 1.25 =35.31 #8, 40 amp breaker@60c

"Do I need to increase the Small Appliance since there is a Fridge, Microwave and Hood?"
I do not see this in your calculations. If added to your standard calc using 220.53 you could use 75% for four or more.

Using all available information will yield a good answer.

Again Sorry about the .5

your calc is really good based on what I have been seeing on name plates.

 

[Dennis Alwon]

If you are doing a load calculation for a service then you do not use 125% for the a/c unit

 

[Tulsa Electrician]

Good afternoon Dennis, if your referring to the 1.25 in the chart. That is the 125 % figured in to base amp for name plate. So it's the MCA.
I'm sure you got that. Now for the 6000@1.25 that for branch circuit OCD. Or 80% for the deweling circuit.
If one used a 30 based on 28.85. 30 amp @ 80% is 24amps. By taking the 28.85 x 1.25 you could size the OCD correctly and most likely fall in line with name plate max fuse of breaker.
As you stated the 6000 if he chooses to use it would not have an multiplier.
I have to do this alot here in tulsa for base cals due to HVAC not providing info for base bid. They either give me BTU or tonnage.
I think it's there way of being a smart guy. We all know when they pick a unit they know the name plate.
I should word item better.
Thanks for clarifying.

 

[wwhitney]

Here is an example of what you would have. I added a few things and have electric range and dryer.

Dennis looking at your load calculation it appears suitable for a 120/240V service (on the face of it, I'm not so familiar with 220 Part III). However the OP is about a 120/208V 3-wire service.

That doesn't affect the neutral computation, but on the service computation your spreadsheet divides the total VA by 240V. That's fine for the 120V loads going into the total VA (based on assuming the 120V loads are balanced on the two legs). But the 208V 2-wire loads should get divided by 208V, not 240.

Since the tally comes up as 41,975 VA total, of which 18,575 VA comprises 120V loads, the correction would be as simple as:

18,575 VA / 240V + (41,975 - 18,575) VA / 208V = 190A

Unless I'm missing something?

Cheers, Wayne

 

[Dennis Alwon]

Dennis looking at your load calculation it appears suitable for a 120/240V service (on the face of it, I'm not so familiar with 220 Part III). However the OP is about a 120/208V 3-wire service.

That doesn't affect the neutral computation, but on the service computation your spreadsheet divides the total VA by 240V. That's fine for the 120V loads going into the total VA (based on assuming the 120V loads are balanced on the two legs). But the 208V 2-wire loads should get divided by 208V, not 240.

Since the tally comes up as 41,975 VA total, of which 18,575 VA comprises 120V loads, the correction would be as simple as:

18,575 VA / 240V + (41,975 - 18,575) VA / 208V = 190A

Unless I'm missing something?

Cheers, Wayne

Yes I was trying to show the OP the layout for the standard calc because he had range and dryer in the top section under lighting and receptacle load... I wasn't thinking about voltages

 

[NAjxBUEEdA7PoKoX7vD2]

Dennis looking at your load calculation it appears suitable for a 120/240V service (on the face of it, I'm not so familiar with 220 Part III). However the OP is about a 120/208V 3-wire service.

That doesn't affect the neutral computation, but on the service computation your spreadsheet divides the total VA by 240V. That's fine for the 120V loads going into the total VA (based on assuming the 120V loads are balanced on the two legs). But the 208V 2-wire loads should get divided by 208V, not 240.

Since the tally comes up as 41,975 VA total, of which 18,575 VA comprises 120V loads, the correction would be as simple as:

18,575 VA / 240V + (41,975 - 18,575) VA / 208V = 190A

Unless I'm missing something?

Cheers, Wayne

My load calc spreadsheet toggles between single phase and three phase.

This is how I handle the appliance load where I need to divide by either 240 or 208 depending on the size of the load. The formula shown is in cell D17.