The use of residential optional load calculations

[bluesprinter]

When is it acceptable to use the residential optional load calculation from the nec. 220.82

I'm adding a evse (vehicle charger) to a existing 200 amp service with the existing typical loads including a heat pump hvac system.
The county permit reviewer for the county is requesting documentation of the load calculation.
when I perform the calculation using the optional methods it comes out to 155 amps on a service rated at 200 amps
I submitted a calculation using 40% derating the furnace of @. 15000kw and he responded back

Heating needs to be at 100%, If heat is supplemented then you need to add 65% of the supplemental heating load unless both don’t work at the same time.
what would be your thoughts and responses that he's not recognizing the option calculation
When I took ibew code class As a student We were told that you use the standard for new properties and the optional for additional loads to existing buildings and homes
but we still must apply 80% of the main overcurrent device rating.

should the load of a evse or other be added after the allowed adjustments in either method of calculation ?

We have i've seen adjustments for led lighting loads vs the 3va per sq foot

Thanks

 

[retirede]

Are you sure the 15KW isn’t the combination of heat pump and supplemental heat?

 

[bluesprinter]

this number came from the ocp , the unit has a backup heat strip for emergency use
the unit is missing the added nameplate adjustment information for the element installed
so all i can do is estimate at this point , its probably between 12 and 14.4 kw

 

[solarken]

When is it acceptable to use the residential optional load calculation from the nec. 220.82

I'm adding a evse (vehicle charger) to a existing 200 amp service with the existing typical loads including a heat pump hvac system.
The county permit reviewer for the county is requesting documentation of the load calculation.
when I perform the calculation using the optional methods it comes out to 155 amps on a service rated at 200 amps
I submitted a calculation using 40% derating the furnace of @. 15000kw and he responded back

Heating needs to be at 100%, If heat is supplemented then you need to add 65% of the supplemental heating load unless both don’t work at the same time.
what would be your thoughts and responses that he's not recognizing the option calculation
When I took ibew code class As a student We were told that you use the standard for new properties and the optional for additional loads to existing buildings and homes
but we still must apply 80% of the main overcurrent device rating.

should the load of a evse or other be added after the allowed adjustments in either method of calculation ?

We have i've seen adjustments for led lighting loads vs the 3va per sq foot

Thanks

The 100% of the first 10,000VA and 40% of the remainder is applied to all the general and appliance and fixed equipment loads other than heating or cooling, and the EVSE should be included with those fixed equipment loads so that it is subject to the demand factor reduction as well. Then the higher of the cooling (at 100%) or the heating (at 100% plus 65% or supplemental strips) is added. If the HVAC is programmed to leave the heat pump compressor off when the strips come on, then you only need to include the higher of the Heat pump + Air handler fan (at 100%) or the air handler fan + 65% of the heat strips.

That is my interpretation of Part IV. I don't see where the code limits which method you can use based on new or upgraded dwellings, seems it is up to you.

 

[solarken]

this number came from the ocp , the unit has a backup heat strip for emergency use
the unit is missing the added nameplate adjustment information for the element installed
so all i can do is estimate at this point , its probably between 12 and 14.4 kw

Isn't the outside compressor unit on a different breaker than the Air Handler inside unit?

 

[suemarkp]

Isn't the outside compressor unit on a different breaker than the Air Handler inside unit?

Usually, but it doesn't really matter as both are part of the HVAC system. What matters is what runs at the same time. Aux heat on a heat pump usually runs with the compressor until the compressor gets locked out at low ambient temperatures. So if heat pump, you have the outside compressor nameplate, and the air handler nameplate at 100%. Heat strips in the air handler get a reduction factor and it isnt always apparent on the nameplate how much is strip heat and how much is fan plus controls. Using 65% for the air handler is probably close enough if it has strip heat.

But putting in HVAC at 40% is wrong.

 

[TX+ MASTER#4544]

2023 NEC TX
You can use the optional method and you may get a lower value than using Part III Feeder and Service Load Calculations. (General Method)
Part IV Optional Feeder and Service Load Calculations
Section 220.82 (A) And use 220.61 to determine your neutral load.
220.82 (B) General Loads (1)-(4)
220.82 (C) Heating and Air Conditioning Load (1)-(6)

220.83 Existing Dwelling Unit (A)(1)-(3)
220.83 (B) T.220.83 (B) (1)-(3)
220.57 Electric Vehicle Supply Equipment....
625.52 Ventilation (A) (B) and the T.625.52(B) (1)(2) for CFM Calculations that may be required.

Thanks for reading
Comments accepted
TX+MASTER#4544

 

[Rdel6937]

Hi all,

been a while since I did existing load calcs and need some help. code sections or just a straight answer would be helpful.

Existing home with a 200-AMP Service
main panel is full and includes the following 240V loads
50Amp Steam shower
20A well pump
30A Pool sub panel
40A Ac condenser
30A Electric Dryer
60A Sub panel
(2) 30A Ovens

I cant get onto the mains due to space issue in the panel so I cannot Amp them out for total load less cooling.

HE wants to add a Level 2 EV charger 11.5kw 48 Amp.
I would need to swing a few circuits to the sub panel to accommodate the breaker however, I think his potential continuous load could exceed 80% of the service rating.

I am befuddled where to look in the code book to determine if the existing service can accommodate an additional 50Amp load.

It remains very possible the dryer, oven AC and Steam shower could all be in use along with the EV charger.

How do I determine the existing load calc. and availability to add the EV load?

 

[solarken]

Usually, but it doesn't really matter as both are part of the HVAC system. What matters is what runs at the same time. Aux heat on a heat pump usually runs with the compressor until the compressor gets locked out at low ambient temperatures. So if heat pump, you have the outside compressor nameplate, and the air handler nameplate at 100%. Heat strips in the air handler get a reduction factor and it isnt always apparent on the nameplate how much is strip heat and how much is fan plus controls. Using 65% for the air handler is probably close enough if it has strip heat.

But putting in HVAC at 40% is wrong.

I only asked the question to help him estimate the load of the compressor unit separately from the air handler since he could not read the labels. If he was giving one number instead of two, and usually the compressor is on a different breaker, so it can help with the calculations. I agree the air handler blower is fairly insignificant compared to the strip heat.

 

[solarken]

Hi all,

been a while since I did existing load calcs and need some help. code sections or just a straight answer would be helpful.

Existing home with a 200-AMP Service
main panel is full and includes the following 240V loads
50Amp Steam shower
20A well pump
30A Pool sub panel
40A Ac condenser
30A Electric Dryer
60A Sub panel
(2) 30A Ovens

I cant get onto the mains due to space issue in the panel so I cannot Amp them out for total load less cooling.

HE wants to add a Level 2 EV charger 11.5kw 48 Amp.
I would need to swing a few circuits to the sub panel to accommodate the breaker however, I think his potential continuous load could exceed 80% of the service rating.

I am befuddled where to look in the code book to determine if the existing service can accommodate an additional 50Amp load.

It remains very possible the dryer, oven AC and Steam shower could all be in use along with the EV charger.

How do I determine the existing load calc. and availability to add the EV load?

You don't start by adding up the breakers feeding the loads you listed. The breaker ratings are not the load rating, right? Go thru Article 220 Part IV optional method. 220.82(B) gives the lighting and gen use receptacle load calc based on sq ft, the small appliance and laundry branch ckts, the fastened in place appliances, cooking appliances, dryer, and water heater, all subject to the demand factor. The HVAC is handled in 220.82(C), where you use the larger of the heating or cooling load, with cooling at 100%, and heating with potential demand factor depending on if there is supplemental heat strips, or electric space heating. For the individual loads, look at the nameplate rating or the manual, not the breaker.

And you need to look at the loads off the 60A subpanel, and include those loads in the calc, not the 60A breaker. If you are lucky they may be included in the general loads and not add anything.

 

[Rdel6937]

You don't start by adding up the breakers feeding the loads you listed. The breaker ratings are not the load rating, right? Go thru Article 220 Part IV optional method. 220.82(B) gives the lighting and gen use receptacle load calc based on sq ft, the small appliance and laundry branch ckts, the fastened in place appliances, cooking appliances, dryer, and water heater, all subject to the demand factor. The HVAC is handled in 220.82(C), where you use the larger of the heating or cooling load, with cooling at 100%, and heating with potential demand factor depending on if there is supplemental heat strips, or electric space heating. For the individual loads, look at the nameplate rating or the manual, not the breaker.

And you need to look at the loads off the 60A subpanel, and include those loads in the calc, not the 60A breaker. If you are lucky they may be included in the general loads and not add anything.

Yes.. I'm aware you don't add up the breakers... it's the connected load.
The code book references help, thank you.
I guess the next question is do you do this work for free to get the job or charge for your time figuring it out fly the customer?
That's alot of leg work.

 

[retirede]

Yes.. I'm aware you don't add up the breakers... it's the connected load.
The code book references help, thank you.
I guess the next question is do you do this work for free to get the job or charge for your time figuring it out fly the customer?
That's alot of leg work.

IMO, you have to do the calculation in order to bid the job properly. It’s part of your overhead.

 

[jaggedben]

When is it acceptable to use the residential optional load calculation from the nec. 220.82

Each optional method says when it's permitted to be used. For 220.82 it's 3-wire service or feeder to a dwelling and so on.

I'm adding a evse (vehicle charger) to a existing 200 amp service with the existing typical loads including a heat pump hvac system.

Seems like you could use 220.83(A).

The county permit reviewer for the county is requesting documentation of the load calculation.
when I perform the calculation using the optional methods it comes out to 155 amps on a service rated at 200 amps
I submitted a calculation using 40% derating the furnace of @. 15000kw and he responded back

Heating needs to be at 100%, If heat is supplemented then you need to add 65% of the supplemental heating load unless both don’t work at the same time.
what would be your thoughts and responses that he's not recognizing the option calculation

Seems like told him you're using 220.82 then he's just asking you to do it properly. Heating cannot be figured at 40% under 220.82. Maybe he would accept a proper calc under 220.83(A).

When I took ibew code class As a student We were told that you use the standard for new properties and the optional for additional loads to existing buildings and homes
but we still must apply 80% of the main overcurrent device rating.

This is incorrect. Only certain optional methods (e.g. 220.83 explicitly, 220.87 by implication) are limited to existing installations. An 80% derating is not required for the non-continuous portion.

should the load of a evse or other be added after the allowed adjustments in either method of calculation ?

We have i've seen adjustments for led lighting loads vs the 3va per sq foot

Thanks

Here's where I'll get real. The code has not been updated to account for EVs in the optional methods, and I'm reluctant to push AHJs on applying the letter here. Had one AHJ who insisted on figuring the EV at 100% on top of whatever other calc I used. And that makes some sense, practically speaking, even if it isn't what the code says. If you are able to show the service is rated for 100% of the EV plus the rest of the load according to an optional calculation then you are on more solid ground for having done your due diligence. If necessary use 220.83(A) which is most lenient. If the AHJ allows a further derating for LEDs then more power to you.

 

[4-20mA]

 

[4-20mA]

Sorry, wrong thread

 

[tortuga]

Each optional method says when it's permitted to be used.

And for me thats where I have hit the snags, especially on service upgrades where what was once a service panel becomes a feeder,
And the feeder no-longer not supplies 100% of a dwelling unit load, like when there is a new meter main outside with a few new breakers then feeder to the old service panel inside. Now that inside feeder no-longer qualified under 220.82 or 220.83.
Or when a service supplies a both a dwelling unit and a guest suite.