Service and Feeder Calculations
Service and Feeder Calculations
Instructors: Michael Caudle, Gary Mullis, Ben Wesley
Class Schedule:
8:00 AM – 9:15 AM Part 1
9:15 AM – 9:30 AM Break
9:30 AM – 10:30 AM Part 2
10:30 AM – 10:45 AM Break
10:45 AM – 11:50 AM Part 3
Full class handouts: www.jadelearning.com/ncclass
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Service and Feeder Calculations
CE Class Information
• This class is worth 4-hours of continuing education credit
for the North Carolina Board of Examiners of Electrical
Contractors.
• Within 2 business days:
e
 You will receive your certificate of completion by email.
 You will receive an emailed discount code for $25 off any
online or homestudy course.
 Your hours will be reported to North Carolina.
If you need to reciprocate your hours to another state or have
any questions, please call the office at 1-800-443-5233 or
email registrar@jadelearning.com
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Service and Feeder Calculations
Course Description
This course will introduce electricians
to Service Calculations:
• Standard (General) Method
• Optional Method
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Service and Feeder Calculations
Course Objectives
Upon completion of this 4-hour
course you will be able to:
• Collect necessary data to initiate a
service calculation
• Perform a standard dwelling unit
service .calculation
• Perform the optional calculating
method
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Service and Feeder Calculations
What is a Service Calculation?
A service calculation is the NEC prescribed procedure for
sizing service conductors, service equipment, and
feeders to meet the electrical demands of a home or
business.
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Service and Feeder Calculations
What is a Service Calculation?
A service calculation is the NEC prescribed procedure for
sizing service conductors, service equipment, and
feeders to meet the electrical demands of a home or
business.
Utility Owned
Service Drop
(not calculated
by the NEC)
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Service Conductors
Service
Equipment
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Service and Feeder Calculations
What is a Service Calculation?
Interesting Fact
NEC 230.66 states: The meter socket
is not considered part of the
service equipment.
Service
Equipment
Not
Service
Equipment
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Service and Feeder Calculations
What is a Service Calculation?
A service calculation takes into account the known loads
that are expected to be installed in the home or business,
as well as the loads yet to be determined.
For example………….
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Service and Feeder Calculations
What is a Service Calculation?
For Example
• What are the specific lighting fixtures?
• What changes will the homeowner make to the lighting in the
future?
The NEC prescribed service calculation will cause that service
equipment ampacity to be large enough based on the square
footage of the dwelling to accommodate that unknown lighting
load.
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Service and Feeder Calculations
What is a Service Calculation?
Another Example
• Which loads will be plugged into the general-use receptacles?
• How many will be plugged in and used at once?
The NEC prescribed service calculation will cause the service
equipment to be large enough based on the square footage of
the dwelling to accommodate these unknown loads that will
connect to the general-use 120V receptacles.
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Service and Feeder Calculations
Two Types of Service Calculations
Standard Method:
• The standard method is the more complex method for
calculating a service.
• Considers loads on more of an individual basis versus
lumping loads together.
• Typically produces the larger number in amps of the two
approved methods.
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Service and Feeder Calculations
Two Types of Service Calculations
Optional Method:
• The second method is referred to by the NEC as the
Optional method.
• Simplest of the two procedures
• Produces a smaller number in amps (generally). This allows
for the use of smaller service conductors and smaller service
equipment.
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Service and Feeder Calculations
Two Types of Service Calculations
Standard and Optional Methods: Both methods are
approved by Article 220 of the NEC.
Even if you prefer one method exclusively in the field,
either method can be on a licensing exam.
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Service and Feeder Calculations
Can the NEC Service Calculation be Wrong?
The NEC prescribed service calculation increases the service
size (in amps) to accommodate two different load types:
(1) The known loads such as heat & A/C systems, trash
compactors, dishwashers, ranges, clothes dryers, etc.
(2) The unknown loads such as customer preferred lighting
fixtures and various loads connected to general-use receptacles.
But the homeowner can always choose to plug enough loads
into general-use receptacles to overload the service main.
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Service and Feeder Calculations
Standard Method for a Dwelling
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Service and Feeder Calculations
Standard Method for a Dwelling
To calculate the electrical service of a dwelling unit
using the Standard Method, two kinds of information
must be gathered during the course of the calculation:
(1) The square footage of the dwelling unit. The square
footage is part of the General Lighting portion of the
calculation. Working in conjunction with Table 220.12, it
informs the electrician how many amps to increase the
service size for illuminating rooms and supplying power for
all general-use receptacles in the house (unknown loads).
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Service and Feeder Calculations
Standard Method for a Dwelling
To calculate the electrical service of a dwelling unit
using the Standard Method, two kinds of information
must be gathered during the course of the calculation:
(2) The known loads expected to be installed in the
dwelling unit. The volt-amps are taken directly from the load’s
nameplate, or conversion formulas are provided in the NEC for
replacing the nameplate ratings.
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting (increases service size based
on square footage of the dwelling to allow for
several types of loads.)
2.
3.
4.
5.
6.
Heat and A/C
Fastened in Place Appliances
Clothes Dryer
Range
Largest Motor
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Service and Feeder Calculations
1. General Lighting increases the service size to allow for not
only lighting & general-use receptacles, but small appliance
circuits & the 120V laundry circuit too!
2And NEC 220.14(J) Establishes this Permission:
InFastened
one-family,intwo-family,
and multifamily dwellings and in guest
3.
Place
rooms
or guest
suites of hotels and motels, the outlets specified
4.
Clothes
Dryer
in (J)(1), (J)(2), and (J)(3) are included in the general lighting
5. Range
load calculations of 220.12.
6. Largest Motor
Appliances
No additional load calculations shall be required for such outlets.
AND…
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Service and Feeder Calculations
1. General Lighting
2. Fastened in Place
Appliances
4. Clothes Dryer
2.
5. H
Ra NEC 220.52(A) Also Establishes this Permission:
3. Fastened in Place
4.
Clothes
Stating
thatDryer
no less than two small appliance circuits, as required
byRange
210.11(C)(1), shall be added to each dwelling unit service
5.
calculation
at 1500 volt-amps (VA) each, and it shall be permitted
6.
Largest Motor
to be included in the general lighting portion of the calculation.
Appliances
AND…
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Service and Feeder Calculations
1. General Lighting
2. Fastened in Place
Appliances
4. Clothes Dryer
2.
220.52(B) Establishes this Permission as Well:
5. HNEC
Ra
3. Fastened in Place
4.
Clothes
Stating
thatDryer
a load of not less than 1500 volt-amps (VA) each
shall
be included for each laundry branch circuit as required by
5.
Range
210.11(C)(2),
and that it too shall be permitted to be included in
6.
Largest Motor
the general lighting portion of the calculation.
Appliances
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Service and Feeder Calculations
Data Collection
d
(Square Footage)
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Service and Feeder Calculations
1. General Lighting (increases the service size to allow for
room lighting & the general-use receptacles in the home, as
well as circuits feeding receptacles in the kitchen & laundry.)
2.
3.
4.
5.
6.
Heat and AC
Fastened in Place Appliances
Clothes Dryer
Range
Largest Motor
To calculate General Lighting the square footage of the
dwelling must be determined.
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Service and Feeder Calculations
How to Determine Square Footage
NEC 220.12
You must determine the outside
dimensions of the dwelling.
But do NOT include:
• open porches,
• garages, or
• unused or unfinished spaces
not adaptable for future use.
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Service and Feeder Calculations
Let’s Calculate Dimensions of this Home (NEC 220.12)
Measurements exclude: Open porches, garages, or unused &
unfinished non-adaptable spaces.
53’ 3”
Length: 53 ft. 3 in → 53.25 ft.
30’ 3”
Width:
30 ft. 3 in → 30.25 ft.
Multiply: 53.25 x 30.25 = 1611
sq. ft.
Subtract the open porch of 46 sq.
ft. and the total square footage is:
d
1565 sq. ft.
x
x
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Service and Feeder Calculations
1565 sq. ft. is the number we will
use when referring to Table 220.12
for our General Lighting Load.
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Service and Feeder Calculations
General Lighting Load by Occupancy (T220.12)
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Service and Feeder Calculations
General Lighting Load by Occupancy (T220.12)
1565 sq. ft X 3 VA per sq. ft. = 4695 VA
But don’t forget the TWO small appliance
circuits and ONE laundry circuit that are to be
included in this General Lighting math. Each is
worth 1500 VA, for a total of 4500 VA.
Let’s look at that math…..
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Service and Feeder Calculations
General Lighting Load by Occupancy (T220.12)
1565 sq. ft. X 3 VA per sq. ft. = 4695 VA
+
1500 VA for each required Small Appliance Branch
Circuit (1500 VA x 2 = 3000 VA)
+
1500 VA for the required Laundry Branch Circuit
4695 VA + 3000 VA +1500 VA = 9195 VA
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Service and Feeder Calculations
Table 220.42 (Saving Us Money on Our Service Size)
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Service and Feeder Calculations
Recap of the General Lighting Load Math
Dwelling sq. ft. (1565) x 3VA = 4,695 VA
Small Appliance (1,500 VA x 2 circuits) = 3,000 VA
Laundry circuit = 1,500 VA
Total = 9,195 VA
3000 VA (of the 9195) at 100% = 3,000 VA
Remaining 6195 VA at 35% = 2,168 VA
Add the original 3,000 VA back to the 2,168 VA =
= General Lighting Load
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
1. General Lighting
2.
3.
4.
5.
6.
Heat and A/C
Fastened in Place Appliances
Clothes Dryer
Range
Largest Motor
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Service and Feeder Calculations
Data Collection
d
(Known Loads)
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
Line
5168 VA
Neutral
5168 VA
2. Heat and A/C
3.
4.
5.
6.
Fastened in Place Appliances
Clothes Dryer
Range
Largest Motor
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Service and Feeder Calculations
Heat and Air Conditioning (A/C)
•
•
•
•
NEC 220.60 Noncoincidence loads
When we hear the word “coincidence” we think of two
events coinciding - occurring at the same time.
Heat and A/C units are considered noncoincidence loads
and are regulated by 220.60 Noncoincidence loads.
220.60 says that we can simply omit from our calculation
whichever unit pulls less VA, since the units do not run at
the same time.
If we calculate the larger unit, the math will support the
smaller unit when it is running.
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Service and Feeder Calculations
Heat and Air Conditioning (A/C)
NEC 220.60 Noncoincidence loads
• Here is the Heating unit and A/C unit going into our 1565
sq. ft. dwelling unit:
• HEAT: 11,000 VA Heat Strip Electric Furnace
• A/C: 2-Ton 24,000BTU 18-amp 240-volt Condensing Unit
You can omit the smaller of these two units
..but which is smaller?
Let’s calculate……
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Service and Feeder Calculations
Heat and Air Conditioning (A/C)
NEC 220.60 Noncoincidence loads
• HEAT: 11,000 VA Heat Strip Electric Furnace
• A/C: 2-Ton 24,000 BTU 18-amp 240-volt condensing unit
Heat is simply 11,000VA at face value.
A/C will require using Ohms Law.
Intensity: 18A
x Electromotive Force: 240V
4,320 VA (A/C Unit)
P
I
E
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Service and Feeder Calculations
Heat and Air Conditioning (A/C)
NEC 220.60 Noncoincidence loads
Heat is larger at 11,000VA and will be added
to our Service Calculation.
P
I
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
5168 VA
1. General Lighting
Neutral
5168 VA
2. Heat and A/C
3.
4.
5.
6.
Fastened in Place Appliances
Clothes Dryer
Range
Largest Motor
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
2. Heat and A/C
Line
5168 VA
11000 VA
Neutral
5168 VA
0
3. Fastened in Place Appliances
4. Clothes Dryer
5. Range
6. Largest Motor
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Service and Feeder Calculations
210.52 (B) Small Appliances
(1) Receptacle Outlets Served. In the kitchen, pantry,
breakfast room, dining room, or similar area of a dwelling unit,
the two or more 20-ampere small-appliance branch circuits
required by 210.11(C)(1) shall serve all wall and floor
receptacle outlets covered by 210.52(A), all countertop outlets
covered by 210.52(C), and receptacle outlets for refrigeration
equipment.
Exception No. 2: In addition to the required receptacles
specified by 210.52, a receptacle outlet to serve a specific
appliance shall be permitted to be supplied from an individual
branch circuit rated 15 amperes or greater.
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Service and Feeder Calculations
Fastened in Place Appliances
NEC 220.53
Here are the known fastened in place appliances being
installed in our 1565 sq. ft. dwelling unit:
1.
2.
3.
4.
5.
4kw (240V) Water Heater
2kw (120V) Dishwasher
1/2 hp 9.8A (120V) Compactor
1/3 hp 7.2A (120V) Disposal
1 hp 8A (240V) Pool pump
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Service and Feeder Calculations
Fastened in Place Appliances
NEC 220.53
x
Let’s convert these appliances to volt-amps (VA)
1.
2.
3.
4.
5.
4kw (240V) Water Heater = 4000 VA
2kw (120V) Dishwasher = 2000 VA
1/2 hp 9.8A (120V) Compactor = 1176 VA
1/3 hp 7.2A (120V) Disposal = 864 VA
1 hp 8A (240V) Pool pump = 1920 VA
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Service and Feeder Calculations
220.53 Appliance Load
It shall be permissible to apply a demand factor of 75
percent to the nameplate rating load of four or more
appliances fastened in place, other than electric ranges,
clothes dryers, space-heating equipment, or airconditioning equipment, that are served by the same
feeder or service in a one-family, two-family, or
multifamily dwelling.
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Service and Feeder Calculations
Fastened in Place Appliances
NEC 220.53
x
Let’s convert these appliances to volt-amps (VA)
1.
2.
3.
4.
5.
4kw (240V) Water Heater =
2kw (120V) Dishwasher =
1/2 hp 9.8A (120V) Compactor =
1/3 hp 7.2A (120V) Disposal =
1 hp 8A (240V) Pool pump =
4000 VA
2000 VA
1176 VA
864 VA
+ 1920 VA
9960 VA x.75
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Service and Feeder Calculations
Fastened in Place Appliances
NEC 220.53
x
Let’s convert these appliances to volt-amps (VA)
1.
2.
3.
4.
5.
4kw (240V) Water Heater =
2kw (120V) Dishwasher =
1/2 hp 9.8A (120V) Compactor =
1/3 hp 7.2A (120V) Disposal =
1 hp 8A (240V) Pool pump =
4000 VA
2000 VA
1176 VA
864 VA
+ 1920 VA
9960 VA x.75
7470 VA
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
5168 VA
11000 VA
1. General Lighting
2. Heat and A/C
Neutral
5168 VA
0
3. Fastened in Place
4. Clothes Dryer
5. Range
6. Largest Motor
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Service and Feeder Calculations
Fastened in Place Appliances
NEC 220.53
x
Let’s find and omit the 240V fastened appliances
1.
2.
3.
4.
5.
4kw (240V) Water Heater =
4000 VA
2kw (120V) Dishwasher =
2000 VA
1/2 hp 9.8A (120V) Compactor =
1176 VA
1/3 hp 7.2A (120V) Disposal =
864 VA
1 hp 8A (240V) Pool pump =
+ 1920 VA
4040 VA x.75
3030 VA applies to neutral side
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
2. Heat and A/C
Line
5168 VA
11000 VA
Neutral
5168 VA
0
3. Fastened in Place
4. Clothes Dryer
5. Range
6. Largest Motor
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
2. Heat and A/C
3. Fastened in Place
Line
5168 VA
11000 VA
7470 VA
Neutral
5168 VA
0
3030 VA
4. Clothes Dryer
5. Range
6. Largest Motor
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Service and Feeder Calculations
Clothes Dryer
NEC 220.54
Clothes dryers can be gas or
electric based on the
customer’s preference, but NEC
220.54 requires that room (in
amps) be made in the electrical
service for no less than a 5kw
(5000 VA) clothes dryer.
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Service and Feeder Calculations
Clothes Dryer
NEC 220.54
Table 220.54 states that up to 4
dryers are calculated at 100%
5 dryers or more are factored into
the service calculation at less than
100% of their combined ratings.
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Service and Feeder Calculations
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Service and Feeder Calculations
Clothes Dryer
NEC 220.54
The clothes dryer being installed in our
1565 sq. ft. dwelling unit is 4kw
(4000VA).
A 4000 VA dryer requires that 5000 VA
be entered into the line side column of
our service calculation, and 70% in the
neutral column, per 220.61(B).
5000 x .70 = 3,500
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
2. Heat and A/C
3. Fastened in Place
Line
5168 VA
11000 VA
7470 VA
Neutral
5168 VA
0
3030 VA
4. Clothes Dryer
5. Range
6. Largest Motor
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Service and Feeder Calculations
The Parts of a Service Calculation
1. General Lighting
2. Heat and A/C
3. Fastened in Place
4. Clothes Dryer
Line
5168 VA
11000 VA
7470 VA
5000 VA
Neutral
5168 VA
0
3030 VA
3500 VA
5. Range
6. Largest Motor
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Service and Feeder Calculations
Ranges (Cooking Appliances)
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Service and Feeder Calculations
Ranges (Cooking Appliances)
• 8kW was determined for our range. This will go on the
line side of the calculation.
• NEC 220.61 governs neutrals not only for clothes dryers,
but ranges too! Both clothes dryers and ranges increase
the neutral side of the service calculation by 70%
• 70% of 8kW needs to be inserted for the neutral side of
the range portion of the service calculation.
8000 x .70 = 5,600
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
1. General Lighting
5168 VA
5168 VA
2. Heat and A/C
11000 VA
0
3. Fastened in Place
7470 VA
3030 VA
4. Clothes Dryer
5000 VA
3500 VA
5. Range
6. Largest Motor
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
1. General Lighting
5168 VA
5168 VA
2. Heat and A/C
11000 VA
0
3. Fastened in Place
7470 VA
3030 VA
4. Clothes Dryer
5000 VA
3500 VA
5. Range
8000 VA
5600 VA
6. Largest Motor
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Service and Feeder Calculations
Largest Motor (25%)
NEC 220.50
x
NEC 220.50 requires us to determine the largest
motor using FLC (amps) from the Motor Tables
(T430.247 – T430.250) in the NEC.
1.
2.
3.
4.
5.
4kw (240V) Water Heater = 4000 VA
2kw (120V) Dishwasher = 2000 VA
1/2 hp 9.8A (120V) Compactor = 1176 VA
1/3 hp 7.2A (120V) Disposal = 864 VA
1 hp 8A (240V) Pool pump = 1920 VA
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Service and Feeder Calculations
Largest Motor (25%)
NEC 220.50
3. 1/2 hp 9.8A (120V) Compactor = 1176 VA
1176 VA x .25 = 294 VA
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
1. General Lighting
5168 VA
5168 VA
2. Heat and A/C
11000 VA
0
3. Fastened in Place
7470 VA
3030 VA
4. Clothes Dryer
5000 VA
3500 VA
5. Range
8000 VA
5600 VA
6. Largest Motor
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
1. General Lighting
5168 VA
5168 VA
2. Heat and A/C
11000 VA
0
3. Fastened in Place
7470 VA
3030 VA
4. Clothes Dryer
5000 VA
3500 VA
5. Range
8000 VA
5600 VA
6. Largest Motor
294 VA
294 VA
36,932 VA 17,592 VA
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Service and Feeder Calculations
Determine the Minimum Size Service
NEC 310.15(B)(7)
Single-Phase Dwelling Services and Feeders.
For one family dwellings and the individual dwelling
units of two-family and multifamily dwellings, service
and feeder conductors supplied by a single-phase,
120/240-volt system from 100A up to 400A shall be
permitted to be sized at 83% of the Service Equipment
rating.
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Service and Feeder Calculations
The Parts of a Service Calculation
Line
Neutral
36,932 VA 17,592 VA
÷
÷
240 Volts
240 Volts
154 Amps
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73 Amps
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Service and Feeder Calculations
175A Service Equipment Rating per NEC 240.6
Calculation:
154 A
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Service and Feeder Calculations
83% of 175A = 145.25 A - Table 310.15(B)(16)
1/0 Cu
at 75°C
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Service and Feeder Calculations
A Look at the 83% Table - 310.15(B)(7)
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Service and Feeder Calculations
Calculating the Neutral Conductor
Line
Neutral
36,932 VA
÷
240 Volts
154 Amps
17,592 VA
÷
240 Volts
73 Amps
220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load shall be
the maximum unbalance of the load determined by this article. The
maximum unbalanced load shall be the maximum net calculated
load between the neutral conductor and any one ungrounded
conductor.
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Service and Feeder Calculations
A Final Note About the Service Equipment as a Disconnect
NEC 230.79
230.79 Rating of Service Disconnecting Means. The
service disconnecting means shall have a rating not less than
the calculated load to be carried, determined in accordance
with Part III, IV, or V of Article 220, as applicable. In no case
shall the rating be lower than specified in 230.79(A), (B), (C),
or (D).
(C) One-Family Dwellings. For a one-family dwelling, the
service disconnecting means shall have a rating of not less
than 100 amperes, 3-wire.
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Service and Feeder Calculations
Determine the Grounding Electrode Conductor
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Annex D - Example
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Service and Feeder Calculations
Optional Method for a Dwelling
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Optional Method
The Optional Method of calculating a service begins
at Part IV of Article 220, specifically Section 220.80.
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Optional Method
What is the Optional Method?
In a Nutshell: The Optional Method allows us to calculate
a service by adding all loads together except the heat and
A/C load. We then apply a demand factor from T220.82(B),
and only then add the heat or A/C load according to
220.82(C).
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Service and Feeder Calculations
Optional Method
NEC 220.82(A) tells us where we can use this
Optional Method. It says the Optional Method
applies to the following dwelling units:
• A dwelling unit having its total connected load served by
a single 120/240-volt or 208Y/120-volt set of 3-wire
service or feeder conductors with an ampacity of 100A
or greater.
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Optional Method
NEC 220.82(A) goes on to tell us that the first step in
calculating a service using the Optional Method is to
add together all loads specified in 220.82(B) & (C).
And 220.61 shall determine the neutral conductor.
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220.82(B) General Load: The general calculated load shall be
not less than 100 percent of the first 10 kVA plus 40 percent
of the remainder of the following loads:
(1)
(2)
(3)
•
•
•
•
•
3-VA per sq. ft.
4500-VA for two small appliance and one laundry branch circuit.
The nameplate rating of all the following:
All appliances fastened in place, permanently connected, or located
to be on a specific circuit.
All cooking equipment (ranges, ovens, etc.).
All clothes dryers not powered by the required 120V laundry
branch circuit (such as gas dryers).
All water heaters.
All motors permanently connected that are not part of the
aforementioned equipment (use amps or VA from the nameplate).
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Optional Method
220.82(C) Heating and Air-Conditioning Load. The largest
of the following six selections (in VA) shall be included in the
calculation.
Select the largest equipment using 6 different
equipment scenarios. Let’s look at those 6 scenarios:
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Service and Feeder Calculations
Optional Method
1. 100 percent of the nameplate rating(s) of the air conditioning
and cooling.
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Service and Feeder Calculations
Optional Method
2. 100 percent of the nameplate rating(s) of the heat
pump when the heat pump is used without any supplemental
electric heating.
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Service and Feeder Calculations
Optional Method
3. 100 percent of the nameplate rating(s) of the heat pump
compressor and 65 percent of the supplemental electric
heating for central electric space-heating systems. If the heat
pump compressor is prevented from operating at the same
time as the supplementary heat, it does not need to be added
to the supplementary heat for the total central space heating
load.
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Service and Feeder Calculations
Optional Method
4. 65 percent of the nameplate rating(s) of electric space heating
if less than four separately controlled units.
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Service and Feeder Calculations
Optional Method
5. 40 percent of the nameplate rating(s) of electric space heating
if four or more separately controlled units.
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Service and Feeder Calculations
Optional Method
6. 100 percent of the nameplate ratings of electric thermal
storage and other heating systems where the usual load is
expected to be continuous at the full nameplate value.
Systems qualifying under this selection shall not be calculated
under any other selection in 220.82(C).
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Let’s Recap the Basics of the Optional Method
1. Calculate the General Load
In the optional method, all loads except heat and A/C are part of
the general load. Add them all together for a total VA.
• The first 10,000 VA is retained at 100%
• The remaining VA is retained at 40%. Add these together for
your total general load.
Remember: Lighting & general-use receptacles are again
based on sq. ft. of the dwelling x 3 VA per sq. ft. The two
small-appliance branch circuits and one laundry branch
circuit are also included at 1500VA each.
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Calculating the General Load Includes All Loads
“All loads except heat and A/C”
really means all loads!
Lights & Receptacles
Sm. Appliance Circuits
Laundry Circuit
Fastened in Place Appliances
Clothes Dryers
Ranges, Cooktops
Cooking Equipment
Water Heaters
Motors
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Service and Feeder Calculations
Let’s Calculate our Dwelling (Optional Method)
Remember our Dwelling?
c
Not counting the garage or
open porch, we calculated
1565 sq. ft.
X
3VA
4,695 VA
x
x
89
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Let’s Calculate our Dwelling (Optional Method)
4,695 VA
+
4,500 VA (2 Sm. App. and
1 Laundry Circuit)
9,195 VA
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Service and Feeder Calculations
Let’s Calculate our Dwelling (Optional Method)
c
Remember our loads?
9,195 VA
+ all loads except
Heat and A/C
1.
2.
3.
4.
5.
6.
7.
Water Heater = 4000 VA
Dishwasher = 2000 VA
Compactor = 1176 VA
Disposal =
864 VA
Pool pump =
1920 VA
Dryer =
5000 VA
Range =
11000 VA
25,960 VA
91
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Service and Feeder Calculations
Let’s Calculate our Dwelling (Optional Method)
c
Remember our Dwelling?
9,195 VA
+
25,960 VA
35,155 VA
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1.
2.
3.
4.
5.
6.
7.
Water Heater = 4000 VA
Dishwasher = 2000 VA
Compactor = 1176 VA
Disposal =
864 VA
Pool pump =
1920 VA
Dryer =
5000 VA
Range =
11000 VA
25,960 VA
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Let’s Calculate our Dwelling (Optional Method)
c
Remember the Rules?
35,155 VA
The first 10,000 VA at 100%
The remaining VA at 40%
That means:
35,155 VA – 10,000 VA= 25,155 VA @ 40%= 10,062 VA
10,062 VA + the original 10,000 VA = 20,062 VA
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Let’s Calculate our Dwelling (Optional Method)
Remember the Rules?
c
20,062 VA is our General Load and it includes everything
except our Heat and A/C
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Let’s Calculate our Dwelling (Optional Method)
20,062 VA is the General Load
Remember our Heat and A/C from the Standard
Method?
Our Heat and A/C units were:
c
• HEAT: 11,000 VA Heat Strip
Electric Furnace
• AC: 4,320 VA 18-amp 240-V
Condensing Unit
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Service and Feeder Calculations
Optional Method
1. 100 percent of the nameplate rating(s) of the air conditioning
and cooling.
2. 100 percent of the nameplate rating(s) of the heat pump
when the heat pump is used without any supplemental
electric heating.
3. 100 percent of the nameplate rating(s) of the heat pump
compressor and 65 percent of the supplemental electric
heating for central electric space-heating systems. If the heat
pump compressor is prevented from operating at the same
time as the supplementary heat, it does not need to be added
to the supplementary heat for the total central space heating
load.
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Service and Feeder Calculations
Optional Method
4. 65 percent of the nameplate rating(s) of electric space heating
if less than four separately controlled units.
5. 40 percent of the nameplate rating(s) of electric space heating
if four or more separately controlled units.
6. 100 percent of the nameplate ratings of electric thermal
storage and other heating systems where the usual load is
expected to be continuous at the full nameplate value.
Systems qualifying under this selection shall not be calculated
…..under any other selection in 220.82(C).
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Optional Method
4. 65 percent of the nameplate rating(s) of electric space heating
if less than four separately controlled units.
11,000 VA Heat x .65 = 7150 VA
Our A/C unit is ---------4,320 VA
The Electric Heat Strip Furnace is the larger of the two.
We shall use it in our calculation.
Let’s combine the Heating Load of 7150 VA with the
General Load we calculated earlier, and we will have
the entire VA for our Optional Method Dwelling Unit
Service Calculation.
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Optional Method
11,000 VA Heat x .65 = 7150 VA
+ 20,062 VA General Load
27,212 VA (Total VA)
Standard Method of calculation produced 36,932 VA which was
154 Amps.
How many Amps will this 27,212 VA calculation produce?
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Optional Method
27,212 VA (Total VA)
÷
240V
113.38 Amps
.
Requires:
125A Service Equipment Rating (240.6)
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Service and Feeder Calculations
125 A Service Equipment Rating per NEC 240.6
Calculation:
113.38 A
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Service and Feeder Calculations
Optional Method
113.38 Amps
125A Service Equipment Rating (240.6)
X .83
83% rule 310.15(B)(7)
Service conductors: 103.75 Amps
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Service and Feeder Calculations
83% of 125A = 103.75 A - Table 310.15(B)(16)
#2 Cu
at 75°C
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Service and Feeder Calculations
Optional Method
125A Service Equipment Rating
103.75A Service Conductors (No. 2
AWG Cu)
This 125A service is much smaller
than the 175A service required by
the Standard Calculation Method,
yet the loads in the dwelling are
exactly the same!
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A Look at the 83% Table - 310.15(B)(7)
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Calculating the Neutral Conductor When Performing
the Optional Method Service Calculation
It is the same procedure as calculating the Neutral
Conductor during the Standard Method, refer to 220.61.
220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load shall be
the maximum unbalance of the load determined by this article. The
maximum unbalanced load shall be the maximum net calculated
load between the neutral conductor and any one ungrounded
conductor.
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Service and Feeder Calculations
Determining the Grounding Electrode Conductor During
the Optional Method Calculation
It is the same procedure as calculating the GEC during the
Standard Method, refer to 250.66
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Annex D - Example
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North Carolina NEC Amendments
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NC DOI – State Specific
NC DOI Link:
http://www.ncdoi.com/OSFM/Engineering_and_Codes/Default.aspx?field1
=Codes_-_Current_and_Past&user=State_Building_Codes
2017 NEC Amendments:
http://www.ncdoi.com/OSFM/Engineering_and_Codes/Documents/2017%
20Amendments%20to%20be%20adopted%20with%20the%20NEC%20V
ersion%201.pdf
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NC DOI – State Specific
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Thank you from all of us at
JADE Learning!
Questions?
Call: 1‐800‐443‐5233
Email: registrar@jadelearning.com
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Common Questions and Answers
• How many classroom hours do I need?
– 4 classroom hours per year for I, U, L ‐ 8 total
– 2 classroom hours per year for SP ‐4 total
• Can these hours be transferred to other states?
– In some cases, yes. Call or email the JADE office to find out.
• If I have not yet submitted payment for this class, how do I pay?
– Call or email the office – we can take your payment over the phone.
• How are my hours reported?
– Your hours are reported electronically, once payment has been received, and you
have signed in on the class roster. Make sure to sign in! If your name is not on the
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