From ABYC Section E-11
11.10. LOAD CALCULATIONS
11.10.1. FOR DC SYSTEMS
126.96.36.199. The following method shall be used for calculating the total electrical
load requirements for determining the minimum size of each panelboard, switchboard, and their main conductors. Additionally this information may be used to size the alternator, or other charging means, and the battery. (See E-188.8.131.52.1 and ABYC E-10, Storage
184.108.40.206.1. In column A of TABLE II, Electrical
Load Requirements Worksheet, list the current
rating (amps) of the loads that must be available for use on a continuous duty basis for normal operations;
220.127.116.11.2. In column B of TABLE II, list the current
rating (amps) of the remaining loads that are intermittent, and total these loads. Take 10% of the total load in column B, or the current draw of the largest item, whichever is greater, and add this value to the total from column A to establish the total electrical load.
NOTE: Calculations are based on the actual operating amperage for each load, and not on the rating of the circuit breaker or fuse protecting that branch circuit.
TABLE II - ELECTRICAL LOAD REQUIREMENT WORKSHEET
Load ~ “A” Amperes ~ “B” Amperes
Additional Electronic Equipment
System (standby mode)
Total Column A ~ Total Column B
10% Column B
Largest Item in Column B
Total Load Required
Total Column A _____
Total Column B _____ (The larger of 10% of Colum B or the largest item)
Total Load _____
11.10.2. FOR AC SYSTEMS
18.104.22.168. POWER SOURCE OPTIONS
The method shown in E-22.214.171.124 shall be used for calculating the total electrical load requirements for determining the size of panelboards and their feeder conductors along with generator, inverter, and shore power
capacities. The total power required shall be supplied by one of the following means.
126.96.36.199.1. Single Shore Power
Cable – A shore power cable, power inlet, wiring
, and components with a minimum capacity to supply the total load as calculated, complying with E-188.8.131.52.1.
184.108.40.206.2. Multiple Shore Power Cables
- Multiple shore power cables
, power inlets, wiring
, and components shall have a minimum total capacity to supply the total load as calculated complying with E-
220.127.116.11.1. All sources need not be of equal capacity, but each power inlet shall be clearly marked to indicate voltage, ampacity, phase (if a three phase system is incorporated), and the load or selector switch that it serves.
18.104.22.168.3. On Board AC Generator(s) or Inverter(s) - On board AC generator(s) or inverter(s) to supply the total load as calculated. Total minimum installed KVA for a single
phase system is as follows:
(Maximum Total Leg Amps. X System Voltage) / 1000
22.214.171.124.4. Combination of Shore Power Cable(s), On-board Generator(s) and Inverter(s) - A combination of power sources, used simultaneously if the boat circuitry is arranged such that the load connected to each source is isolated from the other in accordance with E-126.96.36.199. Shore power cable(s) plus on-board generator(s) and inverter(s) capacity shall be at least as large as the total electrical load requirements as calculated. Generator(s) and inverters(s) installation
and switching shall be as required in E-11.7.3.
188.8.131.52. LOAD CALCULATIONS
184.108.40.206.1. The following is the method for load calculation to determine the minimum size of panelboards and their main feeder conductors as well as the size of the power source(s) supplying these devices. (See E-220.127.116.11.)
18.104.22.168.1.1. Lighting Fixtures and Receptacles - Length times width of living space (excludes spaces exclusively for machinery and open deck
areas) times 20 watts per square meter (2 watts per square foot).
Length (meters) x width (meters) x 20 = _________ lighting watts, or
Length (feet) x width (feet) x 2 = ________ lighting watts.
22.214.171.124.2. Small Appliances - Galley
and Dinette Areas - Number of circuits times 1,500 watts for each 20 ampere appliance circuits.
Formula: Number of circuits x 1,500 = _________ small appliance watts.
Lighting watts plus small appliance watts = _________ total watts.
126.96.36.199.4. Load Factor
Formula: First 2,000 total watts at 100% = _________.
Remaining total watts x 35% = _________.
Total watts divided by system voltage = _________amperes.
188.8.131.52.5. If a shore power system is to operate on 240 volts, split and balance loads into Leg A and Leg B. If a shore power system is to operate on 120 volts, use Leg A only.
Leg A / Leg B
______/______ Total Amperes
184.108.40.206.6. Add nameplate amperes for motor
and heater loads
______ /______exhaust and supply fans
______ / _____air conditioners *,**
______ / _____electric, gas, or oil
heaters* ______ /
_____25% of largest motor
in above items
NOTE: *Omit smaller of these two, except include any motor common to both functions.
**If system consists of three or more independent units adjust the total by multiplying by 75% diversity factor.
220.127.116.11.7. Add nameplate amperes at indicated use factor percentage for fixed loads:
Leg A / Leg B
______ ______Disposal -10%
______ ______Water Heater - 100%
______ ______Wall Mounted Ovens – 75%
______ ______Cooking Units - 75%
______ ______Refrigerator -100%
______ ______Freezer – 100%
______ ______Ice Maker - 50%
______ ______Dishwasher - 25%
______ ______Washing Machine – 25%
______ ______Dryer - 25%
______ ______Trash Compactor – 10%
______ ______Air Compressor
______ ______Battery Chargers – 100%
______ ______Vacuum System - 10%
______ ______Other Fixed Appliances
______ ______**Adjusted Sub-Total
NOTE: **If four or more appliances are installed on a leg, adjust the sub-total of that leg by multiplying by 60% diversity factor.
18.104.22.168.8. Determine Total Loads
Leg A / Leg B
______ ______lighting, receptacles, and small appliances (from E-22.214.171.124.5)
______ ______motors and heater loads (from E- 126.96.36.199.6)
______ ______fixed appliances (from E- 188.8.131.52.7)
______ ______ free standing range (See NOTE 1)
______ ______calculated total amperes (load)
NOTES: 1. Add amperes for free standing range as distinguished from separate oven
units. Derive by dividing watts from TABLE III by the supply voltage, e.g., 120 volts or 240 volts.
2. If the total for Legs A and B are unequal, use the larger value to determine the total power required