COMPANY-----------MicroFIT & FIT------------CONTACT US
GO GREENER!
GO GREENER!

Renewable Energy
Systems & Componets

COMPLETE SYSTEMS

SOLAR PANELS

INVERTERS

TRACKERS & MOUNTING SYSTEMS

BATTERIES

CABLES
& WIRING

ELECTRICAL ENCLOSURES & SAFTEY

CHARGE
CONTROLERS
METERS, COMM.S & SITE ANALYSIS
DC TO DC VOLTAGE CONVERTER INVERTER POWER PANELS
 

SOLAR WATER PUMP

 


Need Help Selecting Components?

Contact Us


PRODUCTS
Batteries
Batteries: Flooded Lead Acid
Batteries: Sealed Agm
Batteries: Sealed Gel Cell
Desulfators
Enclosures
Ventilators/Battery Fans
Watering Caps

Books, Classes & Educational Videos

Classes
Educational Videos
General Renewable
Micro Hydropower
Solar Electric and Passive Solar
Solar Hot Water Systems
Wind Energy

Cables & Wiring

Battery Interconnects
Battery To Inverter
Tools
Wire By The Foot
Wiring For Solar Panels

Charge Controllers

Solar Charge Controllers
Solar Lighting Controllers
AC Charge Controllers
Constant Voltage Regulator
Diversion Load Controllers
Temperature Sensors

Composting

BigBelly Compactor
Compost Toilets
Garden Composters

DC Voltage Converters

Enclosures, Electrical and Safety

Electrical Enclosures
Lightning Protection
Miscellaneous Electrical Parts
NEC Compliant Safety Labels
Outback Flexware Components
Overcurrent Devices (Fuses & Breakers)
Switch Gear Disconnects

How To Section
Inverters
Export Inverters (230V 50Hz)
Inverter Accessories
Marine Inverters
Mobile / RV Inverters
Off-Grid: (No Utility-Needs Batteries)
On-Grid & Off-Grid Capable Inverters
On-Grid: (Grid Intertie-No Batteries)

Kits and Package Deals

Grid-Tied Systems
Grid-Tied with Battery Backup
Off-Grid Cabin Systems
Off-Grid Residential Systems
Other Packages and Special Deals
RV Solar Packages

Meters, Communications
& Site Analysis

Data Communications
Meters & Battery Monitors
Shunts
Solar Site Analysis Tools
System Monitors
Wind Data Instruments

Portable Power

Solar Panel Mounts & Trackers

Active Trackers
Ground Mounts
Passive Trackers
Roof Mounts
RV & Specialty
Side Of Pole
Top Of Pole

Solar Panels

1 to 50 Watt Solar Panels
51 to 99 Watt Solar Panels
100 to 149 Watts Solar Panels
150 Watts & Up Solar Panels
Flexible / Rollable Solar Panels
Foldable Solar Panels
Solar Panels by the Pallet
BIPV - Building Intergrated Photovoltaics
Solar Electricity Education

Wind Turbines

VAWT Wind Turbines (Electric)
HAWT Wind Turbines (Electric)
Wind Turbine Towers
Wind Data Instruments
Wind Power Education

RENEWABLE ENERGY SYSTEMS & COMPONENTS

How to Size Wiring and Cabling for Your System

How to Size Wiring for Your System

Properly sized wire can make the difference between inadequate and full charging of a battery system, between dim and bright lights, and between feeble and full performance of tools and appliances. Designers of low voltage power circuits are often unaware of the implications of voltage drop and wire size.

In conventional home electrical systems (120/240 volts ac), wire is sized primarily for safe amperage carrying capacity (ampacity). The overriding concern is fire safety. In low voltage systems (12, 24, 48VDC) the overriding concern is power loss. Wire must not be sized merely for the ampacity, because there is less tolerance for voltage drop (except for very short runs). For example, at a constant wattage load, a 1V drop from 12V causes 10 times the power loss of a 1V drop from 120V.

Universal Wire Sizing Chart
A 2-Step Process

This chart works for any voltage or voltage drop, American (AWG) or metric (mm2) sizing. It applies to typical DC circuits and to some simple AC circuits (single-phase AC with resistive loads, not motor loads, power factor = 1.0, line reactance negligible).

STEP 1: Calculate the Following:

VDI = (AMPS x FEET)/(%VOLT DROP x VOLTAGE)

VDI = Voltage Drop Index (a reference number based on resistance of wire)
FEET = ONE-WAY wiring distance (1 meter = 3.28 feet)
%VOLT DROP = Your choice of acceptable voltage drop (example: use 3 for 3%)

STEP 2: Determine Appropriate Wire Size from Chart

Compare your calculated VDI with the VDI in the chart to determine the closest wire size. Amps must not exceed the AMPACITY indicated for the wire size.

Wire Size
Area mm2
COPPER
ALUMINUM
AWG
VDI
Ampacity
VDI
Ampacity
16
1.31
1
10
Not Recommended
14
2.08
2
15
12
3.31
3
20
10
5.26
5
30
8
8.37
8
55
6
13.3
12
75
4
21.1
20
95
2
33.6
31
130
20
100
0
53.5
49
170
31
132
00
67.4
62
195
39
150
000
85.0
78
225
49
175
0000
107
99
260
62
205
Metric Size
by cross-sectional area
COPPER
(VDI x 1.1 = mm2)
ALUMINUM
(VDI x 1.7 = mm2)
Available Sizes: 1 1.5 2.5 4 6 10 16 25 35 50 70 95 120 mm2

EXAMPLE:
20 Amp load at 24V over a distance of 100 feet with 3% max. voltage drop
VDI = (20x100)/(3x24) = 27.78
For copper wire, the nearest VDI=31.
This indicates #2 AWG wire or 35mm2

NOTES: AWG=Amercan Wire Gauge. Ampacity is based on the National Electrical Code (USA) for 30 degrees C (85 degrees F) ambient air temperature, for no more than three insulated conductors in raceway in freee air of cable types AC, NM, NMC and SE; and conductor insulation types TA, TBS, SA, AVB, SIS, RHH, THHN and XHHW. For other conditions, refer to National Electric Code or an engineering handbook.

Use the following chart as your primary tool in solving wire sizing problems. It replaces many pages of older sizing charts. You can apply it to any working voltage, at any percent voltage drop.

Determining tolerable voltage drop for various electrical loads

A general rule is to size the wire for approximately 2 or 3% drop at typical load. When that turns out to be very expensive, consider some of the following advice. Different electrical circuits have different tolerances for voltage drop.

LIGHTING CIRCUITS, INCANDESCENT AND QUARTZ HALOGEN (QH): Don't cheat on these! A 5% voltage drop causes an approximate 10% loss in light output. This is because the bulb not only receives less power, but the cooler filament drops from white-hot towards red-hot, emitting much less visible light.

LIGHTING CIRCUITS, FLUORESCENT: Voltage drop causes a nearly proportional drop in light output. Flourescents use 1/2 to 1/3 the current of incandescent or QH bulbs for the same light output, so they can use smaller wire. We advocate use of quality fluorescent lights. Buzz, flicker and poor color rendition are eliminated in most of today's compact fluorescents, electronic ballasts and warm or full spectrum tubes.

DC MOTORS may be used in renewable energy systems, especially for water pumps. They operate at 10-50% higher efficiencies than AC motors, and eliminate the costs and losses associated with inverters. DC motors do NOT have excessive power surge demands when starting, unlike AC induction motors. Voltage drop during the starting surge simply results in a "soft start".

AC INDUCTION MOTORS are commonly found in large power tools, appliances and well pumps. They exhibit very high surge demands when starting. Significant voltage drop in these circuits may cause failure to start and possible motor damage. Follow the National Electrical Code. In the case of a well pump, follow the manufacturer's instructions.

PV-DIRECT SOLAR WATER PUMP circuits should be sized not for the nominal voltage (ie. 24V) but for the actual working voltage (in that case approximately 34V). Without a battery to hold the voltage down, the working voltage will be around the peak power point voltage of the PV array.

PV BATTERY CHARGING CIRCUITS are critical because voltage drop can cause a disproportionate loss of charge current. To charge a battery, a generating device must apply a higher voltage than already exists within the battery. That's why most PV modules are made for 16-18V peak power point. A voltage drop greater than 5% will reduce this necessary voltage difference, and can reduce charge current to the battery by a much greater percentage. Our general recommendation here is to size for a 2-3% voltage drop. If you think that the PV array may be expanded in the future, size the wire for future expansion. Your customer will appreciate that when it comes time to add to the array.

WIND GENERATOR CIRCUITS: At most locations, a wind generator produces its full rated current only during occasional windstorms or gusts. If wire sized for low loss is large and very expensive, you may consider sizing for a voltage drop as high as 10% at the rated current. That loss will only occur occasionally, when energy is most abundant. Consult the wind system's instruction manual.

More techniques for cost reduction

ALUMINUM WIRE may be more economical than copper for some main lines. Power companies use it because it is cheaper than copper and lighter in weight, even though a larger size must be used. It is safe when installed to code with AL-rated terminals. You may wish to consider it for long, expensive runs of #2 or larger. The cost difference fluctuates with the metals market. It is stiff and hard to bend, and not rated for submersible pumps.

HIGH VOLTAGE PV MODULES: Consider using higher voltage modules and a MPPT solar charge controller to down convert to the system voltage (e.g. 12, 24 and 48V) to compensate for excessive voltage drop. In some cases of long distance, the increased module cost may be lower than the cost of larger wire.

SOLAR TRACKING: Use a solar tracker (e.g. Zomeworks or Unirac) so that a smaller array can be used, particularly in high summer-use situations (tracking gains the most energy in summer when the sun takes the longest arc through the sky). The smaller PV array will require smaller wire.

WATER WELL PUMPS: Consider a slow-pumping, low power system with a storage tank to accumulate water. This reduces both wire and pipe sizes where long lifts or runs are involved. A PV array-direct pumping system may eliminate a long wire run by using a separate PV array located close to the pump. Many of our solar water pumps are highly efficient DC pumps that are available up to 48V. We also make AC versions and converters to allow use of AC transmitted over great distances. These pumps draw less running current, and far less starting current than conventional AC pumps, thus greatly reducing wire size requirements.

Return to menu