Conductor Size for Electrical Power Distribution

Electrical and electronic topics for small boats
jimh
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Conductor Size for Electrical Power Distribution

Postby jimh » Sun Mar 13, 2016 10:48 am

Some time ago I wrote an article on the proper wire gauge for electrical power distribution aimed at 12-Volt-DC power distribution on small boats. The only problem was I forgot to create a link to it. In case you have not seen the article, it is located in the REFERENCE section. See

Conductor Size for Power Distribution
http://continuouswave.com/whaler/refere ... rSize.html

jimh
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Re: Conductor Size for Electrical Power Distribution

Postby jimh » Mon Mar 14, 2016 6:50 pm

I have added a new section that introduces a very quick interpolation method for calculating wire capacity. Using the quick interpolation in conjunction with the Hebert's Rule of wire gauge selection makes calculating a wire size for particular lengths of circuit and current in the circuit very simple--for readers with some understanding of electricity.

jimh
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Re: Conductor Size for Electrical Power Distribution

Postby jimh » Tue Mar 15, 2016 6:52 am

Here is another very handy table that I have calcuated. It lists the "Ampere-feet" value for various wire gauges that are calculated for a system voltage of 13.2-Volts and a maximum voltage drop of three-percent. With this table you can quickly determine the length of the conductor from the current or vice versa. The length is the physical span for a two-conductor circuit, so that the total length of wire in the circuit would be twice as much. Since DC power distribution is always a two-conductor circuit, the length parameter is the distance between ends of the circuit.

A Useful Table of Wire Gauge in Ampere-feet for 13.2-Volt Power Distribution
AWG / Ampere-feet
16 = 48.8
14 = 78.4
12 = 124.7
10 = 198.2
08 = 315.2
06 = 501.1
04 = 796.8
02 = 1266.8


For example, to determine a length of conductor:

Q: How far can an 8-AWG conductor carry 15-Amperes?

A: From above table, Ampere-feet = 315.2. Thus at 15-Amperes the distance is 315.2 / 15 = 21-feet

For example, to determine a maximum current of a conductor at a particular length:

Q: How much current can be carried by 4-AWG conductor for 18-feet?

A: From above table, Ampere-feet = 796.8. Thus at 18-feet the current is 796.8 / 18 = 44.3-Amperes

There is one caution: if figuring a maximum current for a short length, the length should not be less than 6-feet, otherwise the current-capacity of the wire itself will be exceeded.

This table is also extremely handy to use for compute what size conductor will be needed for a particular length and current. Find the wire gauge necessary by calculating the Ampere-feet and entering the table to find the wire gauge with at least that much capacity. For example:

Q: What is a suitable wire gauge to distribute 30-Amperes a distance of 20-feet?

A: Multiply 30-Ampere x 20-feet to get 600-Ampere feet. Enter table to find suitable wire with 600-Ampere-feet or more capacity; 4-AWG has 796.8-Ampere-feet, so it can handle this current and length.

The table is based on the resistance per foot value of the conductors for copper wire. Note that the values in the table are ONLY applicable to a 13.2-Volt system. I chose that voltage because that is the nominal charging voltage of a so-called 12-Volt battery. If you wanted to use a different system voltage, you can scale the Ampere-feet values up or down in proportion. If you wanted to calculate on the basis of 12.0-Volts, you would scale the Ampere-feet down by a ratio of 12.0/13.2 = 0.909. If you wanted to calculate on the basis of 24.0-Volts, you would scale the Ampere-feet up by a ratio of 24/13.2 = 1.818.

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Re: Conductor Size for Electrical Power Distribution

Postby jimh » Thu Mar 17, 2016 8:30 am

I added two more pre-computed tables to the article; one for 12-Volt and another for 24-Volt. If you wish to be particularly conservative, use the 12-Volt table for distributing 12-Volt battery power.

jimh
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Re: Conductor Size for Electrical Power Distribution

Postby jimh » Tue Jan 16, 2018 10:58 am

I have added an an addendum to the original article. The addendum investigates and explains how properties of copper conductors are consistent across many wire sizes, and establishes the basis by which Hebert's Rule works. This further confirms the validity of using the rule in selecting conductor size for distribution of electrical power. See

Conductor Size for Power Distribution--Addendum
http://continuouswave.com/whaler/reference/powerConductorSize.html#addendum

jimh
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Re: Conductor Size for Electrical Power Distribution

Postby jimh » Thu Jan 18, 2018 1:51 pm

As an adjunct to the problem of properly selecting the size of an electrical conductor, I became curious to know how to compute the resistance of electrical conductors. That investigation led to a new article:

Electrical Conductor Resistance
http://continuouswave.com/whaler/reference/copperConductorResistance.html

Readers with similar curiosity about such topics may find my short explanation and demonstration of the calculation of a conductor's resistance to be informative. The article also describes how to compute wire diameter from its American Wire Gauge number.