Wire and Cable Types

electricity from the sun by John Drake II | home

On this page we will cover different types of wire and cable for use in a stationary or mobile

photovoltaic system for low voltage direct current circuits.

What is the difference between cable and wire - you have me on that one.

To me, 2 gauge and larger is cable, 4 gauge and smaller is wire.

Whatever sounds good to you.

For now we will call everything cable.

Please Note:

This one-sided discussion is about Copper cable and wire.

I do not believe that aluminum wire has a place in an alternative energy system.

An insulated copper cable is composed of many individual wires (conductors or strands) which are sometimes

wound up in bundles then surrounded by an insulating sheath or jacket.

The more strands in the cable, the more supple (flexible) it is.

The more finely stranded cables make better connections, especially in low voltage applications.

Stiff cable works fine in a house or building that is conventionally wired for 120 / 240 volts a.c.

In a mobile application or static where you have devices that create vibrations, a flexible cable is

preferred.

If you look under either the hood or dash of your vehicle - none of the wires or cables are very stiff.

This is because the stiffer the cable is, the more it will telegraph vibrations to the connections on the

ends.

Imagine the positive wire coming from the starter solenoid on your car - if it was not flexible the vibrations

from the engine would be telegraphed to your battery post. How long would the post connection last?

In an off-grid application you can have vibrations from d.c. to a.c. inverters as well as cable movement as

the cable or batteries heat up and cool down.

The finer the strands in your cable, the more intimate contact will be made at any of your connections.

The less surface area touching, the more likely that there will be a drop in voltage and heating at the

connection.

The main types of wire/cable you will encounter are common building wire, battery cable, welding cable,

portable power cable, boat / marine cable, USE (underground service entrance) and tray cable.

We will discuss the pros and cons of each.

Copper wire is not cheap, but the difference in cost between doing it right and doing it wrong is usually

very little.

Common Building Wire:

This is the wire you will find at your local home center or electrical supply house.

For our application is it not a very good choice.

It has large, but very few, strands and is not very flexible.

Around batteries and inverters it is a poor choice - on a mobile application it can be a disaster.

I tried it once and will not use it again for anything over 10 gauge.

Let's move on to cable that makes sense in our systems.

Battery Cable:

We have all seen battery cable, when you lift the hood of your car and scratch your head.

It is fairly flexible and the insulating jacket is designed to be heat resistant and to be immune

to the petroleum products used by the engine.

It is a pretty good choice for low voltage setups.

One downside is that in some installations it is still too stiff to make connections such as in

power distribution panels, circuit breaker boxes and inverter housings.

It is not rated for use in sunlight nor for direct burial.

We have used it a lot in battery to battery connections.

Welding Cable:

Welding cable is very fine stranded to make it supple for use by welders.

The cable must be soft enough so it can be wrapped over your arm or shoulders without

tugging on the welding torch or stinger.

In some instances, such as the picture on the left shows, each strand is tinned (plated) to prevent

corrosion.

It is ideal for alternative energy systems as long as it is kept out of the weather.

Most welding cable is not U.V. rated and the insulation will eventually break down in sunlight.

The example shown above on the left has a paper sleeve inside the insulation and the strands are tinned

for corrosion resistance.

The picture on the right shows bundles of very fine wires (strands).

Portable Power Cable:

Years ago I got a deal on some 2 gauge portable power cable.

I did not really know what it was but could not pass up the price.

The piece shown above has the finest stranding I have ever seen.

The conductor has a paper sleeve, a flexible plastic sleeve and

a very tough jacket - the thickness of the jacket layers is about 3/8".

The information is not inked on the jacket, it is embossed into it.

Boat Cable, also known as Marine Cable:

The piece shown above is a two conductor cable with fairly fine strands which are

tinned.

The heavy jacket makes it a good choice for use in inhospitiable locations but it

should not be used outdoors because of degradation in sunlight.

I have used this in sizes up to 8 ga. for wiring charge controllers and running lighting circuits.

Tray Cable, also sometimes known as Underground Service Entrance (USE) cable:

tray cable for alternative energy applications

One of the handiest cables available is tray cable.

It is a multi-conductor cable in a special jacket which is sunlight resistant and suitable for direct

burial applications.

Some tray cables, as those shown below, have cords or a nylon rope in them to add strength for aerial

runs.

I have used tray cable in two, three and four conductor variations.

One of our TriMetric battery monitors uses about seventy-five feet of 18/4 tray cable in an aerial run.

Most of our pv modules use tray cable for both interconnects and for bringing power down from the

roof or racking supports.

Our 48 volt system uses 10 gauge / three conductor cable from each panel into a NEMA 4 box on the

roof. There they are wired in series, for a nominal 48 volt, and output through about 95 feet of

6 gauge / three conductor cable to the charge controller.

The voltage drop is pretty much nil.

You will notice on the left picture that all of the conductor insulation has the same color.

Usually in a case like this, each conductor has a number spelled out so you can keep track of which

wire is which from one end to the other.

Tray cable can be found like this or with different insulation colors for each conductor.

Underground Service Entrance - 2:

This is a single conductor wire with a heavy insulating jacket and is rated for direct burial.

The "-2" indicates that the jacket has a high temperature "wet" rating.

Most wires and cables used in direct burial or outdoor applications will have two temperature ratings.

For example, some USE cables will have a 70 degree C rating in wet environments and a 105 degree C rating in

wet environments.

This can come into play when using them on roof tops panel interconnects.

Temperature ratings of wire and cable insulation.

Voltage ratings of wire and cable insulation.

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