No-Gas Tin-Coated Landscape Lighting Wire
Buried landscape lighting wire is subject to the same type of corrosive exposure as wiring on
boats and marinas. For that reason, No-Ox landscape lighting wire is marine-grade tin-coated.
This same wire is used for wiring all our fixtures.
No-Gas Marine-Grade Tin-Coated Landscape Lighting Wire is highly corrosion resistant and
retains its conductivity far longer than all-copper wire.
The corrosive effects of the outdoor environment present unique challenges to Landscape
Lighting. Every component of the lighting system is subject to heat, moisture and physical abuse.
Landscape Lighting wire is especially critical since its corrosion leads to degradation of lamp
performance and (eventually) to complete system failure.
The following discussion addresses these key factors that determine long-term integrity of
landscape lighting wire:
Inhibition of wire corrosion
Preservation of wire conductivity
Optimization of wire solderability – during both initial installation and future additions of
fixtures to the system
What Happens to Landscape Lighting Wire after Installation
1. All outdoor wire is subject to 'wicking'. This is the migration of water and electrolytes
under wire insulation. This moisture travels from wherever the wire has been cut
including splice points, socket connections and transformer terminals. Wicking causes a
progressive oxidative corrosion of the wire.
The wicking problem has long been recognized by marine engineers since moisture is
constantly present in the marine environment. These engineers, working in concert with
regulatory and advisory agencies, developed marine-grade standards for boat wiring.
These standards require tin-coated copper wire. (UL 1309 and 1426)
The presence of moisture in the landscape makes outdoor lighting wiring more akin to
marine applications than to wiring used in the low-moisture indoor environment. For this
reason, CAST has adopted the Marine-Grade standard by introducing No-Ox tin-coated
wire.
2. Oxidative corrosion of copper and its effect on conductivity. Electrical conductivity is a
measure of a materials ability to carry an electrical current. Copper is an excellent
conductor making it ideal in all electrical applications. However, in the presence of air
and moisture its surface oxidizes forming a layer of copper oxides that conduct electricity
very poorly. This layer is not initially a problem since the layer is very thin and actually
serves to protect the underlying copper.
In an outdoor corrosive environment, however, the oxide layer progressively extends
deeper into the copper strand and eventually oxidizes the entire thickness. The resultant
decrease in conductivity severely compromises the lighting system. Landscape lighting
wire is especially prone to this severe corrosion because it is a stranded wire with very
thin strands. Lighting installers often see the devastation of this effect when they pull old
wire from the ground and see the strands completely blackened and brittle.
Tin-coating the wire protects from this type of progressive corrosion and loss of
conductivity in two ways.
1. Sacrificial. The tin coating differs in electrical potential from copper in a way that causes
the tin to be oxidized in preference to the copper. In other words, instead of a progressive
deepening of the corrosion into the strand, the tin must completely oxidize before the
copper interior is subject to corrosion.
2. Greater Conductivity of Tin Oxides. While copper oxides are very poor electrical
conductors, tin oxides maintain good conductivity. This benefits the long-term
conductivity of the entire wire bundle. Note: the initial conductivity of the tin coating is
lower than copper, leading to a slightly higher voltage loss at time of installation. This
difference is offset over time since the tin coating largely maintains its conductivity while
the oxidized copper conductivity significantly decreases over time.
Solderability – Differences between Tin and Copper.
Landscape lighting installers use a variety of methods for making wire connections in the field.
Of these methods, soldering provides the most secure, corrosion-resistant splice points. CAST
teaches this soldering method at all its seminars and workshops.
Since tin solder is the preferred type, it stands to reason that tin-coated wire is the best recipient
of this solder. The resultant connection provides a seamless surface of tin that extends from the
solder point along the entire length of the wire.
This is critical for corrosion prevention since corrosion occurs most aggressively when two
dissimilar metals are in contact with each other and exposed to the environment. A tin solder
connection on an all-copper wire is an invitation for corrosion to occur at the copper-tin
boundary.
Soldering can be especially problematic when old wire is soldered. This situation occurs
frequently since installers are often called upon to add fixtures to an existing system. Tin-coated
wire maintains good solderabilty as it oxidizes over time. Copper oxides, on the other hand, are
extremely resistant to solder.
An installer trying to add new fixtures to a system with all-copper wire, may be forced to replace
entire wire runs while a system with tin-coated wire may be cut and re-soldered to make the new
connections.
More Reasons to use Tin-Coated Wire
1. UL specified. In addition to the Marine-Grade applications mentioned above, tin-coated
copper wire is required (various UL listings) for the internal wiring of any appliance
subject to heat and humidity. CAST also uses tin-coated No-Ox wire for all internal
wiring of its fixtures and transformers.
2. Homeowner Perception. Homeowners readily see the value in using Marine-Grade wire.
If you, the professional, assure them that the use of this wire will add longevity and
reliability to their lighting system, they will be willing to absorb the extra cost. (Keep in
mind that No-Ox wire is just a few dollars more than all-copper wire.)
3. Reputation. No-Ox wire is unquestionably the highest quality wire available. Lighting
Designers who maintain an uncompromising attitude toward quality will earn the best
reputations and get the best jobs.
Sources
Sources for this article include various documents from UL, NEMA and IEC, as well as a
thorough research of journals on corrosion and metallurgy. In addition, several experts in these
fields were interviewed and overwhelmingly corroborated our conclusions.