Why Tin-Coated Marine-Grade Wire?
CAST Lighting abandoned the use of all-copper wire for Landscape Lighting - here is why.
Author: Steve Parrott
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:
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.
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.
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.
(Document No. 00044: Created on: 07/07/08 Last modified on: 08/25/09)