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Fabric & rubber insulated copper wire (C) Daniel Friedman Paul Galow Tinned Copper Electrical Wire Identification
Identification & safety of tinned-copper electrical wiring

  • TINNED COPPER ELECTRICAL WIRE - CONTENTS: about the history, testing, & safety of tinned-copper electrical wiring. How to avoid mistaking tinned copper electrical wire (safe) for aluminum electrical wire in building branch circuits (unsafe). Modern tinned copper wire is also known as "busbar wire". Illustrations of tinned copper solid conductor wire and tinned multi-strand copper wire are compared with copper wire to which solder was later applied. .
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Tinned-copper Elecrical Wiring identification, safety, production methods.

This article describes methods for accurate identification of tinned-copper or "plated copper" electrical wiring and its safe use in buildings. Tinned copper wire should not be mistaken for aluminum electrical wire in buildings. Modern tinned copper wire is also known as "busbar wire". This article includes illustrations of tinned copper solid conductor wire and tinned multi-strand copper wire are compared with copper wire to which solder was later applied.



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Avoid confusing copper-clad wire with tinned-copper plated wire or with COALR or CU-AL Devices

Closeup of tinned copper electrical wire surface (C) InspectApedia

Here we describe observations that prevent confusing tinned copper wire or plated copper wire (safe in buildings) with solid single-conductor aluminum branch circuit wiring in buildings (unsafe).

Our page top photograph illustrates rubber and fabric-insulated copper wire that may have a dull silver color on the actual wire surface. Our photo with the red and blue arrows, adapted from a contemporary tinned-copper electrical wire advertisement [Amazon.com] we can see the reddish copper color of the wire beneath its plating in two locations: at tool marks and scrapes on the wire surface and at the cut-end of the wire.

In modern applications tinned coppe wire is used where extra corrosion resistance is needed such as in marine applications or "boat wiring".

In contrast with tinned copper or plated copper wire, below we see both a solid single strand and a multi-strand aluminum wire connected to circuit breakers.

Scratch the tin plating on this wire and you'll see shiny, reddish copper of the wire core. From that step we know that this is a tinned copper electrical wire, not aluminum wire.

Below in our photograph of wires inserted into several circuit breakers, even without any disassembly we can see a solid conductor aluminum wire (blue arrow) double-tapped (two wires under one connector) into a circuit breaker.

We see a copper wire and on top of it a silver-colored solid conductor electrical wire that is probably aluminum wire.

The large multi-strand red-insulated wire is a multi-strand aluminum conductor.

Watch out: Double-tapping electrical wire connections is improper and unsafe unless the connector is specifically designed for that purpose and is so-indicated by its manufacturer.

Double tapped aluminum and copper wire in a CUAL breaker (C) InspectApedia

But from just this photograph alone one cannot be sure if the silver colored wire is aluminum or tinned "plated" copper.

Note: Tin plated copper wire was generally a practice used before 1965 on small-sized 14-12 copper wire. On second look, the size of the silver-colored black insulated wire shown above is likely to be a size 10 or 12 AWG aluminum. Further, tin-plated copper presents a "dirty silver" look. - D'Agostino (2014)

A closer look will be needed to confirm the opinions of our note above. Notice that the circuit breaker itself is marked CU-AL indicating that the manufacturer represented that the breaker could be used with either aluminum or copper wire, notwithstanding that CU-AL-marked devices are not an accepted nor recommended repair for aluminum electrical wiring.

Watch out: In addition to the improper double-tapping in the center circuit breaker shown above, copper wire in contact with an aluminum conductor in an AL-CU rated circuit breaker is not covered by the UL-listing. The device is listed for use with either copper-only or aluminum only.

Details are at ALUMINUM WIRING REPAIR COALR & CU-AL.

Solid conductor aluminum electical wire closeup for identification (C) Daniel Friedman

An easy photograph for aluminum wire identification is shown above right. This is of course from a different electrical connection - a splice that used a twist-on connector.

We can see silver-colored (soft) metal that is aluminum at three locations:

  1. The wire surface, silver colored. If this were all we could see we might not know (unless aided by printing on the wire insulation) whether we're looking at aluminum wire or plated copper wire.

    But that white plastic insulation tells me this is not an older rubber-insulated wire so on that basis I'm already ruling out plated copper. But the next two observations confirm that conclusion.
  2. The interior of nicks into the wire that would have most likely cut through any plated skin - so we are pretty sure that this is not tin-plated copper wire
  3. The square-cut end of the wire, silver colored throughout, so we know for sure that this is solid alumium wire

Fabric & rubber insulated copper wire (C) Daniel Friedman Paul Galow

Watch out: tin-plated copper wire is a completely different product that, because its conductors sport a thin plated silver colored surface, might be mistaken for unsafe alumium wire. It is not aluminum and it is safe unless, as with any electrical wiring, it has been damaged in some manner.

Not all rubber insulated copper wire is plated, but if you suspect that the silvery-colored wire is plated copper, it's easy enough to determine: with the wire disconnected from any power source, scratch the silver colored surface of the rubber-insulated wire and you'll see its red copper interior.

In REDUCE THE AL WIRE RISK: DETAILS, as well as in Aronstein (2011). There Aronstein describes plated-copper wire as:

Plated copper wire [tinned copper wire] is relatively common in older homes, and it looks like aluminum wire. It was commonly used with rubber-based insulation. Identification can be made by careful inspection of a cut end of the wire.

In general, plated copper wire would not be present in nonmetallic sheathed cable ("Romex"), it is most generally found in metallic sheathed cable ("BX"). Cable of the "BX" type is not likely to contain aluminum wire. - Aronstein (2011)

Cross section view of coppe wire and aluminum wire (C) Daniel Friedman

Above we show solid aluminum conductor wire and solid copper conductor electrical wire in cross section.

Watch out: don't confuse references to copper-clad aluminum wire or tin-plated electrical wire with devices such as electrical receptacles and switches marked COALR or CU-AL.

The latter two are device labels not wire types and are not a recommended repair for aluminum electrical wire. COALR and CU-AL and their field performance and safety warnings are described in more detail at ALUMINUM WIRING REPAIR COALR & CU-AL

Tinned Copper vs Solder Applied to #12 Multi-Strand Copper Wire

Tinned copper multi-strand wire ca 1960 (C) Daniel Friedman

Above: tinned copper multi-strand #12 copper wire used in wiring a fluorescent light ballast in a Minnesota home constructed in the 1960's. You will note the two layers of insulation: rubber covered with a fabric, perhaps nylon, though earlier fabric covered wires also may have used asbestos cloth.

The tin coating on this copper wire appears to have successfully resisted corrosion that occurred between earlier copper wires and high-sulphur-containing vulcanized rubber wire insulation. That history is discussed at COPPER-CLAD ALUMINUM WIRE

Below I've scratched the factory-tin-plating off of four of the strands of copper wire as you will notice in the bottom of the photograph.

Strands of tinned copper in a multi-stranded #12 copper wire from a 1960's light ballast (C) Daniel Friedman

The electrician who installed the fluorescent light fixture in which this ballast was used wanted to make a very reliable connection between the ballast wire ends and the electrical circuit - or perhaps the factory sold the ballast with its wire ends also solder-coated. In my photo below you can see the remains of solder in the end of this ballast wire that had been inerted under the connecting screw of the fluorescent light fixture.

Solder on end of tinned copper multi-strand #12 wire of a 1960's fluorescent light fixture (C) Daniel Friedman

Click to enlarte the photo above and you can see the additional solder that someone (perhaps the installing electrician) applied to the end of this wire to prepare it for use at a wire connector.

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