Photograph of a melting purple twister twist on wire connector repair for aluminum wire the Ideal 65 Twist-On Connectors for Aluminum Wire - US CPSC Staff Concerns

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Aluminum wiring repair:

Concerns about using twist on connectors. This document has been scanned verbatim from the CPSC document and is straight ASCII text.

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Twist on connectors for aluminum wiring repair? Photograph of Aluminum wire in the
electric panelVerbatim scan of US CPSC documents obrained under FOIA.

May 1, 1995

Mr. James Beyreis
Vice President and Chief Engineer
Underwriters Laboratories Inc.
333 Pfingsten Road
Northbrook, IL 60062-2096

Subject: CPSC Staff Concerns Regarding Recently Listed Aluminum Wire Twist-On Connectors
Dear Jim:
As you are aware, the CPSC has worked cooperatively with Underwriters Laboratories (UL) over the past two decades. I hope to continue and improve this cooperation to ensure public safety is adequately protected, maintained, and where necessary, improved. I briefly discussed the subject of this letter with Mr. David Dini of UL on April 20, 1995. I suggested we arrange an open meeting to discuss this issue further.

To aid in the discussion, attached are CPSC staff concerns regarding the subject connectors. Members of The CPSC staff are concerned wit this product and its applications in homes with aluminum wiring. I propose that The topics in the attachment be the agenda for our technical discussions. Mr. Dini indicated he would discuss this matter wit you, and someone would be in contact wit me to arrange a date for these discussions.

I look forward to meeting with you and discussing this product safety issue in the near future. If you have any questions regarding this matter, please feel free to call me at 301-504- 0504, extension 1290.


Andrew G. Stadnik, P.E. Associate Executive Director Engineering Sciences Attachment as noted. D. Haataja, UL-Washington, D.C. T. Castino, UL-Northbrook, IL

CPSC Staff Concerns with the Application of Twist-on AL/CU Wire Connectors

The principal application for a listed, twist-on, AL/CU connector is homes wired with aluminum wiring during the mid-I 960's to early 1970's before safety concerns resulted in aluminum wiring no longer being used. Many consumers living in these homes will believe that such a connector is a safe, permanent repair for aluminum wiring connections at outlet terminals and splices. The CPSC staff has the following concerns with the application of these connectors:

1. Wiring Used to Test the Connectors Differs From Wiring Installed in Many Homes - Many of the estimated 2 million homes with aluminum wiring have a hard-drawn grade of aluminum wiring (ECHi9 and other grades) that is not adequately represented by the aluminum alloy currently used to qualify connectors for use with aluminum conductors. Testing is also conducted using fresh samples and not with contaminated and distorted conductors representative of wires in the field that have been previously used

2. UL Standard for Twist-on Connectors Lacks Environmental Testing - UL testing does not appear to include testing under appropriate conditions of ambient temperature, humidity or household contaminants.

3. Connectors Likely to be Mis-Applied by Consumers - The availability of a manually applied, twist-on connector for use with aluminum wire will result in many consumers attempting to repair and service their aluminum-wired homes themselves. Prior to that time, consumers would not have available to them the proper special crimping tools needed to follow the CPSC- recommended repair procedure. These crimping tools are made available to trained electrical contractors on a lease arrangement to assure proper correction of this recognized fire hazard. It does not appear that a UL evaluation for twist-on AL/CU wire connectors takes into account that untrained, do-it-yourself consumers will likely undertake using such a connector with aluminum wiring. Even if a connector performed satisfactorily when installed in accordance with the installation instructions, the likelihood for improper installation is very high especially if inordinate and unique special instructions when using aluminum wiring are included for this rather common-looking connector.

4. Anti-Oxidant Compound Flammability - Compounds that are used with AL/CU wire connectors are often petroleum-based greases that are flammable. With such materials, excessive heat and direct exposure to flame should be avoided. However, excessive heat is the consequence when a connector fails and the twist-on connector when used with aluminum wiring has a propensity to fail.

5. Connector Body Flammability - Connector bodies often consist of non-flame-retardant grades of thermoplastic materials. Once ignited, they will continue to burn with a flaming drip. In the presence of a failing connection, this represents a serious fire hazard.

6. Connector Violates Principle of Safe Wire-to-Wire Electrical Splices - A twist-on connector is intended to join two or more wire conductors within its cap. The purpose of the cap is to hold the wires together, Electricity is intended to flow from wire-to-wire. In the case of two solid wire conductors joined by a twist-on connector without pre-twisting the wires, the two wires connect with each other along a longitudinal line of contact. This results in poor performing contact surfaces when the conductor material is aluminum because the aluminum oxide that exists on the surfaces of aluminum wires is nonconductive. While initially a connector may appear to perform in a satisfactory manner, the conduction may be related more to the wiping action of the steel spring commonly used in such connectors. The steel spring gouges the outer surfaces of the aluminum wires, penetrates the aluminum oxide, and provides a principal path for the electric current. The steel spring becomes part of the electric circuit, and not simply as a means to apply pressure between the two wires to hold them in contact with each other. Using steel as a circuit bridge between an aluminum wire and another wire violates design practices for connecting aluminum wire, and violates provisions of UL's own standards.

7. Aluminum Wires Installed in Homes Are Weak in Resisting Shear Fracture - The twisting action that takes place when applying a twist-on connector to aluminum 'wires, given the physical properties of aluminum wires used in homes, results in forces that can readily sever the aluminum wires where they enter the cap of a connector.

8. Field Failures Involve Twist-on Connectors With Aluminum Wire - CPSC has received many reports of failures of twist-on connectors. In response, UL proposed and adopted revised requirements for these connectors when rated for use with aluminum wiring. CPSC staff on several occasions expressed reservations to UL in writing regarding the adequacy of the revised requirements. These CPSC concerns were never addressed to CPSC staff's satisfaction. Meanwhile, the reports of field failures involving twist-on connectors and aluminum wire continue, including reports of disappointing performance of a special service twist-on connector made with a copper alloy spring and used in Canada for a time.

9. Mechanical Integrity With No. 10 and 12 American Wire Gage (AWG) Solid Aluminum Conductors - Experience with using twist-on type connectors and the relatively stiff wires characteristic of aluminum wiring used in homes indicates poor performance because the resulting connection often lacks mechanical integrity. When such splices were positioned into the limited volume provided in outlet boxes installed in homes, the connections would readily come apart.

10. Limited Technical Data to Support Twist-on Connector For Aluminum Wire - No scientific rationale or engineering design analysis that addresses the long term safety of a twist-on AL/CU connector product has been presented. Such documentation is appropriate since the experience with previous forms of this product resulted in unsafe and unsatisfactory performance in the field.

Aluminum Wiring Repair Articles


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