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New aluminum wiring

Introduction

From 20 March 2019 Year in Russia enacted №2 Change to SP 256.1325800.2016 "Electrical residential and public buildings". Changing №2 permits the use of cables and wires with cores made of aluminum alloys brands 8030 and 8176 (table 1) in electrical wiring during the construction of residential and public buildings. This change also introduces some additional rules for working with aluminum conductors and cables.

Changed rulebook JV 256.1325800.2016 It enables the use of wires and cables with conductors made of aluminum alloys, not only in the distribution networks of buildings, who exercise the power of apartments, but in the apartments themselves.

Table 1 - Chemical composition of the aluminum alloys 8176 and 8030
GOST P 58019-2017 (subject to amendments to IMS No. 5 2018 g.)

Below is an overview of the problems and solutions of the aluminum wiring, as well as the practice of the aluminum wiring in the US and Canada.

The "old" aluminum wiring

aluminum wiring, which are installed in residential buildings from the mid-1960s, It is believed, It was the cause of many fires. Therefore, 2003 , in Russia it has been banned for use in housing construction. The conductors of the wiring while the wire was cold-worked aluminum AD0E mark GOST 4784 (table 2). The main cause of the problems with this aluminum wiring was weakening and overheating of contact connections of aluminum wire with so-called wiring products, ie with rosettes, switches, etc.. P.

Similar problems occurred with the aluminum wiring and abroad. for instance, in the US and Canada, these problems started after, as, beginning with 1965 of the year, due to the shortage and high cost of copper began to massively use aluminum wires and cables, including, for routing of electrical wiring within buildings. This wiring was a conductor of aluminum brand 1350 in the cold-worked condition H19. Chemical composition of the aluminum brand 1350 (table 3) practically coincides with the chemical composition of AD0E [1].

Table 2 - The chemical composition of the aluminum grade AD0E (GOST 4784-97)

Table 3 - Chemical composition of the aluminum brand 1350 according to ANSI H35.1 standard [2]

aluminum brand 1350 It has been successfully used and is still used in overhead transmission lines from power plants to transformer substations. In this case, the aluminum has advantages over the copper because of its low specific weight.

Problems “old” wiring and their solutions

causes problems with "old" with the aluminum wiring conductors made of aluminum or brand marks AD0E 1350 the following features of its properties are considered in comparison with copper wiring [2,3]:

  • creep up
  • lower ductility
  • higher thermal expansion
  • oxidation of the contact surfaces
  • galvanic corrosion in contact with brass and steel.

1) Creep

Problem:

  • Aluminum grade AD0E (1350) under constant load in the contact joint exhibits creep, which leads to a weakening of the electrical contact (figure 1). Creep - it, simplistically, slow plastic deformation at stresses below the yield stress. See. more here.


Figure 1 - Aluminum creep and contact weakening [13]

Decision:

  • Aluminum alloy wires 8030 and 8017 have a higher resistance to creep, which is close to the, which have copper wires. This is achieved, primarily, due to the suspended iron content (figure 2).

Figure 2 [13]

2) Plasticity

Problem:

Of aluminum wire 1350 used in the aluminum wiring in the fully cold-worked condition H19. In this state, the tensile strength only slightly higher than the yield stress, and elongation is only 1,5-2 % (drawing 3) [6]. A related "fragility" of the aluminum wire and its notch sensitivity and dents.

Figure 3- Change ultimate strength and ductility
during cold working and annealing of aluminum [5]

Decision:

  • Aluminum alloy wires 8030 and 8176 have a condition H2X, i.e. with intermediate annealing, which gives an elongation of not less than 10 % [7].

3) Thermal expansion

when heated aluminum increases its size and volume to a greater extent, than other materials, who are with him contact connections, for example, brass or steel. This causes thermal stresses and, often, plastic deformation, which leads to a decrease in the contact area and to its even greater heating (figure 4) [8].

(and)

(b)

Figure 4 [9]

Decision:

  • The coefficient of thermal expansion of aluminum is practically independent of alloying elements or technology [2]. To compensate for the high thermal expansion of aluminum wiring special contact devices of the materials used, close in temperature expansion (figure 5) [8].
  • For aluminum wiring categorically do not use the so-called plug-in contacts, when the wire "sticks" into the contact device [9]. These contacts are very sensitive to the differences of thermal expansion of the materials of the contact device and the aluminum conductor.

Figure 5 [8]

4) Oxidation of the contact surface

Problem:

  • Fresh aluminum surface immediately covered with a film of aluminum oxide. Alumina is an electrical insulator. The thickness of this film depends on the temperature and humidity of the environment.

Decision:

  • At a temperature 25 ºC oxide thickness is only 2-50 nm. mechanical force, which is attached to the aluminum wire screw or plate easily "breaks through" brittle layer of aluminum oxide. Moreover, voltage, which is used in the distribution networks of buildings (usually from 120 to 480 C) enough, to overcome the insulating properties of natural aluminum oxide [3,4].
  • For, to get the highest good connection is better to remove the oxide layer from the surface of the aluminum wire and cause it conductive grease. This is especially important for conductors, which operate in a humid or corrosive atmosphere,, at high temperature or during long-term service life. Conductive grease prevents further growth of the oxide film and, Moreover, excludes the ingress of moisture at the contact surface or another electrolyte, which excludes galvanic corrosion (see. below).

5) Galvanic corrosion of aluminum

Problem:

  • materials, which are used in contact with the aluminum compound, may be other metals, for example, steel or brass. In the presence of moisture, this can lead to the formation of a galvanic pair and cause galvanic corrosion of aluminum (see. Figure 3). This deteriorates the contact corrosion conditions and also can cause overheating of the contact connection.

Decision:

  • The use of special contact devices from materials, not causing galvanic corrosion of aluminum (see. Figure 4);
  • Application of a special contact lubricant (see. above item 4)).

The "new" aluminum alloys in the United States and Canada

Electrical alloys series 8000

Back in the early 1970s, a number of new aluminum alloys have been developed in the United States and Canada for the production of aluminum wire and cable. Standard ASTM B 800 [8] includes 6 such alloys, some of them have been patented. They all have a high iron content, as well as some other additive elements. The main differences of the chemical composition, for example, aluminum alloy 8030 and aluminum brand 1350 shown in Figure 6.

Figure 6 – Comparison of the chemical composition
aluminum alloy 8030 and aluminum brand 1350 [13]

At the present time for the production of aluminum wire and cable used only two aluminum alloy - 8030 and 8176 (table 4) [8-12]. The European standard EN 573-3 also includes a series of 8000 only these two electrical aluminum alloys (table 5). For ease of comparison, the table also shows the 6 Alloys with a chemical composition 8030 and 8176 GOST P 58019.

Table 4 - alloys 8030 and 8176 в ASTM B 800

Table 5 - alloys 8030 and 8176 в IN 573-3

Table 6 - Chemical composition of alloys 8176 and 8030 GOST P 58019-2017

"American" and "Russian" alloys 8030 and 8176

Note, that Russian alloys 8030 and 8176 significantly differ from their American and European counterparts (see. tables 4-6). In figures 7 and 8 shows the limits of the content of the main alloying elements in the alloy 8030 (iron-copper) and 8176 (iron-silicon) acc. to ASTM B 800 and GOST R 58019. Russian alloys have a much lower content of alloying elements – gland, copper and silicon.

Figure 7 - Limits of iron and copper in the alloy 8030
by ASTM B 800 and GOST R 58019

Figure 8 - Limitation of silicon and iron content in the alloy 8176
by ASTM B 800 and GOST R 58019

Aluminum conductors in the US NEC

According to the American National Electrical Code (NEC), all aluminum conductors must be made from electrical aluminum alloy series 8000:

  • whole – dimensions 12, 10 and 8 AWG
  • stranded – from 8 AWG and more.

Aluminum wires less 12 AWG (3.31 mm2) are not considered in the Code.

Reference:

  • American wire gauge (AWG) is a standardized sizing system for round conductor diameters from 40 to 0000(4/0). The greater the number of AWG, the smaller the physical size of the core. Detail table AWG cm. on the image 9.


Figure 9 Detail AWG table

The use of aluminum conductors in the US and Canada

In the US and Canada is currently the aluminum alloy wire 8030 and 8176 available on the market only since the size of AWG 8 (8.37 mm2) [10]. It can also be seen in catalogs and presentations of manufacturers of aluminum wire and cable, who in the 1970s were the first to use alloys 8030 and 8176 – Alcan Cable и Southwire [11-13]. For internal wiring need aluminum wire sizes AWG 10 и AWG 12.

Alcan's presentation provides a visual diagram of the typical use of aluminum wires and cables for the transmission of electricity from power plants to residential buildings (Figure 10) [13]: everywhere, but not inside the houses themselves!


Figure 10 – Application of aluminum wires in the USA and Canada [13]

During the construction of new homes for wiring internal wiring, usually, use copper wires - this is directly indicated on the website of the American Aluminum Association [14].

At the same time, to connect major residential consumers of electricity - dryers, conditioners, boilers, Cooktop - usually used is aluminum cables. Moreover, in many American homes for supplying electric power from a common power grid to the home electrical panel is also used cables with aluminum conductors. In these cases, use aluminum conductors 8 and 6 AWG (8,37 и 13,3 mm2) [6].

For the last 20 years, the use of aluminum wires as "feeder" (supply) electrical lines for high-rise buildings has increased significantly, hospitals, hotels, stadiums and, It has recently, data centers [3].

Learning to work with aluminum wires and cables

American Aluminum Association is making great efforts to promote the production of aluminum, including, aluminum cable products. An example of this is the, for example, a voluminous guide to aluminum electrical conductors Aluminum Electrical Conductor Handbook [15].

The American Aluminum Association and the National Electrical Contractors Association (NECA) jointly develop and regularly update the NECA / AA Standard 104-2012 [9] on the rules for the installation of aluminum wires and cables in electrical networks of buildings. This standard provides guidance on working with aluminum conductors and cables, which includes a lot of detailed illustrations.

Conclusion

1. Working with aluminum conductors and cables for internal and external wiring of buildings, including, alloys 8030 and 8176 It requires additional knowledge and skills compared to working with copper wires and cables. For this, for example, US and Canada, developed and distributed by special standards, guidelines and recommendations, as well as seminars and workshops.

2. In the US and Canada, cords and cables from aluminum alloys 8030 and 8176 used mainly, from size 8 AWG. These cables are used to connect large residential consumers, such as dryers, boilers, air conditioning, as well as for power supply from the network to the general distribution panel individual houses. For wiring internal wiring in the construction of new homes Aluminum wires and cables with dimensions 10 AWG и 12 AWG hardly used.

3. Over the past two decades in the United States and Canada has increased the use of wires and cables made of aluminum alloys 8030 and 8176 for supply (feeder) power lines for high-rise residential, office buildings and data centers, as well as large structures, for example, stadiums.

Sources:

  1. Change №2 to the joint venture 256.1325800.2016 – 19.09.2018.
  2. Aluminum and Aluminum Alloys / ed. J.R. Davis - ASM International, 1993.
  3. Power cables with the conductors of aluminum alloys for wirings in residential buildings / Kamensky MK, Nedayhlib TA, Frik A.A. - Cables and wires – №3, 2018.
  4. Aluminum Alloy Conductors: 45 Years of Reliable Installations /Christel Hunter – Îäèí News magazine – January 18, 2016.
  5. Design of Aluminium structures: Selection of Structural Alloys Structural Design according to Eurocode 9 /R. Gitter – EUROCODES: Background and Applications, 2008.
  6. ASTM B 230 Standard Specification for Aluminum 1350–H19 Wire for Electrical Purposes.
  7. ASTM B 800 Standard Specification for 8000 Series Aluminum Alloy Wire for Electrical Purposes – Annealed and Intermediate Tempers.
  8. Evaluation of Aluminum Cable / Breck Booker, Southwire – 2011.
  9. NECA/AA 104-2012 Recommended Practice for Installing Aluminum Building
    Wire and Cable.
  10. The Evolution of Aluminum Conductors Used for Building Wire and Cable – National Electrical Manufactures Association (NEMA), 2012.
  11. Building Wire – Product Catalog – Alcan Cable
  12. https://www.southwire.com/Building-Wire/c/building-wire
  13. Stabiloy, Aluminum or copper? /Alex Mak – Alcan – 2008
  14. Technical Information on Electrical Aluminum – Aluminum Association, 2019
  15. Aluminum Electrical Conductor Handbook /Aluminum Association, 1989.