aluminum wiring

It is known, aluminum is born electrical conductor. Additional advantages of aluminum conductor gives their low specific weight.

Aluminum and power transmission

It is a standard aluminum material for electrical conductors when electrical energy transmitted from all stations and just before entering the house or flat. It is used there for more than a hundred years. High-voltage wires on poles - is always aluminum wires. This is due to the fact, aluminum wires in two times lighter than copper. Aluminum makes it possible to use two smaller towers, than copper. Moreover, from substation to distribution transformers aluminum cables and wires, are also standard conductors, for air, and for underground networks. On this site is sometimes used copper wires, but basically still applies aluminum.

Figure 1.0 – Electrical properties of aluminum [3]

aluminum wiring

However, for internal wiring of buildings and premises of the main wiring material is copper. Aluminum is no longer used as the standard internal wiring of buildings because of problems, who were with the aluminum wiring in the past, in the already distant 1960-70-ies. Since then, much has changed, but distrust of the aluminum wiring is left.

Regulatory document "Electrical Installation Rules" in the 7th edition of 2002 year (PUE-7) categorically prescribes in paragraph 7.1.34 in the buildings' use cables and wires with copper conductors ". For supply and distribution networks, that is, wires and cables from the substation directly to consumers, in front of, prescribed use, usually, cables and wires with aluminum conductors, if the calculated cross section is 16 mm² and more. Moreover, the power of the engineering equipment of buildings, as pumps, fans, heaters, air conditioning units etc., also permitted to perform a wire or cable with aluminum conductors section of at least 2,5 mm².

In the same vein, limit the use of aluminum wiring in buildings and Building Regulations SP 31-110-2003 in its section 14.3.

Currently used in Russia in the construction of buildings of copper wire is much more expensive, than aluminum. Naturally there is a desire to save money and go with a copper to aluminum wiring. However, any designer and manufacturer of electrical work required to act strictly according to state regulations - rules, standards and regulations. With all of this, millions of people live in houses and apartments, which were built before the year 2000, and equipped with the very same aluminum electrical wiring.

See. also Aluminum wiring in Russia

Aluminum wiring in the US

In 1960-70-ies American cable industry produced aluminum wires for internal wiring of buildings. They were from the aluminum brand, and that the high-voltage wires, a, exactly, aluminum brand 1350. After some time with this aluminum wiring made of aluminum 1350 had difficulty, mainly from overheating contacts, as a result of which form a stable negative attitude to the use of aluminum wiring in residential construction.

Negative on aluminum wiring

The negative attitude to the aluminum wiring is based on 6 popular belief, some of which have already become just myths [1]:

1. Aluminum wiring is fragile and difficult to install.
2. The aluminum wiring is exposed to an increased thermal expansion, which weakens the electrical contact.
3. Excessive propensity to creep aluminum wiring weakens the electrical contact.
4. Aluminum wires must be much thicker, than copper, to provide the same amperage, and that the copper wire.
5. Oxidation of aluminum wiring creates a large electric contact resistance.
6. Aluminum wiring may corrode and deteriorate outdoors.

Figure 1 - Attenuation of electrical contact
due to differences in thermal expansion of metal

Figure 2 - Attenuation of electrical contact
due to creep of aluminum 1350

American "PUE» - NEC

In the US, the Russian analogue of PUE is NEC - National Electrical Code. This code never explicitly forbade the installation of aluminum wiring inside buildings. However, there was a period in the early 1970s,, When the authoritative American certification body Underwriters Laboratories has withdrawn from its list of permits for a few years, all the wires of aluminum for the internal wiring of buildings. Aluminum wiring is returned to the list already in the form of wires, aluminum alloy series 8000.

Wires from brand aluminum 1350

To 1970 year for all aluminum wires used in the US aluminum brand 1350 as far as cold-worked condition, H19. Domestic analogues of this brand is the brand of aluminum wrought aluminum AD0E GOST 4784-97 or mark A5E primary aluminum GOST 11069-2001 . This solid aluminum 1350 H19 has been specifically designed for self-supporting overhead cables, and continues to be used currently for overhead power lines of power to distribution transformers.

Aluminum 1350 has a high electrical conductivity (62 % on copper conductivity), but it must be completely cold-worked, and even overloaded (H19), a position to, to provide a high tensile strength, which is necessary for its use as an internal electrical wiring. This fully aluminum cold-worked condition has a very low ductility with elongation of only about 1,5 %. With this and its associated "fragility".

Wires of aluminum alloy 8030

ALCAN company in the early 1970s, developed a special aluminum alloy - no longer mark – called Stabloy, to increase the strength properties of aluminum wire, while maintaining its high plastic properties. This aluminum alloy has been registered as an aluminum alloy 8030.

Compared with the brand aluminum 1350 This aluminum alloy 8030 It has:

• increased iron content - up 0,8 %;
• increased copper content - up 0,30 %.

Iron solves two problems at once:

• It provides high strength in the annealed state
• excludes aluminum propensity to increased creep.

Copper contributes to maintaining the strength properties at elevated temperatures.

Aluminum alloy 8030: the benefits of iron

The iron atoms in the aluminum alloy 8030 reinforce the crystalline lattice aluminum and thereby greatly reduce the tendency to creep of aluminum. Moreover, iron additives provide an increase in the strength of aluminum while maintaining good plastic properties [1].

Figure 3 - The iron atoms prevent the creep of aluminum

Aluminum wire thicker 1,5 fold

Aluminum has twice the electrical conductivity per unit weight, than copper. However, per unit volume, electric conductivity of aluminum is only 60 % of it, that have copper. As a result, typically aluminum wire should have sectional area twice, than copper wire to provide the same current intensity.

oxide film Problem

Aluminum oxide film forms immediately after contact with oxygen. This limits the film itself, and therefore does not grow thicker 200 nanometers or 0,2 micrometers. The average thickness of this oxide layer is between 5 to 200 nanometers.

Really, Aluminum oxide is a good insulator with a dielectric strength 16,7 KB. However, since the thickness of the oxide film is very small, the electrical breakdown voltage is only 3 volt. Thus, obtained, that at a voltage, let us say, 220 volt, This oxide film creates special problems for electrical contact wires aluminum.

Nonetheless, in some types of plug-in sockets for the aluminum alloys to solve this problem using special paste to prevent oxidation of the surface of contact of aluminum wire.

Contact pads for aluminum wiring

In the past - in 1960-70 for the aluminum wiring to apply the contact pads, who were then, and are, naturally, They have been developed for copper wires. These contact pads made of copper and steel. Since the aluminum expands when heated to 30 % more, than copper and steel, there is a problem with the weakening of the aluminum wiring contacts.

At present, we have developed special contact devices, which are made of aluminum alloys. They are suitable for both copper, and for aluminum wiring.

Figure 4 - Terminal block for aluminum wiring

Electrical series aluminum alloy 8000

Besides aluminum alloy 8030 several electrical aluminum alloys have been developed.

American Standard ASTM B 800

American Standard ASTM B 800, beginning with 1988 of the year, specifies requirements for aluminum alloys series 8000, of which are made circular wire for electric cables and wires single.

According to this standard aluminum wire is made of aluminum wire rod having the chemical composition, which is listed in Table.

Table - Aluminum alloys for electric wires

The wire is supplied in intermediate cold-worked states:

• N1H - only strain hardening and
• H2X - ​​strain hardening and partial annealing.

Tensile strength of the wire from a series alloys 8000 in these states is cold-worked by 103 to 152 MPa, and the elongation is not lower than 10 %.

Wire of aluminum brand 1350 with her 1,5 % elongation withstand only 5-6 kinking, followed by brittle fracture. Wire series alloys 8000 It has an elongation more 10 % and kept under variable bending much longer.

The European standard EN 1715-2

This standard specifies requirements for rolled aluminum, which is used to make electrical wire. Besides aluminum brand 1110 to iron with a content of 0,8 %, it includes aluminum alloys 8030 and 8176 (cm. (see table above).

Unfortunately, domestic electrical wire analogues standardized series of alloys 8000 we do not know.

So

Foreign experience in the use of aluminum wiring in the last 30 says the following years.

For the effective and safe use of aluminum wires as internal wiring in residential buildings, it is necessary:

• use when installing aluminum wiring contact devices (terminal blocks, contactors), It is specifically designed for aluminum wires, including with the use of a special paste to protect the wires from oxidation;
• use of wires aluminum wire of a series of alloys 8000.

Sources:
1. Materials companies ALCAN
2. American Aluminum Association
3. TALAT 1501