Power management
ALUMINUM
Publicis; Sourcee: Finanztreff.net
Power distribution
COPPER
2009
2010
2011
Cost-effective or highly dangerous?
Aluminum versus Copper
In times of disproportionate increases in the price of copper as a raw material,
aluminum gains greater consideration as a potential conducting material in
low-voltage power distribution. But are the cost savings compared with copper
really that great? And what factors must be kept in mind in addition to price?
T
he numbers speak for themselves.
In the last three years, the price of
copper has increased from
roughly €4,000 to €6,000 per ton, and
the price of aluminum from approximately €1,300 to €1,600 per ton. But if
aluminum is to be used as a conductor,
the roughly 60 percent larger conductor cross sections required due to the
lower conductivity compared with cop12 E-Installation | 02-2012
per make a big difference. However,
aluminum is roughly 35 percent
lighter than copper.
If these factors are taken into account
and aluminum is used instead of copper, the raw material costs are reduced
by 80 percent. However, aluminum features special properties that must be
taken into account in addition to the
pure raw material costs.
Greater space requirements,
less flexibility
When aluminum is used, the larger conductor cross sections require more
space. Although this does not matter
with high-voltage lines, it can be a significant problem in a densely loaded
control cabinet. In addition, an aluminum cable is much stiffer than a copper
8,000
2012
1,000
2,000
3,000
€ per ton
4,000
5,000
6,000
7,000
vantages for a particular application, connecting copper conductors usually
additional special properties of alumi- have a cable opening that is more or less
num must be kept in mind in the selec- rectangular. When a round aluminum
tion of the devices to be connected and cable is connected, clearances remain in
their terminals, as well as in the han- the corners of the terminal, into which
the aluminum conductor can flow. Terdling of the cables.
An oxide layer with high contact resis- minals specially developed for alumitance forms on the surface of aluminum num conductors, such as prism termiwithin a short period of time. If such an nals, usually have a round, oval, or
aluminum cable is connected, the V-shaped opening for the cable, which
clamping point often heats up to an greatly reduces the risk that the clampunacceptable extent. Depending on the ing point will be loosened through the
amount of current and voltage con- flow tendency of aluminum.
The surfaces of these terminals are
ducted through the clamping point, this
also generally designed especially for
can cause a fire.
use with aluminum conductors. For the
coating of the surface, a material that is
Tool selection during the installation
near aluminum in the electrochemical
For this reason, the oxide layer on the series is used to reduce the contact erocable must be removed before it is con- sion. With regard to its special propernected, and new oxidation must be pre- ties, this material is usually between
vented through the application of tech- copper and aluminum, allowing the ternical petroleum jelly to the cable. minals to also be used for copper conAccording to the electrochemical series, ductors. The terminal surfaces are also
aluminum is a relatively base metal and often provided with ribs that are better
requires that no residue from the tool able to penetrate any residue of the
remain on the cable after removal of the oxide layer on the cable, thus ensuring
oxide layer, as such residue could in safe contacting. For example, all
turn increase the contact resistance due Siemens 3NP1 fuse switch disconnecto electrochemical corrosion. In prac- tors of size NH00 and up can be
tice, the oxide layer is shaved off with a equipped with prism terminals, and in
devices of size NH1 and up prism termicommercially available electric knife.
In addition, aluminum has a greater nals can even be installed in duplicate.
cable with the same current-carrying tendency to deform in the clamped state The latter then allow two conductors to
capacity. In applications in which a flex- compared with copper. This can loosen be connected to one terminal. A prism
ible cable connection is required, cop- the clamping point and increase contact terminal can be retrofitted by simply
per remains the first choice.
resistance. The clamping point thus screwing it onto the contact lug of the
When aluminum is bent around a needs to be retightened before the plant flat-type connection.
tight radius, micro-cracks can form. is commissioned and after 100 to 200
Plant vibrations during operation can hours of operation.
The bottom line for
cause the line to completely crack after
material selection
an extended period of operation under Requirements for the terminal
Although aluminum is much less expencertain circumstances. In a worst-case
scenario, a plant fire could be caused by The terminal must be approved by the sive than copper as a material for cona serial electric arc. But even if none of manufacturer for use with aluminum ductors, its handling is more complex,
these issues result in any grave disad- conductors. Conventional terminals for and additional costs are incurred for the
special terminals required. For distribution with small cable cross sections,
copper is usually the more cost-effective
alternative, but in low-voltage power
Aluminum cables require
Box terminal
Prism terminal
distribution with large cross sections,
special terminals for
aluminum offers savings potential. If
connecting devices: a
prism terminal envelops
appropriate terminals are selected and
Terminals
the cable much more
open
the lines are properly handled, it is also
tightly than a box
a safe alternative.
+
terminal and allows very
little space for flow of
aluminum in the closed
state
LINK TO THE TOPIC:
Siemens AG
Terminals
closed
+www.siemens.com/lowvoltage
CONTACT:
+support.automation@siemens.com
E-Installation | 02-2012 13