PEMSA
The strength and flexibility of the
steel wires allows maximum use of the
capacity of the tray while it maintains
a good adaptation to the installation
path. This allows for any subsequent
changes or alterations to be easily
made which can then result in labour
and cost savings.
In the case of fire, steel wires do not
present any risk since they are non-
combustible and do not cause any toxic
fumes or propagate the fire, unlike PVC
or plastic systems which can collapse
and destroy the installation whilst
generating a large amount of corrosive
and opaque smoke.
Corrosion resistance
As you can read in the Best Practice Guide
to Cable Ladder and Cable Tray Systems
from BEAMA:
‘In planning any cable ladder or
cable tray installation the choice of an
appropriate corrosion resistant material
and finish is always a key issue at the
specification stage. The correct choice has
long term implications and is crucial for
ensuring the longevity and the aesthetics
of the complete installation.’
This is why manufacturers continue
to improve the characteristics of their
finishes or coatings.
The current BS61537 Cable
Management (Cable Tray and Cable
Ladder Systems) classifies the resistance
against corrosion from C0, for non-
declared or non-tested material, up to
C8 for components made of steel with
metallic coating and C9 for stainless steel.
For example, a steel component
with a zinc coating, such as hot
dip galvanising, is one of the most
popular choices for humid or exterior
installations. With a mean coating
thickness of 70μm of zinc this would be
classified as C7.
The future edition of BS61537 will
probably include a new classification
table to consider other metallic coatings,
such as the ones based on alloys of
zinc-aluminium (similar to Aluzinc or
Galfan) and zinc-aluminium-magnesium
(similar to ZAM), and new high resistance
protections such as the Black C8.
These new finishes have excellent
aesthetics and high resistance so they
are perfect for environments with high
humidity, as they improve both the barrier
effect against humidity and the ability of
self-healing in any damaged areas.
With the current edition of BS61537
they can be tested by carrying out a
neutral salt spray (NSS) test. Providing
that the corrosion of the surface of
the sample has not been exceeded,
according to the duration, after passing
850 hours they can be classified only as a
maximum of C8.
Zinc whiskers
Pemsa’s Black C8 coating avoids the
emergence of the phenomenon of ‘zinc
whiskers’, or loosening of filaments of
zinc, which can be a serious problem
within the electronics of clean rooms of
data processing centres.
In data centre installations or IT data
facilities hosting microelectronic devices,
especially sensitive to impurities, it has
been shown that the use of electroplated
zinc access floor tiles may be the origin
of zinc whiskers or microscopic filaments
of zinc.
These zinc whiskers would be
formed from the electroplated zinc finish
covering the large surface of the tile, due
to intergranular stresses generated in
the material surface. It seems that with
the hot dip galvanised finish, due to the
different metallurgical composition of
the surface layers, this process would
be different. The zinc filaments, in time,
could eventually break off and move
into the environmental atmosphere and,
finally, enter into the equipment. Due to
their electrical conductivity they could
cause electrical shorts within the circuit
boards or microelectronic equipment.
From this fact there is no adequate
technical justification to generalise the
Mesh trays
have proved to
be significantly
easier and faster
to install than
the conventional
perforated or plain
sheet cable trays.
exclusion in these rooms of all items
or accessories with any galvanised
protection, such as electroplated or
galvanised trays. Wire mesh trays have
much lower surface area and they are not
experiencing the same stresses generated
in the face of the access floor tiles.
A sealant coating will avoid the
emergence of the possible zinc
whiskers if they were to grow, and
therefore this finish does not contribute
to the effects on the electronic
equipment within data centres.
Cable & Cable Management
August 2017 | 13