METAR TRAY
METAR TRAY
TECHNICAL DATA
LOADING INFORMATION
To enable the selection of the most appropriate METAR cable tray for a particular
installation it is necessary to consider the loads which must be supported and the
distance between supports (the span). These loads are broadly classed as dead
loads, imposed loads and point loads.
Dead Loads
Dead loads include the weight of any cables, pipes and
secondary equipment carried on or installed on the
cable tray plus the self weight of the cable tray and
any component of the cable tray (covers, connectors,
accessories, etc.).
Weight data for cables is readily available from the cable
manufacturer or supplier and is usually quoted in terms of
kilograms per metre (kg/m). The weight per metre from the
cables (or pipes, etc) is the sum of the individual cable (or
pipe, etc) weights.
Weight data for secondary equipment should also be
readily available from the equipment manufacturer or
supplier and is usually quoted in terms of kilograms (kg).
The unit weight for the secondary equipment can be
converted into an equivalent weight per metre by using
the following formula:
Equivalent weight
per metre Wm = 2 x unit weight of equipment (kg) kg/m
Span (m)
For example, a secondary item of equipment with a weight
of 12kg has an equivalent weight per metre Wm of 16kg/m
for a span of 1.5m. This figure should be added to the
sum of the individual cable weights (or pipe, etc). When
determining the location of secondary items of equipment,
care should be taken to either mount these items centrally
across the cable tray or place these items adjacent to, or
directly onto, the cable tray side walls and as close to the
cable tray supports as the installation will allow.
The allowable loading figures given in the tables below
include the self weight of the METAR cable tray. The
weight data for additional installed components (covers,
mounting accessories, etc) for the METAR cable tray
system can be provided on request by our Design Team.
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Point Loads
Point loads are often applied inadvertently to the cable
tray during installation and during in-service inspection.
Care should be exercised to avoid these undue point
loads, particularly on light duty & medium duty cable
trays which are not designed for this type of loading.
In situations where point loads are applied to heavy duty
cable trays, an allowance can be made for the influence
of point loads at the design stage when determining the
total load to be carried by the METAR cable tray system.
When specifying a point load requirement at the design
stage it should be noted tha t the value of the point load
should be kept to a minimum as incorporating the point
load will reduce the allowable cable load for the METAR
cable tray. Loading graphs which include the influence of
a mid span point load are available on request.
METAR cable tray is not intended to be used as a
walkway and on no account should localised point loads
be applied onto the bed of the cable tray. On those
occasions where it is necessary to apply a point load care
should be taken to apply the load evenly onto both side
walls of the cable tray, preferably using a board or similar
support to distribute the load over as long a section of
the cable tray as possible.
Where doubt exists, further guidance should be sought
from our Design Team.
Loading Graphs
When correctly mounted and secured, cable
tray can be considered to be a ‘continuous
beam’. This implies that the cable tray run
is regularly supported and that the cable
trays at the extremities of the run are firmly
anchored. The following tables are used to
calculate the safe working load and have
been verified by testing in accordance to BS
EN 61537.
200
180
160
140
120
100
80
60
40
The load bearing capacity of a cable tray
is limited by the lesser of the maximum
allowable stress induced in the tray section
or the maximum deflection acceptable
between the supports. The maximum
allowable stress is usually limited by the
materials lower yield stress; this gives a
safety factor of 1.7 against the ultimate
tensile strength. Maximum deflection, (in
the absence of a particular customer need)
is not allowed to exceed 1/360th of the
distance between supports (span).
20
0
1
1.25
1.5
1.75
2
2
2.25
2.5
220
200
180
Although unusual, there may be occasions
when it is difficult or indeed impossible to
anchor the cable tray securely in position.
Under these circumstances the tray is
‘simply supported’ and its load bearing
ability is substantially reduced. As a rough
guide maximum loads should be limited to
two thirds of those shown in the loading
tables and increased deflection values
should be accepted for each span. The data
given in the graphs is for tray installed as a
continuous beam and allows for the weight
of the tray itself.
Loading information is available for other
gauges and for heavy duty cable trays with
increased side wall heights – contact our
Design Team for details
160
140
120
100
80
60
40
20
0
1
1.75
The METAR cable tray system, components
and accessories have been tested to BS EN
ISO 61537:2002.
Further details can be provided by our
Design Team.
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