Cable tray selection and selection of parameters to calculate how
1. Cable tray selection
1.1 in engineering design, cable trays shall be arranged based on a comprehensive comparison of economic rationality, technical feasibility, operational safety and other factors to determine the best solution, but also to fully meet the construction, installation, maintenance, repair and cabling requirements .
1.2 cable tray height from the ground level is generally not less than laying in 2.5m, 1.8m following section should be added to protect the metal cover from the ground vertical laying, except electrical rooms laid in time. Cable tray laid in the mezzanine level or troops on track and less than 2.5m, should take measures to protect the earth.
1.3 cable bridge, trunking and hangers for use in corrosive environments, corrosion should be used for manufacturing rigid material. Or take anti-corrosion treatment, anti-corrosion treatment should meet the environmental and durability requirements of the project. For corrosion resistance demanding or require a clean place, should use aluminum cable tray.
1.4 cable bridge in the fire safety requirements of the sector, in cable ladder, adding with a fire-resistant or flame-retardant properties tray plate, net material enclosed or semi-enclosed structure, and take the bridge and its support brushing the surface coat hanger fire protection measures. Its overall fire resistance shall meet the requirements of the relevant national standards or specifications. In engineering fire protection requirements of the higher places. Should not use aluminum cable tray.
1.5 EMI shielding required cabling. Or when an external protection such as outdoor sunlight to shadow n, oil, corrosive liquids, flammable dust and other environmental requirements. Should be used without holes cable tray.
1.6 easy to accumulate dust place, cable trays should be used in the cover; or in public access across outdoor road segments. Should add non-porous plate or tray on the bottom tray.
1.7 different voltages, different uses of the cable should not be laid in the same layer cable tray:
(1) 1kV and above 1kV and the following cables:
(2) the same path to power a load of double-circuit cable;
(3) emergency lighting and other lighting cables:
(4) power, control and telecommunications cables.
If the different levels of cable laid in the same cable tray, intermediate separator should be increased isolation.
1.8 When the steel cable bridge line segment length exceeds 30m, aluminum cable bridge over 15m. Or when the cable tray after construction should stretch (settlement) seam allowance leaving O-30mm compensation. Its retractable connector should use the connecting plate.
1.9 cable ladder, tray width and height should be chosen to meet the requirements of the filling factor, the cable under the ladder, tray filling rate in general, the power cables desirable 40% -50%, 50% control cables desirable. 70%. And should set aside a l0% 252 project development margin.
1.10 When choosing cable tray load rating, cable bridge work uniform load should not exceed the load rating of the selected cable tray rated uniform load, if the actual span cable tray hangers is not equal to 2m. The work uniform load should be met:
Where qG ---- work uniformly distributed load, kN / m;
qE ---- rated uniformly distributed load, kN / m;
LG ---- actual span, m.
Calculation of total cable tray load G G total = n1q1 + n2 + q2 + n3q3 + ......
Where: q1, q2, q3 ...... for the cable weight per unit length (kg / m)
n1, n2, n3 ...... for the corresponding cable should be less than the number of G cable tray permissible load (see load curve chart)
When the cable tray when they are outdoors or with shields, but also included a water-borne and wind load and other factors.
Calculation of the cable tray width d: 1, power cable
b = n1 (d1 + k1) + n2 (d2 + k2) + n3 (d3 + k3) + ......
Where: d1, d2, d3 ...... for the cable diameter; n1, n2, n3 ...... the number of the corresponding diameter of the cable;
k1, k2, k3 ...... spacing for the cable (K-value of not less than the minimum d / 4)
Calculation control cable bridge width b :( cable tray fill rate generally take about 40%)
The total area of the cable carrier: S0 = n1π (d1 / 2) 2 + n2π (d2 / 2) 2 + ...
The cross-sectional area required bracket: S = S0 / 40% S = S / h = S0 / 40% h
Where: h clear height of the cable tray.