Comprehensive Estimation Methods for Weak Current Engineering Projects

Comprehensive Estimation Methods and Formulas for Weak Current Engineering Projects

Weak current systems often require precise cable estimation methods that cannot be easily calculated mentally. This article provides a systematic approach to estimating cable requirements for weak current projects.

1. Comprehensive Cabling System

1.1 Horizontal Subsystem Cable Estimation Method

• Average cable length = (farthest information point horizontal distance + nearest information point horizontal distance) / 2 + 2H (H – floor height)

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 6)

• Number of cable runs per box = box cable length / actual average cable length

• Number of boxes needed = total information points / number of cable runs per box

Note: The farthest and nearest information point horizontal distances are measured from the floor distribution frame (IDF) to the information point, including the actual horizontal route distance. If multiple floors share an IDF, the respective floor height should be included. The "average cable length" formula applies to scenarios with one or three floors sharing an IDF.

1.2 Backbone Subsystem Copper Cable Estimation Method

• Average cable length = (farthest IDF distance + nearest IDF distance) / 2

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 6)

• Number of cable runs per reel = reel cable length / actual average cable length

• Number of reels needed = total IDFs / number of cable runs per reel

Note: The farthest and nearest IDF distances are measured from the floor distribution frame (IDF) to the main distribution frame (MDF) at the network center, primarily determined by floor height and the horizontal distance from the weak current shaft to the MDF. The large pair cable number is calculated at a 1:2 ratio (one voice point configured with two twisted pairs), choosing 25/50 pair cables for reasonable design. Generally, 100 pair large pair cables are not selected due to construction difficulties.

1.3 Backbone Subsystem Fiber Optic Cable Estimation Method

• Average fiber optic cable length = (farthest IDF distance + nearest IDF distance) / 2

• Actual average fiber optic cable length = average fiber optic cable length × 1.1 + (termination allowance, usually 6)

• Total fiber optic cable required = total IDFs × actual average fiber optic cable length

Note: The farthest and nearest IDF distances are measured from the floor distribution frame (IDF) to the main distribution frame (MDF) at the network center, primarily determined by floor height and the horizontal distance from the weak current shaft to the MDF. If the tender document specifies the choice of fiber core number, single-mode or multi-mode, follow the requirements. Generally, 6-core multi-mode fiber optic cables are chosen.

2. Cable Television System

2.1 Star Wiring Calculation Method

Defined as all floor branch distributors concentrated in the weak current room, with a single RF cable laid from each user terminal (socket) to the corresponding weak current room connected to the branch distributor.

• Horizontal cable (usually RG6) calculation method:

• Average cable length = (farthest user terminal horizontal distance + nearest user terminal horizontal distance) / 2 + 2H (H – floor height)

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 3)

• Total cable required = total user terminals × actual average cable length (meters)

Note: The farthest and nearest user terminal horizontal distances are measured from the floor distribution box to the farthest and nearest user terminal sockets, including the actual horizontal route distance. If multiple floors share a floor distribution box, the respective floor height should be included.

2.2 Serial Connection Wiring Calculation Method

This method divides the wiring into household cables, horizontal cables, and main (vertical) cables.

• Household cable (usually RG6):

• Average cable length = (farthest user terminal distance + nearest user terminal distance) / 2

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 3)

• Total cable required = total user terminals × actual average cable length (meters)

Note: The farthest and nearest user terminal distances are measured from the branch distributor to the nearest and farthest user terminal sockets.

• Horizontal branch cable (usually RG11):

• Average cable length = (farthest branch distributor/terminal resistor distance + nearest branch distributor/terminal resistor distance) / 2

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 6)

• Total cable required = total horizontal cables × actual average cable length (meters)

Note: The farthest and nearest branch distributor distances are measured from the floor distribution room's distribution box to the farthest and nearest branch distributor, including the actual horizontal route distance. If multiple floors share a floor distribution box, the respective floor height should be included.

• Main cable (usually RG12 or RG11):

• Average cable length = (farthest floor distribution box distance + nearest floor distribution box distance) / 2

• Actual average cable length = average cable length × 1.1 + (termination allowance, usually 6)

• Total cable required = total floor distribution boxes × actual average cable length (meters)

Note: The farthest and nearest floor distribution box distances are measured from the floor distribution box to the satellite or cable TV center equipment room, primarily determined by floor height and the horizontal distance from the weak current shaft to the satellite or cable TV center equipment room.