Catenary Design Calculator

Design overhead catenary system parameters: messenger wire sag, contact wire height, wind deflection, dropper count, and electrical clearances.

Span length

Messenger wire tension

lbs

Contact wire tension

lbs

Contact wire height

Design wind speed

mph

System voltage

Tab to move between fields

Messenger wire sag

21.3 in

≈ 6 credit cards

Messenger wire sag1.77 ft

Messenger height at support21.77 ft

System height at support3.77 ft

Wind deflection3.1 in

Deflection within limit1

Droppers per span12

Recommended pre-sag1.5 in

Min electrical clearance31 in

Span classification1

How to Use This Calculator

Enter Span length, Messenger wire tension, and Contact wire tension.
Set Contact wire height, Design wind speed, and System voltage.
Review the Messenger wire sag (in) result.
Use Messenger wire sag (ft) and Messenger height at support (ft) to inform your decision.

How the result changes with Span length

Span length: Distance between catenary support structures.
Messenger wire tension: Mechanical tension in the messenger (catenary) wire.
Contact wire tension: Mechanical tension in the contact wire for pantograph interaction.
Contact wire height: Contact wire height above top of rail (min 14 ft general, 22.5 ft at crossings).
Design wind speed: Maximum wind speed for deflection check.
System voltage: Catenary system voltage (common: 25 kV AC, 3 kV DC, 1.5 kV DC).

Messenger wire sag: Mid-span sag of the messenger wire under dead load.
Messenger wire sag: Same sag in feet.
Messenger height at support: Required messenger wire attachment height above rail.
System height at support: Vertical distance between messenger and contact wire at supports.
Wind deflection: Lateral displacement of contact wire under design wind.
Deflection within limit: 1 = within 12-inch pantograph limit, 0 = exceeds limit.
Droppers per span: Number of dropper wires connecting messenger to contact wire.
Recommended pre-sag: Upward offset at mid-span to compensate for pantograph uplift.
Min electrical clearance: Minimum distance from live parts to grounded structures.
Span classification: 0 = short (≤150 ft), 1 = standard (150-220 ft), 2 = long (>220 ft).

Identify Input Parameters
4 parameters
Span length = 200, Messenger wire tension = 3500, Contact wire tension = 2500, Contact wire height = 18 = 6 input(s) provided
Calculate Messenger wire sag
Messenger wire sag = totalLoadPerFt * spanLengthFt * spanLengthFt / (8 * messengerTensionLbs)
21.3 = 21.3
Calculate Messenger wire sag
Messenger wire sag = totalLoadPerFt * spanLengthFt * spanLengthFt / (8 * messengerTensionLbs)
1.77 = 1.77
Calculate Messenger height at support
Messenger height at support = contactWireHeightFt + messengerSagFt + 2.0
21.77 = 21.77