3FT
Composite post insulator 3FT
3FT
- HTV silicone housing (multi-shot injection molding) on an ECR fiberglass core (electrical and corrosion resistant)
- Overmolded end fittings seal the triple point against moisture ingress and minimize electrical field stress
- Station post and line post duty: busbar support, inclined/braced line post, jumper support, spacers and crossarm (CICA)
- Flexible product length up to 5.5 m in 12.5 mm increments; units stackable for greater total height
- Two shed profiles (creepage factor 3.5 / 4.2) per IEC 60815-3 (AC) and IEC 60815-4 (DC)
Busbar support in HV substationsInclined and braced line postJumper supportInterface and interline spacersComposite insulator crossarm (CICA)
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3FT covers up to 800 kV of the long-rod & station post range (≤ 800 kV across the category, √ scale).
Specifications
Main
| Product type | Composite post insulator (station post / line post) |
| Family | 3FT2 – 3FT7 (core diameter 63.5 / 76.2 / 88.9 / 100 / 120 / 150 mm) |
| Current type | AC and DC |
| Applications | Busbar support in HV substations, support below HV equipment, inclined and braced line post, jumper support, interface & interline spacers, composite insulator crossarm (CICA) |
Ratings
| Specified Mechanical Load (SCL) | 18 – 150 kNm, type-dependent (equivalent to ceramic breaking load) |
| Maximum Design Cantilever Load (MDCL) | 9 – 75 kNm, type-dependent |
| Lightning withstand | > 1600 kV to > 3050 kV, length-dependent |
| System voltage | Electrical-field simulations validate operation up to 800 kV; larger corona rings required at higher system voltages |
| Creepage factor (creepage/arcing) | 3.5 or 4.2, per shed profile |
Mechanical & environment
| Housing | HTV silicone rubber, multi-shot injection molded — aging-resistant, hydrophobic, UV-resistant |
| Core | ECR fiberglass rod (electrical & corrosion resistant), 63.5 – 150 mm diameter |
| Unit length | 0.5 – 5.5 m in 12.5 mm increments; stackable for greater total height |
| End fittings | Four types: tapped flange, through-holes flange, drop-hole tongue, flat & gain bendable base; overmolded to seal the triple point |
| Adhesion system | Extensively tested primer system bonding housing, rod and end fittings, with continuous production quality control |
Standards & certifications
| Line post | IEC 61952, ANSI C29.17 |
| Station post | IEC 62231, ANSI C29.19 |
| Shed profile | IEC 60815-3 (AC), IEC 60815-4 (DC) |
| Testing | Fully tested to IEC and ANSI standards; Factory Acceptance Test (FAT) option in Asia and Europe |
Options & variants
SCL = Specified Mechanical Load (equivalent to ceramic breaking load); MDCL = Maximum Design Cantilever Load. From the 3FT type overview table in the Siemens Energy 3FT flyer (2026).
| Type | Core Ø | SCL | MDCL | Length | Lightning withstand | Creepage factor |
|---|---|---|---|---|---|---|
| 3FT2-4 | 63.5 mm (2.5") | 18 kNm | 9 kNm | 0.5 – 3.0 m | > 1600 kV | 4.2 |
| 3FT3-4 | 76.2 mm (3.0") | 32 kNm | 16 kNm | 0.5 – 3.0 m | > 1600 kV | 4.2 |
| 3FT4-4 | 88.9 mm (3.5") | 46 kNm | 23 kNm | 0.5 – 4.0 m | > 2150 kV | 4.2 |
| 3FT5-4 | 100 mm (3.9") | 50 kNm | 25 kNm | 0.5 – 5.5 m | > 3050 kV | 4.2 |
| 3FT6-3 | 120 mm (4.7") | 78 kNm | 39 kNm | 0.5 – 5.5 m | > 3050 kV | 3.5 |
| 3FT6-4 | 120 mm (4.7") | 78 kNm | 39 kNm | 0.5 – 5.5 m | > 3050 kV | 4.2 |
| 3FT7-4 | 150 mm (5.9") | 150 kNm | 75 kNm | 1.0 – 5.5 m | > 3050 kV | 4.2 |
Compatible accessories
end-fitting
Tapped flange end fitting (4x/8x M16 or M20, D127)
end-fitting
Through-holes flange end fitting (4x/8x D18–D24, D127–D254)
end-fitting
Drop-hole tongue end fitting (3FT2 – 3FT4)
end-fitting
Flat & gain bendable base end fitting (3FT2 – 3FT4)
accessory
Corona ring for higher system voltages
Documents & downloads
Flyer 3FT composite post insulators — Engineered for extreme performance (Siemens Energy, 2026)
Also covered in the technical library
Brochure Our portfolio of surge arresters & composite insulators — Siemens Energy
Ordered designations
Representative orderable type designations of this family — searchable via the catalog search.
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