Vacuum Feedthroughs for Cables: KF Sizes, Capacity and Selection
How to bring thermocouples, PT100, Ethernet, USB and power safely through a vacuum chamber wall — with the right cable bundle, flange size and epoxy potting.
In this article
A cable feedthrough looks like a simple component, but it has to solve two conflicting problems: carry electrical signals or power through the chamber wall while keeping the vacuum boundary permanently sealed. The flange is only one part of the design. The actual outside diameter of every cable, the conductor construction, the temperature at the port and the required terminations all matter.
Practical reference: A KF40 feedthrough can hold roughly 50 thin cables with a 2.4 mm outside diameter. Thick cables or mixed bundles reduce that number — the occupied cross-sectional area is what determines the real capacity.
What a vacuum feedthrough must do
Every cable can create several leak paths: around the jacket, underneath it and lengthwise along stranded conductors. Simply embedding a bundle in resin is not enough. A dependable feedthrough requires cable preparation, controlled positioning and a potting compound designed for vacuum service.
Epoxy-potted assemblies are particularly useful when many different signals have to enter one chamber. Instead of fitting a separate hermetic connector for every sensor, temperature probes, data lines and selected power cables can share one flange.
Why use a potted elbow?
In a KF elbow feedthrough, one leg clamps to the chamber port. The cables run through the bend and leave through the potted second leg. This offsets the epoxy core from the chamber opening. Pull on the cable bundle acts less directly on the sealing face, while the assembly remains compatible with a normal KF clamp.
Typical construction
The conductors are prepared before potting, critical internal leak paths are closed and the cables are packed according to their real diameters. The elbow is then filled with degassed two-component vacuum epoxy and cured under controlled conditions.
Which cables can share one feedthrough
The main advantage of a potted assembly is the freedom to mix cable types. Mechanical capacity is determined by outside diameter; electrical separation, shielding and connectors are selected for the application.
| Category | Typical cables | Key design point |
|---|---|---|
| Temperature sensing | Type K/T thermocouples, PT100, PT1000 | Probe type, accuracy class and measuring junction |
| Data | Ethernet, USB and custom signal cables | Shielding, connector and permitted bend radius |
| Power | Supply and heater cables | Current, conductor area, heating and electrical clearances |
For reliable sizing, every physical cable is counted once at its jacket diameter. Conductor count alone says little about the space required: one shielded data cable may occupy more area than several thin thermocouple lines.
Choosing the KF size and cable capacity
Cables do not sit side by side in a single row. Different diameters nest inside the usable potting circle. Realistic sizing therefore considers the circle packing of the complete bundle, including the epoxy webs required between cables.
The WAVE configurator packs each selected line at its actual outside diameter and then chooses the smallest suitable assembly. Standard sizes are KF16, KF25, KF40, KF50, ISO-K 63 and ISO-K 100 (DN 100). Larger or unusual bundles are engineered as custom parts.
| Flange size | Typical application | Note |
|---|---|---|
| KF16 / KF25 | Small sensor bundles and individual data lines | Compact when cable diameters and bend radii stay small |
| KF40 | Larger sensor bundles and mixed signal packages | Reference: about 50 × Ø2.4 mm |
| KF50 | Mixed bundles with thicker data or power cables | More reserve for bend radius and epoxy webs |
| ISO-K 63 / 100 | Large bundles and a higher share of power cables | For configurations above normal KF capacity |
A simple cable count is useful only when every cable is identical. For a mixed bundle, the online vacuum feedthrough configurator gives the better answer: select cables and lengths, then see bundle diameter, flange size and price immediately.
Vacuum, temperature and application limits
Epoxy-potted cable feedthroughs suit rough and fine vacuum down to approximately 10−6 mbar and continuous operation up to 80 °C at the feedthrough itself. They are an economical choice for freeze dryers, vacuum ovens, coating systems, test chambers and drying equipment.
The system is bakeable UHV, the potting will exceed 80 °C, or the specification requires a certified hermetic glass or ceramic seal. Those applications call for a specialist feedthrough.
Mounting position matters as well. The epoxy core should not sit directly on a deeply chilled condenser or cold trap. Epoxy and stainless steel contract at different rates. A port that stays near room temperature is the safer location.
Design checklist
Information required for a useful specification
- Cable types and quantities: list sensing, data and power separately.
- Actual outside diameter: do not rely only on conductor count or nominal area.
- Inside and outside length: measure from the feedthrough to the real connection point.
- Terminations: open end, probe, coupler or custom connector.
- Installation point: check vacuum, temperature, media exposure and available flange size.
- Test documentation: decide whether a certified helium leak test is required.
WAVE pressure-checks every feedthrough; a helium leak test with certificate is optional. Standard configurations typically ship from Vienna within 5–10 working days. Sensors outside the catalogue, unusual connectors, straight flanges and custom plates can be quoted as special assemblies.
Frequently asked questions
How many cables fit a KF40 feedthrough?
As a reference, about 50 cables with a 2.4 mm outside diameter. For mixed bundles, capacity depends on every actual jacket diameter and the resulting packing.
Can thermocouples, PT100 and Ethernet share one feedthrough?
Yes. Sensor, data and selected power cables can be combined in one potted bundle when space, shielding and electrical requirements are considered.
Is an epoxy feedthrough suitable for ultrahigh vacuum?
It suits fine vacuum down to roughly 10−6 mbar. A bakeable UHV system should use a glass or ceramic feedthrough.
What is the largest standard size?
The standard configurator covers KF16 through ISO-K 100, also referred to as DN 100. Larger bundles are available as custom assemblies.
Size a vacuum feedthrough online
Select cables, lengths and terminations. The configurator finds the smallest suitable flange, displays the 3D packing and calculates the price instantly.
Configure a feedthrough