How to Choose a WetLink Penetrator

Introduction

We love the WetLink Penetrator product line, and we think you will too! The WetLink Penetrator (WLP) enables us to seal the wide variety of cables that are found in our products. We’ve found it so useful that we’ve provided you with a full range of WLP sizes for your own projects, covering cable diameter sizes from 3.7 to 9.8 mm, with more to come in the future.

WLP-promo-3

We’ve learned a lot about what makes a reliable cable seal underwater, and we want to share with you what we’ve learned through this guide. We’ll cover how the product line works, how to choose the right WLP size for your cable using our technical specification tables, and things to check for during and after assembly to make sure you won’t have a leak!

Our testing so far has shown that on correctly assembled WetLink Penetrators with properly sized cable, you can achieve a reliable seal that withstands hundreds of cycles to 950 msw depth.

How WetLink Penetrator Works

The WetLink Penetrator works by compressing a rubber seal around the cable, forming a watertight interface. It’s a simple concept, but there are a few things to know if you’re experimenting with your own cables. Let’s start by reviewing the names of different parts of a WLP assembly and parts of a cable that we will be referring to in this guide.

WLP-CROSS-SECTION-GUIDE

Parts of a Cable

wlp-how-to-chs-parts_of_cable

Seal Sizes and Plug Compressions

Currently, there are six nominal seal sizes: 4.5, 5.5, 6.5, 7.5, 8.5, and 9.5. For each nominal seal size, there are two plug options: high compression (HC) and low compression (LC). Low compression plugs work for cable jackets at the nominal diameter, while high compression plugs increase the amount of compression, allowing you to seal smaller cables using the same seal size.

Full WLP product line with high and low compression plug options for each seal size.

Full WLP product line with high and low compression plug options for each seal size.

By having two plug compression options for each nominal seal size, we allow for compatibility on a wide range of compatible cable diameters.

For example, a WLP-6.5MM-LC is compatible with jacket diameters of 6.5±0.3 mm, the WLP-6.5MM-HC shares the same bulkhead and seal but uses a high compression (HC) plug which makes it compatible with smaller jacket diameters of 6.0±0.3 mm.

The compatible cable jacket diameter range increments by 0.5mm between plug compression options, and on each increment there is a ±0.3 mm tolerance, so there is always some overlap between increments. This enables the WLP product line to cover most cables from 3.7 mm to 9.8 mm in diameter!

The Size Index table below lists the nominal seal sizes with their corresponding bulkhead sizes, plug compressions, and compatible cable jacket diameter range. We will go into more detail on how to use the Size Index table in the “Choosing a WetLink Penetrator For Your Cable” section below.

Size Index

Seal SizeBulkhead SizesConductor Bore DiameterPlug CompressionJacket Diameter RangePart Number
4.5M06
M10
3.3 mmHigh (HC)4.0 ± 0.3 mmWLP-M06-4.5MM-HC
WLP-M10-4.5MM-HC
Low (LC)4.5 ± 0.3 mmWLP-M06-4.5MM-LC
WLP-M10-4.5MM-LC
5.5M104.0 mmHigh (HC)
5.0 ± 0.3 mm
WLP-M10-5.5MM-HC
Low (LC)5.5 ± 0.3 mmWLP-M10-5.5MM-LC
6.5M104.8 mmHigh (HC)
6.0 ± 0.3 mm
WLP-M10-6.5MM-HC
Low (LC)6.5 ± 0.3 mmWLP-M10-6.5MM-LC
7.5M105.7 mmHigh (HC)
7.0 ± 0.3 mmWLP-M10-7.5MM-HC
Low (LC)7.5 ± 0.3 mmWLP-M10-7.5MM-LC
8.5M106.0 mmHigh (HC)
8.0 ± 0.3 mm
WLP-M10-8.5MM-HC
Low (LC)8.5 ± 0.3 mmWLP-M10-8.5MM-LC
9.5M147.5 mmHigh (HC)9.0 ± 0.3 mmWLP-M14-9.5MM-HC
Low (LC)9.5 ± 0.3 mmWLP-M14-9.5MM-LC


What Makes a Cable Compatible with WLP?

Even though we’ve designed the WetLink Penetrator product line to be very robust, every cable is unique! There are no hard rules on what makes a cable compatible or not, but we’ve provided some guidelines below.

The amount of compression of the seal around the cable jacket is the most important factor when determining if a WetLink Penetrator will seal reliably on a cable. Your goal when selecting a WetLink Penetrator is to get just the right amount of compression of the seal around the cable jacket, not too much and not too little. Too little compression will result in a leak through the seal or the cable pulling out easily when strained. Too much compression may cause the cable or conductors to break. We will show you how to check if you have the right amount of compression later in the “Choosing a WetLink Penetrator For Your Cable” section of this guide.

Along with the amount of compression, the following factors also affect compatibility:

  • Jacket material: soft jackets typically require more compression than harder jackets. If the jacket is very soft, like a foam jacket, higher compressions are typically needed than are specified in the table.
  • Cable construction: some cables have tighter constructions, which typically require less compression, and some have a looser construction with lots of free space, which typically need more compression.
  • Jacket surface finish: slippery jackets will pull out easily when strained because the seal can’t grip them as well.
  • Operating temperature: higher temperatures (usually >60°C-70°C) translates to more compression set (loss of compression over time) in both the seal and the cable jacket.
    • High temperatures in combination with high compression can lead to the cable reducing in diameter to the point where either the cable breaks, or there is total loss of seal pressure and the interface leaks.
    • High temperatures in combination with too low of a compression can lead to total loss of seal pressure and the interface leaks, or is unable to withstand any strain.

With this understanding of how the WetLink Penetrator works, you’re ready to experiment with your own cables!

Choosing a WetLink Penetrator For Your Cable

This section will guide you through the process of choosing a compatible WetLink Penetrator for you cable. Please note, all of the tables mentioned are also found in our WetLink Penetrator Technical Specifications document as well as the Technical Details section of the WetLink Penetrator product page.

All cable and tether manufactured by Blue Robotics has a compatible WetLink penetrator. If you are using Blue Robotics cable or tether or are installing a WetLink Penetrator on a Blue Robotics product, you can find the compatible WetLink Penetrator in the Tested Cables table or the technical details section of the cable, tether, or product you are using. You can then skip the rest of this guide and proceed to the WetLink Penetrator Assembly Guide.

If you have a requirement for a type of cable that is not manufactured by Blue Robotics, check the Tested Cables table below to see if there is already a tested cable for your needs. Blue Robotics has tested a number of cables from other manufacturers and found the correct size WetLink Penetrator to use for each. If one of these cables suits your needs, the compatible WetLink Penetrator part number and link is provided in the “Compatible WLP Part Number” column. You can then skip the rest of this guide and proceed to the WetLink Penetrator Assembly Guide.

Compatible WLP Part NumberCable Part Name / NumberManufacturerApplicationJacket DiameterJacket MaterialConductorsTested Current¹Nominal VoltageMax Temp Recommended²
WLP-M06-4.5MM-HC
WLP-M10-4.5MM-HC
Fathom Slim TetherBlue RoboticsTether4.0 mmPUR Foam1x UTP 26AWG--50°C
WLP-M06-4.5MM-LC
WLP-M10-4.5MM-LC
Lumen/Gripper CableBlue RoboticsPower / PWM4.5 mmPUR3x 22AWG--60°C
Ping CableBlue RoboticsPower / Serial4.5 mmPUR4x 24AWG--60°C
Ping 360 CableBlue RoboticsPower / Ethernet4.7 mmPUR3x UTP 28AWG--50°C
WLP-M10-5.5MM-HCchainflex® control cable CF9 (CF9-02-06)IGUSPower / Signal5.0 mmTPE6x 24AWG-300V60°C
WLP-M10-5.5MM-LCEtherline® (2170283)LAPPCat5e5.6 mmPUR2x SFTP 26AWG-125V60°C
WLP-M10-6.5MM-HCUnitronic® (302206)LAPPPower / Signal5.8 mmPVC6x 22AWG-300V60°C
WLP-M10-6.5MM-LCT200 Thruster CableBlue RoboticsPower6.4 mmPUR3x 16AWG48A-60°C
Etherline® (2170300)LAPPCat5e6.3 mmPUR4x SFTP 26AWG-1000V60°C
WLP-M10-7.5MM-HCFathom ROV TetherBlue RoboticsCat5 / Tether 7.8 mmPUR Foam4x UTP 26AWG--50°C
WLP-M10-7.5MM-LCCAB-PUR-2-22AWG-4UTP-26AWG-X1
coming soon!
Blue RoboticsPower + Cat57.5 mmPUR4x UTP 26AWG + 2x 22AWG--60°C
WLP-M10-8.5MM-HCchainflex® control cable CF9 (CF9-02-12)IGUSPower / Signal7.7 mmTPE12x 24AWG-300V60°C
WLP-M10-8.5MM-LCHigh Power CableBlue RoboticsPower8.3 mmPUR2x 12AWG60A-60°C
¹ Current ratings evaluated at ambient temperatures in water.
² Sustained high temperatures can lead to performance loss over long periods of time.


For all other cables, follow the steps below:

1. Start by measuring the jacket diameter of your cable.

wlp-choosing-measure

2. Take the cable jacket diameter and refer to the Size Index table below. Find where your cable jacket diameter falls in the “Jacket Diameter Range” column. The compatible seal size and necessary plug compression will be listed in their respective columns in the same row. This will give you a good starting point, but be aware that the final fit depends on the specific cable, so we recommend getting a small range of sizes (like one size above and below) to test with before committing!

If your cable jacket diameter falls in the overlap between sizes, then it may not matter if you choose one or the other. We recommend testing with both, and choosing the size with the best looking compression seat as outlined in Step 5.

Size Index

Seal SizeBulkhead SizesConductor Bore DiameterPlug CompressionJacket Diameter RangePart Number
4.5M06
M10
3.3 mmHigh (HC)4.0 ± 0.3 mmWLP-M06-4.5MM-HC
WLP-M10-4.5MM-HC
Low (LC)4.5 ± 0.3 mmWLP-M06-4.5MM-LC
WLP-M10-4.5MM-LC
5.5M104.0 mmHigh (HC)
5.0 ± 0.3 mm
WLP-M10-5.5MM-HC
Low (LC)5.5 ± 0.3 mmWLP-M10-5.5MM-LC
6.5M104.8 mmHigh (HC)
6.0 ± 0.3 mm
WLP-M10-6.5MM-HC
Low (LC)6.5 ± 0.3 mmWLP-M10-6.5MM-LC
7.5M105.7 mmHigh (HC)
7.0 ± 0.3 mmWLP-M10-7.5MM-HC
Low (LC)7.5 ± 0.3 mmWLP-M10-7.5MM-LC
8.5M106.0 mmHigh (HC)
8.0 ± 0.3 mm
WLP-M10-8.5MM-HC
Low (LC)8.5 ± 0.3 mmWLP-M10-8.5MM-LC
9.5M147.5 mmHigh (HC)9.0 ± 0.3 mmWLP-M14-9.5MM-HC
Low (LC)9.5 ± 0.3 mmWLP-M14-9.5MM-LC

3. Assemble the penetrator onto the cable in accordance with our WetLink Penetrator Assembly Guide, but first:

  • Check that the conductors will fit through the conductor bore by trying to insert them into the back of the bulkhead.
  • wlp-choosing-measure-back
    • If conductors do not fit, try moving up to the HC plug of the next seal size. Bigger bulkheads have bigger conductor bores for the conductors.
  • Check that the plug and seal fits the cable, the plug should not be difficult to fit onto the cable, if it is, try moving up to the HC plug of the next seal size.

4. After assembly, lightly pull on the cable with about 5-10 lbs of force for 5-10 seconds (this feels about the same as picking up an adult cat). If the cable pops out:

  • You may not have enough compression. If using an LC plug, switch to the HC plug of the same nominal seal size.
  • The cable jacket may be too slippery. Try wiping the cable with acetone or alcohol and try again with a new section of cable.

5. Check the level of compression around the cable jacket. This is the most important factor when determining if the WLP will seal reliably. Let the assembled WLP and cable sit for at minimum 6 hours (or overnight), then disassemble the cable and compare the level of compression to the pictures below.

  • Too much compression. The seal has compressed too tightly around the jacket and there is risk of damage to the cable or conductors. Try again with a lower compression plug and a new section of cable.
  • wlp-choosing-too-much-compression
  • Too little compression. The seal has not compressed around the cable jacket enough and will likely leak or pull out easily when strained. Try again with a higher compression plug and a new section of cable.
  • wlp-choosing-too-little-compression
  • Ideal compression.
  • wlp-choosing-ideal-compression

If the compression looks good, make sure to assemble some more and test them in your application. Then happy diving!

Feedback

We’re always trying to make our documentation, instructions, software, and user experience better. If you’d like to leave feedback about how we can make this guide better, let us know here.