We are using WetLink penetrators for a sensitive underwater robotics project, so waterproofing reliability is extremely critical for us.
Could you please confirm if it is safe to use wet link penetrators seal along with epoxy as an additional sealing layer around WetLink penetrators.
If not recommended, what sealing method/material do you suggest for extra waterproofing?
Hi @Ferbin, welcome to the forum 
The context of your application and reliability requirements is fundamental to your question here.
WetLink penetrators do not water-block the cable internals, so while they are extremely reliable for preventing water ingress from outside the cable/enclosure (when installed correctly, of course), if your cable gets nicked or cut then water can potentially enter your enclosure through the cable jacket / along the wires.
If you have a high risk application where a waterproof penetration is insufficient then you’ll need to look into water-blocked connector options, extra rugged cables (often at the cost of some flexibility and extra drag), and/or something like an oil-filled enclosure that removes the pressure differential (so water isn’t trying to “come in” in the first place.
Adding epoxy to a pottingless seal could hide and/or exacerbate installation issues, while also losing the benefits of using a pottingless seal in the first place (namely that you can remove, maintain, and replace it if need be). That seems like extra work for minimal (if any) gain, and potentially significant detriment, so wouldn’t be recommended.
We are building a ROV with 8x T200 thrusters. Running 4x 4 AWG cables (10.3mm OD) through endplate for ~275A at 12V.
Problem: 4 AWG won’t fit WetLink Penetrators (9.8mm max). I already have M10→M14 thread adapters.
Plan: Pot the 4 AWG cables through the M10→M14 adapters using Loctite Marine Epoxy.
Question: Is this reliable at 30 feet depth ? Or am I asking for trouble using thread adapters instead of proper potted penetrators?
Operating in saltwater, max depth 20ft.
What else are you planning to run with that power? At 12V T200 thrusters are expected to draw max 17A, so 8 thrusters would use about half of your available power capacity (assuming you’re using all of them at full throttle simultaneously, which would be quite unusual).
Would it perhaps make sense to use a smaller wire gauge, with less current capacity, and/or use a higher voltage, so less current is required to achieve the same thrust?
Without a shoulder for the cable jacket to butt up against, push-through is a concern. Without a tested bond between the cable jacket+epoxy and epoxy+adapter pull-out is a concern.
If you’re able to achieve a decent bond and no air bubbles then that approach could potentially work to the relatively limited depths you’re asking about, although you’d likely need to handle the penetrations with extra care, and it’s possible bending or flexing the cables transversely (or rapid heating or cooling cycles) could break the bond even if it seems fine when tested using direct (in-line) pushing and pulling forces in a standard environment. We obviously can’t recommend this approach, or guarantee it would work, so you’d be taking full responsibility for the penetration yourself.
Hi I’m new here. I have a similar issue with my system. I want to power 11 m200s (8 are thrusters) but I don’t know what cables to use to power it I have a 12 V 100Ah battery to work with. But what gauge would be recommended to carry the power to the ROV? I was thinking of multiple 6AWG cables but I don’t have a reliable way of water proofing them. I also thought of getting multiple T500 subsea cable and using that to power the system? I don’t know how viable it could be but that seems to be the only cable I can use that would work with the 9.5 penetrators I have. Will the epoxy method be a good option for normal cables?
Hi @Adam77 and @Ferbin -
I avoid epoxy in sealing applications at all cost! You might get something that works, passes a vacuum test, and a field test. But after transport, vibration, and exposure to hot or cold water, that seal can fail with no warning!
Operating at minimal depths can help your situation, but it’s still a risky path.
I’d recommend increasing your supply voltage, and not planning to accomedate current from all 8 thrusters running at full power - this is unlikely to ever be necessary! With a standard BlueROV2 heavy with 8x T200s, I rarely see current use more than 100A…
@Adam77 - welcome to the forums!
The BlueROV2 (currently) uses all 6 conductors in two thruster cables to carry power from the battery to the main electronics enclosure - 3 positive, 3 negative.
Can I ask how much power the ROV2 consumes? I was planning to have a cable length of 20m and was worried about the voltage drop that comes with using smaller gauge cables.
We are currently building an ROV equipped with 8 Ă— T200 thrusters and 3 Ă— M200 motors (for auxiliary functions). Our power system consists of two 12V 100Ah LiFePO4 batteries.
We are using a Blue Robotics end cap with 24 penetrator holes (12 Ă— M10 and 12 Ă— M14). I wanted to ask if it is feasible to use the Subsea T500 cable as the main power cable for this setup.
If it is possible, could you please advise the proper and recommended way to integrate and wire it safely?
Hi @Adam77
That depends quite a lot on what you’re doing with the ROV! If you’re in a pool, and not overcoming currents, running at 25% gain will keep power at 100-400 watts. It’s possible to draw 1500+ watts at full gain in some situations!
I’d recommend this calculator for figuring out power vs. cable length vs. voltage drop - increasing the voltage can help quite a lot, but safety is a critical key factor! If you can’t afford a line isolation monitor, keeping tether voltage low may be required - if this is for a MATE competition you may not be allowed to boost the voltage from the 12V battery level?
@Ferbin Are those two batteries on the vehicle or at the surface, powering the system over the tether?
The context of what you’re trying to do is just as important as in Adam’s question - it’s unlikely you’ll need to ever run all 8 thrusters at full power, and how much power an M200 consumes depends entirely on what you’re using it for. The T500 power cable could work for your setup, depending on the length you intend to use. You may find using 2x (or more) T200 thruster cables makes more sense, or some other low-gauge single wire with two Wetlink Penetrators to make the connection. That calculator should help you solve your application as well!
In our case, the power source (batteries) will be kept on the surface, and we will be delivering power to the vehicle through the tether. Our target tether length for the current prototype is approximately 100 ft.
The vehicle will be running a multi-thruster configuration along with onboard electronics (Pixhawk + companion computer + sensors). We understand that in real operation it’s unlikely we’ll run all thrusters at full load continuously, but we want to design the tether/power delivery system to safely handle peak draw scenarios with minimal voltage drop.
We are currently evaluating the best approach for tether wiring. If the T500 power cable can support our 100 ft requirement with acceptable voltage drop, we are open to using it.
If possible, could you confirm what cable configuration you would recommend for a 100 ft tether surface-powered setup, assuming a multi-thruster vehicle with intermittent high-load operation?
Hi @Ferbin -
Using that calculator, and leaving the voltage at 12V, you’ll find that a single 12 gauge conductor 100’ long can only effecticely move about about 100 watts to the vehicle. That’s not very much, and it leaves one of the three conductors completely unused! If you use two cables, with three wires each, you could use about 300 watts, which is likely a reasonable amount for most ROV activities, if the gain is kept low at 25%…
However, two cables that long is going to be quite heavy, and encumber the ROV as it moves around!
I’d review your 100 foot requirement, and potentially look to source cable of another construction more locally (at a hardware store?) I would assume you aren’t allowed to boost the voltage going down the tether?
This guide has a whole section on this general problem…
It’s also worth noting that ArduSub has a parameter you can set that will attempt to limit the power consumption below a given setpoint (MOT_BAT_CURR_MAX) - you can also achieve this by lowering the max/min throttle points for all thrusters. See this thread for more detail.
Hey , I am trying to do something similar . So i have a 14.2 V 150 AH battery for 5 - T200 thrusters, I am planning to use the 7.5mm HC (7±0.3mm) wet link penetrators with silicone insulated gauge 8 wires .
The wire outer dimension is 6.5±0.2 mm , core diameter being 3.75mm. (Since the cable dia is high , I was planning to strip a little bit of the silicone jacket (around 0.5 - 1mm) and resolder / connect inside to match the inner bore diameter (i believe the outer diamater with the seal is the only dimension needed to match to seal the penetrator , please confirm that ).
Regarding the potted penetrator , As mentioned above in this thread , by someone , I am not sure about the bonding of the epoxy with silicone so please guide me on that as well.
Based on the blue robotics voltage drop calculator , An 8 gauge cable single and 2 conductor at 14.2 input voltage at 25 - 30m are allowing me an output voltage of around 12.5 volts. I am further locking PWM to 1800 (expecting a 9A current pull at 12V based on T200 graph).
At this configuration , I am doubtful is the penetrator choice and cable choice is correct. I would optimally want to step up outside and step down inside but i am not sure of the heat generation component and if it would lead to unexpected issues inside the sealed hull itself.
Could you suggest a better way to do this configuration given the fact that if I want to go to a higher PWM i will have to go for better cables and at some point have an outside boost converter. What is a good way to manage heat from ESCs and step down converters and at what temperature should I call it quits while testing.
Hi @seaArch -
Welcome to the forums!
If the wire going through the WetLink Penetrator has an outer diameter of 6.5mm, you need to use a 6.5mm LC seal, as documented in this guide.
Binding any epoxy to silicone does seem challenging.
Heat from internal ESCS or DCDC power supplies can become a problem with a long enough mission, but the aluminum enclosures on your vehicle typically provide enough of a path for heat to escape.
Your power loss happens along the long “resistor” of your cable. Increasing the voltage on this cable carrying power reduces resistive losses.
Great , That covers a lot of my doubts , Thanks @tony-white .
Just to follow up, would you suggest a silicone based sealant (would silicone sealant be better at bonding with silicone cable? , i have seen options that show bonding strength of upto 1000psi which i assume would hold if the bonding is viable with silicone itself).
In general, what would be a better sealant type for a silicone cable ?
Hi @seaArch -
I don’t have much experience with sealants - outside of loctite marine epoxy. Generally - o-rings work! And sealants may initially and for some time, but never forever…
Roughing up the surface of any cables you’re using with sealant, with sandpaper, can help ensure a good bond.
