A smear of Vaseline?

Vaseline is fine in high pressure contacts, as it gets driven out at the point of contact - copper slip is less satisfactory as it actually slightly 'gritty' at a microscopic level. The Vaseline complication is that it is highly inflammable - you do not want to get it to ignition temp (at a push it makes a reasonable fire starter once massaged into the cotton wool balls from the 1st aid kit when you are on camp and it has rained on the kindling)

I have been known to either heat or dissolve Vaseline in IPA to make it runny enough to paint it onto things post installation.

But how is this box vented - a lot of water in the box problems arise from poor venting strategy ideally you want pressure equilisation without damp air being drawn in.

M

Iso-propyl achohol, not India  Pale Ale

I use a Superlube synthetic grease for any terminals and screw threads that might corrode, especially screws that might need to be undone in the future. To reduce corrosion I always drill a small drainage/vent hole or two in the bottom of general domestic outdoor enclosures. It prevents condensation build up. Anything that keeps the damp off the vulnerable parts may be good to reduce corrosion like Vaseline.

Z.

There was no provision for drain holes when the isolator was fitted (unlike various makes of external sockets) and none had been drilled.  Venting was via a rear mounted 20mm PVC conduit which led through the wall beneath floor level.

My intention is to drill a small hole in the bottom face of the isolator and to seal the 6mm T&E in the PVC conduit (Plumbers Mait non-setting putty).

Would silicone grease be a good choice to smear on the cable end and terminals before tightening?

Clive

I like copper grease. I put it on my cars' wheel nuts and valve stems. If it keeps corrosion away there, it will work anywhere.

If you really want to go to town Clive a little Calcium based underwater grease will probably prevent corrosion forever. I expect you have a tin of stern tube lubricant somewhere? It has the advantage of being difficult to burn too Mike. It is often suggested that silicones are a bad idea on electrics, but I have at last discovered that some high temperature silicone oil actually fixes EGR valves on my Vauxhall engine (actually Isuzu) for a useful period, where petroleum based ones burn off very quickly!

Apply Prysmian's R391 compound after termination? Not used it myself; just saw it while looking up the jointing pastes we use but I don't think it's designed for liberal application over the finished joint and this comes with a voltage rating for the avoidance of doubt.

NB: No link to either Prysmian or ETS

Technical_Data_Sheet_Multi_Purpose_Grease.pdf (super-lube.com)

Z.

The amount of moisture in the atmosphere at the time of sealing an enclosure, will contribute to the condensation on temperature cycling within the enclosure; close up when the weather is warm. Also, try using a "getter" as used commonly in instrumentation cases. Alternatively, sealing is ineffective causing "breathing".  

Jaymack

My experience of antenna housings outside with RF electronics in is that the only things with any  control penetrations you can make truly sealed are ones with an elastic wall that moves to allow the air inside to expand and contract without actually sucking water in past the seals. But in almost all cases this is impractical, and the next best thing is to arrange things so there is an outer protection like a hat or an overhang so that rain is thrown far off, and then a box nominally sealed except where it is vented at the bottom, but with a slug of fibreglass or similar in the vent tube  to prevent ants setting up home.

Anything to be buried or where water coverage is expected, to be potted or gel packed. Desiccant will work in a well sealed box (dual O-rings sort of level of well sealed with a test port to pump it up and down and a pressure test certificate. ) but you need an program of regularly inspecting and replacing or drying it out when it gets tired.

Really expensive things that must be kept working get a humidity sensor and a temperature sensor inside as part of the design, and it calls home when it it detects the onset of problem. And all PCBs get a varnish-like  concoat.

M

Back in the 1980s I was appointed to mv City of Durban a container-ship 

https://www.shipspotting.com/photos/3004847 for a 2-year period. The plan was 12 weeks on, 12 weeks off. In total, I was on that ship for 12 years on all her various re-names: Portland Bay, City of Durban, ACT8, Pegasus Bay.

Besides the conventional radio station, MF/HF WT & RT 1.5kW a compact HF transceiver for Radiotelex was also fitted circa 1985 rather than using the main equipment which was not too user friendly. The transceiver was a Skanti TRP-750 750 watts fully solid state with an auto-tuning ATU. When it was installed I was critical of the weatherproofness of the ATU https://i.ebayimg.com/images/g/vroAAOSwCFRi1~Xk/s-l500.jpg I am not certain that there were the two centre screws top & bottom of the case. I was assured by the installing engineer that there would be no problems..

Anyway, crossing the Tasman between Botany Bay (Australia) and Auckland (NZ) we had quite a thunderstorm. The next morning no reception of Sydney Radio/VIS. The ATU was on the monkey island, open up the ATU and from the tide mark could see that it had been about 4 inches deep in water. Due wind and sea spray, not just rain water.... I removed the internals - all on one PCB rinsed it off with fresh water and found a warm place for it to dry off.

I could see that the trifilar wound toroidal receiver matching transformer - top RH by the three reed relays was charred.

https://www.qsl.net/p/pe2jeb//foto/Skanti_HF_TRP-8000/TRP-8750/640%20antenna%20tuning%20unit.pdf

(The aerial was an 8 metre whip - not the Dieckmann & Klapper MAS 140 aerial, a cage vertical with top whip, you can see in the ship photo) While the pcb was drying out, found some thin wire and rewound the toroid and was back in business.

The bos'n found me some Denso Tape which was tacky enough to stick all the way around the ATU and prevented future water ingress.

The Skanti transceiver was a useful piece of kit. It covered 1.6 to 30 MHz and besides full power at 750 watts could also be used down to around 10 watts.  Playing around, I could communicate with BT's Portishead Radio (Rx)/Rugby Radio (Tx) on 12 MHz from Cape Horn just using 10 watts.

Clive