Submersible terminations

[wirenut60]

First... I'm new to this site, so please bear with me...
I have been asked to look into waterproof terminations / submersible junction boxes for a waste water screen project. Our client has a waste water screen located in a vault about 30 feet fom the Ohio river. When the river over runs it's banks, the vault becomes completely flooded and the electrical equipment usually has to be replaced. Voltages involved are 480v 3p for the pumps and screen motor and 120v for a couple of lights and the controls. We are not able to locate anything above ground and hydraulic motors are not acceptable. So i'm left with looking for submersible power junction boxes and submersible terminations. I'd like to hear about other's experiences with these types of materials... and similar circumstances... thanks...

 

[stephenw22]

You might be able to use threaded explosion-proof products that have been well-coated with liquid teflon or some other pipe dope. They're rated for being hit with a fire hose and staying watertight, but you need to be careful that you have enough threads engaged to make a good seal. Try Appleton, Crouse-Hinds, Killark, or any other manufacturer.

The only completely waterproof, submersible connections/terminations I know of are for pumps. It's basically a butt splice connector and a piece of special heat shrink. The heat shrink has a glue layer on the inside that melts and seals any small holes when it's shrunk over the connection. However, they're only for single conductors. I've seen those type of connections outlast pumps on a regular basis.

I guess what you could always do is to put waterproof connections inside of explosion-proof rated boxes, for double protection.

 

[davidbeach]

Explosion-proof and watertight are not the same thing. In many cases the explosion-proof allows venting in the case of an internal explosion, but the route of the escaping gas is long enough that it has cooled sufficiently to not cause ignition outside the enclosure.

 

[BJC]

Look at Flygt pumps and some of the components they use.
I know the motors and limit switch j-boxes and connections are water tight. Starters I'm not sure of but I know of installations that would flood every couple of years.
the enclosures of theirs that I have seen are gasketed, have many bolts, gland seals around cord connections and the motors have moisture detectors in the case.

 

[stephenw22]

"davidbeach (Electrical) 30 Jan 07 17:59
Explosion-proof and watertight are not the same thing. In many cases the explosion-proof allows venting in the case of an internal explosion, but the route of the escaping gas is long enough that it has cooled sufficiently to not cause ignition outside the enclosure. "

That's why I specifically said to use threaded XP boxes and fittings, not flanged. With 5-7 engaged threads and a good thick coating of pipe dope on them, they'd be pretty waterproof. You can get them with o-rings as well, to make them extra tight against moisture.

 

[stevenal]

http://store.anchormarina.com/anchor/details.php?ITEM=3309203

 

[HCBFlash]

Yeah wirenut, I do it a lot. If you do this stuff, and it will be submerged for lengthy periods, you've got to go fully insulated and coated. No terminal blocks.

"explosion proof" stuff will give you the kind of durability you'll probably want, but if it's installed like an ordinary x-p installation you'll have trouble.

Where metallic conduit is necessary, use "Ocal" or Robroy wherever you can. Use PVC and cable wherever possible. You can get gasketed wire connectors like those used on jetskis, snowmobiles, dirt bikes, ATVs, and other vehicles, but in most places it won't be worth it. Even they only perform acceptably when filled and coated with an inert silicone type grease.

Splices with mastic, rubber tape, heat or cold shrink with insulating and waterproof gels inside, and "potted" connections are what will work and hold up.

Heat cycling is what causes the most trouble with moisture. Heating will expel warm gases, and cooling will draw moisture into your enclosures or imperfectly sealed splices, and damaged cable jackets. This includes ALL temperature changes including water temperature and weather! The old standard "Hoffman boxes" are excellent for retaining water, but sure can't keep it out in demanding situations. Hoffman DOES make some great stuff these days, and the glass-filled and some other non-metallic products of theirs is very durable and watertight, but nothing I've ever yet seen will keep a dry interior cavity when submerged for long periods of time.

I hope you understand the differences between NPSM and NPT pipe threads and where each is used. ONLY use NPT with coppercoat on the threads and one of the PVC coated conduit types mentined above and/or Scotchcoat over all fittings.

It IS possible for circuit boards to be submerged, but must be coated both before and after wiring terminations are made to them. Fuseholders are available which can be safely submerged, if filled with silicone gel and coated outside after the fuses have been installed.

Boxes that will at all times be above water, but have conduits or even cables entering them that are partially submerged need to have dessicants in them, and possibly heaters.

There are 3 ways to deal with panelboards or control cabinets:
1)- above high water - even pole-mounted if need be, with drying systems
2)- sealed vaults with emergency powered bilge pumps and vent stacks above high water, again with drying facilities
3)- pressurized (purged) enclosures, again with back-up pressurization facilities,,,, and drying provisions.

I wish someone would have told me (or gotten me to remember) this stuff a long time ago.

Please let us all know how this works out for you! and don't forget faq731-376

 

[wirenut60]

Thanks for the information. One small detail i purposely left out is the fact that the vault and screen area is Class 1 Div 1... and since we cannot install anything above grade, there is no ventilation to lower the classification. However, the req'd conduit seals will benefit by keeping water from rising into the conduit. Water will get into the conduit because of the nature of explosion proof boxes... i can't do anything about that, but keeping the water from rising past the exp proof sealoffs will be a benefit. My plan is that the terminations will be in a box above the elevation of the equipment in the vault, but still remain flush with or below grade. From most of the responses, i see suggestions involving seal conduit and boxes more that addressing terminations, which seems to be the best approach. In the old "pre-plastic" days, people would make an underground splice, tape it and maybe coat it, then put it inside of a glass jar then bury the assembly upside down. The idea that water will not rise up into the jar to the terminations... (back yard approach, but somewhat effective). Also... all of my termination can be made within (2) 12x12 boxes... any thoughts of a nitrogen purged arrangement? Didn't telephone companies do this at one time? Again... thanks for all the responses...

 

[stevenal]

I don't understand from your statement above what you consider to be the best approach. Your best and last defense is to seal the termination. With no gas involved, there is no heat cycling pressure changes to deal with at this level.


I have a pressurized septic system, components supplied as a package. Pump and float switches connect together in a Carlon box above normal liquid level, but below grade. Cables enter through rubber sealed strain reliefs with O rings against the box. Box cover is fully gasketed. Splices inside are made with the heat shrinkable connectors I linked above, except the common used a large silicone filled wire nut. When I had to change a bad float switch (what a fun job!), I found some sort of liquid in the bottom of the box. Connections inside were still good.

The gases trapped by an inverted jar are water soluble. This arrangement won't remain dry indefinitely.


If you really want a dry box, pressurize it with dry air or nitrogen and use a soap solution to check for leaks. Then make sure that regular pressure checks are part of the maintenance program.

 

[HCBFlash]

What most telco's do these days for buried and submersible connections is basically a bag full of silicone grease that they put their splices into, squeeze any air out of and ty-rap it in place.

 

[wirenut60]

Thanks for everyone's input. The biggest issue is the class 1 div 1 location. The solution is to install a manhole immediately adjacent to the screen vault and route all circuits, unspliced from each piece of equipment, through sealoff fittings into the new manhole. Once outside of the Class 1 Div 1 area i can install a waterproof box with waterproof terminations inside. Controls, circuit breakers, etc will be located 300 yards away in a bldg. We will be changing the control system voltage from 24v to 120v when the new screens and grinders are installed. It's not perfect, but given the circumstances it's the best we can do. Thanks again for the input.

 

[HCBFlash]

wirenut:
Don't go AWOL on us, let us know how things are working and turn out. I'm sure your experience will give you some insights that I'd like to know of, and I'm pretty sure a lot of others would too.

Please let us all know how this works out for you! and don't forget faq731-376