Flood through conduits

[jaymiess]

Working on a case where transformer pit flooded and water entered underground conduit and entered homeowners basement where electrical service enters the house. Caused major flooding damage because house was downhill from transformer. Beginning of conduit in transformer pit was resting on the ground and wide open (unsealed). Question is, is there anything in NEC or other code or standard procedure requiring opening of conduit to be above surface of bottom of transformer pit to prevent water from entering it when pit gets flooded? Thanks so much in advance for any help on this.

 

[jraef]

The answer is yes, there is, although not specific to transformer conduits etc. Article 300.5.G.

"(G) Raceway Seals. Conduits or raceways through which
moisture may contact energized live parts shall be sealed or
plugged at either or both ends." This should have been caught by the inspector (assuming it was inspected), when the home was built. It may be that the home predates the transformer installation, so the utility that installed the transformer would bear responsibility.

However, no conduit can be thought of as completely watertight, condensation forms even if sealed. That is why you must use water resistant cable inside. In reality, the installation at the house should have addressed this issue IMHO. The underground feed should have come up the outside wall and entered the building up high with a weather head. That way any water in the feed conduit would just stay there and eventaully drain out when the weather dries up, or worst case, overflow the top of the conduit and not eneter the building. Every basement electrical service entrance I have seen is designed that way, overhead or underground feed.

"Venditori de oleum-vipera non vigere excordis populi"

 

[davidbeach]

The NEC assumes that anything underground is full of water. The installation at the house is where the problem occurred.

 

[jaymiess]

Thank you very much for the helpful replies. As you can see I'm a structural engineer and could use a few hints when it comes to these subjects.

Now a follow-up question (or two). Is it standard to raise the opening of the conduit up off of the bottom surface of the transformer pit or use something drainable such as crushed stone at the bottom of the transformer pit? It just seems that leaving the conduit laying at the bottom of the pit unsealed is inviting bulk water into the conduit.

Also would an inflatable cable seal be sufficient at the customer's service box for resisting water pressure with about ten feet of head? That's what they've added since the incident, but it seems to me that they should raise the elevation of the next conduit that actually enters the customer's basement so that any floodwater that happens to pass that seal will just drain out of the meter box insead of entering the basement. The opening of the conduit entering the CT box is at the bottom of the box, and the conduit exiting the CT box and entering the basement is also at the bottom of the box. It would seem to me that this second conduit opening should be raised.

 

[stevenal]

From the NESC 322B4:

Conduit installed through a building wall shall have internal and external seals intended to limit
the likelihood of the entrance of gas into the building. The use of seals may be supplemented by
gas-venting devices in order to minimize building up of positive gas pressures in the conduit.

If it's gas proof, it's water proof too I think. NESC covers the utility side of the installation.

 

[itsmoked]

I can't imagine ANY inflatable seal working on wires in a conduit or staying inflated for 50 years...

 

[jraef]

I agree with itsmoked. Any inflatable product is deflatable at some point in time. Unless you meant an expanding foam type of sealnt. Some of them may work, but I would be suspect of their ability to hold back static pressure for any reasonable length of time. Still, you could try it, but I would seal both ends of that conduit.

http://www.rainbowtech.net/catalog.php?pid=1188&moreinfo=1&cat=1

"Venditori de oleum-vipera non vigere excordis populi"

 

[BJC]

The best water seals I have ever used are made by The Jack Moon Company. You have to search under JackMoon. They are located in Southern California and are part of Tyco.
They use rubber seals with stainless steel compression fittings. They are expensive and have to ordered to fit the conduit and cabel size. Worth the time and money if you have water with a head on it.

 

[jraef]

Yes, and Fire Stop seals a.k.a. Transit Seals are rated for holding back water pressure for long periods of time as well. They are used in passing cables through bulkheads on ships. but not very practical for the average retrofit application because you would need to dismantle everything to install it, and if you were to do that, just redesign the conduit entry correctly.

"Venditori de oleum-vipera non vigere excordis populi"

 

[itsmoked]

What is the stuff you buy in a blue/white can at your electrical supply, add water, stir, then spatula into EXP enclosures? Would that stuff work in a constant water environment?