In a Chicago high rise, feeders to a fire pump are below the floor of a parking garage. Fire pump controller is from around 1959. 480V 3 phase/ 150hp.

About 250' from the meter, there is a junction box in the floor. It is about another 100' to the fire pump. There is 3" conduit, and fiber bushings, at opposite ends of the rectangle shaped box. The box is falling apart. The conduit end, at the fire pump side of the box, is collapsing and closing in on the wire. There are 3 feeders. The insulation from one of the feeders is not cut but is "bulging" from the squeeze.

If after I megger the wire and find it to be OK. Can I just repair the damaged feeder? Is it acceptable to "sleeve" the damaged conduit end with an insulator?

That answer is best for you IF it comes from the local AHJs.

What is an AHJ?

Authority Having Jurisdiction. Inspectors.

I agree with John. Get your local electrical inspector in there, show him the problem and see what you can work out.

From the sound of it, you might be chipping up some floor. These days with diamond saws and air tools, it is usually not that big a deal. You might be meeting a guy from the concrete worker's union tho (in Chicago).

Once you get it opened up you should be able to get back to clean pipe and extend it a little, into your new enclosure or just use a bigger box.

Thanks. I was looking into cutting the floor and a new box as the next option.

The point of where I was going with a suggestion is that you should have a talk with the electrical inspector, and possibly the fire inspector before you plan any repairs.

Discussion regarding what is acceptable, and providing details (sketch) is a lot easier than doing something & not having it approved.