A standard sized, exterior (weather proof) electrical enclosure can be fabricated using the plans herein. It has many features that make it especially suited to the railroad environment, including positive closure of the cover against a closed-cell neoprene gasket, glove knobs and plenty of room inside for components. Altering the size of the box itself is easy (just scale up/down the appropriate dimensions) but we have found this particular size to be useful in many situations.
This enclosure can be fabricated from carbon or stainless steel. If you choose carbon steel, give it a couple of coats of epoxy paint before the components are installed and wired. We suggest using 16 gauge steel, if you use carbon steel. If stainless is employed, 18 gauge should be sufficient. A 36" brake and a MIG welder are needed to fabricate the box shown. We use a spot welder to weld the channel to the cover. Incidentally, if the box is made of stainless, you may want to bend the angles out of stainless sheet instead of using cold-rolled sections.
The layout and cutting drawings, as well as the fabrication drawings are in Structural_BoxCtrl, which can be downloaded as a PDF.
Components can be mounted using screws, threaded through the box. Typically, we weld a nut on the back of the box for each screw so that they cannot be easily stripped out. You may want to put a thin piece of cork (1/16") under plastic parts (e.g. terminal blocks) so that they can't be cracked when you reef down the screws. Caulking is liberally applied to any through screw hole or other entry that may leak.
Once the box is complete, we test fit it in place and then weld on whatever brackets are needed to mount it. Short bits of 3/16" x 1-1/2" x 1-1/2" angle work well for mounting brakets. Once they are on and the box is mounted, conduit entry/exit holes can be drilled/punched.
Although the drawing shows tumb screws, we actually use glove knobs for the lid hold-downs since unscrewing a thumb screw is a little difficult in the field. A good choice is the aluminum glove knob from Carr-Lane manufacturing (CL-3-HK2T, Grainger #1X578). Also, for ease of opening, when you close the box for the first time, put a tiny bit of grease on the screw's threads.
To get the lid to line up and compress the gasket properly, use four short pieces of 1/4" by 1/2" flat stock. Weld all of the parts onto the lid (angle and hinges). Lay the lid flat, put the four pieces of flat stock in the gasket groove and flip the box upside down so that it rests on them. Proceed to weld the lid stop and hinge mounting strip onto the box in the correct position. Mark, drill and tap the hinge holes at this time too.