Some others have hit on the basics. In my experience you're going to be dealing with two groups of people. The product standard people and the hazardous location people.

The product standard is just a document that describes all the boxes you have to check in order to have your product listed. The product standard for a toilet would say it has to support a certain amount of weight, flush a certain volume of solid/liquid waste, must be made of a non-corrosive material, must have the volume rating printed on the back in contrasting letters, etc. etc.

It will also specify a bunch of tests that your product will have to be subjected to. In your case it probably will have to undergo a rain test where they put it under a shower and make sure it still works and doesn't electrocute anyone. There might be a shake test where they put it on a vibrating table and make sure it doesn't break apart.

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Once you have a product that's designed to a standard, you'll have to deal with the hazardous location people. They're responsible for making sure that your product meets design standards for the protection method (explosion-proof, intrinsically safe, dust-proof, etc) and location (Class I Div 1, Class II Div 2, etc) you're getting it listed for.

There are standards that describe the requirements and tests for hazardous locations similar to the product standards.

Getting your product certified for international standards at the same time as US standards doesn't add a lot of complexity to the process.

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The basic process is that once you have a product standard, you submit drawings and other documentation (like your manufacturing and QC processes) to the product standard people. They review it on paper and tell you whether it meets the standard or not. If it does, you can submit actual product that they will test (or they come to you on site, depending on what it is).

Same thing happens with the hazardous location people.

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Once everything is approved, you can label your product with the agency logo with the product standard and hazardous location rating.

Then for as long as you're selling it as a certified product, someone from the agency comes by and audits your facility once, twice, or four times a year depending on what the certification is.

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Time and money to get this done depend on a lot of factors. Time factor is mostly dependent on how backed up the agency is and whether you have someone that can be johnny on the spot with drawings and documents when they tell you to change something.

There are consultants that can help you navigate all this and will probably speed things along. A big part of the help they can offer is identifying what product standard your product will fit into. I'm also convinced that they get to cut in line ahead of people who are doing things on their own.

Ongoing costs I think are about $20k per year for our product. This is just the cost of maintaining your certification. Don't know if that varies from one standard to another.

Gut feeling is that you're probably looking at 6-12 months and $50k-$100k for the initial listing.

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These companies are gigantic bureaucracies and I've never had much fun dealing with them. Just accept that before you go into this. If your product is industrial I'd go with UL.