My experience is ancient and particular to one local. No idea how it applies now, in your area, or with the IBEW but I'll hitb you with it anyhow.
We would generally interview 100 or more applicants over two days for around ten openings. That means each applicant only got a few minutes of time (answering set questions) to stand out from the pack. The panel consisted of trustees from both labor and signatory contractors. The LU Training Coordinator observed and maybe a State lrepresentative sat in did too. There were three main focus areas for the trustees. What does the applicant bring to the training program? The apprenticeship is thousands of dollars worth of education and the trustees don't want it squandered by immaturity or flakiness. And they want someone who can hack it academically. Management trustees will be looking for an apprentice that has work ethic and a work history that indicates he/she will work hard and make them money on a job site. Labor trustees will be looking for an apprentice that will represent the union brotherhood well. And both sides loved to get someone with previous trade experience either military or working a nonunion job. That apprentice might come in as second or third year shortening the time to turn out and opening an early apprentice training slot. And the labor guys liked that there was one less skilled "rat" out there. You don't have electrical experience so focus on your other strengths. Go out of your way before hand to meet and talk to journeyman from that local union and management of a signatory contractor if you can. Find out what they want to see in an apprentice. I know, easier said than done and networking always is. And one of the people you meet might be a well respected union member or have "an in" with a trustee and that persons written reference can go a long way to getting you short listed. There is a lot more to it than that. The point is treat this like something you really want. Put in the effort learning about the work, the union, the program, and be able to show them what you bring to the table and can do for them.