On a personal note - I would never under any circumstance pay someone up front to do work for me. I have built a few homes over the years for myself and every sub was hired with a handshake and not paid until thier work was completed in full. I would personally be offended if they asked for a deposit which would imply that they think I'm going to rip them off.
The line about "needing to pay my suppliers" doesn't fly either. If you buy materials the first of the month, you have until 30 days after the end of the month to pay your supplier. That's 60 days!
The best part about this system is that it weeds out the little "up and coming" electrical contractors. (No offense) They can't afford to go without their money that long.
I would say the best part about this system is that everything is in your favor.
The subs carry all the risk.
Asking for a deposit implies that you're going to rip them off?
So if a sub asks for a deposit does that imply that the sub is going to rip you off?
Are you afraid that you'll pay the deposit and the sub won't do the work?
Why would you balk about paying a deposit unless you worried the sub is going to rip you off?
Sound to me like you wan't the subs to trust you but you don't wan't to trust the subs.
No deposit and no contract means you have the upper hand.
You have all the control over the money.
There's nothing written that says when and how much the sub will get paid.
If you trust your subs like you want them to trust you a down payment and written contract shouldn't be a problem.