Outbound Routes

We currently are subscribed to two sip providers in case one goes down, we can switch over to the other provider. In the outbound routes section in freepbx when I configured my default route to go out in the trunk sequence I put our main sip provider and then after that the backup account. When the first sip provider goes out how come asterisk doesn't automatically use the second sip provider int he the trunk sequence?

I have been thinking that maybe the trunk sequence isn't used for that and if so is there another way of having asterisk switch providers when one goes offline for a couple of minutes?

Thanks
Blake