I need a relay (120v coil), 2 pole or 4 pole(parallel) all contacts to close (NC), when power is lost. Also, the contacts need to be rarted 15A or higher DC; preferably 50A DC.
The small end of ABB's R-Series range of contactors might be of interest for your application, being rated at 63A. They are not particularly cheap, but have proven very reliable in arduous duty on DC motor switchgear applications. This general design of contactor - regardless of manufacturer - is well suited to breaking inductive DC loads, and usually incorporates a magnetic blow-out to assist arc extinction.