It requires a 2-pole 20 amp breaker. I have a Square D 200 amp service panel (house is new -- about 3 years old) and I have installed a new QO 20 amp breaker (model QO220CP) to be dedicated to the surge suppressor connection: http://tinyurl.com/7kxbbub
However, I noticed the Leviton SPD has what appears to be stranded aluminum wires rather than copper which I thought was unusual. Is it acceptable to attach the stranded aluminum wires to the breaker even though the breaker has copper terminals? Do I need to use an anti-oxidant compound on the wires before connecting them to the breaker?
QO breakers can use copper or aluminum conductors for one-wire applications. if using two-wire terminations (i.e. two conductors on the load terminal), then they must be copper. Stranded or solid doesn't matter.