As on other Atlas Customline Turnouts, the Atlas Customline Mark IV Turnouts are constructed so that regardless of switch point setting, both branches are powered. As a result, this new metal frog is insulated and carries no current. Most locos will span the insulated frog without loss of electrical pickup on the customline turnouts: however, engines of extremely short wheelbase or diesels with single-truck pickup may hesitate or stall at the frog. The problem can be easily overcome by equipping turnouts with an Atlas Snap-relay which when wired to the remote switch machine, will energise the frog with track current of correct polarity depending on the switch point setting.