We have just fitted a 2 way dual dimmer switch to replace old one - one switch controls 6 x 50w spotlights which have own transformers - both dimmer switches are designed for up to 400w - other switch controls 4 x 50w, again with individual transformers - if we switch only the switch controlling 6 x 50w, after about 20 minutes the casing gets warm, it seems better if we reuce dimmer, but is it safe for dimmer casing to get warm externally ?