I have a VOLT 150 watt transformer with 20 VOLT MR16 5 watt LED bulbs on three runs all from the 12V taps. When I add a 21st fixture, the breaker in the transformer trips usually after an hour or two. Once it trips, it will trip again right away when I reset it. The total watts is well below the capacity of the transformer and VOLT gave me a brand new transformer under warranty and it's still happening so it's not a transformer problem. I checked and am getting 11 volts to the last fixture on each run. I do not know what to try next. I called VOLT and Richard told me it sounded like an overload issue. He also said that some of the bulbs may be drawing more than 5 volts but even if all 21 were drawing 6 volts, this transformer should not trip. Anybody have any ideas?