How do I know how many lights?

If you run a 12 gauge bus wire and it is not overly long,the wires wont melt as the transformer breaker will protect the wire.  Connect each string in parallel with the bus. Not sure which Christmas lights you are using. Depending on type of incandescent bulb they could use from 2 to 5 watts each. Some mini lights even less.  So 60 to 150 bulbs..

Dale H

Simplest rule is to remember volts X amps= watts. Soo now by division 300 watts divided by 12 volts equals a max of 25 amps and in the malibu transformer there are no circuit breakers you need to put one on the output line to protect your lines or fry your lights and accessories. On my RR I use 8 300 watt malibu units to supply lighting and accessories and animations and have done so for 5 years with no problems just remember to add the breaker.

Don

I do not have the Malibu but I use 4, 600w Hampton Bay ones. They have excellent breakers. It is hard for me to believe the Malibu has no circuit protection on the secondary side. If it does not it would be a dangerous device. a short even at 12 volts with a 25 amp transformer could melt wire and cause a fire.

Dale H

Do yourself a favor and install a couple of circuit breakers that are also switches on the output of the Malibu to break up the load to easier-to-protect branches.  You can also use the switch function to work on or troubleshoot various areas of the layout.

The Malibu's internal protection may be OK for beefy bus wire, but what is protecting all of the runs to the individual lamps?  If you have a short at/near a bulb, the wire running back to the bus will burn up.  Multiple branches with reduced current ratings will help avoid this problem.

Please enlighten me !  What is a MALIBU LIGHT TRANSFORMER ?

It's a brand of garden lights, typically they are 300 to 600 watts, 12VAC.

Malibu lighting is designed for outdoor use. The UL listing is based on that. The normal accessory wire designed for garden lights that we have installed is #10, though #12 wiring is available.  

I have the Malibou transformer as above, 300 watts at 12 volts, but no circuit breaker.  Where do you get them and what are they called please?

See http://www.mouser.com/catalog/catalogusd/645/1982.pdf for rocker switch version I prefer.