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Joined: May 2007
Posts: 55
Up2code Offline OP
Hello All! I have 2 customers whose 12V landscape lights keep prematurely burning out. I examined some of the bulbs and they were completely blackened. Both customers live on top of hills, both have water wells withing 200 ft. of residence. Both customers 12V landscape transformers are GFCI protected, which never tripped. Any ideas would be appreciated.

Joined: Mar 2004
Posts: 251
What is the output of the transformer? Much above 12 will shorten the life of the bulbs. Make sure the bulbs are not getting wet. Dark or black bulbs usually indicate the bulb cracked (air in the bulb). Water hitting a hot bulb will many times cause the bulb to crack at the base where the wires go in.

Joined: Oct 2000
Posts: 2,722
Broom Pusher and

Welcome to ECN!!!

As mentioned by WESTUPLACE, please let us know the rated output Voltage of the Transformer, and if the Primary side is being fed with rated Voltage.

Also, check to see if the Lamps are exposed to Water while at high operating temperature.

Could there be someone (Persons or Animals) hitting the fixtures during operation?

Looking for your replies.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Apr 2003
Posts: 139
Based on your topic title, are you thinking lightning is involved someway?

Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter
Joined: May 2007
Posts: 55
Up2code Offline OP
Thanks for the replies. XFR is 120V primary, 12V secondary.(Basic Kichler 900W landscape XFR). Customer#1= out of 80 bulbs, 40 were burnt out, definitely blackened, some did have water in sockets.(None of the filaments looked broken) Customer#2- Out of 12 bulbs, 8 were burnt & blackened, broken filaments. All sockets completely dry. Water well seems to be common denominator. GFI's never tripped on either. Am I barking up the wrong tree assuming lightning surges are the culprit?

Joined: Apr 2003
Posts: 139
1. Check to make sure you are not exceed output rating of the transformer.
2. Check to make sure their are no unintentional grounds or shorts in the wiring or connectors that may be causing overload and/or surges.
3. Missouri doesn't have significant lightning strike density, thus likely not the problem, but adding a tvss/gfci receptacle, or TVSS to the branch circuit supplying the landscape lighting would help against ANY surging events within or from outside the premise wiring.
4. Could simply be a manufacturer's defect or lack of product quality. Upgrade transformer/fixtures to higher quality and performance.

Good Luck...

Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter
Joined: Jul 2004
Posts: 787
XFR is 120V primary, 12V secondary.(Basic Kichler 900W landscape XFR). Customer#1= out of 80 bulbs, 40 were burnt out, definitely blackened, some did have water in sockets.

Bulb life goes down by the square of over voltage. 12.5 V supplied vs. 12 V designed. 4% over voltage squared equals 16% shorter life.

Measure the voltage at the transformer output terminals, the voltage at the closest lamp socket, and the voltage at the farthest lamp. I would expect that the transformer is probably putting out about 14 V. If this is the case, as the closest bulbs burn out, the voltage rises for the rest of the bulbs, and they burn out going down the line.

900 W / 12 V = 75 Amps

Check if there is a voltage adjustment tap to reduce the output voltage.

Joined: Jun 2007
Posts: 14
Some of the fancier transformers actually have multiple voltage taps, they have screws for 12, 13 and 14 volts. Thats to overcome voltage drop on long runs. The one I worked on like that they weren't labeled at all on the case either, just 4 screw terminals. So it's possible that they really are running the lights at 14 volts even without there being anything wrong with the transformer. A quick google for a Kichler 900W transformer, the pro model at least does have 3 taps like that.

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