# Low Voltage Transformer Trouble

Discussion in 'Landscape Lighting' started by jimmy1111, Jan 19, 2009.

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1. ### INTEGRA Bespoke LightingLawnSite Platinum Memberfrom Muskoka, Ontario, CanadaPosts: 4,102

Well I have posted over 2000 times on this forum, and I have to say that this thread is probably the worst yet. Even "Pete's" participation was better then this drivel.

Jimmy, you do what you need to do, and the rest of us will do what we know is right.

Now, can we end this?

2. ### jimmy1111LawnSite Memberfrom philadlephia, paPosts: 56

James...go your rocket science LED made-up already !!!...we are all expecting free 20 LED supplies ...or you need to chip some your canadian stack to this site by now after 2000 posts for your LED...let's admit it you owe it to this site

3. ### INTEGRA Bespoke LightingLawnSite Platinum Memberfrom Muskoka, Ontario, CanadaPosts: 4,102

Pardon me? Perhaps you could re-state that in english?

5. ### Chris JLawnSite Silver Memberfrom Maldive IslandsPosts: 2,830

Bartender, I'll have another.

6. ### TXNSLightingLawnSite Fanaticfrom DFW, TXPosts: 6,462

Make that a double.

7. ### VenturewestLawnSite Senior Memberfrom Rocky Mountains!Posts: 513

Okay Jimmy, I am going to be nice and answer this question once and for all and hopefully end this thread. I apologize in advance if this has been answered somewhere in the previous 9 pages!!!!

A widely accepted formula for calculating voltage drop is:

Vd= Length x Watts/ Cable Constant

There is a chart that lists the cable constants for low voltage cable: I will list the relevant few:

#12 CC is 7500
#10 CC is 11920
#8 CC is 18960

If you use the loop method and come back to the transformer you are effectively using 2 runs of 12 gauge wire. This is a common meathod, not a big deal.

You end up with a wire constant of 15,000

So, 2 x 12 gauge has less drop than 10 gauge but a little more than 8 gauge.

If you do one of your examples:
250 Watts at 100' and run a 12 gauge loop then formula as follows.

100' x 250/ 15000 = 1.67 volts as your drop
That is basically what you came up with.

As you can see the loop isn't magic and it also isn't intrinsically evil. It doubles your wire.

One thing to keep in mind is that you still can't exceed the amps for your wire but you seem to know that.

Also, you could just have 2 separate runs of 12 gauge, say one runs to 3 lights and the other runs to 3 lights instead of a loop that runs to all 6.

One other thing to note also. This is a parallel circuit as is every other method of wiring in low voltage AC. Same as in a home.

The only way to effectively combat VD is with antibiotics. But Vd can be dealt with using effective wiring methods.

8. ### VenturewestLawnSite Senior Memberfrom Rocky Mountains!Posts: 513

One more note. 12 gauge wire is only rated at 20 Amps. That is 240 Watts at 12 volts of course.

I guess NEC requires any electrical device operating 3 hours or more to be derated to 80% capacity. (I got this out of Unique's lighting manual)

9. ### jimmy1111LawnSite Memberfrom philadlephia, paPosts: 56

Thanks for the details....but the VD seems to be conflicting with other sources.

10. ### JoeyDLawnSite Silver Memberfrom Escondido, CAPosts: 2,933

you need to multiply by 2.........