# COMMUNITY FORUM

lava96

12:21AM | 10/10/03
Member Since: 10/09/03
I have 2 questions.
First of all...how many amps will a 300w 12v low voltage landscape light transformer draw?
I am confused...do I need to divide 300w by 12v or do I divide 300w by 120v since it is actually plugged in to a regular 15amp circuit?
I am so confused...300w divided by 12v is 25amps...that doesn't make any sense at all. I thought these lights were supposed to be low voltage. 25amps is almost as much as my dryer! But if it is the draw that the transformer draws and it is 300w divided by 120v then that makes much more sense.

Second...I want to install a new receptacle to plug in my transformer. I have a 15amp circuit that currently has a GFI receptacle wired in first, then 2 more receptacles wired off of the first one. The only box I can access is the first box. Can I wire the new receptacle up to that one? The box is crowded now...It has a 14g wire on the load side and 2 14g wires on the line side. Can I somehow put a 3rd 14g wire to the line side? And how do I do that?

joed

11:08AM | 10/10/03
Member Since: 09/17/02
If the lamps total 300 watts then you divide the 300/12. 25 amps is correct from the 12volt side of the transformer. That will convert to 2.5 amps on the 120 volt side. The transformer is 10:1 ratio. Volts go down by 10x and amps go up by 10x.

lava96

12:22PM | 10/10/03
Member Since: 10/09/03
OK...so in terms of how much it would actually cost...it is like running 3 100w light bulbs?????? Right??????

I just thought 25amps was A LOT of electricity...didn't think of it in terms of 12v vs. 120v.

How about my second question...ANYONE?

joed

02:57PM | 10/10/03
Member Since: 09/17/02
300 watts of 12 volt lights is about the same as 300 watts of 120 volts lights. Watts is the same on both sides of the transformer. The voltage and current change to maintain the same watts. There are some losses in the transformer so it would very slightly higher including the transformer losses.

lava96

03:33PM | 10/10/03
Member Since: 10/09/03
Cool...so I have a NEW question...
How do I figure how to convert watts into kilowat hours (what the electric company charges me for)
For example...what does a 100w light bulb draw in terms or kilowatt hours?

And anyone have an answer to my ORIGINAL post (2nd question)?

Tom O

02:24AM | 10/11/03
Member Since: 09/17/02
Well, you have probably answered question #2 on your own by saying the box is crowded.

If I read your post right, you already have 3 #14 cables in that box. If you add a 4th cable, that box must have a capacity of 22 cubic inches. The largest single gang box that I know of only has a capacity of 21 cubic inches. The answer to your second question is most likely no.

lava96

04:15PM | 10/11/03
Member Since: 10/09/03
Tom O....

Do they make a single gang box with more than 21cubic inches that I could use?
And you are right, I would be adding a 4th wire to that box.
So if I can't add the wire to the crowded box and I can't get a bigger box, how would I go about splicing the NEW wire into the middle of an existing line?

Tom O

03:44AM | 10/12/03
Member Since: 09/17/02
You might be able to get the needed cubic inch capacity by installing a surface extension box onto the existing box.. Another option would be to replace the box with a 2 gang box.

Tom

Joe Tedesco

10:05AM | 10/12/03
Member Since: 07/27/02
Be sure to comply with 300.14 in the NEC calling for a full 3 inches of unspliced conductors beyond the edge of the box, if an extension box is used. This thread has gone far enough, please change the box to one that will be large enough and hire a qualified person to take a look at the work before it will be inspected. It is going to be inspected, yes? If not the insurance inspectors will have some problems with that if the work led to an accident or a fire.

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