Newbie design plan

[JanC]

I’ve spent quite a bit of time on the web, and this site seems to be more DIY friendly than any other site I’ve visited. I’m searching for some advice/suggestions on my first low-voltage landscaping project.
I have a plan sketched out - is the best way to get feedback to scan the plan and post it or just attempt to describe it (I thought I'd read something about a problem with attachments)?
Warning... I'll have lots of questions!
thanks in advance,
Jan

[sitelights]

Pictures are worth a million words but unfortunately the image upload capability of this site has been lost; the problem should be fixed within the next 3 months depending on my ability to produce discretionary income.

In the interim you might wish to use an alternate image posting site. As an example there are a number of photo sharing sites where you could post your digital inages. You could then post a link on lowvolt.org and hope for the best.

The perception of this site as DIY friendly is only partially accurate but there are a few highly qualified professional designer/installer members that may take the time to help you.

[JanC]

I didn't mean to imply that this site would welcome DIY'ers with open arms. I realize it is a site for professionals by professionals for sharing knowlege. I was hoping some of the professionals would take a moment to lend some advice. Most other sites come right out and say "No DIY'ers allowed".
Here goes.
Based on what I’ve read, a run of wiring should only contain about 80-110 watts worth of fixtures and that multiple runs of wiring can be attached to the same lugs of the transformer as long as the total watts plus a voltage drop factor plus allowing for additional fixtures stays under the transformer rating.
Assuming that is correct, I’m planning on 6 runs of cable that will connect to a 600W multi-tap transformer – 240w total fixture load on one circuit and 255w total fixture load on the other. This is a back yard lighting project involving beds around a terrace at the house and two remote beds in the back of the yard.
Here are some questions. Any advice would be greatly appreciated.
1) 2 of the 6 runs are to landscape beds in the back of the yard. I don’t have an option of centrally locating the transformer, so one run will be 200’ of which about 145’ will be from the transformer to a “T” using #8 wire, then one leg of the “T” will go 2’ to a 20w fixture, then 24’ to a 20w fixture and the other leg will go 32’ to a 20W fixture. The total load on this cable run will be 60w. The other run will be 162’ of which 132’ will be from the transformer to a “T” using #8 wire, then one leg of the “T” will go 18’ to a 20w fixture, the other leg of the “T” will go 2’ to a 35w fixture, then 12’ to a 20w fixture. The total load on this cable run will be 75w. This looks doable depending on who’s voltage drop chart I look at (yes, I read the comments on those charts!). From a real world view, is that doable? Should I run #8 on all legs of the “T” or switch to #10 for the runs to the fixtures?
2) The other runs are shorter. Is it better to have a single loop cable run that contains 6 20w and 2 35w fixtures or two sequential cable runs that each contain 3 20w and 1 35w fixtures? If the amount of cable required is about the same or a little more, it seems better to do the loop. In the case where the amount of cable required would be much more to do a loop versus a sequential cable run, then is the sequential better?
3) This may sound really stupid, but exactly how with a voltmeter do you check voltage at the fixtures? With a line voltage system, I’d just poke the leads from the meter into the wire nuts and get a reading from that. With low voltage and assuming I use the pierce connectors, do you just remove the bulb and touch the contacts there?

Thanks in advance for any pointers you can provide. I have pages of notes taken from reading the postings at this site. I wish there was a way to get all the information in a book!!
Thanks,
Jan

[sitelights]

The technical design aspects outlined in your post are all feasible.

(1) The 8/2 gauge cable is difficult to work with and, of course, the pierce point connectors will not fit on 8 gauge. A transition to 10 gauge at the splice to the 8 gauge should work well.

(2) If the cable lengths are roughly the same looped or as sequential runs the loop advantage is merely in providing more uniform voltage within the loop. If the sequential runs are center fed (as a "T" of 10 gauge) the difference in the brightness of the lamps should be approximately the same using either method. If looped be careful to maintain polarity.

(3) In a Hadco LVC3 connector (and other pierce point types) the fixture wire (18 gauge) and the main cable (10 gauge) can be pierced so that the 18/2 tail at the connector will protrude enough to allow stripping the separated strands of the 18 gauge. You can make your voltage check at that point and then cut off the ends of the 18 gauge to eliminate the exposed bare wires. If you take a reading at the socket do not set the lamp pins fully into the socket; that will allow a reading at the exposed pins with all lamps operating.

With a 12-15v multitap transformer you can adjust your final voltage to provide a maximum 12v at the first fixture of each run and know that the voltage is incrementally is less for the balance of the fixtures on that run.

[JanC]

Sitelights,
thanks for the response. I'm ready to plow ahead.
I do have another question related to transformers. I am down to either a Kichler 15PRD600SS that can be readily had at a local supplier or a Vista MT-600 I found on the web. I searched this site on "vista" and found it mentioned, but no real recommendation information. My dilema is that I can buy a 900W Vista for the same price as the 600W Kichler, or go with the 600W Vista and put the $150 saved into fixtures. I noticed a comment in one of your posts where you had a project with 750W of fixtures and spread that out over 2 600W transformers with an average of 180W per 300W core. I'm wondering if my 475W total load would be better split into a 900W transformer instead of 600W. Or if I'm okay and the Vista and Kichler are comparable, use the savings to reduce the cost of this project. I do like dealing with someone local, but $150 is alot of money...
thanks again for all your help and the good info on this site.

[sitelights]

While it is true that most quality low voltage landscape lighting transformers can carry their full, rated load there are a number of reasons to not max out a transformer. (1) Planning for about 20% headroom will provide the necessary capacity if fixtures are added to expand the system. (2) All lighting transformers will run cooler if not loaded to their maximum rating. (3) A load of about 80% capacity will allow for the "forgotten" wire load often missing from load calculations. (4) A 20% reduction in the load will improve the transformer's ability to maintain the desired output voltage under varying conditions such as seasonal fluctuations in souce voltage.

Thus if you are planning for 240w and 255w on the two cores the theoretical limit of 240w (.8x300=240) per core is already at the top of the target range.

If the 600w and the 900w have similar or identical features at about the same price it would be wise to opt for the 900 for reasons stated above.