Common Tap question...

[GreenLight]

I was on a service call today and I came across a loaded 300 watt Hadco transformer. Here is the scenario..

a) One transformer on job and it's a 300 watt Hadco that has 1 common tap and a 12,13,14,15 hot taps.

b) Customer says when it was initially installed it had one single homerun going to 9 20 watt path lights. (in this case he is already at 180 watts on that transformer not including wire wattage)

c) Eventually he decided he wanted 2 extra path lights and 3 downlights from the trees, so 5 more 20 watt fixtures were added, but this time they simply ran another wire home run and duel tapped the common. (now he is at 280 watts of fixtures on transformer and two home runs which both tie into the only common tap)...

d) The problem is he has lost power to 7 lights on the original run and he believes there to be a cut somewhere after the first 2 lights...


Now here is my problem, im pretty sure I could locate and eventually find the cut home run on the original and fix it, but of course I opened my big mouth and told him that the transformer was really overwatted and that it should really be a 600 watt transformer broken into two home runs.

Secondly, I told him that he shouldn't have two home runs sharing a common tap...Well you know what happens next, he calls the original installers of the lights and they call me and of course we differ on opinion.

They say that it worked when they did it just fine and I should simply fix the wire and be on my way.

I said I felt like they were overwatted for the transformer to which he responded "hadco is actually rated for 350 watts, so don't worry about it, it will be fine"....

Next I told him that I didn't think it was a good idea to have two home runs sharing the same common to which he replied "what difference does it make, it's simply a common tap?"

I know I am theoretically right about the wattage being too high on the transformer, but now I have two parties arguing against me...

Secondly, maybe I am wrong, but I thought having two home runs tying into one common (even if they are both small runs of low watts) was supposed to have bad results and not work properly? Am I incorrect here, or does it matter?

Sorry for the long post, just trying to paint the picture here...

[Firefly Prof. Lighting]

It is fine having multiple wires sharing one common as long as the sum wattage of the runs doesn't exceed the circuit capacity. You should never exceed 80% of max capacity on the transformer. The recomendation for a new transformer is sound advice. I have however seen transformers loaded up to full capacity before and running away although I personally would not recomend it.

[TXNSLighting]

It is fine to have two home runs in one common. every one here doesn it, but everything else you are right.

[MAGLIGHTING]

Your advice regarding the tap was incorrect and technically your advice about the 280 watts was incorrect as well. The 25 amp magnetic breaker is good for 300 watts and rated for 32 amps before tripping. Good bad or indifferent most manu's use a breaker that has quite substantial headroom before tripping. This means potentially unsafe overloads or slight shorts may go untripped. This is rare but possible. You should never under any circumstances load past 25 amps or 300 watts on any given circuit. To do so is definately a code violation. The 350 watt remark by the original installer was probably referring to the 32 amp trip threshold of the breaker and didn't help things either.

ohms law Volts X Amps =watts
12V X 25amps = 300 watts

NEC recommends loading to 80%
Manufacturer says you can put a full 300 watt load on the transformer and you can without issue. Whether you should or not is your personal decision.

No one would fault you for recommending an upgrade however you have to have your facts straight before bringing your argument to the homeowner. Otherwise you lose total credibilty and it looks like to the owner that you are trying to recommend frivalous upgrades for your own gain even when you weren't.

[GreenLight]

Thanks a lot for the respones, I learned something about the common tap with your responses. Gambino, I understand your point about the wattage "technically" being within range, I was more or less explaining to the homeowner that it is not recommended to go over 80 percent of the load on the transformer and I felt it was overwatted a bit...Thanks all!

[MAGLIGHTING]

Thanks a lot for the respones, I learned something about the common tap with your responses. Gambino, I understand your point about the wattage "technically" being within range, I was more or less explaining to the homeowner that it is not recommended to go over 80 percent of the load on the transformer and I felt it was overwatted a bit...Thanks all!

No problem that's what we are all here for to learn.

[Pro-Scapes]

I think there should also be a concearn the system is daisy chained. If so chances are the splices are not the greatest. I would check the splice at the last working fixture before continuing.

280w of lamp load depending on the lenght of the wire is pushing overload anyways.

You already got the right answers about the common taps but i think its clear here a larger transformer is needed here and quite possibly a reinstallation of this lighting job. I wouldnt even service it because it then could make you liable for it.

[MAGLIGHTING]

I was thinking about this very situation today. I did a paid consultation for an owner this morning who had an electrician install a 200 plus fixture system 5 months ago. The system has alot of major problems.
The owner has had the original installer back several times for problems and told me he no longer will be calling him back again.
Voltage drop
Red wire nuts
cable and connections above the ground
Risers were made from galvanized pipe and fittings spray painted green all of which are starting to rust badly
Too many fixtures per run.
Mostly 50 watt Mr-16's where 35 and 20's would suffice
Not nearly enough homeruns
Daisy chaining
etc.

The estate home is in a very exclusive area of LA. Several celebrity neighbors .Probably worth more than 10 million dollars.

Seems to have all of the best materials used for all other aspects of the property. Stone all over the place in and out, Custom fountains, pool, outdoor kitchen, full sized craned in trees, beautiful landscaping.

So what would posess an owner to allow such shoddy landscape lighting workmanship to take place when everything else seems to be in top order?

It's because owners don't know the difference until it's too late. And because landscape lighting is last on the list and the first to get shaved when everything else goes over budget on a new or remodel project.

Fixing this job is not an option right now because the owner has been stung bad already and he will have to live with this headache until he can no longer bear the pain anymore. When he is ready I will be happy to help. Until then he will remember the bad experience every night when he looks at his yard. This is not a good thing for the landscape lighting industry as a whole. It's unfortunate that this happens so often but it's a reality that undermines all of us.

[Pro-Scapes]

I just tore out such a system. Electrician had emt conduit used for risers on pagoda lights. Daisy chained all around the pool. Alluminum fixtures+saltwater pool= nightmare. Alluminum stakes had corroded so badley fixtures were laying on their sides. System... 3 yrs old.

It now has nice copper mr16 pathlights..magnum transformers...and coppermoon bullets. Owners jaw dropped at the difference. They were very hessitant to go with another low voltage system due to the experience they had. It took a strong refferal from a previous client who knows them for me to get the project.

[Firefly Prof. Lighting]

The misrepresentation of low energy systems is alive and well all over the US out there. I have run into many instances like Mike was describing. They call an EC simply because they expect them to know what the heck they are doing and they are left with a mess and are out of money to fix it. Most ECs simply have no clue about it. Their EC classes in school probably spent a sum total of no more than just a few hours going over it. Probably all theory and no practise of course. Most all of the ECs I know won't touch it because they don't understand how to regulate the voltage. I know of a few who have ES certificates, (electrical specialist), who specialize in low energy applications, however they are mostly in relation to the alarm and data industry and sadly never apply to the principles of lighting.