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Mike M
07-06-2008, 06:25 PM
Okay.

I always played it safe, using CAST's sensible recommendations and guidelines, such as 10 gauge cable for hubs beyond 100 feet, etc.

Unique and Cast specify max lamp wattage load, and I was wondering if I shouldn't be getting more out of my wire by pushing more toward the max of #12 cable.

Using Unique's quick-reference-slider-card, I can see the benefit of higher (17 plus) taps.

I assume this is okay, but is this why Unique pushes the fuses at hubs?

The only downside I can see for higher taps and pushing toward the max load, is for possible future add-ons at the hub, or if I need to up the wattage from 20 to 35 on a couple fixtures.

I'm not trying to be cheap or hazardous, just efficient.

I suppose I should do the math for maximum load at my distance (per code), with a margin for a possible add-on or two, or some possible bulb-upgrades. In other words, keep the lamp load below max (192w/#12)(or 16 amps), even with the possible add-ons (e.g. 40 watts). This would mean 152w on #12 might work for a specific application which I feel confident I won't go beyond 40 more watts.

The Lighting Geek
07-06-2008, 08:50 PM
the fuse at the hub is so that only that home run is out if the problem is between the fixture and the hub. Otherwise the whole system goes down.

I would try to plan your home runs under 100-150'. Depending on the load, I always leave at least 35-40 watts available on every home run.

Remember, when you use the higher taps, it is a trade off for capacity. in other words, you will not be able to fit as many fixtures on a transformer when using the higher taps (17-20v).

Mike M
07-06-2008, 10:40 PM
Tommy;

I have been installing transformers based on lamp wattage to not exceed 80% of the rated capacity. Are you saying the higher taps/long runs/12 gauge cable will decrease the lamp wattage I can use?

I have an amp probe, but is there a chart somewhere as a reference for this?

Thanks.

Chris J
07-06-2008, 10:54 PM
I think what he's trying to explain is this: With longer home runs, the resistance in the wire generates the equivalent of more wattage. If you use any of the voltage drop calculator software, you will see this measurement built into the calculations. As a desk estimate, you can use ohms law. For instance, lets assume you have 100w on 100' of 12ga home run. Watts / volts = amps, so 100 / 12 = 8.3 amps. Now, take the amps and mutiply by the correct voltage tap your in to get true (realized) watts. In this case you would be in the 14v tap, so: 14v x 8.3amps = 116.2 watts, not 100.
This is what's called a desk estimate, so it is not "exactly" what you might see with your amp meter. But it's close.

Mike M
07-06-2008, 11:15 PM
Thanks, Chris.

This is why they say not to use the full rating. I will play with the calculations to see how much I should be able to load up on the cable when using higher taps.

I will also check in the field with the amp probe.

The Lighting Geek
07-06-2008, 11:33 PM
Chris explained it better than I did.

The reason they say to use 80% is because NEC says so. If you amp probe all your home runs and they are under 16 amps (provided that you are using 12/2), your fine. Your transformer also has an amp rating as well. Amp probe the primary and make sure you are not exceeding that rating. That's really it. Try to keep it simple or you will over think it.

David Gretzmier
07-06-2008, 11:36 PM
I think different transformers play into the equation of what you can do on a 12 guage wire as well. I know that with FX trans, i can easily exceed every chart I have found on voltage drop, and it just amazes me. I know what it starts with and what I end with, and it does not make sense, but it works. by the same token, I am often shocked at how much voltage drop I get on Nightscaping trans. A load of 20 watts at 40 feet should not drop a new trans by 1/2 volt. yet it happens. Also, older trans seem to drop volts over time, with higher loaded trans tending to drop more voltage.

So I feel confident in recommending not to push things. In fact, it seems I've gotta go the other way- the first systems I put in 10-15 years ago with 8 guage wire that were ridiculously overbuilt and over "transed" have held up very well. When I sense I am close to 75-85% max on 12 guage, I go to 10 or 2 12's. when I am bidding systems I always seem to jump to a higher trans when I get close to 60-70% capacity. This has always paid dividends when I need to add lights later, and Ultimately I feel the systems that are overbuilt are the ones still working in 20-30 years.

The Lighting Geek
07-06-2008, 11:40 PM
well said David

Mike M
07-07-2008, 06:37 AM
Tommy,

What I am trying to do is go with more 12 than 10, and learning where the cut off margin should be.

Nate advocates this, and I'm not looking for info on trans load, but on realistic wire load numbers. NEC states "max" load, not "recommended."

There is a huge gap between the "recommended" load on 12 gauge as published in the CAST installation guide, and the "Max Load."

I was wondering where others tend to be, and I assume with the frequent use of #12, that Unique installers know how to get a lot from their wire while still staying under the max load.

The CAST manual says if you lamp over 100 watts, you should use #10. This is a nice, safe number, but way below the max.
Also, they say if your distance is over 100, you should also use #10, without mention of watts.

NightScenes
07-07-2008, 07:41 AM
Mike, remember that the NEC says max load on 12/2 is 20 amps but it also says that you can only load that 12/2 to 80% of that max.

The Lighting Geek
07-07-2008, 09:18 AM
what you are referring to is the same type of info I got back in the 80's when tf only had a 12v tap. You had to upsize wire for every 100' to compensate for voltage drop. It is a way for the occasional installer to get it right most of the time. But with advent of multi-tap tf's, you could now use higher taps instead of bigger wire. I only use 12/2 wire, a volt/ohm meter, and a amp probe. That said I also try to stay away from long home runs if I can.

nate mullen
07-07-2008, 09:26 AM
you really need to check out thew 24 volt system you can get 480 watts on 12/2 and better yet................use 14/2 wire which is good for 345 watts.............save $ and be green at the same time.

Pro-Scapes
07-07-2008, 02:00 PM
Tommy,

What I am trying to do is go with more 12 than 10, and learning where the cut off margin should be.

Nate advocates this, and I'm not looking for info on trans load, but on realistic wire load numbers. NEC states "max" load, not "recommended."

There is a huge gap between the "recommended" load on 12 gauge as published in the CAST installation guide, and the "Max Load."

I was wondering where others tend to be, and I assume with the frequent use of #12, that Unique installers know how to get a lot from their wire while still staying under the max load.

The CAST manual says if you lamp over 100 watts, you should use #10. This is a nice, safe number, but way below the max.
Also, they say if your distance is over 100, you should also use #10, without mention of watts.


Using a lower wire size decreases your effeciency. Your losing more wattage in the wire than you would with 10ga. When I explain why my systems are alot more than the other guys the subject of energy effecient always comes up.

As lighting proffesionals we should be asking clients if there any future plans for the property and help to anticipate future needs. If you can foresee explosive growth to a group of trees your lighting you should definatly leave plenty of avalible power to add on to your system in the future.

David Gretzmier
07-07-2008, 04:55 PM
Ok, I tend to use 120 watts max as a rule of thumb 40 feet and less. I can add a fixture or two or bump up all fixtures on wattage if necessary in the future. between 40 feet and 80 feet, I shoot for 80 watts. again, my max install new but leaves room for 1 or 2 fixtures at 20 watts. 80-130, 60 watts, but I'll do 70 watts on 2 35 watt fixtures. 130-180, 40 watts. on a single fixture, 20-35 watts, I have gone 250-300 feet away, but even at the 15 volt tap, nightscaping and ryco and several other existing transformers ( when I am just adding a light on existing system) just can't go that far without hitting 9 volts. FX is the only trans I have found that can take the really long runs, regardless of load or any chart.

You can pretend that what trans you use has nothing to do with what load you can put on 12 guage wire, but anyone with experience with different transformers will tell you otherwise. The reality is some transformers respond to loading much better than others, and that allows you to load more on a 12 guage wire.

If you don't believe me, do a test yourself. pick 3 different brands of transformers, use 150 feet of 12 guage loaded with 60 watts . check the voltage drop on the wire on each trans, testing voltage at the trans and at the fixture connection. You will find that the voltage drop will run from 1.5 to more than 3 volts in some cases. Perhaps if you see it yourself from a test you do yourself you will then believe wire can behave differently for different trans, and overbuilding systems is the way to go.

JoeyD
07-07-2008, 06:19 PM
we have done this test that David states above, and our units sustain voltage better then them all...and that includes the FX!

Our rule of thumb is 200ft 200w on 12/2 cable...that will require the 22v tap. we say 200w as a way to remember but it really is for 192w.

if you are using an FX trans or any other trans that is limited to 15v then your rule of thumb is now 100ft 100w on 12/2.

You can do so much in terms of distance with 12/2 cable when you have higher taps at your disposal. For example on a run of 12/2 at 500ft I can still power up 80w with a 22v tap!

Mike M
07-07-2008, 07:09 PM
Thanks, everyone.

The Unique chart was very helpful, and I'm not sure why Cast is so conservative with their recommendations being so far below the 80% of max load permitted by the NEC. CAST has the higher multi-tap transformers. ??

I went ahead and used all 12 gauge cable at my install today. This was a first, and I plan to pay more attention to my math and formulas in the future.

As for 24V, I think it is superior to 12V halogen-based systems.

Pro-Scapes
07-08-2008, 08:01 AM
We could argue this all day but bottom line tho when your doing long runs of 12ga your wasting trans capacity which makes you step up the trans size.

Example. Joeys 80w at 500 ft. That's 80w lamp load but around 150w total load with wire. use 10ga and your around 125w 8ga around 105 w..not to mention you can get 40 more watts of lamp load out there with the 10ga. See where this is going ?

Better yet have line voltage installed out there and be even more efficient.

All the wire savings comes at a cost of trans capacity and the wasting of power. If your going to run that far and cant put in line voltage then the 24v would be more efficient.

JoeyD
07-08-2008, 09:34 AM
I was making an example Billy......just like I can go 1000ft and still put 12v to 20w on 12/2 cable!!! Point is, you dont HAVE to go to bigger cable and you DONT HAVE to go to line voltage! Higher taps can allow you to do a lot with smaller wire. Effecient or not, I would love to see just how much more effecient the 10/2 really is...........splitting hairs. GIT R' DONE!

Chris J
07-08-2008, 07:01 PM
Here's a question, but not necessarily my opinion:
If you have very long runs, what would be better for you; hire an electrician to put in a circuit, or use the available methods, rent a trencher and make all the money instead of subs getting part of it? Just food for thought....

Mike M
07-08-2008, 10:34 PM
Chris, good point. Not only is it another cost, but another day to work with someone else's schedule.

Pro-Scapes
07-09-2008, 12:25 AM
Last couple of jobs we have installed the line voltage wire per the EC's spec and he has made the connections.

Joey is right you can go a long way with the higher taps but from what we have seen its usually cheaper to install the line voltage where needed than multiple long runs of wire and more transformers.

If I absolutly had to go that far with low voltage then I wouldnt hessitate to use Uniques 24v system.

nate mullen
07-09-2008, 08:49 AM
It's called value Engineering

Pro-Scapes
07-09-2008, 10:24 AM
For the project I just prewired... I will make a spread sheet on it detailing the cost of using a high tap trans vs using multiple 15v vs installing remote line voltage and estimate the project numbers that way.

I just put over 6000 feet of low voltage wire in the irrigation trenches and will be wiring the job in hubs at a later date. I will be using unique sub teraneans which will go to 22v but I still dont think I will need over 15v (many zones are yet to be determined based on final landscape installation)

Some may say its overbuilt but I see it as piece of mind should they decide to add more lights later. The transformers will also be sized at 50% capacity.

JoeyD
07-09-2008, 10:32 AM
I dont think anyone thinks that your way isnt the best way Billy. I myself think that you are doing you and your customers a great service by overbuilding the system. The point I was trying to convey is to show what is possible with higher taps. You may come across a situation where maybe a 300 or 400ft run of 12/2 is already existing, and with the higher taps you can utilize it.

Your way of installing is definitley the correct way, however sometimes it may be unneccesary should you be desinging your job just so that you dont have to go beyond 15v.

Again not to beat the dead horse but whats so wrong if you need 16v or 17v? I know you (Billy) have no problem but for those who read this my point to them is know what is available to you and dont make your job harder on yourself. If you have a situation where a 18v tap will save you a lot of time and money and not jeapordize your homeowners system then by golly use it!

NightScenes
07-09-2008, 11:10 AM
I always overbuild our systems. It sure does save a lot of time and effort when it comes time to update or add onto a system.

Pro-Scapes
07-10-2008, 07:25 AM
Way I see it is our clients are paying for something that is overbuilt.

Mike M
07-10-2008, 09:33 PM
Billy, not sure if you mean that as good or bad.

Obviously, it's good biz sense to speculate future needs, investing a little extra if you think there is a good chance it will save you a lot of time and money down the road. But what I'm trying to do is pay more attention to my measurements.

On this last job, I took the time to study the calculations, instead of conservative guestimation numbers, and realized I've been too safe using so much #10. I totally eliminated it, whereas just recently, I would have been using it for anything over 100 feet.

Seems to me the biggest bang for the buck is the higher multi-tap trans combined with smaller wire. The 24v system is better than the twelve for the same reason. What I need to see is LED's available in 24v in the future. Then things will really kick arse.

I see a future in wire configuration that is similar to line voltage; a few big circuits with multiple places to tap in leads. It's not just copper wire conservation, it's also less labor/trenching. Chaining will replace hubs as well as multiple runs.