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Old 03-01-2013, 03:07 PM
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JimLewis JimLewis is online now
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N.E.C. (National Electric Code) - As It Relates to Low Voltage Lighting

I was in a lighting class recently and they went over some installation rules from the NEC. Some of the rules I hard heard before and forgot. Other rules I hadn't even ever heard before. So I thought I'd start a thread. I'd like to be clear on what the main NEC rules are that we should all know when doing outdoor low-voltage lighting. I'll start with a few of the ones I remember from this class and then please continue with other NEC rules that you think are relevant.
  • No low-voltage light fixtures witin 10' of a pool or sauna.
  • Cannot use anything less than 12 gauge wire in a low-voltage system
  • Wire must be buried at least 4" deep and in dirt (not mulch).
  • Any wire going through a wall must be in a conduit
  • When installing fixtures in water, the transformer must be listed/rated as a swimming pool or spa transformer

Now the class was a few months back. And I'm going off memory too. So if I got some of this wrong, please correct me. Also, I'm not the one who said this stuff, it was the trainer, from one of the lighting manufacturers.

So add to the list please!
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Last edited by JimLewis; 03-01-2013 at 03:12 PM.
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Old 03-01-2013, 05:18 PM
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I couldn't find the entire Article 411 code online, but I am pretty sure the wire size uou listed must be incorrect. Most of our landscape lighting fixtures come with a 16 gauge lead. Also, the AOLP guidelines mention landscape lighting wire as small as 18 gauge.
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Last edited by starry night; 03-01-2013 at 05:22 PM.
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Old 03-01-2013, 10:00 PM
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WARNING: According to the National Electrical
Code (NEC) all fixtures in or within 10 feet of
water (including waterfalls, ponds and other
type of water features) must be powered
by a pool and spa rated transformer. Vista
Transformers meet this rating with the following
modification. In addition to this modification,
transformers must be installed in accordance
with the National Electrical Code (NEC) and
local codes. Failure to do so will void the
warranty and may result in serious injury and/or
damage to the transformer.

This is straight from the instruction manual that comes with Vista's MT series transformers. I did a job where I had one light 7' from the pool and another 9' and it passed with the MT transformer.

This is from an article on the web:
Section 680.22(B)(4) permits luminaires to be installed within 5 to 10 feet horizontally of the poolís edge only where a ground-fault circuit interrupter (GFCI) protects the luminaires. Since low-voltage landscape luminaires are supplied by a low-voltage power supply, such as a transformer, providing GFCI protection on the primary side of an isolation transformer will not provide GFCI protection on the secondary side. GFCI devices will not operate at the 15-volts or less supplied by the secondary of the power supply. This leaves only two options: one is to locate all low-voltage landscape lighting at least 10 feet from the pool or fountain edge; or, two, to use a special power supply.
There are low-voltage lighting power units that are marked ďFor Use with Submersible Fixtures or Submersible Pumps.Ē In this case, a special transformer is used that complies with the requirements in 680.23 for underwater luminaires installed below the normal water level of the pool. This transformer is specifically listed for this use and is an isolated winding type transformer with an ungrounded secondary similar to the low-voltage landscape lighting transformer, as required by 411.5(B). The low-voltage pool lighting transformer has one additional feature in its design. It has a grounded metal barrier or shield between the primary and the secondary. This metal barrier or shield prevents a direct internal short between the primary and the secondary of the transformer. If a short does occur on the primary side, it will short to the metal shield and the primary overcurrent protective device will operate. If a short develops on the secondary side to the shield, the secondary overcurrent protective device, if provided, will operate. If there isnít a secondary overcurrent protective device and the primary is providing protection through the transformer, the primary device should operate
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Old 03-01-2013, 11:32 PM
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Quote:
Originally Posted by starry night View Post
I couldn't find the entire Article 411 code online, but I am pretty sure the wire size uou listed must be incorrect. Most of our landscape lighting fixtures come with a 16 gauge lead. Also, the AOLP guidelines mention landscape lighting wire as small as 18 gauge.
Right. I understand that most fixtures don't come stock with 12g wire. Obviously, I've seen a lot of those fixtures too. And that's the first question I asked as well. This was one of Kichler's lead designers/engineers who is now their national trainer, by the way. And that's the first question I asked him after the class. If we have to use 12g wire, then why do your fixtures come with the smaller wire?

It's a complicated explanation of why this rule is in effect, from what I understand. And I'm just taking this from what I heard from one person. I may not be able to explain it correctly. But I'll try my best to explain it how I understood it; Transformers have internal breakers in them, or at least some do. Not the breakers we see when we take the cover off. This breaker is way inside, in the part you cannot see. This breaker turns off the transformer if it gets too hot, or too much amperage. So let's say that number is 15 amps. At 150 feet, 12g wire can safely handle 15 amps all the way back to the transformer. So if it gets over 15 amps, it will trip this breaker. And let's say there's a pathway light out at around 150 feet. And someone backs into it with a car on the way out of the driveway. So now the pathway light is broken, leaning over, and the wires are shorting/sparking. If you had 12g wire all the way up to it, it would start to draw more than 15 amps, and when this draw hit the transformer it would trip the breaker and turn off the transformer. That way, the transformer notices the danger and turns itself off, hence avoiding danger and maybe a fire. But let's say you didn't use 12g wire. You used 16 gauge wire. So now that same fixture is broken/shorting/sparking. But since the 16g wire you installed cannot handle a 15 amp load, it cannot draw the 15 amps that the short is trying to cause. It only draws 10 or 11 amps. So the transformer doesn't trip. It doesn't realize there's a problem, because your wire isn't big enough to basically "report" the problem back to the transformer. So the transformer just keeps sending the electricity out there, not knowing there's a problem down line. It just keeps running and running, causing the fixture to short/spark, etc. even more. Now we have a problem.

That's how it was explained to me. And that's why he said NEC requires 12g wire. Now maybe it's more complicated than that. Maybe you only have to use 12g wire on transformers that are set to trip at 15 amps. I don't know. Or maybe the law says that you can use whatever wire you want, as long as it's strong enough to carry the draw that the transformer needs to trip, in case of a problem. All I know is he just said we need to be installing 12g wire or larger. Nothing smaller.

As to why the fixtures use smaller wire? Well, I gather that it's because those leads are really short. He said that's why they keep their leads short at Kichler. Because they can carry a 15 amp draw (or whatever the number is) for a short distance. But they couldn't carry it back 150 ft. So I guess it's okay to use a smaller wire as long as it's just a little bit.

I don't know any of this for sure. This is just what I heard from a guy who is an engineer at a lighting company. And I knew he understood all this a lot more than I did.
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Old 03-02-2013, 11:21 AM
GreenLight GreenLight is offline
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At times, the nec not only seems ambiguous, but sometimes hypocritical. They will list open air well lights with par 36 bulbs that have exposed connections and carry bulbs that can be up to 75 watts (an exposed 75 watt bulb alone covered by some really dry leaves comes across as risky to me). I have done repairs on well lights after heavy rains where the connections are still wet from sitting in water and not being able to drain fast enough to avoid potting the water. The Nec also has a bunch of rules that bounce between temporary and permanent connections.

You can drape 120 volt christmas lights over trees on the inside and out, hang them from your gutters, etc, etc as long as it's only a "temporary" application. What is temporary, 1 day or 3 months?

As for the 12 gauge wire requirements, that's new to me, but doesn't surprise me. Kind of goes against the practice of 25 foot leads that many manus use, but im not sure what the rules are. From what I have seen on the NEC requirements, permanent low voltage lighting systems require 6 inch depth, plus 18 inch depth under hardscapes. I have seen a few commercial jobs that are close to this practice, but probably 1 out of 50 residential jobs that are. Im not saying that this makes it ok, im just saying.
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Old 03-02-2013, 11:22 AM
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Jim,

There was a good session on UL1838 and NEC at the AOLP conference. You've got a couple of these wrong, you can use smaller than 12 gauge wire in an LVL system, you just need to make sure the fuse or breaker is sized correctly for it. If you have a 25A breaker, you need 12ga wire.

The burial depth is actually 6" below grade. Grade is the dirt level, like you said, not mulch.

That 18" under hardscape is if it's not in a conduit. You can go 6" if you use a rigid conduit.
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Old 03-02-2013, 01:22 PM
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Thank you Bernie! Yes, that is the one I was referring to. 12g wire required if your transformer has a 25a breaker. I didn't get all the details exactly right. But I knew I heard something like that.

I figure it's just safer to do use 12g or greater anyway.....

That's another one I need to keep in mind - use conduit if we go under sidewalks!

Thanks for correcting me on these items.

Anything else discussed in that meeting? Other NEC rules we need to keep in mind?
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Last edited by JimLewis; 03-02-2013 at 01:29 PM.
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Old 03-04-2013, 01:40 AM
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The AOLP session covered some of the same topics, more about UL 1838 and how it applies to what we do.

The 12ga wire issue was an eye-opener for me as well. Here's how I now see it: (please fill me in if I'm wrong...I don't want to go to the next conference and see I've screwed it up for another year!)

You cannot use wire that is rated at less than the current rating of the circuit protection of the circuit. So, 25A breakers need to be at least 12ga.

The fixture wires are much smaller (18ga or 20ga sometimes), but should be minimized (trimmed off) to not be excessively long.

25' fixture leads are fine IF they are tied into a hub that is fused, with the fuse being rated at no more than the load rating of the wire. So, if using 16ga 25' leads, your hub fuse cannot be more than 12.5A (the amp rating of 16ga wire) correct?

This is the problem I have with certain manufacturers that do not provide secondary protection at the transformer. If using a 600w transformer and you only have a 5A fuse on the primary, would you not need to use wire rated at no less than that amount on the secondary, or 50A, which would mean you can use no less than 8ga wire? Maybe thats why I have seen so many of them burn up 12ga wires.

In order to be able to use 12 guage main runs, and 16ga branch runs, you'll need a 25A breaker, with a 12.5A fuse at the hub, which would in effect be tertiary circuit protection (primary being the panel breaker, secondary being the 25A low-voltage breaker).

Now, does the 80% rule not apply to this? If so, the breaker would have to be rated for 20A to use 12ga wire would it not? Therefore any load on the 25A breaker would need to be on 10ga or larger wire runs?
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Old 03-04-2013, 09:17 AM
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Andy,

You got it. Jack said something about the 80% rule only applying on the primary side and it's already built in at the panel (14ga wire being on a 15A breaker even though it can carry 20A). I'm not entirely clear on this though.

I've been using 16ga main runs on some small jobs recently (like 6 - 8 fixture jobs) and am going to just start putting a small fuse block in or next to the transformer so I can fuse those wires correctly. While the cost difference isn't that much on one job using 100' of wire, 12ga wire is 2x the cost of 16ga wire so over 10 jobs, it starts to add up.
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Old 03-04-2013, 08:34 PM
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Don't mean to hijack or get off topic, just a fyi.

Is the AOLP lobbying Texas legislature on members behalf for the potential of having to have a Texas Residential Appliance Installers License to install repair any low voltage systems. There have been rumblings heard. They have already hit the pool service/repair industry in Texas a couple of years ago. Stay informed and protect your interest.

State Info
http://www.license.state.tx.us/electricians/elecfaq.htm

Pool Industry Lobby Info
http://www.apectexas.org/index.html
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