How to Troubleshoot a Low Voltage Lighting System with a Clamp Multimeter

It seems like a good place to to
develop some test topics. Mostly, we’re going to use the slideshow to introduce
the concepts and give some diagrammatic kind of stuff you can only do in a
slideshow, but I’ve got a table top here with a little lighting system set up so
I can show you how the principle meter we’re going to use gets applied for
this kind of testing. We’ll carry on here. I want to cover key electrical concepts. Some folks that are listening to
this probably will have been using lighting systems and electrical stuff
before, they know it. Some people it’s brand new, they need to understand some
concepts. Some folks just want to learn some more about it so we’re going to
make sure we touch bases on the the simple underlying concepts. We’re
also going to touch base on the lighting systems that are used. A couple of
primary differences in lighting systems and landscaping in the
low-voltage realm. Today we’re talking about low voltage, not 120 volt
systems, but more like 12 volt systems. LED and incandescent lighting is
used in both of those and the testing techniques are a little bit
different. And then we’re going to just talk a little bit about
troubleshooting and how to use a meter to find things that are wrong or right,
that matters. Since we’re testing, there must be something wrong. Well not always,
of course, we’re doing a health check on the system that seems to be
working, making sure the design is okay before you turn it over to someone. But
often, there’s a problem and that’s why we’re doing testing. The whole system can be
dark. That’s an easy one, usually there’s a single point issue somewhere you can
figure out. You might have one light fixture that isn’t working
and you try to change the bulb and it didn’t help so you’re down to more
troubleshooting. Out and down the line one part of the system is dimmer than
another, that’s a very common kind of problem that happens in incandescent
systems, fuses and breakers are popping. Tasks that you are getting stuck with in lighting systems pretty commonly if you’re troubleshooting. So of course, one
of the problems is that this usually happens in daylight. Troubleshooting
a lighting system in broad daylight is a little more difficult. That’s one of the
reasons you can use a meter. A meter helps you see things that are not
normally visible, of course; you’re in daylight. The equipment list that
we’re talking about today is very much simpler than some of the other
topics we’ve used. We’re talking about landscape lighting and in this case, a clamp-on voltage and current multimeter is the best tool. Not to say you can’t get by, as
I show my diagram there with a couple of aides that can help you figure out some
stuff pretty quickly without delving into the system.
A simple multimeter like a little Pro30, which is an example I use because it’s
commonly available and our distributor system is able to check voltage and
resistance and that sort of thing pretty simply, but it doesn’t do some of the
tricks that you need to do so we really recommend one of these automatic clamp
multimeters. I show some voltage cubes there, those are handy for
checking AC outlets which is something that we often have to do. I thought it
was worthwhile mentioning the parallels between an irrigation system and a
lighting system, especially for people that are water people. In our
industry, green industry, irrigators, our water and plant people, they’re not
lighting electrical people and if you’re crossing between those two disciplines
this can be a useful analogy. In an irrigation system, we’re taking something
that is, let’s see if I can turn on my little pointer here, we’re going from a main
water line and if you’re taking water from a system somewhere, piping it down and
spraying it out onto the ground somewhere and in between has a
lot of things that control the spring, controls a lot of aspects of it, all the
way down to where water sprays out onto our target at the end. Lighting is the
same kind of thing. We’re taking voltages from the primary system and running it
downstream through some wires and spring light out on stuff at the end. It’s a
pretty common kind of concepts here. I’ll show you in a second what I mean by that
in just a second here. So, those two systems are very much
similar in a lot of ways. There are analogies between them. This slide here
illustrates some of that stuff. In an irrigation system, there’s a lot of stuff
kinda in between the stuff we fiddle around with, especially when chasing, but the idea is to keep soil moisture constant in a particular area. The way we
do that is we take a reservoir of water and we run a pipe out to the area we’re
trying to do it and this reservoir is under pressure. If we make a hole in the pipe at the right place, then water will
shoot out and make the ground wet and that is what’s going on here. We have a
pipe that has a pressure on it and when there’s a hole in the pipe, then flow
occurs and water flows out into our target area. In much the same way the
electrical system is doing the same thing. The reservoir is in watts
electrical power and we’re running it to the field on a pair of wires instead of
down a pipe but it’s pretty much the same thing. A voltage flow provides a
pressure at one end of the wire and if we make an opening, in this case, an
electrical loop down the wire, then current will flow. If that hole we
make is a lighting bulb system, then what happens is lumens of light spray out
onto buildings and plants. Ultimately this is what we’re working with here
today. We’re delivering lumens to the field. We’re talking a lot about
watts and resistance and voltage and different things but we just want light
to come out in the end. We have to keep those basic things in mind all the
time. This helps visualize a little bit, I
guess, because I have a diagram that I talk about the different things in the
chain. When we’re doing troubleshooting, we’re always working on kind of a
systematic thing going left to right, top to bottom. We’re working on different
bits in the system but what you see at the top there is what you’ll really see
in the field. You’ve got, typically, stainless steel or a black box hung on a
wall somewhere plugged into a 120 volt outlet. It’s got a bunch of stuff
under the cover and then we’ve got wires going out to the field to lighting
fixtures. So in typical fashion we would troubleshoot from the source of the
power out toward where we’re using the power. The diagram a little bit
below it there shows you kind of the same thing only in block
diagram. We’re starting with 120 volts. That can be interrupted by a breaker
which is another typical thing you check for. But in the transformer box, as it’s
known, we have a number of things that affect whether this system is
working right or not. It has a timer for, obviously, turning on the lights when you
want them to come on. It has a photocell so you can put in an automatic mode; if
it gets dark, the lights come on. You have the main power stuff that’s
going on including a circuit breaker or fuse, depending on the system. All
these things are happening inside that box and are worthy of troubleshooting
when you get down to it. Most of those things in the box can be checked by a
mark one eyeball. You make sure that the timer is plugged in, make sure that the photocells working, and swap it out if it doesn’t seem to be. Then
we’re into the field, looking at the light fixtures to see what’s going on
out there. Just by way of illustration, here is an example of the difference
between an LED and an incandescent lamp. There are quite a few important
differences here. One of them is that the incandescent lamps, which are the things
that have been used in systems for outdoor lighting systems for a long time,
are pretty hot. They consume a lot of power, they draw a lot of current on a
wire, they take a fair amount of heavy wire in order to keep the light
properly exposed and all the way along the chain. Now the LED systems, which are
becoming more popular, are more expensive but they have some real benefits and
you’ll see how that develops when we’re doing some of the testing stuff here.
They are more expensive to put in but they consume so much less power that the
wiring and cable and the system doesn’t have to be as robust. The kinds of
problems that occur in incandescent systems because of the heavy current
going to the bulbs, the bulbs at the end of the chain can be a little
bit darker and you can see that certain areas in your lighting system are not
quite as bright as others. That’s a real problem with a lighting system. What
people have been doing in many cases is replacing the incandescent fixtures with
LED fixtures and getting some of the same lighting effects without any of the
drawbacks. There are some drawbacks to that, as you know, because most of the
transformers people put in were made for the incandescent system but it’s not
really a danger; it’s something that is commonly done. This is kind of a geek
diagram. It’s because I’m a geek, I’m an electronics engineer, so I don’t know as
much about lighting and water and plants as you folks do but this is
one of the ways that I think about what’s happening in a lighting system.
From the left hand side to the right, if we’re going from the power source, the
transformer, out toward the field, what happens is the voltage we’re putting on
the cable starts to drop as we get out there and that voltage is the pressure. It’s like the cable is a kind of narrow pipe and we make the opening as large as we can economically, but the fact is that the
pressure drops as you get out into the field toward the lighting system. When
you’ve got a bunch of holes in there like lamps that are putting out light,
the drop in the pressure in the system is bigger and bigger the longer the run
is. So that analogy works here. If you have a 12-volt system, you’re putting 12
volts on a pair of wires and it’s going out to the field, you can see in the
diagram that little solid line in the middle area illustrates how the voltage
drops as you get out and the yellow bar shows the incandescent operating range.
If you have an incandescent lighting system, you have to keep the voltages in
that range of say, 10.8-12 volts or the bulbs don’t work
right. So as you go out into the field, make sure the voltage stays up
high enough and you can do that by making the wire heavier, putting fewer
lamps on it, by splitting the system into two different tap drops, that kind
of thing. I won’t go into this very much right now but it is a way of
illustrating how the transformer can be overloaded, how the wire can be
overloaded, and how you fix it. So we’re delivering voltage at the end of a wire.
An important concept you’ll hear, and there are some really pretty good, I
think, kind of lighting tutorials and things out there on YouTube and I
have an example of one later on that Unique Lighting put out that I went to and
that I kind of liked. What you’ll find is a lot of these tutorials
talk about the Ohm’s law. Ohm’s law is the fundamental electrical relationship
law that is used in these systems. Typically what you mean here, one
example, is voltage is equal to the current times the resistance. But what
does that mean in real terms? That means that a fixture that’s drawing three
amperes of current down 100 feet of number 12-gauge wire is going to lose a
volt and pressure from one end to the other by the time it gets down there. That’s what Ohm’s law means there, and there’s a little table and
calculation thing you can do. Pick the wire, 12 gauge 2-conductor wire from so
and so, and this is a 35 watt fixture I’ve got from Unique or someone.
So how much voltage drop is there going to be? Is it going to be okay?:
Ohm’s law. Second version of Ohm’s law, right below it, it shows that the power
is equal to the current times the voltage. So more voltage, more current,
more power. In this case you could say, “Well, I’ve got a transformer that’s rated
at 300 watts and it can put out… and the rate on these things typically is they say 80 percent of the transformer’s capability is all you should really try
to use. In this example here, this P equals I times V, 300 watt transformer
can supply about 20 amps of 12 volts with a little bit of margin. So don’t
plan on putting more than 20 amps worth of bulbs out on the end of the string
there and actually have the transformer work without sagging once you start to
load it up with lights. Even if you have the wire done properly, you’ll have
the voltage sagging and then you’ll have dimness in the system. So one of the ways
that people deal with this and I mention this partly because when I showed the
equipment list earlier, we’re just talking about a meter. You may sometimes
need to have a locator. A wire locator is a very useful thing in almost any
outdoor buried system especially. You can’t see what’s going on. Even in
lighting systems that are very commonly not very deep, they’re right along the
edge of a sidewalk, they’re jammed down with a sod shovel, or
something like that. You still have to spot them and one of the reasons you
might have to track them out is not just to know where they go but whether
they’re organized differently. In order to deal with these lighting problems
with current and voltage distribution, that sort of thing,
sometimes they are laid out in a way that causes them to tee off some of the
lights so that they’re not as far from the transformer electrically to split in
multiple loads, to put in the hubs. Hubs are a popular deal.
You work from the transformer, you run one big fat wire out to a distribution hub
and then run smaller wires to the individual lights, another popular method.
But you kind of have to know it’s organized like that when you start going
into the field and troubleshooting, trying to figure out where things
are connected. This is the end result. I like this picture. One of the things
that is good about irrigation is when you see these beautiful turf situations
with hedges and palm trees and that’s the end result. You’re just putting some
moisture in the ground and what happens, you get this beautiful green stuff. Same
thing with lighting. You spray some lumens on buildings and
plants and it looks great. So, you know, even if you’re having some trouble
getting this stuff in, remember what it looks like in the end. And it only looks
this way in the dark, by the way, so that’s another one of our challenges.
Equipment list: There’s some other things you can use
but really you’re down to having a clamp meter if you’re going to be
working with lighting systems. Best, if you’re working with LED systems, as
you’ll see, we need to have a true RMS clamp meter. The clamp meter allows
us to measure currents without disrupting any of the circuit very
easily. This is what you’ll see anyway, when you’re down there troubleshooting,
this is the source of our power and probably where we always start our
troubleshooting. This is a transformer unit for a lighting system, kind
of a simple one actually, not a very big one. But it has the bits and pieces
that we’re talking about here. Behind of that metal panel in that side,
that stainless steel box, is a transformer that steps down the line
voltage ten to one. It takes 120 volts from the wall outlet, converts it to 12
volts or approximately 12 volts, and puts it out on a little terminal strip
on the back and that’s where you connect the wiring that goes to the field. But in
between, our timers and photocells commonly. You can have one of these
systems that doesn’t have the timers inside the box. Maybe you don’t use a light and dark kind of a photocell, but
those things are plugged into the face of this example here which is kind of
common. If you’re having problems with the timer or with the photocell you
may have interrupted system problems too. This is the practical thing that
we’re looking at. The reason we like this clamp meter is that
these multimeters do resistance, voltage and current. That’s kind of the
definition of a multimeter, they measure all those things. In our case, our
primary concern, we want to be able to look at voltage because voltage is
going to tell us the health of our system. You can decide from the voltage
whether your currents are too high sometimes. It’s good to be able to
measure the currents though because you can clamp on, you can check the total
current, check whether you’ve over rated the system. If you’re popping
fuses, for example, a very good way of troubleshooting where the currents are going and
what’s causing the problem. You can measure resistance with these things but
for today, for lighting, resistance is only particularly useful and checking an
incandescent bulb or a fuse. LEDs can’t be tested with a meter like this.
I’ll illustrate that in just a second. Here’s the deal when we’re doing some
troubleshooting. Here’s my diagram again, we’re moving from the power source out towards the field, checking out if the main powers okay, checking all the stuff in-between, and making sure that the current and the cable is up
to snuff; not too high, not too low. If you’ve got a dead fixture or
interruption in the cable, you can find out where it is by clamping over the cable
and deciding where the current is stopped or where it’s excessive. All the way out at the end, we check the voltage on the fixture and I’ll show you
in a second what we mean by that. So one, two, three, four, five. Check out the source,
under 20 volts, make sure the timers and stuff in the box is alright, the
voltage is coming out of the box, make sure that the wire current and the
wire isn’t way over or way under what you expect it to be, and then go all the way
to the end of the cable and make sure it’s still 11 volts at the end of the cable. If it’s
not, you might be having some problems. What I want to do just quickly here is,
it’s going to take me just a second to switch over, I’ve got a table set up with
some lighting things on here and it’s always good to see the physical things
instead of looking at slides all day. That’s my feeling so let me switch over on
my camera to my table. It’ll take just a second to come up. Here we go. I hope you
can see that alright. What I’ve got here is not a full-up kind of
commercial lighting system, I went to Home Depot and got a Malibu system.
Here’s the transformer, it does have the features of the one I just showed in the
sense that it has a timer and it has a photocell. It’s a 200 watt model and it’s
just a Malibu thing like you’ll use in a residential circumstance but it helps me
to illustrate the stuff that we’re talking about here. This is a
clamp multimeter. This one is probably my favorite one, it’s our Pro93 and we
actually sell this at Armada but you can get different meters and different
places to do this job. This device allows me to clamp over a cable
and measure current. It has test leads on it that allow me to measure a voltage
and resistance. The voltages again is a very specially important thing and I’ll
make some measurements here just to show you in a second. So what I’ve got on the
table, confused as it is, I’ve got a main cable going to the field, I have a lighting fixture in midstream, and
I have a lighting fixture at the very end of the of the channel. The Malibu
system uses this kind of squeeze-on lighting connection. It comes with a
pigtail. All these lighting fixtures come with pigtails that suit
some connection system or another. This one’s a squeeze-on, this works pretty
well for things like residential applications and some commercial
applications. You slide this thing over the wire and you squeeze it down
and the teeth bite into the wire and make an electrical connection.
In a really wet situation, it’s probably not the best way to go but one of the
interesting things about this is that this end of the cable, what it does is
leaves the cable exposed, if you can see that. The electrical cable is
exposed to the air at the end. But it allows us to check the voltage, just
handily enough, and for that matter I can use it to actually check an
LED bulb. Let me just illustrate how this works briefly. I kick on the system;
boom, on come the lights. This is a health check because we don’t have
trouble in this system right now. We’re just going to use it to illustrate what
things we’re looking at. I’m going to take my clamp meter and put it
in AC amps because that’s the critical current measurement that we’re doing. Here at my main system, I’ve got the cable going to the field. Now I
notice there, of course, are two wire cables because all electrical
currents work in loops and in order for us to measure the current in the
cable, we need to clamp over one side so we don’t have a balanced system,
we can actually measure the current that’s flowing. Here you can see, I
clamped over this thing and I’ve got just under 2 amps, 1.9 something amps, going out to the field, running two fixtures. This is kind of interesting and
this is a true RMS meter which is actually measuring the kind
of heat power that’s being delivered to the field.
It’s very true and accurate to the wattage of the system and it’s a good
thing to have a true RMS meter. One of the things about this is that these
fixtures are rated, you know, it’s seven and a half watts. Malibu rates these
fixtures and they’re drawing an amp at 12 volts. So kind of interesting. Don’t believe the specs on everything. If you’re having some problems, you might
suspect that some of these fixtures are drawing more power than they’re
supposed to. Let me then switch over, I can go out into the field, I can go all
the way down to the last fixture in the field and do the same thing. Clamp over the cable and let the meter settle down here, a
little less than an amp at this fixture. These two fixtures are slightly
different and one is drawing a little more power than the other. But very quick and
easy measurement. Now, I’ve been able to check that okay, I’ve got two amps coming
from the head end and it’s drawn about an amp out at the pigtail at each of the
fixtures. If I’d had some kind of a fault where I had a corroded junction,
something like that, the current would have been missing. You could figure
out at what fixture the current went missing, even in the daylight
and by using the clamp meter. So, great way of doing some of that kind of
troubleshooting. Here’s an example of a LED lamp. A LED lamp is
physically, you know, kind of similar to some of the others you might see in incandescent. If you look at the face of it, you can see little chip
lights on the inside. These are difficult to test. In an incandescent
system I can put this meter in the resistance mode and I should find a
short-circuit across the pins of an incandescent bulb, but an LED bulb is
different. It behaves different electronically. You need to put voltage on it to test it and this is one of the
reasons I like this system is it’s got exposed cable on the end. I can touch my
LED pins to the cable and if it’s a good bulb, I get light. Yeah, okay, that was a
good quick check. I could have also used a 9-volt battery. A 9-volt battery will
usually turn one of these on. It’s a good, quick way of checking them. Another way,
if I had a different kind of a system and I couldn’t test the voltage at the
at the tip ends of the wire here like it was handy, meters like this one, if you
can see, have a very kind of a sharp point on them. The inexpensive meters
don’t have a really penetrating type of point but these are almost needle tips.
If I was trying to check the voltage in this cable and I didn’t want to undo
all the stuff, all the the splices and what have you, you can literally take
these test probes, the voltage test probes from the meter, and jam them
right through the insulation. They’re sharp enough. So I can poke through the
black and the red across the two wires and read a voltage. Switching my scale
here of course, I go to AC volts and read the voltage on the cable. At the end of the cable, if you remember one of our very
specific checks, we want to make sure we have at least 11 volts at the end of the
cable for most kinds of wiring systems. That’s what this stuff looks like.
This is my favorite meter, it’s a clamp multimeter. I can use it to do all the
things that we need to do, powered by a couple of double-A batteries.
$270 class in user price for a meter like that.
You can pay $500-600 for one if you want but this is my favorite. We
have another one that measures true RMS that’s a little simpler, that’s another
fifty bucks less or so. But I like this one because I’m an engineer and it reads out three digits. So three decimal places, I like that stuff. Not everyone
wants to pay a little more for that. So that’s what the lighting system looks
like. We’ll just kick back here… So, that is a simple table top kind of
illustration of how the clamp meter works and the things you can do with it
using a Malibu, which is not, you know, most lighting folks go, “Oh, don’t use
Malibu.” But it works great and I got a good system from Home Depot for not
too much money so I think it illustrates those points pretty well. Again, clamp
multimeter. Voltage and current are important in this measurement and we can
clamp on and measure the current without opening any wires.
I like to take my sharp little probes that go around stabbing the wires, looking
for voltages and figuring out what’s good and bad in my system. I can check
resistance, that’s not so important. You can see when I want to check an LED bulb,
I need to put voltage on it to check it. Repeating a tip here, if you’re going to
measure current in these systems make sure you clamp
over one of the two wires, not over both wires and use a true RMS meter. A true
RMS meter like this, this is the simpler one that I show here. It happens to be
an Armada Pro91. It’s a true RMS clamp meter. It’s a computing meter; the currents and voltages in a LED lighting system are not
consistent and are not smooth enough for regular meters. You have to have a true
RMS meter that computes the current and the real power in the system. I mean, you can use all kinds of simple tools to do some basic
troubleshooting but if you really want to know how much power is being consumed
in the system and you’re having circuits pop or you’re having bulbs that are
under voltage, you need to use a true RMS meter. This next picture
kind of illustrates that pretty well I think. I use this lighting system
and I put three different meters on clamps around the same power
distribution cable and you can see that they all read a little differently. On
the left-hand side is a RMS meter. This is the system I just
showed you. It has 1.9 amperes worth of current going to field, two fixtures that
consume a little less than an amp apiece or close to an amp. That’s good.
It’s an RMS meter which tells me that I’m really measuring the
amount of power being drawn from the box. There’s my other favorite meter in the
middle, the Pro93. It has a little bit more significant readout. It reads 1.94
amperes but it’s true RMS and it’s telling me what’s really going on.
I’m happy with that. To illustrate what a regular clamp meter does, that Pro90, you can just barely read it over on the right hand side there. It’s reading a
1.4 amperes and based on the RMS measurement we just made, we know that
it’s almost 2 amps flowing in the system. That clamp meter, which is an averaging, non- RMS clamp meter, is reading 1.4. It’s
reading like 30% low. That is because of the weird waveforms that LED fixtures
have in power in the cable. So, understand that if you have one of these
meters and you’re going to use it, you know, you need to figure out it’s reading
about 30% low if you’re really trying to figure out what power is being consumed
there. So anyway, in the interest of keeping us within the half an hour, I appreciate
your joining us. I hope you join us in the future for another one of our
sessions. Here are some resources I’ll just touch on. YouTube, as I
said, has got lots of lighting troubleshooting and other demonstration
videos. Brian Quall from Unique Lighting, I went to one of his landscape
architect’s presentations on troubleshooting and there’s the
YouTube address there for the one but you could also search for him when
you get to the YouTube channel. For that matter, when you get to YouTube
you can search for our channel: ArmadaTech, We have over 20 videos that include
recordings of these Friday sessions that we do. So if you miss one and you want to see it again or someone else missed it or they care about lighting or really
care about ground faults, you can go back and see one of my Friday presentations.
Another place for application info, our site: A list of all our seminars, application notes, diagrams,
downloadable stuff. We’re also at On the web, We have datasheets and other product information available there. I am Jim Carefoot, I can be contacted at [email protected] One final note here, while I’m
switching over: Next week’s session is going to be discussing ground faults. Excuse me a second here, this thing just switched
over. I want to reiterate that we have this session again next week and
next week will be returning to ground fault location. How
to find a ground fault using an a-frame or ground fault locator. The week beyond that, we’ll be talking about more advanced locator features using
connectionless modes to do wire tracking and troubleshooting. So that can be of
interest, using clamps and antenna broadcast systems that are built into
the locators to track wires without having to expose the wires or the
connections. So with that, I thank you for attending today and we hope to see you
at a future session.

7 thoughts on “How to Troubleshoot a Low Voltage Lighting System with a Clamp Multimeter

  1. Darn, this starts great, but I was really hoping it would actually show how to test my transformer, not just tell me to test it. It's almost a sales pitch for how great a clamp multimeter is, rather than showing me how to test the voltage on my transformer. (I should already know how to do this, but when I get really wonky numbers that don't make sense, I verify online that I'm doing it right before I return the potentially broken transformer, and this video doesn't actually show HOW to troubleshoot. Oh well.

  2. Thank you for this! Just what I needed to analyze the LED issues for my landscape lights.

  3. Nothing about testing transformer in the video and very little trouble shooting

  4. Why did you set your meter to test AC current when the transformer is surely delivering DC current?

  5. LED are great for saving power, but I have yet to find LED bulbs/lights that are not too bright. Even the "warm glow" LED lights are far too stark white.

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