WBCCI – New England Unit
Wally Byam Caravan Club International, Inc.
Troubleshooting Electrical Circuits
“Half-Splitting Method”
This article was copied and modified, from EC&M magazine
November 2006 issue
Original article by Daryn Lewellyn, Lewellyn Technology, Inc.
Contrary to popular belief, the act of
troubleshooting is not always about your tools; it’s
often about your mind. Many people are too quick
to begin making some type of repair to their unit,
such as immediately replacing components, before
they have the first clue about what’s causing the
problem. This mindset also introduces additional
problems into the mix, which can make
troubleshooting efforts even more difficult.
Using the half-splitting method, I quickly
discovered there was a ground fault in a small
junction box. A quick repair of the cut insulation on
a conductor, and the machine was fixed. Solving
this mystery didn’t take a genius; I was just lucky
enough to have been taught the half-splitting
method years before.
Pure Probability. Let’s review an old card trick to
help demonstrate this method. Ask someone to pick
a card from a 52-card deck of standard playing
cards. By asking six “yes” or “no” questions, you
can figure out what card was picked. The first
question would be, “Is your card red?” Let’s say the
answer is “no.” Now we know the card is black,
having already eliminated 26 cards from the deck –
not too bad with one question. The next question,
“Is your card a club?” “Yes,” eliminating 13 more
cards. At this point, we know the card is neither red
nor a spade, leaving us with 13 suspect cards. You
ask, “With the ace being high, is your card a 7 or
below?” A “no” and we’re down to seven cards –
after asking only three questions. We now know the
card is a club (8 or higher). Half-split again by
asking if the card is a jack or higher, a “yes” takes
us down to four cards. Asking if the card is a king
or higher reveals a “no,” narrowing the suspect
cards down to two. The next question solves the
problem. “Is your card a queen?” Another “no,” and
we know the card is the jack of clubs. Asking six
questions eliminated 51 of the 52 cards.
If used properly, one method that’s been around for
years can save you valuable troubleshooting time,
and that’s the half-splitting method. The logic
behind this approach is simple. With every step in
the process, you eliminate approximately half the
circuit as the cause of the problem. Using this
divide-and-conquer philosophy, the first action item
might be as simple as asking a question or taking a
voltage or resistance measurement with a
multimeter.
Putting this approach into practice, remember one
instance when I was called to the scene of a
machine that was down. Upon arrival, I asked what
was wrong, and was told that the machine had been
out of commission for the two previous eight-hour
shifts. At this point, virtually everything had been
changed, including the programmable logic
controller, power supplies, and a motor drive. The
perplexed repairmen from the previous shift told me
that no matter what they did, the machine continued
to blow a small control fuse.
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WBCCI – New England Unit
Wally Byam Caravan Club International, Inc.
which can be very time consuming, you’ll want to
test for a complete circuit in the middle of the
switch run. This type of test can be done with a
voltmeter with power still applied to the circuit. Just
remember to follow your facility’s electrical safety
procedures and those outlined in NFPA 70E.
A good first step is to measure voltage across
the coil. If no voltage is present, but we know that
the circuit control voltage is functioning for other
parts of the same control circuit, this would lead us
to believe one of our 10 switches has a problem.
Leave one of your voltmeter leads on the relay coil
opposite the switches. Put the other lead in the
middle of the switches. Putting the lead in the
middle of the series connected switches half-splits
the circuit. If the circuit control voltage is still
present, then the five switches between that point
and the source are closed, leading you to believe the
problem is in the five switches between your
voltmeter leads.
With this one measurement, you’ve proven the
functionality of the other five switches. Your next
step is to half-split once again. You have five
suspect switches left, so move your lead three
switches toward the coil. If voltage is still present,
you have proven that those three switches are
functioning properly. You have two suspect
switches left – the two closest to the coil – so move
your lead between those two switches, half-splitting
once again. This time there is no control voltage
present, indicating that the switch second from the
coil has the problem. This could be a switch out of
adjustment, a broken or loose wire, a safety door
open, or pressure too high in the system. Although
you still have to find out what is wrong with this
switch and fix it, at least you’ve identified the
culprit.
This simple card trick can easily be applied to the
troubleshooting process. Simply look at a circuit as
a group of individual components. You know one of
them is not functioning properly. Therefore, what
questions can you ask that will begin to eliminate
the largest group of components?
Sample situations – Let’s take a look at some
electrically focused hypothetical examples to
further explain this method.
Example 1 – Say you’re working with a piece of
equipment with 20 doors. For safety reasons, all of
these doors must be closed in order for the machine
to operate. Each door has a normally open limit
switch that is held closed when the doors are closed.
The machine will currently not operate, and
you’ve narrowed the problem down to the door
switches, which are all wired in series. Rather than
checking each switch, check 10 of them first. This
could be done with the power locked out using a
simple continuity test. If the first 10 switches show
continuity, they are not the problem. You have 10
left, so half-split those by checking five of them. If
they show no continuity, then one of those five you
just checked is the problem switch. Half-split those
by checking three, then two, then one – and you’re
there.
Example 2 – Trouble is reported on a machine
that will not start. A “circuit enable” light on the
control cabinet tells you that the start or circuit
enable relay is not energized.
This piece of equipment has 10 safety switches
that have to have their contacts in the closed
position before the machine can operate. These
switches are all wired in series and might consist of
pressure switches, flow switches, limit switches,
and temperature switches.
When all of these contacts are closed, the coil of
the start relay will energize. Rather than locating
and testing each individual switch one at a time,
Safety First – Whenever you’re troubleshooting, it
is extremely important that you follow all safety
precautions and procedures. Live circuit (120 volt
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WBCCI – New England Unit
Wally Byam Caravan Club International, Inc.
Putting this approach into practice with my
Airstream, I recently had a grounded circuit in my
trailers running lights. Using the half-splitting
method, I quickly discovered there was a ground in
the license plate light wire. After a quick repair of
the wire insulation, which had chafed on a sharp
edge at the license plate bracket, we were good to
go. I also was lucky enough to have been taught the
half-splitting method years ago.
and higher) troubleshooting is very dangerous and
should only be carried out by qualified individuals.
Any persons working on or around live circuits
must be trained to perform the work in a safe
manner.
Although seemingly simplistic on the surface, the
half-splitting method of troubleshooting electrical
circuits can often uncover commonsense cures for
what may initially appear to be a complex problem.
My Airstream Situation – Let’s take a look at the
problem I had with the running lights on my trailer.
The running lights were not working, I checked and
the fuse in the truck had blown. My first half-split, I
disconnected the trailer and replaced the fuse, the
fuse held eliminating the tow vehicle as part of the
problem. Next I took out the Airstream manual to
check the wiring diagrams. After finding the correct
diagram I discovered the color of wire used for the
running lights. The next half-split was removing
one of the vent trims (I new the wiring ran adjacent
to the vent), found the proper color wire and cut it. I
found that the circuit from the trailer connector to
the wire I cut was clear, so I knew the ground was
beyond my split. As most of you know access to
wiring in an Airstream trailer is very limited. At this
point I could not make any other half-splits, so I did
the next best thing. I knew the tail light assemblies
each have 2 running lights. I pulled out the tail light
assemblies one at a time and everything looked
good but the circuit was still shorted. This
eliminated another 4 lights. Now I was down to the
last 4 lights, all single lights with out access to
wiring between them. I choose poorly and checked
each of the upper 3 marker lights first, all were fine.
Then I finally pulled out the last light the license
plate light and found about 18” of wire with the
insulation burnt off. I replaced the burnt section of
wire back to a splice, where it was chafed and all
repaired and working.
Applying this approach. It may not always be parts
of a circuit you’re trying to eliminate. Instead, it
may be entire parts of a machine or process. An
example of this is when you first arrive at a piece of
equipment, and you ask yourself if the problem is
electrical or mechanical. This obvious first step is
often overlooked. An example might be a conveyor
belt that will not move when started. If the conveyor
belt will not move but the drive motor is turning,
this could indicate a broken belt or problem with a
pulley.
Half-splitting can be used to find many electrical
problems aside from open switches. Removing parts
of the circuit and testing to see if the fault is still
present can also be used to find ground faults. Halfsplitting can also be used in all types of circuits, not
just series-wired switches. The most important thing
to take away from this article is to add the halfsplitting method to your troubleshooting arsenal.
Trust me when I say – it will save you hours of time
spent in vain.
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