You asked;
What's the best way to check 3-way switch that may be defective ?
Reply;
If you are trying to check a switch device itself you have two
ways of doing so. The accuracy is not exact due to a set of
contacts in the switch device showing enough contact to test ok
by a continuity tester or even a voltage tester. If the contacts
in that switch device is pitted with a poor connection when in
the on position the voltage or continuity will show ok until a
load is applied [resistance of a light fixture] then that poor
connection fails. This often is the case. I advise considering
the inexpesive nature of replacing those switches whether they be
single pole, three way, or even a four way, I would just replace
them with new ones. If you want to test a switch there is one
screw that is an odd color than the other two screws. This odd
color screw is the common. Place one prong of a continuity tester
on the odd colored screw and the second prong of the continuity
tester to each of the other two screws. One screw will show
continuity yet the other will not show continuity. When you turn
the three way switch to the other position on the toggle the
reverse will happen. The one that showed continuity will now not
show continuity and the one that didn't show continuity will now
show continuity. The first prong stays on the odd colored screw
throughout both tests.
The second way to test a three way switch is to use a voltage
tester. Connect 120 hot line to the odd colored screw. Touch the
first voltage tester prong to a white grounded conductor then
touch the second voltage tester prong to the two empty screws.
The voltage will show on one and again if you flip the toggle of
that switch to the other position then the other screw will show
voltage.
On a three way switch the two screws that are the same color are
called the travelers. Reason is that the voltage travels through
one or the other at all times cycling back and forth as you
change the toggle position of the three way switch.
You asked;
How about a circuit with a 4-way switch ?
Now we have a different question that may be interpreted two ways
as a question, read on.
To test a four way switch you will find to screws one color and
two screws a different color. The continuity passes across the 4
way switch to the oppisit side and back as you change positions
of the toggle on the four ways switch. A four way switch is
tested in the same method as above only you have two three way
switches and two commons in the same switch device. The first
prong touches the common and test as above. If that tests good
then the first prong of the tester switches sides to the other
common of the same switch. The two commons are always in contact
with the travelers on the other end of the 4 way switch device
where the second commmon is not in contact and they reverse back
and forth between commons touching that common screw.
The levers in a three ways switch device has a contact point on
each side of that lever and moves back and forth between the two
traveler screws as the toggle of that three way switch changes
positions.
The levers in a four way switch device is in an X form same as
two three way switch levers in the same switch device.
Now if your switches test good we have a picture style scematic
of three and four way switch systems of each wiring designs
available on both three and four way switch systems on this
homewiring home site. Just click on the link showing home wiring
home page above on this page and then you should see the three
and four way links there. Pick the schematic that you switch
system is wired like and follow the picture as you test out your
system in you home.
If you need more help try to be more specific what your problem
is and we will try to be more explicit as you explain your info.
Let us know how you come out.
Good Luck
Wg
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