A: More than one mat can be connected quite easily but
there are few important rules to follow:
ONLY just like shown below for two mats (4
connecting wires) and Elektra UCCG programmable thermostat:
+ Ground from the box
4 cold wires
PARALLEL CONNECTION for 2 Elektra MG mats and
Elektra-Microline MTC2991 thermostat with floor temperature
The thermostat floor temp. sensor flex conduit is approx 1/4"
thick so the small channel for it will be needed. This will be the same as when
installing just one mat or cable.
Note the plugged up thermostat floor temp. sensor flex conduit.
Make sure the sensor is all the way in. Note the distance kept between heating
wires of both mats. One wire is right next to the conduit housing the thermostat
floor temperature sensor.
2. Observe the maximum Amperage draw of the
mats. Both thermostats are limited to 16 Amps! Check or ask your
electrician to check the allowable load on the particular circuit.
If the circut allows for more Amperes than the thermostat then
the contactor is needed.
Typical situation when the contactor will be needed is for
instance when large floor area is to be covered by the heating mats.
Contactors come in many shapes and forms.
A contactor or relay is an electrical device that takes a
control signal usually 12 volts DC, or 24, 120, 208-230 volts AC and creates a
magnetic field to pull in a set of contacts that controls another device that
may or may not get its electrical power from the same circuit.
Contactor is like a switch in the OFF position. When
appropriate voltage is applied to the contactor's coil terminals, 'the switch
turns itself ON' making the connection between the power supply and the
In his case the coil voltage is applied by the thermostat
calling for the heat.
Contactor is meant to take the load of the control device
- a thermostat in this case. Please note how the contacts of the
thermostat (where normally the floor heating would be hooked up), are
connected to the coil of the contactor and the contactor is handling the
connection between the power source (GRAY wire) and the load of the
floor heating mats (4 white cords) in this case.
FIVE MD ELEKTRA in-floor heating mats controlled by one
programmable thermostat by way of Furnas Definite Purpose Contactor.
Thermostat floor temp.
sensor Five MD
Two parameters of the definite purpose contactors are
If the thermostat voltage is 120V then the contactor's
coil voltage HAS TO BE 120V, but the mat(s) can be
240V BUT CONNECTED BY WAY OF A CONTACTOR TO 240V power source. The
same can be said about 120V when connected to 120V power
- but again - by way of the contactor.
Contactor's coil voltage has to agree with the
device 'driving it', the thermostat in this case.
Mats (or cables) voltage has to agree with the voltage of the
power source regardless of the contactor's coil voltage. Mat's (or cables) TOTAL
AMPERAGE has to be smaller than the one of the contactor AND THE AMPERAGE
OF THE POWER SUPPLY.
Please Note: nothing should be subjected to operation under
full load for long periods of time even if allowable by specs.
This said, if the thermostat max. load is 16A, and if the
real load from floor heating is 14A or more: USE THE CONTACTOR! Definite purpose
contactors are inexpensive and not difficult to connect.
It is normal for the contactor to wear out over time like brake
pads on a car. If the contactor shows any signs of wear it should be replaced as
a preventative measure or as part of maintenance. The electrical box hausing the
contactor should be closed. First, because of the safety - there is line
voltage present there and also because you can have problems with spiders
building nests in the contactor; the silk is an insulator and will prevent
electricity from flowing!
Replacing a contactor is a simple matter and
they are readily available. We will ship you one if you ask. Costs vary from
about $20 to several hundred dollars depending on the size and current carrying
2 phase definite purpose contactor in the dual gang electrical
4 large 1200Watts/240V mats connected to the
bottom side of the definite purpose contactor. 2 wires (black and white)
from the load side of the thermostat connected to the left and right side of the
contactors coil. Pleased note:
1. All the ground wires (YELLOW/GREEN) connected together
2. All the mat's BLUE wires connected to one phase of the
contactor and all the mat's BLACK wires connected to the second phase of the
contactor. Yellow power wire not connected yet.
Before connecting, each 133 sq.ft. (12m²) 240V, 1200Watts mat
resistance was 43 Ohms. When connected in parallel like shown above the
resistance of this set is 10.9 Ohms. Based on the Ohm's law: 240V/10.9Ώ = 22 Amps.
The limit for the resistive load of this particular
contactor is 30Amps.
Here, the contactor box is under the heated floor:
Three large mats are connected. Each is 1200Watts
@230-240V. The limit of the thermostat is 3800 Watts but the use of this
inexpensive $20, 30 Amps. contactor will help to greatly prolong the life
of the thermostat as the load is handled by the contactor. As a matter of fact
inside of the thermostat there is also a contactor but a small one.
No thermostat can
handle this load of 18,000 Watts (18 kW) installed here under the cement slab
driveway for snow melting.
A box with three inexpensive contactors (three zones) can.
Please remember: Electricity can be deadly and
wiring done incorrectly can kill and start deadly and destructive fires even
when "just replacing one small
ARE DEALING WITH LINE VOLTAGE, not low
EVER attempt to work or even touch the inside of the electrical components
without being 100% sure that the power is
you are not an electrcian and if you have the slightest doubt about your wiring
ability, please contact a licensed electrician and/or repairman before
doing any diagnosis, repairs or installations. The products shown here
are deemed SAFE and sound by various testing authorities but the wiring
process can only be SAFE when done with safety precautions. Please
read manuals and/or ask pros when not sure. Most of the simple
installations shown here can be done by yourself or you can have someone
qualified do it for you and THEN have the electrician check it and connect it to