Heated driveway?

Commercial snow melting. (E.g. TOYOTA + ELEKTRA).


ONDOL - The Korean invention

American Legend: Architect Frank Lloyd Wright

From STONE COLD to NICE WARM floors in just 2 hours?

New Kitchen Project. (Part 1)

New Kitchen Project. (Part 2)

Radiant heating in one day?

From cold slab floor to comfort and beauty.

How to connect UCCG-9991 programmable thermostat for radiant floor heating?

How to connect MTC-2991 manual thermostat for radiant floor heating?

How to choose the in-floor radiant heat ELEKTRA mat?

Many components of the Great Real Estate. (Part 1).

Many components of the Great Real Estate. (Part 2).

How to connect more than 1 mat?

The problem on the roof

Installing radiant floor heating in just one afternoon.

Cathedral ceilings effect & Medieval Hypocaustum (floor heating)


How to connect many Elektra mats?

How to properly connect more than 1 mat?

Q: Can I connect more than one mat? If so, how?


A: More than one mat can be connected quite easily but  

there are few important rules to follow:


1. PARALLEL CONNECTION ONLY just like shown below for two mats (4 connecting wires) and Elektra UCCG programmable thermostat:

                                       Power + Ground from the box

 4 cold wires


PARALLEL CONNECTION for 2 Elektra MG mats and Elektra-Microline MTC2991 thermostat with floor temperature sensor:  



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 heating system.  

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 ELEKTRA mats


Two parameters of the definite purpose contactors are important:


  • Max. Amperage.
  • Coil Voltage.


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 capacity.


2 phase definite purpose contactor in the dual gang electrical box.



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. (12m) 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 receptacle". 


NEVER EVER attempt to work or even touch the inside of the electrical components without being 100% sure that the power is disconnected!

If 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 power.    

Feedback is something that really keeps us going.

Please comment on the FORUM or send us your comments or requests for any specific topic that you would like us to feature.

Learn More

  New York International Tile and Stone Show
Read More
  A carry-over from the ancient past? 1000 year old technology?
Read More
  IBM - PL. Why no driveway or steps will need to be shoveled or salted when winter arrives.
Read More
  We almost lost the count where all those ELEKTRA heated floors are!
Read More
  Smart remodelling will increase the value of your home.
Read More

No Items

IBM - PL. Why no driveway or steps will need to be shoveled or salted when winter arrives.
Is electric radiant floor heating ENERGY EFFICIENT?
Likely yes
Likely no
Don't know