Replies

1. 
   jimjimjim | Jul 15, 2009 08:47am | #1

   Westcoast -

   P = I x E  where P is power in Watts, I is current in Amps and E is voltage in Volts, so

   P = 10A x 120V = 1200 Watts

   or

   P = 5A x 240V = 1200 Watts

   So both matts would use the same amount of power.  120V requires a 1-pole circuit breaker; 240V requires a 2-pole breaker.  Wire must be sized for current flow (I), so 120V matt requires larger wire (or a greater portion of the total circuit) and will potentially (No pun intended) have more voltage drop (i.e. wasted power) than the 240V version.

   Jim x 3

1. 
   Jeff_Clarke | Jul 15, 2009 03:20pm | #2

   Isn't it more efficient at 240V because the current loss is 1/4 the amount at 120V?   Leaving more amperage at the mat?Jeff

1. 
   Stuart | Jul 15, 2009 04:07pm | #3

   There really isn't any difference in efficiency - watts is watts, and they both have the same rating.  For something this small it's mainly personal choice if you get the 120vac or 240vac model.  There may be a little more voltage drop with a 120vac mat (and not enough to matter unless the mat is a LONG ways away from the breaker panel), but the current is constant, no loss there.

2. 
   Westcoast | Jul 15, 2009 05:02pm | #4

   Good stuff thanks for that!So basically the only difference is the one takes up another space in the elec. panel and that's it? Is there any reason to go for the 240 volt system?

1. 
   jimjimjim | Jul 15, 2009 05:47pm | #5

   Westcoast,

   As Stuart mentioned, if there is a really long run from the panel then 240V will be slightly more efficient, with 2 panel spaces vs. 1.

   If your have a lightly loaded 120V circuit and the mat manufacturer doesn't require a dedicated circuit for the heater, then you might be able to install the 120V mat without running a new circuit all the way back to the panel.  But you can't put the mat on the 20A circuit serving receptacles in bathrooms.  And you shouldn't put it on a 20A circuit serving everything in a single bathroom - 1200W plus a 1500W hair dryer will trip a 20A breaker.

   If you are installing new wire, then the wire will be minimally (or nearly) sized anyway so no real cost diff 120V vs. 240V

   The mat manufacturer probably requires GFCI protection.  GFCI breakers are more expensive than regular breakers.  120V GFCI devices (not breakers) are readily available, 240V are not.  Some heater manufacturers build the GFCI into their thermostat, so a separate GFCI or GFCI breaker isn't needed.

   Jim x 3 

2. 
   Billy | Jul 18, 2009 04:19am | #6

   If it's a large mat you may have to use 240V because a single 120V breaker cannot handle the amperage.  Think of the mats in terms of watts per square foot...

   Billy