agrimats for plants

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FREEBALL

Senior Member
Location
york pa usa
The info for these mats says to stay below 500 watts to avoid tripping the GFCI. The mats are 120v heating mats. Can anyone say why this is, hair dryers in bathrooms are more than 1000 watts and connected to GFCI's. Just curious.

thanx
 

tom baker

First Chief Moderator
Staff member
The 500 watt limit is due to leakage current on the mats. Are they self regulating?
A hair dryer is not required to be used on a GFCI. A GFCI is required by its installation location.
 

FREEBALL

Senior Member
Location
york pa usa
The mats are individual mats plugged into a GFI, they each have a controller and are 100 watts each, from what Im understanding now is that there are a few installed on the same GFI. I understand the requirements of a hairdryer by the way, just so happens they usually are connected to a GFI. OK what does the wattage have to do with leakage current. if there is leakage current the GFI should trip at its inherent value of approx. 6ma. I was asking a general question on this type of heat mat in comparison to the functionality of a hair dryer which draws more than 500 watts. thankyou for your post.
 

tom baker

First Chief Moderator
Staff member
Guessing the wattage is related to leakage current on the mats.
I don't see how a direct comparison can be made to a hair dryer its an appliance and has no leakage current, unless dropped in a sink, which is why hair dryers have leakage current detectors LCDI on the end of the cord.
 

PetrosA

Senior Member
Leakage current in a mat will be very different than what you'd have from a hair dryer since the hair dryer doesn't have anywhere to leak its current to, but similar to a UF cable which leaks current along its entire length. UF cable will trip a GFCI outlet or breaker even without a load once you go beyond a certain distance (75' IIRC) because of the length of wire involved. Similarly, the mat will have a relatively long cable running parallel to some surface that's able to induce current and a limited thickness of insulation. Add enough mats together and you reach your 3-5 mA limit on a GFCI very quickly.
 

kwired

Electron manager
Location
NE Nebraska
Wattage itself doesn't have much to do with how much leakage there is, but these units are likely a fixed size for a specific wattage. They have determined capacitive leakage for a 500 watt or up to 500 watts of units is less then the trip threshold of a GFCI, if you go over 500 watts of units they are saying "normal leakage" may be too high and will cause troubles on GFCI protected circuits.
 

FREEBALL

Senior Member
Location
york pa usa
OK I think I get this it just threw me when it said to stay under 500 watts I was looking at the wattage as the factor, not the cumulative cables that amount to 500 watts. Thanx for your replys as always informative and educational.
 
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