Question 1

I have 12 Gauge on a double throw 30 amp breaker. Sould i install 20 amp breaker for 3000 watt heater ?

Accepted Answer

Good Morning Jimi,.

You are sort of on the right track, but you need to calculate the load draw of the heater in order to determine the correct wire size for over current protection ( circuit breaker size).
First off the heater is 3000 watts at 240 volts ac. To arrive at the max amperage for the heater we take the 3000 watts and divide by the required voltage (240vac), that answer is 12.5 amps.
That is the maximum amperage the heater should draw. 
Now lets look at the required wire size for a load of 12.5 amps. 14 gauge wire has a maximum rating of 15 amps but by electrical design practices it is never good to load a conductor (wire) to more than 80% of its rated value.
80% of a #14 gauge wire is 12 amps, 1/2 amp lower than the 12.5 amps required for the heater. Using 14 gauge wire would not be recommended, so you would move to the next size conductor, #12 gauge which you say you have installed. The permitted maximum load rating of a #12 gauge wire is 20 amps, with a 80% load rating of 16 amps, well within the required range for your heater.
Now that we have established the correct size wire for the heater and we know our wire size is correct for our load, we now know what our over current (breaker size) should be. The circuit breaker should be a 20amp 2 pole base on the size of the wire, #12, with a maximum ampacity or connected load of 20 amps. the circuit breaker not only protects the device (heater), but also the conductor or wire correctly.
A 30amp breaker would be oversized and allow the wire, and the heater to overheat and possibly cause a fire should it ever fault.
Sorry about the long winded answer but when you do this every day like I do tend to do the math.
Hope this helps.

Steve

Question 2

Hi, i am running 100' to the circuit box. is 12-2 ok or should i use 10-2 for the longer run? thx!

Accepted Answer

12-2 is OK.  No need to use 10-2 wire.
The heater draws 12.5 amps of current, and you will get a voltage drop of 1.81% (source: Southwire voltage drop calculator) or less when supplying 12.5 A for 100 feet on a 240 volt system.

Question 3

Can this unit be used as a stand alone unit, not installed in a wall if wired correctly with a 220v plug and  outlet?

Accepted Answer

Short answer, no. 
It needs to be mounted inside if something, ie. a wall.

Question 4

Does this unit come with a surface mount trim ?

Accepted Answer

The grill mounts to the fan housing, is larger than the unit mounting cutout opening and fits tight to the mounting surface (wall).

Product Dimensions	41.91 x 49.53 x 34.62 cm; 5.22 kg
Item Weight	11.5 Pounds
Form factor	wall heater
Heating method	Convection
Is assembly required	No
Number of pieces	1
Batteries required	No

Cadet Com-Pak Twin Electric Wall Heater Complete Unit with Thermostat (Model: CSTC302TW, Part: 67526), 10236/7677 BTU, 240/208 Volt, 3000/2250 Watt, White

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