Can I use this wire with a 40amp 240v breaker for a 240v 2000w wallheater?

Yes, it is possible to carry a 2000w 240V load on a 12/2 NM-B cable like this one. No, it will not pass an electrical inspection. The breaker must protect the wire, and if someone comes along and adds load to your heater circuit they could easily overheat the 12/2 and the 40A breaker would just let it fry as long as it never pulls 40 amps. Neither #12 nor #10 is good for 40 amps - both would overhead on a 35A load. You can drop down the breaker to a 240V 20A circuit breaker and both the cable and the load would be protected. It still would not pass inspection because of the improper color coding of this 12/2 cable. If the next owner of your home calls an electrician to rewire the house, he will think that your wall heater is 120V because standard household color coding is : black = +120 volts (Bus A) white = 0 volts (neutral wire) red =-120V bare = equipment ground (no current flow in during normal operation) That is why people are advising you to use 12/3 or 14/3 cable - 3-conductor Romex-type cables have a red jacketed wire in the bundle which is the proper color to use alongside the black cable for the two "hot" wires in a 240-volt circuit. This NM-B cable has an insulation rating of 600V, so it can tolerate 240V operation. I have used 12/2 to feed a 240V circuit - I fed the cable from a 240V 20A circuit breaker and used a red felt-tip permanent marker to color the white wire. This still would not pass an electrical inspection but it addresses the safety issues associated with serving your heater with 12/2 cable as long as the wire remains dry. I don't know the National Electrical Code well enough to say whether or not a black electrical tape on the white wire would pass an electrical inspection - that is also a obvious signal that the white wire is not a neutral wire. The calculations of 8.3 amperes drawn by your 2000-watt heater are correct. Using a 15A 240V breaker instead of 20A would introduce no further safety issues. Please do not use 12/2 to serve this load unless you mark the circuit as 240V in a can't-miss-it fashion, or the next person who tries to work on your wiring may assume that the white wire had 0 volts on it when it actually has 240 volts relative to the black wire - you may forget about it yourself and hurt yourself or your property sometime in the future. Misidentified wire is a cruel wiring mistake to leave behind. Happy wiring!

The description says this is a filter for a honeywell ac unit!! so is this wire or a filter??

This is 12/2 nmb wire, we are working with amazon to get this fixed.

would this work to run a plug for a 8ooo btu air cond ?

If its 110 volt yes, if it is 220 volt you will need 12/3. As long as it doesn't draw more than 20 amps, I would think an 8000 but air conditioner word be 110 volt and draw less than 20 amps.

I'm rewiring my whole house is this too good wire to use

Heres where a little math is needed. 14G wire is good in most places for 15 amp breaker and runs. Your avg 75 watt light pulls .6 amps (75/120) roughly, 40 watt = .3 amps, etc. You can run continuous at 90% amps, or 13.5 of 15. So u need to figure how many watts u will be running at a time, and if its continuous, no more than 13.5 amps. This probably confused you but its the basics.

ASIN	B000BQSL3G
Brand	Southwire
Brand Name	Southwire
Colour	Yellow
Customer Reviews	4.8 out of 5 stars 3,796 Reviews
Global Trade Identification Number	00032886263088
Item Weight	4 Pounds
Manufacturer	Southwire
No. of wires	2
Number Of Wires	2
Number of Cable Strands	2
Strands	2
UPC	032886263088
Unit Count	1.0 Count
Voltage	600 Volts

Southwire 28828222 12/2WG NMB Wire 50-Foot

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