I am currently finishing up some renovations on a bathroom and have installed a Tub Whirlpool. There is a 1HP motor on the tub that requires a double 15amp breaker at the panel. Existing is a heater with a double 20amp breaker with a red electrical wire (inside a red, black and ground wire, as far as I know in this system the red is hot, black nuetral? ) which is controlled by a thermostat. I am looking at changing the thermostat to a single switch. I am also looking at extending the existing wire from the old heater (which has been taken out) to the pump with a regular 300watt wire which has a black, white and ground wire inside(white colored on the outside). 1. The pump calls for a 15amp breaker but can I use the 20amp? 2. Can I connect the red to black and black to white and the two ground to make the connection between the different but both 300watt wires? 3. The single light switch can just be changed over from the thermostat by just replacing the two wires that come into the thermostat and putting them on the two screws that come into the single switch? Thanks

Where are you located?

USA or UK?

What is "regular 300watt wire" ?

I am in Canada and what I seem to have with the red wire is black, red and a ground and with the white wire I have black white and a ground. I meant that the 300watt wire with the white outside is what I am used too not the red wire.

Since you say the breaker is a double pole the old heater should have been a 240 volt unit, with 120 volts across the black and ground, and 120 volts across the red and ground. This circuit has no neutral.

To extend the 240 volts with the cable with the black and white wire, the 240 volts will be across the black and white, the white will be hot, here in the US, we now must label hot whites as hot with some other color than white.

I still am not sure what the 300 watt cable is. What size/gauge wire is it?

I do know that Canada uses different types of cable, with different names and looks, but still uses the American Wire Gauge to size the copper wire.

And, back to your first question, as the 20 amp breaker can be used for the 1HP motor.

The wire is 300volts and 12awg. I went out and found the same wire to extend from the switch. Inside the switch the red wires are connected together and the black wires go into the switch and out to the pump. At the pump it is a green, white and black wire set up. Would it still be the same as you were saying. I have tried it and the pump starts but automatically cuts out after a half a second?
Thanks for the helps so far.