30 Amp 240-Volt Non-Fuse Indoor Safety Switch

Only if the heater doesn't pull more than 30Amp

I don't see why not, you would be using one less wire.

If you are using a 10/2 or 12/2 wire, either of those will have two hot wires & one ground which should be grounded in your main breaker box. The two hot wires coming from your 30 S breaker will connect to two of the three contact lugs that make contact when the switch is on & break when it is off. Connecting the third wire that is grounded in the main breaker box grounds this box as well. Make sure all connections are tight.

This unit does have 3 hot wire connection points in it and a ground connection, but NO BREAKER or FUSE. It simply uses a contact bar that opens & closes the contacts across all three conductor points. It is rated for 30 Amps, but I'm pretty sure I saw one just like this one that was rated for 60 Amps. You can use the 60 Amp model on a 30 Amp circuit, but not the other way around. The 60 Amp model was more expensive though and you won't gain anything by using it. I only needed to use 2 of the live connections because I am using a Single Pole 30 Amp breaker in my main breaker box with a 2-wire conductor and a ground wire. Disclaimer: I am not a certified electrician. I may not have enough information to give you good advise on how you need to wire it, but let me ask, are the 15 Amp breakers in the disconnect box that broke or are they in your main breaker box? I ask that because some disconnects have breakers or fuses inside them.and in the case of a short in your dryer, the breaker or fuse in that disconnect should trip or blow before the breaker or fuse in the main breaker/fuse box. What is between your old disconnect and the dryer? Did the old disconnect have a built-in power outlet, or is the outlet separate from it and wired to contacts in the disconnect. If the later is the case and you can use the old disconnect as an example then you should have a one for one guide to follow. In this switch the conductor comes in thru a knockout in the top and each wire goes to one of three connection points above the contact bar. you would need to match that wire to whatever wire your old disconnect used. white to white, black to black, red to red, etc. I'm surprised there is no common ground wire. Good luck, be careful.