National Electrical Code 2014

Chapter 1 General

Article 100 Definitions

Disconnecting Means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

This can include a switch, a circuit breaker, a cord and plug connection (sometimes), or a group of the aforementioned devices.

There are other stipulations within the code that dictate how these devices can, and cannot be used. But at the core of it, any device that can disconnect the conductors of a circuit from their source of supply, is a disconnecting means.

In the context of a separate building, typically either circuit breakers or a switch type device will be used.

the Idea you have is good , but the components although "rated" for 10 amps really will not hold up long at that level. I usually only load these small relays at 50% and as low as 10% if it has a short cycle time. the problem is contacts in the mechanicial ones will soon stick and overheat your hot plate , The electronic ones the solid state relays internally short untill the junction is blown apart but usually dammaging the divice they are driving. as for plastic it melts, maybe a plastic liner in a metal box or standoffs in metal but use caution it will probably work for a while but when it fails thats when things get ugly