You registered and posted this on the same day. The problem is not electrical and there is no electrical solution-- it is a people problem.
Discussion and agreement is the best choice. If you insist on being in control, as I might do if all else fails, remove the space heaters from the premises just as fast as they are brought there.
Space heaters present significant fire danger, even the newest ones. The "guest" could help pay the utility bill.

It will however be illegal under the NEC. You can not put 15A receptacles (normal wall outlets) on a 10A circuit. Further, the code almost certainly requires a full 15A circuit.

Would this permanent house guest be your daughter? It's time to put on your big boy pants and be a parent and set some rules. Or start charging her rent to cover the electric bill.

Or just go down to the circuit breaker panel and flip the breaker off manually whenever you know she's turned on the heater and claim ignorance.

"It will however be illegal under the NEC. You can not put 15A receptacles (normal wall outlets) on a 10A circuit."

Just curious about the logic or reason (if any) for the rules about receptacle vs circuit size. In another thread it was stated that 15A receptacles on a 20A circuit were OK, which seems wrong because the circuit will let you draw more current than the receptacle is rated for (this is what my electrician just installed and the inspector passed) while putting an over-capacity receptacle on a lower amperage circuit (eg a 20A receptacle on a 15A circuit) might let you plug in a 20A plug--if you could ever find one in the wild--, but the breaker wouldn't allow you to pull that many amps through the circuit. This seems backwards of what would be safe.

I know of no reason that 15 amp receptacles could not be on a circuit protected at 10 amperes. But ongoing issues in this case would not be resolved by doing that. And in the ensuing (not electric) power struggle, tampering is likely.
In my shop I have an industrial 1/2 hp door operator on a 20 x 14 door. The motor has a thermal protector and additionally it is plugged into a ceiling receptacle which is protected by a 10 amp time-delay plug fuse. I see no safety issues with that.

Article 210.21 precludes it. If it was a single receptacle, you could legally use it the rule says the receptacle rating is not less than the branch circuit rating. However, I suspect highly we're talking at least one duplex receptacle, then it has to be one of the combinations in listed (none of which involve a 10A circuit).

210-21 refers to outlet devices, not to the short circuit and overload protection. So how could a 15 amp receptacle be unsuitable, per 210-21, for a 10 amp circuit?

210.B(3) says SHALL. There's no provision for having multiple 15 or 20A receptacles on a 10 amp circuit. These are the rules on what receptacles can be installed on what circuits. There's no provision for multiple 15A receptacles on a 10 amp circuit.

In fact, it doesn't give provisions for ANY receptacles on a 10a circuit. "Receptacle ratings shall conform to the values listed in Table 210.21(B)(2)". That table doesn't have a 10a value under "circuit rating" therefore, NO 10a branch circuits feeding two or more receptacles of ANY rating are allowed.

Notice that the words "Total" and "Maximum" appear there. Nothing about minimums. If your interpretation is correct, then a motor that should be protected per Article 430 at 10 amperes- or some value less than 15- could not use a cord and plug for the disconnect. But a motor protected at 15 amperes could -- not very logical. 210-19(A)(1) does not specify the minimum rating of circuits. 240.6(A) lists interesting information about ratings of Fuses and Fixed-Trip circuit breakers.
For a bedroom circuit- forget the 10 amps. Any such would have to be in addition to, not as a substitute for, the minimum 15 amp circuit(s) required by 210.52(A).

This post was edited by bus_driver on Wed, Feb 6, 13 at 18:03

Apart from any rule contradictions, where is the breaker panel located? They're going to be running to the panel to reset it all the time, and it's bad for the breaker. Too many trips could make it fail, and it might fail to trip.

As others said, it's a people problem. If the house is actually reasonably warm, they might have a thyroid problem!

An electric blanket might be a better option for them, with a timer so they don't leave it on too long. They're quite cheap to run.

If it's not resolvable through diplomacy, maybe you need to ask them to leave, or pay more towards the energy bill.