Having fuse box issues with my Ninja

Check out steambrite.com under electrical adapters.  You can buy an adapter that can plug into a standard dryer outlet, and allows you to plug in up to 4 15 amp plugs.  Dryer outlet is 220v and 30 amps. 

Mytee makes one that splits the dryer outlet into 2 20 amp circuits.

Sounds like a great option to me.  I haven't bought one yet, but I soon will.

My comment about the brushes is based on personal experience and that of others over here in the U K.  We all experienced the same problem of tripping, usually accompanied by a burning smell. We all replaced motors, but I stripped one and found it to be very easy to replace the brushes.

The carbon brushes in the vacs need replaced, simple and inexpensive to do

All good above.. What one overlooks is your ext.cord.. If its twisted inside from the hand to shoulder wrap you will pull more amps.. It increases the magnetic field.. More amps more circuits blown..

Buy a circuit locater.

plus what Michael and Doug said

Doug has the recipe for success, safety. Simple tips: 1) don't share a circuit; 2) when possible, use an outlet the washer/dryer uses; 3) the vacs pull more power than the heater, so give them priority when evaluating circuits; 4) best case scenario: plug one into the laundry room and the other into a kitchen socket (older homes often have the entire kitchen on one circuit, so you may want to unplug the fridge if you don;t have better options). Like doug said, if you can plug into the stove, that's great. I'm my experience, the stove outlet is hardly ever accessible though.