I bought an older home in west Trail two years ago. I want to put a hot tub in our backyard. So, yesterday I looked at the main electric panel to see if I had room to add a 40 amp breaker. To my surprise the 70 amp main panel is full and I found a weird box on the side of the panel that has a label “load miser”. What is it? Can I still add an extra breaker somehow?

From your description it seems very unlikely that you have enough electrical capacity to provide an additional 40 amp circuit for a hot tub. For instance, your 70 amp panel is full. You could possibly extend the service with a sub panel but this is quite unlikely, especially if you have an electric stove, clothes dryer and / or hot water tank. All of these appliances demand considerable current and any combination of them with a hot tub would likely overload a 70 amp service.

Another indication of your electrical capacity is the fact that your home is equipped with a “load miser”. Often, when a house lacks sufficient 240 volt circuits in the main panel for the number of major appliances in the house, a load miser is installed. This usually indicates that the electrical capacity in the house is marginal for the number of major appliances in use. For example, commonly, a clothes dryer and an electric hot water heater are served by their own dedicated 240 volt circuits. In your home it is likely that they share the same circuit with a single 30 amp breaker and a single 10 gauge wire.

The load miser is a switching devise that supplies current to one of these two appliances at a time since there isn’t enough current carrying capacity in the 10 gauge wire to operate both appliances simultaneously. Therefore, the load miser gives one of the appliances priority. The load miser cuts off power to the non-preferred appliance when the current flowing through the miser reaches 80% of the upstream fuse or breaker rating.

For instance, in the example of the hot water tank and clothes dryer, the hot water heater may be drawing power most of the time. But, when the clothes dryer is in use, the load miser will cut electrical flow to the hot water tank and supply only to the clothes dryer.

 It is very unlikely that you will have enough electrical capacity to heat a hot tub given that there are apparently not enough circuits or capacity for your existing appliances. You may be faced with an upgrade to your electrical service. This will probably entail installation of a new 100 amp service wire and main panel. However, before you begin this project, I recommend that you consult with a certified electrician who will be able to assess your electrical loads and corresponding service size.