How can I measure the actual amperage rating of my circuits so I can match it with correct fuses/breakers?

Question

My house has a fuse panel instead of a circuit breaker panel, and as such it's way easier for the wrong ones to be installed. I don't trust that the previous tenant had the right ones in the right sockets. Is there a way I can measure the actual capability of each circuit so I can be sure I'm installing the right amperages?

Answer 1

... the previous tenant ...

This indicates to me that this is a rental property. Call the landlord and ask him to review to be sure that his property doesn't burn down.

Sure, you can do simple work in a rental without being a licensed electrician - replacing a blown fuse should be one of those things, but 99.9% of work in a rental property cannot (in the US) be done by the tenant or the property owner. You're not allowed to put someone else's life or property at risk.

It should be up to the owner to either:

• know what fuses should go where because he's familiar with the property and knows how it should be set up, or
• get a licensed electrician to figure it out to protect his property and your life.

Answer 2

Fuses are color-coded same as breakers used to be.

• Blue = 15A (#14 wire)
• Red = 20A (#12 wire)
• Green = 30A (#10 wire)

You might take appropriate hobby paint or nail polish and mark the area around each fuse socket with the appropriate color once you have identified the sizes of the wires in the circuit. If a circuit has mixed wire sizes, the smallest size controls.

Answer 3

The breakers are to protect the wiring, not the load. You can generally size by the wire size example for 60C rated wire: AWG 14=15 amps, AWG 12 = 20 Amps, AWG 10 = 30 Amps. It is dependent also on the type of wire. This link will give you the appropriate table. https://www.usbreaker.com/docs/UL489_US-Breaker_Wire_Size_Chart.pdf

The easiest way to size would get an experienced electrician, that person will know the wire size by looking at it. Also they make cheap gauges to check the gauge, many times they are giveaways from some vendors. You need to size the breaker to the smallest wire (highest gauge number) in the circuit so if there is AWG 14 you are limited to 15A. Conversely if you are not comfortable playing a 20 amp breaker (AWG 12 wire) on a circuit a 15 amp is ok. It would be a good idea to note why.