Rating for this circuit breaker at 120 voltsAC

The short answer is that if they both have an 8A in their name then they can replace each-other. The details of the fuse are important if your supply can source very high currents(100s of amps) or if you need to deal with issues such as irregularly but short current trips that should not cause a fault.

What does the H mean?

The confusion comes from fuse nomenclature. It is not surprising either as my google fu did not easily return a list of what identifiers refer to.

This document points me to a useful table though. It seems as thought that 'H' refers to the maximum current that the fuse guarantees it can interrupt. .

Omega's document on fuse selection that I mentioned previously has quite a large amount of information to learn from if you would like to learn more about fuses. Choosing a fuse to protect circuitry without faulting regularly for no reason is something EDN and Electronic design magazine have had good articles about.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Bench test mains power supply.

How it works

• The transformer XFMR1 is a 1:1 mains power transformer. You need to figure out what's the most powerful appliance you need to test and size accordingly. e.g., for 1000 W use a 1000 VA transformer.
• The transformer will isolate the load from the mains and if there is an earth leakage fault on the appliance it will prevent your main RCD and the one on this setup from tripping. (More later.) It will also protect you while the EARTH TEST switch is open.
• The lamp serves as a current limiting test device. Open the FULL ON switch before you plug in the device. The brightness of the lamp will give an indication of the current draw. If it goes to full brightness on a small appliance, for example, you may have a short circuit but current will be limited to 0.5 A (230 V AC lamp) or 1 A (120 V AC lamp). If all appears well then switch FULL ON.
• If all is well then close the EARTH TEST fault switch. Now if there is an earth fault on the appliance some of the current will return on the earth-wire instead of the neutral (N). The RCD will detect a difference between the L and N current and trip out. This would usually only trip if there's an earth fault to a metal-cased appliance.
• Size the RCD (current rating) to protect the transformer.

That should help you sort out most problems on the bench.