You're absolutely right in your thinking! Let's break down why: Continuous Load Definition

A continuous load is a load that operates at its maximum current for 3 hours or more.

NEC 210.20(A) - Overcurrent Protection (OCP)

The NEC (National Electrical Code) states that the overcurrent protection device (circuit breaker or fuse) must be rated at not less than 125% of the continuous load. This 125% is precisely why you multiplied 15A by 1.25 to get 18.75A.

Your Calculation

Your math is correct. 15A 1.25 = 18.75A.

NEC 240.4(B) - Standard Ampere Ratings ( Round Up Rule )

The NEC also has rules on standard breaker sizes. The intent is to use the next higher standard size of OCP device if the calculated load (after applying the 125% factor for continuous loads) doesn't match a standard breaker size.

The Issue with a 20A Breaker

A 20A breaker is generally rated to handle a maximum of 80% of its rating continuously. That translates to 20A 0.8 = 16A. Your calculated continuous load (18.75A) exceeds this 16A limit. Using a 20A breaker would likely lead to nuisance tripping of the breaker.

Why a 30A Breaker is Appropriate



Compliance

The 30A breaker satisfies the NEC requirement that the breaker be rated for at least 125% of the continuous load (18.75A < 30A).

Safety

The 30A breaker will not nuisance trip under normal operation.

Wire Sizing is CRITICAL

You

must ensure that the wiring you are using is rated for at least 30A. Using a breaker that is too large for the wire gauge is a serious fire hazard. Common wire gauges and their corresponding ampacities (in normal conditions) are: 12 AWG copper wire is typically rated for 20A (consult NEC 310.16 for adjustments) 10 AWG copper wire is typically rated for 30A (consult NEC 310.16 for adjustments) 8 AWG copper wire is typically rated for 40A (consult NEC 310.16 for adjustments) In your case, you MUST have at least 10 AWG copper wire. Important Considerations



Local Codes

Always adhere to your local electrical codes, as they may have specific requirements or amendments to the NEC.

Consult a Qualified Electrician

If you are unsure about any aspect of this, it's best to consult with a qualified electrician. Electrical work can be dangerous, and it's crucial to ensure it's done safely and correctly.

Equipment Listings

Also check the nameplate rating of the specific equipment you are powering to ensure it's compatible with a 30A circuit. In conclusion, you should use a 30A breaker,

IF, and ONLY IF, your wiring is appropriately sized to handle 30A (at least 10 AWG copper wire). If the wiring is only rated for 20A (e.g., 12 AWG copper wire), you cannot simply upsize the breaker. The wiring would have to be replaced. Flag for review