Yes, you are absolutely right to question this. Here's a breakdown of why, and what the likely issues are

The Problem: Mismatched Ratings Create a Hazard
Over-Current Protection

The entire circuit, from the breaker in the panel to the receptacle and the appliance, should be designed to handle the maximum current the appliance could draw. A 20A receptacle connected to a 20A breaker is designed to supply up to 20A.

Plug as the Weak Link

If the plug is only rated for 15A, it becomes the weakest link in the circuit. If the appliance attempts to draw more than 15A (due to a fault, overload, or even normal startup surge), the plug could overheat, melt, and potentially cause a fire before the 20A breaker trips.

Code Violations

Electrical codes (like the NEC in the US) require all components in a circuit to be rated for the intended load and the overcurrent protection. Using a 15A plug on a 13A appliance plugged into a 20A receptacle is likely a code violation.

Why the Engineer Might Have Specified a 20A Receptacle (and Why it Needs to Be Corrected)



Future Proofing

Perhaps the engineer anticipated a future need for a higher-current appliance at that location. This is reasonable planning, but the appliance plug and cord also need to be rated accordingly.

Misunderstanding of Appliance Needs

It's possible the engineer was working from incomplete information about the appliance's actual power requirements.

Common Practice

In some industrial or commercial settings, 20A receptacles are used as a standard to allow for flexibility, even if the initial appliance doesn't require that much current. However, the plug and cord must still match the receptacle rating for safety.

What Needs to Happen


The Safest Solution



Replace the Plug and Cord

The ideal solution is to replace the 15A plug with a properly rated 20A plug and a cord suitable for 20A. This ensures all components are matched and safe.2.

Alternative (Potentially Risky, Needs Careful Consideration)



Downsize the Breaker and Receptacle

If replacing the plug is not an option or you want to be certain no future higher load is connected, you could downsize the breaker to a 15A breaker. If that is done, the receptacle must also be replaced with a 15A version.

Important

Do not downsize the breaker without replacing the receptacle. If you use a 15A breaker with a 20A receptacle, you can still plug in a 20A plug and overload the circuit before the breaker trips. This may not be appropriate if the wiring to the receptacle is only rated for 15A and you need 20A at some point in the future.3.

Verify

A licensed electrician should perform any wiring modifications to ensure proper wiring practices are followed and that the circuit is up to code.

In summary, it is not safe or code-compliant to use a 15A plug on a 13A appliance plugged into a 20A receptacle connected to a 20A breaker. The plug should be upgraded to 20A along with a cord suitable for 20A. Flag for review