Recently had a generator installed for the business. Electrician mistakenly added 15amp power outlet within the generator housing unit. Need to change this to 20amp to plug in the block heater. My assumption is that the breaker is a 15amp breaker. If we change the outlet at the generator, will we have to make sure the breaker is 20amp also?. or can we get away without doing this?

You actually do not have to change the outlet if you don't want to. A 15 Amp receptacle can handle 20 Amps.

However, the same is not true of the Breaker and the conductors to the receptacle. 15 Amp cables use #14 AWG conductors. To use 20 Amp, the conductors have to be changed to #12 AWG and the breaker to 20 Amps.

A #14 AWG cable becomes a fire hazard if you run 20 Amps through it.

For a 20 A load the wire size has to be 12 AWG and the breaker must be 20 A.

You can, however, have a 15 A outlet, 12 AWG wire and a 20 Amp breaker.

The breaker protects the wiring: 12 AWG wire, 20 A breaker allowed; 15 A breaker allowed; Receptacle rating should not be less than breaker rating.

14 AWG wire, 15 A breaker, 15 A receptacle.

Donf:

I challenge you to find me a spec. where a NEMA 15-5R receptical is rated for 20 amps.