Nameplate rating exceeds minimum breaker size... calculation?

[Ricko1980]

Hi Folks,

Question here about service calculation when there's a device with specifications that include a LOWER minimum breaker size than the nameplate rating.

I'm looking at a Frigidaire induction stove that's going into an existing dwelling, so I'm using 220.83, but I'm interested in the question more generally, since this situation might arise with other devices.

In the manufacturer's specs they indicate:

Minimum circuit required: 40A @240, single phase

and yet, on the machine, the nameplate rating is clearly indicated:
15.5kW @240 ---> which is 65A!

For the service calculation, can I limit the machine's demand to 40A @240 = 9.6kW, or does the nameplate rating have to be used, in which case you're reserving space on the service that might only be used for a brief while until the breaker tripped?

Anecdotally, I've been doing a year-long load study that suggests these machines in practice don't draw more than around 32A.

Ricko

 

[winnie]

See: https://forums.mikeholt.com/threads/residential-range-circuit-calculation.135885/

The range can pull 15.5kW if all of the elements are on full blast at once. But think about the chance that this could actually happen, especially when you consider thermostatic control. So code permits a demand factor to be applied to even an individual range circuit.

Jon

 

[suemarkp]

Depends whether you are using the standard or optional calculation. The standard calc and the branch circuit calculation are similar rules. Treat the first 12kw as 8kw and then add a fractional factor for the rest. This allows a 40A or less load for most ranges.

For the optional calc, the full nameplate goes in along with all other fixed appliances except hvac. Then a 40% factor is applied.

 

[Ricko1980]

Mark-

So that means for the optional calc, it has to be treated as a 65A load, even if it's on a 40A breaker and the wires are correspondingly sized for 40A (since it's not a continuous load)? This doesn't seem to make sense.

 

[retirede]

Mark-

So that means for the optional calc, it has to be treated as a 65A load, even if it's on a 40A breaker and the wires are correspondingly sized for 40A (since it's not a continuous load)? This doesn't seem to make sense.

Load calcs for sizing a service have nothing to do with branch circuit conductor and OCPD sizing.

 

[suemarkp]

Mark-

So that means for the optional calc, it has to be treated as a 65A load, even if it's on a 40A breaker and the wires are correspondingly sized for 40A (since it's not a continuous load)? This doesn't seem to make sense.

Would it make more sense if the service load value is 26A and the branch circuit is 40A. The 26A is 40% of 65.

Service and feeder loads can get factorized. Branch circuits are usually sized for the max rating. But electric ranges have a long history so the code allows a demand factor on them since the heating elements cycle. You would need to verify if that range fits on a 40A circuit. It is probably right at the limit.

 

[topgone]

Would it make more sense if the service load value is 26A and the branch circuit is 40A. The 26A is 40% of 65.

Service and feeder loads can get factorized. Branch circuits are usually sized for the max rating. But electric ranges have a long history so the code allows a demand factor on them since the heating elements cycle. You would need to verify if that range fits on a 40A circuit. It is probably right at the limit.

Agree. The effective amps drawn will be the maximum rated current draw multiplied by the square root of the cycle duty!