Which is considered a continuous load?

[kwired]

So maybe in a commercial/industrial application, a broiler might be considered a continuous load.

But for the run-of-the-mill residential application, I now understand how it isn't.

What about a convection oven, operating for 5 hours? Is the continuous fan a significantly smaller load than the thermostat cycling heat element?

The fan itself would be "continuous" in that instance, but when it comes to heating effects and determination of branch circuit conductor ampacity - that fan is maybe only an amp of load but the heating element maybe is as low as 12 amps or as high as 20 amps on a typical household oven. When you size the conductor to handle the heater plus the fan - the ampacity is well covers the continuous portion of the load for this particular application.

 

[Smart $]

The fan itself would be "continuous" in that instance, but when it comes to heating effects and determination of branch circuit conductor ampacity - that fan is maybe only an amp of load but the heating element maybe is as low as 12 amps or as high as 20 amps on a typical household oven. When you size the conductor to handle the heater plus the fan - the ampacity is well covers the continuous portion of the load for this particular application.

Suffice it to say a combined continuous and noncontinuous load defaults to being a noncontinuous load.

The question remains whether such a noncontinuous load would be 'considered' continuous where the load does not fall below the 'demand' load for 3 hours. It seems everyone wants to attack the question from the standpoint of the actual load not being 100% of rated load for 3 hours.

 

[kwired]

Suffice it to say a combined continuous and noncontinuous load defaults to being a noncontinuous load.

The question remains whether such a noncontinuous load would be 'considered' continuous where the load does not fall below the 'demand' load for 3 hours. It seems everyone wants to attack the question from the standpoint of the actual load not being 100% of rated load for 3 hours.

If we throw out the fact we are talking about a household cooking appliance where we get to apply demand factors for most calculations - though the cyclic nature of these loads is the basis for those factors - and say we have a feeder supplying two separate branches involving a continuous load fan a heating element of same size that because of nature of what is being heated requires it to cycle to maintain a set temperature - we then have a fan that needs applied at 125% of it's rated current plus a heat element that needs applied at 100% of it's rated current for most of the calculations you would be using involving these two loads. Put same two loads together in a listed appliance and it may change how they get treated and you calculate NEC loads based on the appliance nameplate - plus any factors allowed by NEC for specific load types - such as household cooking appliances. The fan is part of the appliance in those applications, but is still somewhat insignificant in demand from an appliance that has a heat element of maybe ten times the current the fan has.

 

[Smart $]

If we throw out the fact we are talking about a household cooking appliance where we get to apply demand factors for most calculations - though the cyclic nature of these loads is the basis for those factors - and say we have a feeder supplying two separate branches involving a continuous load fan a heating element of same size that because of nature of what is being heated requires it to cycle to maintain a set temperature - we then have a fan that needs applied at 125% of it's rated current plus a heat element that needs applied at 100% of it's rated current for most of the calculations you would be using involving these two loads. Put same two loads together in a listed appliance and it may change how they get treated and you calculate NEC loads based on the appliance nameplate - plus any factors allowed by NEC for specific load types - such as household cooking appliances. The fan is part of the appliance in those applications, but is still somewhat insignificant in demand from an appliance that has a heat element of maybe ten times the current the fan has.

Forget the dang fan... :blink:

Let's say we a have a self-cleaning oven (not a self cleaning oven in a range). Wikipedia says the self cleaning cycle lasts for approximately 3 hours. Let's say it goes over 3 hours. Is the oven considered a continuous load?

Now let's say we have essentially the same oven included in a range. Demand permits us to reduce the rated load but the demand load is less than the self-cleaning load. Is this range considered continuous or noncontinuous? Remember that your branch circuit is sized based on the demand load.

 

[kwired]

Forget the dang fan... :blink:

Let's say we a have a self-cleaning oven (not a self cleaning oven in a range). Wikipedia says the self cleaning cycle lasts for approximately 3 hours. Let's say it goes over 3 hours. Is the oven considered a continuous load?

Now let's say we have essentially the same oven included in a range. Demand permits us to reduce the rated load but the demand load is less than the self-cleaning load. Is this range considered continuous or noncontinuous? Remember that your branch circuit is sized based on the demand load.

Does the self cleaning cycle apply continuous voltage to the element during the entire cycle or is it just a situation of a higher set point then during regular operation and it will cycle when that set point is reached? I always presumed they still cycled once desired temperature is reached, but honestly don't know much about what happens either. I do know they reach dangerously high temps and that the door locks and will not unlock above a certain temperature.

 

[Smart $]

Does the self cleaning cycle apply continuous voltage to the element during the entire cycle or is it just a situation of a higher set point then during regular operation and it will cycle when that set point is reached? I always presumed they still cycled once desired temperature is reached, but honestly don't know much about what happens either. I do know they reach dangerously high temps and that the door locks and will not unlock above a certain temperature.

IDK either... but for the sake of discussion, let's say the elements are full on for the duration. In reality the question is whether wire I?R (internally-generated heat) causes the conductor temperature to exceed its insulation rating temperature.

 

[kwired]

IDK either... but for the sake of discussion, let's say the elements are full on for the duration. In reality the question is whether wire I?R (internally-generated heat) causes the conductor temperature to exceed its insulation rating temperature.

Well that also depends on if your conductor is at the upper or lower end of a particular row/column in ampacity table to begin with, plus the fact that we often use 75C minimum for terminations but can use 90C for adjustments to the insulation means that the insulation will not get too hot if the termination is sized correctly unless ambient temp or number of conductors in a raceway has to be applied.

 

[Smart $]

IDK either... but for the sake of discussion, let's say the elements are full on for the duration. In reality the question is whether wire I?R (internally-generated heat) causes the conductor temperature to exceed its insulation rating temperature.

Well that also depends on if your conductor is at the upper or lower end of a particular row/column in ampacity table to begin with, plus the fact that we often use 75C minimum for terminations but can use 90C for adjustments to the insulation means that the insulation will not get too hot if the termination is sized correctly unless ambient temp or number of conductors in a raceway has to be applied.

Granted.

So let's look at it from the perspective of termination temperature rather than insulation temperature...???