Which is considered a continuous load?

[petersonra]

Im taking my journeymans exam in a couple of days and while studying I came across a question which has me stumped.

Which of the following is NOT considered a continuous load?

A. a stove
B. a flood light
C. a water heater
D. a fixed space heater

I answered a stove because most likely it would not be on for more than 3 hrs. at a time. Also the heating element doesn't continuously stay on while cooking.

A flood light would most likely be on all night. But based on what I am reading it says the answer is a flood light.

While studying I am finding a lot of info that is wrong. Could anyone please clarify this for me?

I would say the most likely answer is "A".

Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more.

A flood light would be expected to be on for 3 or more hours on a regular basis. that is just the nature of such lights. You could create a scenario where it is not true, but the majority of the time most spotlights one would EXPECT to be on for 3 continuous hours or more.

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L (120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.

So most common water heaters will be continuous.

424.3 (B) Branch-Circuit Sizing. Fixed electric space-heating
equipment and motors shall be considered continuous load

Fixed electric space heaters are always continuous.

This is a good example of a poorly worded question.

 

[kwired]

I don't know that it is all that poor of a question, but do disagree with the given correct answer. The flood light would be my first pick as to which is definitely the most continuous load from that group.:huh:

 

[infinity]

Never? :blink:

I agree a stove will not within reasonable probability. But that one extreme chance that it will is still out there. :happyyes:

Consider this scenario. Sub-zero temperatures outside. The gas furnace breaks down. Your HVAC guy can't make it until tomorrow. You have no backup means of heat other than the stove. Hey Mikey, let's turn on all the stove burners on high and set the oven on broil.

Yes, as I said never.

If so the NEC wouldn't allow us to connect a 12KW range to a 40 amp circuit.

 

[gadfly56]

I don't know that it is all that poor of a question, but do disagree with the given correct answer. The flood light would be my first pick as to which is definitely the most continuous load from that group.:huh:

Then you should re-read the question, and not the topic heading. Which one is NOT considered a continuous load?

 

[Smart $]

Yes, as I said never.

If so the NEC wouldn't allow us to connect a 12KW range to a 40 amp circuit.

But that does not automatically make it a noncontinuous load under all conditions. In fact that actually puts a stove closer to being a continuous load. I realize this is contrary to popular perspective, so bear with me for a moment and keep an open mind.

When determining maximum current for service, feeder, or branch circuit, Code requires it to be the calculated load per Article 220, i.e. the calculated load, correct? [210.19(A)(1), 215.2(A)(1), 230.42(A)] Code doesn't actually state it this way, but couldn't we say 'demand load'?

Where does Code say a stove shall not be a continuous load? Rhetorical question because it does not.

So we have a 12kW range with a [Code permitted] maximum demand of 8kW. At 240V, that's 33.3A. Considering this FACT and the definition of continuous load, the stove would only have to draw 33.3A for 3 hours?not 50A?to be a continuous load!!! :angel:

 

[charlie b]

Sorry, Smart $, but I am not buying that reasoning. The definition of continuous load speaks of drawing the maximum current, not the calculated (demand) current. In any event, the heating elements do not remain on continuously, or else the oven would never be able to maintain the set temperature.

 

[Smart $]

Sorry, Smart $, but I am not buying that reasoning. ...

I expect many to be of the same persuasion.

There are many out there that'll claim to have an open mind... but the only thing their mind is open to is their own mind. :slaphead:

...The definition of continuous load speaks of drawing the maximum current, not the calculated (demand) current. ...

That's an assumption of fact not yet in evidence.

Look at 215.2(A)(1) for example. It refers to load as calculated in Article 220. If we do not use the calculated load as the basis for maximum current, then when you calculate the noncontinuous load plus 125 percent of the continuous load, you'd have to use 12kW as the basis for noncontinuous stove current...

...but I don't see you as agreeing with that rationale either. :happyno:

...In any event, the heating elements do not remain on continuously, or else the oven would never be able to maintain the set temperature.

Last time I checked, BROIL and HIGH settings are typically full on and not thermostatically controlled. FWIW, I will admit I haven't had an electric range in well over three decades.

 

[mbrooke]

I expect many to be of the same persuasion.

There are many out there that'll claim to have an open mind... but the only thing their mind is open to is their own mind. :slaphead:


That's an assumption of fact not yet in evidence.

Look at 215.2(A)(1) for example. It refers to load as calculated in Article 220. If we do not use the calculated load as the basis for maximum current, then when you calculate the noncontinuous load plus 125 percent of the continuous load, you'd have to use 12kW as the basis for noncontinuous stove current...

...but I don't see you as agreeing with that rationale either. :happyno:

Last time I checked, BROIL and HIGH settings are typically full on and not thermostatically controlled. FWIW, I will admit I haven't had an electric range in well over three decades

.

If the oven gets to hot they do shut down, but even then the broil element is only at most 16 amps at 240 volts (3,800 watts). Heck lets say 25 amps for high ends. It will never reach the 40 or 50 amps of the circuit. Id would even say that applies to an in wall oven as well.


What is the rational behind this question, I still cant grasp it.

 

[Smart $]

....

What is the rational behind this question, I still cant grasp it.

Don't worry about it. It stems from probability analysis and inferred (or not) definition of terms.

 

[kwired]

Then you should re-read the question, and not the topic heading. Which one is NOT considered a continuous load?

I was aware of the question - I just happen to think the heat lamp is definitely a candidate for being most continuous of the items in that list - yet the "correct" answer to question indicated this was least likely candidate for being a continuous load.:roll:

Last time I checked, BROIL and HIGH settings are typically full on and not thermostatically controlled. FWIW, I will admit I haven't had an electric range in well over three decades.

That was typical for older and maybe still is for new open type heating coils. But I don't think those coils would last for 3 hours without a huge pot of water to sink the heat away from them either. Maybe some designs with lower watt density might - but they also wouldn't heat fast enough to be very popular for the cooks.

I have an electric "glass top" range at home. If you turn the cooktop elements on "high" they do cycle to prevent too rapid heating of the top, is especially noticeable if no cookware on the top.

 

[Smart $]

...

That was typical for older and maybe still is for new open type heating coils. But I don't think those coils would last for 3 hours without a huge pot of water to sink the heat away from them either. Maybe some designs with lower watt density might - but they also wouldn't heat fast enough to be very popular for the cooks.

....

FWIW, I was once in the faulty-furnace scenario I posted earlier long, long ago. No Mikey involved, but all elements on high for more than 3 hours. They did not cycle and they did not burn out.

 

[kwired]

FWIW, I was once in the faulty-furnace scenario I posted earlier long, long ago. No Mikey involved, but all elements on high for more than 3 hours. They did not cycle and they did not burn out.

If they had air flow over them they are in "normal operating conditions", if no air flow they likely shut down because of operation of high limit thermostats, but will cycle if high limit is automatic resetting.

 

[Smart $]

If they had air flow over them they are in "normal operating conditions", if no air flow they likely shut down because of operation of high limit thermostats, but will cycle if high limit is automatic resetting.

It was an old oven by today's standards. It probably had a bimetal thermostat for controlling oven temperature... and that's it. Air flow was by convection only. No fans were in use.

 

[kwired]

It was an old oven by today's standards. It probably had a bimetal thermostat for controlling oven temperature... and that's it. Air flow was by convection only. No fans were in use.

Well then you had an item designed to operate at pretty high temp to begin with, my comment was based primarily on fan forced heating appliances - lose the fan and often the watt density is high enough the elements will melt down without any air flow over them, but I did not know any details of your application either.

 

[Carultch]

I answered a stove because most likely it would not be on for more than 3 hrs. at a time. Also the heating element doesn't continuously stay on while cooking.

What about when you are cooking a large pot roast or another huge cooking project, that requires 4 hours to cook? Although someone who has a cooking project that large, would most likely have a gas stove.

How about ovens? Certainly ovens operate for more than 3 hours when it is Thanksgiving, and the people are cooking turkeys for 5 hours, or even overnight as I like to do.

 

[david luchini]

What about when you are cooking a large pot roast or another huge cooking project, that requires 4 hours to cook? Although someone who has a cooking project that large, would most likely have a gas stove.

How about ovens? Certainly ovens operate for more than 3 hours when it is Thanksgiving, and the people are cooking turkeys for 5 hours, or even overnight as I like to do.

Even if you cook your turkey overnight, the oven will not be a continuous load. The "maximum current" of the oven will not continue for 3 hours or more, the oven will cycle on and off with thermostatic control.

 

[K8MHZ]

FWIW, I was once in the faulty-furnace scenario I posted earlier long, long ago. No Mikey involved, but all elements on high for more than 3 hours. They did not cycle and they did not burn out.

The switches used in the above were likely 'infinite control switches' which were very common. On the HI setting, the element contact is held closed for a 100 percent duty cycle.

http://www.electrical-forensics.com/ElectricRanges/ElectricRange.html

 

[GoldDigger]

Even if you cook your turkey overnight, the oven will not be a continuous load. The "maximum current" of the oven will not continue for 3 hours or more, the oven will cycle on and off with thermostatic control.

Just about the only time the oven is likely to run continuously is when you have switched on the broiler element and set the oven door partially open.
Even then you would have to keep switching in new food to broil to need 3 hours continuous.

 

[Carultch]

Just about the only time the oven is likely to run continuously is when you have switched on the broiler element and set the oven door partially open.
Even then you would have to keep switching in new food to broil to need 3 hours continuous.

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?

 

[GoldDigger]

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?

Yes, the fan power is usually negligible compared to the heating element.

So the unit is not pulling anywhere near the maximum rated current all the time.