80% breaker restriction

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cflava

cflava

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Greensboro, NC
I have a question about the 80% restriction mentioned in the NEC 2005 230.208 (B). With that in mind, do have to take this into account when figuring the load for lighting. Say, if you know that a certain 20A circuit will have 75W bulbs do you just take the 120V and multiply that by the 20A (2400W) and that will give you your maximum light per circuit or do you also have to factor in the 80% (1920W)? Outside of lighting, what other types of loads would you apply this to? I know that continuous loads and motors have different calculation methods. Thanks for any input you can provide.
 
If this is a commercial installation the lighting is most likely a continuous load and the 80% would be applicable. If you know the load will not be on for three hours at a time you can use the circuit at 100%.

Roger
 
Roger, what about other loads. Does this apply to say, receptacles. Basically, outside of motors, does the 80% only pertain to continous and not to non-continous?
 
cflava said:
Roger, what about other loads. Does this apply to say, receptacles. Basically, outside of motors, does the 80% only pertain to continous and not to non-continous?
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It is very difficult to determine what 80% of a receptacle load is unless you know exactly what is plug in and what won't be plugged in. How would you load a receptacle to 100% or 80% for that matter?
 
iwire said:
That will be less than 80% of the circuit rating....unless you have changed the cord cap.


Now plug in two...
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Not really, I'm looking at a heater right now rated 120v 1500W 12.5A and it has a standard 15A plug on it(no modifications done). Now if you plug that in on a 15A circuit you will be over the 80%.
 
chevyx92 said:
Not really, I'm looking at a heater right now rated 120v 1500W 12.5A and it has a standard 15A plug on it(no modifications done). Now if you plug that in on a 15A circuit you will be over the 80%.
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Firstly, we are talking about a 20 amp circuit and secondly, that is my point-- how do you know what others will plug in. So what is your point in refernece to what I was responding to. Are you saying that when you install outlets you know how to install them at 80% or 100% of the load.?
 
Dennis Alwon said:
Firstly, we are talking about a 20 amp circuit and secondly, that is my point-- how do you know what others will plug in. So what is your point in refernece to what I was responding to. Are you saying that when you install outlets you know how to install them at 80% or 100% of the load.?
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No that's why its called a "general purpose branch circuit". You asked how would you load a receptacle to 100% or even 80%. I just told how you could. And what you quoted me was a response to Iwire.
 
chevyx92 said:
No that's why its called a "general purpose branch circuit". You asked how would you load a receptacle to 100% or even 80%. I just told how you could. And what you quoted me was a response to Iwire.
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My response was to you. Yes you could load a circuit by finding the right amp appliance or whatever and plugging it in but the OP asked about loading a breaker to 100% or do you have to load it at 80% max. On continuous loads (more than 3 hours) you would have to load the breaker to 80% of its capacity.

He then asked if receptacles would fall under that rule. My point was there is no way to know what 80% or 100% of that circuit will be on general purpose receptacles. At any given time the load will be different so how do you figure it at 80% or 100% load when you are designing the circuit.
 
Dennis Alwon said:
My point was there is no way to know what 80% or 100% of that circuit will be on general purpose receptacles. At any given time the load will be different so how do you figure it at 80% or 100% load when you are designing the circuit.
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I agree you don't do that for general purpose receptacles.
 
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