How do you determine continuous vs. non-continuous?

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ericsherman37

ericsherman37

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I've been doing lots of practice calculations at class lately and the issue keeps popping up. How do you decide if something is a continuous load or not? I know the definition is something that runs or operates for 3 or more hours at a time, but there are lots of types of equipment that you can't really be sure on.

A garbage disposal in a house is definitely not likely to be continuous. But what about like.... a sump pump motor? If it's iffy, should I just play it safe and figure the circuit for 125%?
 
ericsherman37 said:
I've been doing lots of practice calculations at class lately and the issue keeps popping up. How do you decide if something is a continuous load or not? I know the definition is something that runs or operates for 3 or more hours at a time, but there are lots of types of equipment that you can't really be sure on.

A garbage disposal in a house is definitely not likely to be continuous. But what about like.... a sump pump motor? If it's iffy, should I just play it safe and figure the circuit for 125%?
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NEC 2008 Definition
Article 100-Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.
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If it is expected to run for 3 hours, assume it is continuous.
 
ibew441dc said:
NEC 2008 Definition


If it is expected to run for 3 hours, assume it is continuous.
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"Run" for more than 3 hour and being "on" for 3 hours are not the same thing. Say it were an oven? It might be on all day, but the elements would shut off once it reached tempature.
 
ericsherman37 said:
I've been doing lots of practice calculations at class lately and the issue keeps popping up. How do you decide if something is a continuous load or not? I know the definition is something that runs or operates for 3 or more hours at a time, but there are lots of types of equipment that you can't really be sure on.

A garbage disposal in a house is definitely not likely to be continuous. But what about like.... a sump pump motor? If it's iffy, should I just play it safe and figure the circuit for 125%?
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A sump pump is a motor - treat it like one. ;)
 
e57 said:
"Run" for more than 3 hour and being "on" for 3 hours are not the same thing. Say it were an oven? It might be on all day, but the elements would shut off once it reached tempature.
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And your point? Run = slang for on at max
 
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Gotcha!

Gotcha!

e57 said:
Point = just because it is on it may not be under full load that whole time. Other words like RUN are the same. What is RUN - electrically?
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I see what your poking at:wink:.....
When I made original post.....I was assuming that one would consider the sump pump in question. I don't remember seeing a sump with two speeds, so I was assuming it would be running at max speed (or max current), for more than three hours.
 
ibew441dc said:
I see what your poking at:wink:.....
When I made original post.....I was assuming that one would consider the sump pump in question. I don't remember seeing a sump with two speeds, so I was assuming it would be running at max speed (or max current), for more than three hours.
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Odds are unless there is major flooding (At which point there are other problems...) - it would run for a minute or two at a time - it would otherwise be off due to the flow switch. See 430.24~26
 
ibew441dc said:
A vacuum is a Continuous Load if you have a really big house;):grin:
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No matter how large our house is, I'm sure my wife would never vacuum for 3 hours straight. If she did, I'd need to be somewhere else when she got done cuz she'd be a smidge grouchy. :) I don't want to hear "if you could afford a house that big, you could afford to pay someone to clean it" either. I used to say that, and now I've lived long enough to know it isn't true. :D

A motor does not make a motor load. The list could go on with ceiling fans, HVAC units, washing machines, etc.

I agree that the sump is an appliance. I've got a sewer manhole right outside my house (everyone in my sub-division does) that kicks on a pump to empty it when it fills to a certain point. If that motor has ever been on for more than 1 minute continuously I'd be very surprised.
 
But motor bc conductors are sized at 125% and some, such as pumps are sized at 140%
Here is the table-it didn't come in right, take a look in the NEC
Table 430.22(E) Duty-Cycle Service

Nameplate Current Rating Percentages
Classification of Service 5-Minute
Rated Motor 15-Minute
Rated
Motor 30- & 60-
Minute
Rated
Motor Contin-
uous
Rated
Motor
Short-time duty operating valves, raising or lowering rolls, etc. 110 120 150 ?
Intermittent duty freight and passenger elevators, tool heads, pumps, drawbridges, turntables, etc. (for arc welders, see 630.11) 85 85 90 140
Periodic duty rolls, ore- and coal-handling machines, etc. 85 90 95 140
Varying duty 110 120 150 200
Note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use.
 
ericsherman37 said:
I've been doing lots of practice calculations at class lately and the issue keeps popping up. How do you decide if something is a continuous load or not? I know the definition is something that runs or operates for 3 or more hours at a time, but there are lots of types of equipment that you can't really be sure on.

A garbage disposal in a house is definitely not likely to be continuous. But what about like.... a sump pump motor? If it's iffy, should I just play it safe and figure the circuit for 125%?
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There is the definition of Continuous Load in Article 100.
There are also other locations in the NEC that deal with what may be considered as continuous load, such as 422.1 Storage-Type Water Heaters and 424.3(B), etc...
 
Well maybe the sump pump was a bad example. It was just something that popped into my brain. My point was, what if you come across some sort of equipment that you're not really sure if it might operate continuously or not? Thinking about it now, I suppose it's obvious that I would go on the safe side and size it for a continuous load just in case.
 
There is a difference between continuous load and continuous duty. Example D3(a) in Annex D is so helpful in making this distinction.
 
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