And to build onto that....review 422.3(B) and 440 for additional insight before you head over to 215.2(A) as well.take a look at 215.2(A).
IMO & based on the definition of continuous load which working continuously for a min 3 hrs, the water heater is not a continuous load & for the air conditioning (all fans are continuous loads and compressors are non-continuous loads).
You'r right but don't you see a conflict with the definition of the continuous load?When and where in this thread was water heater mentioned?
Water Heaters are considered continuous loads per 422.13, 2011.
Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more.
Your family does not take three hour showers?You'r right but don't you see a conflict with the definition of the continuous load?
I'm sorry but where home was mentioned in OP? my proposal pertains to commercial applications, aside from that the water heater in homes are switching off automatically based on thermostat control even if the shower takes 10 hrs.Your family does not take three hour showers?
More seriously, if you look at the ratio of the power input of an instant (on-demand) water heater to that of a conventional water heater, you may be willing to consider that a conventional heater may have a low enough recovery rate that occasionally household use will result in the heater element staying on for three hours or more?
You'r right but don't you see a conflict with the definition of the continuous load?
Not really....You'r right but don't you see a conflict with the definition of the continuous load?
True, but what size elements do you have in your water heater? I have 50-55 deg incoming water temp and a 4500 watt 80 gallon water heater, I can have fairly warm water in about half an hour - it will not last for too long at this point for baths or showers but if no water is being used I'd think it likely is able to get to 120 degrees before 3 hours are up.Not really....
Fact is, if the ground water coming in to a water heater (recently drained by a teenager who likes to take a 40 minute shower) is very cold it may take the elements more than 3 hours to come up to 120 degrees. The rate of rise may be only 15-20 degrees an hour and if the water coming in is 50 degrees, it will take 3 or more hours to come up to the temperature settings. So to acknowledge this fact, Section 422.12 considers this a continuous load when sizing the branch circuit.
Makes perfect sense to me.
Just say "Yes" you are correct MasterTheNEC and end it with that true statement...True, but what size elements do you have in your water heater? I have 50-55 deg incoming water temp and a 4500 watt 80 gallon water heater, I can have fairly warm water in about half an hour - it will not last for too long at this point for baths or showers but if no water is being used I'd think it likely is able to get to 120 degrees before 3 hours are up.
OK I just looked up how much heat is needed to raise the water a specific temp, it should take 12.69 kilowatt hours to raise 80 gallons of water 65 deg F(120-55). If a 4500 watt element ran for 3 hours it would use 13.5 kilowatt hours, so the 80 gallon tank should fully heat to 120 within three hours if incoming temp was 55, if no water was used during this time. If water is being used it gets more complicated as it will depend on the rate it is being used, but you could have periods of over three hour run time pretty easily I would guess.
Yes you are correct.:happysad: An electric water heater will heat ground water to 120? in less than an hour with the standard 4500 watt elements. But why are we on water heaters?Just say "Yes" you are correct MasterTheNEC and end it with that true statement...
... But why are we on water heaters?
We got slightly derailed from OP at determining what is a continuous load, plus OP is addressing feeders and not branch circuits - so maybe the question is can a load be continuous for branch circuit calculations but not for feeder calculations? I say sometimes it can be that way.But why are we on water heaters?