Instant water heater

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steve66

steve66

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Illinois
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120 V. instant hot water heater draws 29 amps.

I consider it continuous, so I'll spec. it on a 40 A breaker. (29 * 1.25 = 36 amps, and 40 is the next standard size.)

Can I still specify #10 wire (since the load is only 29 amps), or do I need to use #8?

I guess I normally size the wire from the breaker size, so I would normally call out #8, but I'm just wondering if this is really necessary.

Steve
 
Why would you consider it continuous ? Does it operate 3 hours or more continuously ? Is it a "storage type" water heater (422.13) ?
 
I think he meant "continuous" because the current doesnt change in the operating period. It stays in 29 amp while somebody is using the instant water heater, in a shower I suppose.

If this is the case, then I have to say that my opinion is that it wont remain in 29 amp, because the current will increase or decrease depending on the caudal of the fluid flux.

"hope i mean what i meant, in the mind of the ment, I mean in the way that everybody mint..." :D
 
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No, its not a storage hot water heater. It's an instantanous hot water heater.

If someone leaves the sink on overnight, the hot water heater will run constantly.

If this is the case, then I have to say that my opinion is that it wont remain in 29 amp, because the current will increase or decrease depending on the caudal of the fluid flux.
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I'm not sure if you are serious or not:) I think the current will stay at 29 amps indefinately as long as the water runs.

Steve
 
Steve, I doubt this is considered a continuous load. Do the instructions make any recommendations?

If all else fails, pick a wire size depending on the type of conductors and the length of the circuit.
 
steve66 said:
I'm not sure if you are serious or not:) I think the current will stay at 29 amps indefinately as long as the water runs.
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Sorry, caudal = Discharge

Yes I was being serious in that line.

Dont you think it depends on how much water runs?

For example,

If you have a discharge of 1 m^3/s or one liter per second of water flowing in a pipe, It will take to the water heater, say 1 ampere to rise the temperature of that amount of water. Rise to a "Tf" temperature

What happens if you increase (open the valve) that discharge to 2 liters per second? Would you need the same amount of current to rise to the "Tf" temperature? would it get to the "Tf" temperature as well?

That was my point.
 
You could prove me wrong, but I would agree with Mayimbe in that it would be unusual for the load to remain at 29 amps. My experience has been the load fkuctuates with the water temperature.

If you wish to consider it a continuous load, and I can't say under certain unusual conditions it might be, then the calculated load would be 36 amps as you say. The next larger breaker would be a 40.
210.3 syas branch circuits will be rated in accordance with the ampere rating of the overcurrent device so, IMHO, the conductor would have to be a #8
 
augie47 said:
You could prove me wrong, but I would agree with Mayimbe in that it would be unusual for the load to remain at 29 amps. My experience has been the load fkuctuates with the water temperature.
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That would depend on whether it uses one or several elements, and how they're switched.
 
Mayimbe said:
Sorry, caudal = Discharge

What happens if you increase (open the valve) that discharge to 2 liters per second? Would you need the same amount of current to rise to the "Tf" temperature? would it get to the "Tf" temperature as well?

That was my point.
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I'm following you now, but I think these heaters are dumb devices, and they are either on or off.

If you turn the water on slowly, you get nice hot water, if you crank up the flow, you get luke warm.

For public restroom sinks, I know the State of Illinois has had some issues with these instant heaters, to the point where the manufacturers make a slightly different model that is "State of Illinois Compliant". I think there also has to be a mixing valve after the device to limit the water temp. Again, that's an Illinois Plumbing Code requirement.
 
augie47 said:
If you wish to consider it a continuous load, and I can't say under certain unusual conditions it might be,
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I'm having second thoughts about that continuous load thing.

The definition of continuious load says it is a load that would "be expected to run for 3 hours or more." It doesn't say every load that "could run for 3 hours or more."

It would be very unusual for someone to leave the water on for 3 hours. I think I can say that is not the "expected" mode of operation. So now I'm thinking #10 on a 30A breaker.

Steve
 
steve66 said:
I'm having second thoughts about that continuous load thing.

The definition of continuious load says it is a load that would "be expected to run for 3 hours or more." It doesn't say every load that "could run for 3 hours or more."

It would be very unusual for someone to leave the water on for 3 hours. I think I can say that is not the "expected" mode of operation. So now I'm thinking #10 on a 30A breaker.

Steve
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480sparky said:
The general consensus is there are no continuous loads in residential.
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I would agree with that but how do you look at 422.13? It says "...shall be considered a continuous load for the purposes of sizing branch circuits."
 
1793 said:
I would agree with that but how do you look at 422.13? It says "...shall be considered a continuous load for the purposes of sizing branch circuits."
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This is not a storage type water heater. It's an insta-hot type that only heats the water as it flows through it. By definition this is not a continuous load.
 
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