# Tankless Water Heater



## jar546 (Aug 8, 2019)

If an electric, tankless water heater has a tag showing it is listed by an approved agency with the following information on the label:  240v, 10kw, 42A, what size wire and circuit breaker would be required by code in the absence of manufacturer's installation instructions?

Please don't turn this into a discussion about manufacturer's instructions.  This is a legit code question.  You have all the information you need.


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## mark handler (Aug 9, 2019)

Distance from Panel?


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## jar546 (Aug 9, 2019)

mark handler said:


> Distance from Panel?



20'


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## chris kennedy (Aug 9, 2019)

I would use a circuit breaker that is 
2” x 2” x 2 1/2”


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## BLangley (Aug 9, 2019)

Spent lunch reading and looking at a bunch of tables...

6 AWG and a 55-amp breaker

We don't have a conductor to carry 45-amps, so we step it up.

I got my head spun around a few times on the breaker sizing, so I've got two reasons (or one 2-part reason) to use a 55 vs a 45:

1) no manufacturer instructions saying a 100% uptime 45-amp is okay
2) 42*125 = 52, so to get a breaker that isn't loaded at more than 80% if the heater runs over 3-hours continuously, we go 55

Some of the reading I was doing mentioned over-sizing the conductor the same way, but I don't know if that is required here...don't have the actual code, just snippets and parts in articles


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## mark handler (Aug 9, 2019)

*Wire Size*
6 Copper  4 Aluminum 
https://www.electricaltechnology.org/2014/04/electrical-wire-cable-size-calculator.html


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## cda (Aug 9, 2019)

Non electric-an answer 

8 on the wire

And 40 on the breaker


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## jar546 (Aug 9, 2019)

chris kennedy said:


> I would use a circuit breaker that is
> 2” x 2” x 2 1/2”


You are an ass.  Lol


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## Rick18071 (Aug 9, 2019)

chris kennedy said:


> I would use a circuit breaker that is
> 2” x 2” x 2 1/2”



How about a black one?


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## jar546 (Aug 9, 2019)

Rick18071 said:


> How about a black one?



Or white breakers.


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## jar546 (Aug 9, 2019)

I would like if those interested would take the time to read NEC 422.11(E) and see how this applies to this situation.


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## BLangley (Aug 12, 2019)

Applying 422(E)(3) suggests a 65 amp is okay (42*1.5=62, step up to a 65), but doesn't that get into potentially enough amperage to overheat the conductor without tripping the breaker?

Still reads to me like the 55 is better- doesn't exceed the 150% max.


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## jar546 (Aug 12, 2019)

BLangley said:


> Applying 422(E)(3) suggests a 65 amp is okay (42*1.5=62, step up to a 65), but doesn't that get into potentially enough amperage to overheat the conductor without tripping the breaker?
> 
> Still reads to me like the 55 is better- doesn't exceed the 150% max.



Yes, I too am having issues with applying 422.10(E)(3) but it is legit


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