Tankless Water Heater

[jar546]

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.

 

[mark handler]

Distance from Panel?

 

[jar546]

Distance from Panel?

20'

 

[chris kennedy]

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

 

[BLangley]

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

 

[mark handler]

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

 

[cda]

Non electric-an answer

8 on the wire

And 40 on the breaker

 

[jar546]

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

You are an ass. Lol

 

[Mr. Inspector]

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

How about a black one?

 

[jar546]

How about a black one?

Or white breakers.

 

[jar546]

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

 

[BLangley]

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.

 

[jar546]

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