Instantaneous water heater

[hhsting]

I have on plans instantaneous water heater 10kw at 277V single phase. The breaker size provided on plans is 50A. The full load amps of heater comes out to 36.10a.

The water heater manufacturer instruction recommends minimum branch circuit cable size of #8 awg at 75 deg C. The instruction says protected by the correctly rated circuit breaker but does not say the size nor if water heater is considered continuous or non continuous load.

The water heater is Eemax Spex100T. Below link is the water heater’s instruction manual:

https://s3.amazonaws.com/WebPartners/ProductDocuments/0C61D402-27CC-4BC0-B2EB-0ECF742898CF.pdf

Question:

1. Where does NEC 2017 section 422 talk about instantaneous water heater breaker sizing?

2. What size is the breaker should be based on instructions and NEC 2017? It gets confusing

 

[don_resqcapt19]

422.11(E)(3)

 

[Buck Parrish]

I am pretty sure water heaters are considered continuous. So I think you're good with a 45 or 50 amp breaker. With exceptions like If it's THHN in conduit.

 

[hhsting]

I am pretty sure water heaters are considered continuous. So I think you're good with a 45 or 50 amp breaker. With exceptions like If it's THHN in conduit.

Huh? Instantaneous water heater are they not non continuous so breaker size should be 40A breaker however where is this in NEC 2017 or in the water heater instruction?

 

[Buck Parrish]

I don't think that's in the NEC. I heard it some where, so it's hear say But some people use a lot of hot water

 

[Buck Parrish]

You may be right. It may be non continuous look in the definitions of article 100

 

[hhsting]

You may be right. It may be non continuous look in the definitions of article 100

definition of what? Instanteous water heater?

 

[Buck Parrish]

I don't think it's in Art 100. We know continuous is in their.

Are you using romex NM ?

 

[hhsting]

I don't think it's in Art 100. We know continuous is in their.

Are you using romex NM ?

No Emt. This is for commercial office space and wtr htr is in pantry. Why?

 

[robertd]

No Emt. This is for commercial office space and wtr htr is in pantry. Why?

NM can only be used at it's 60 degree C ampacity, even though it's insulation is rated at 90 degrees C.

 

[augie47]

Post #2, the plans are correct, and the mfg instructions are correct.
Not continuous (see definition)

 

[suemarkp]

I am pretty sure water heaters are considered continuous. So I think you're good with a 45 or 50 amp breaker. With exceptions like If it's THHN in conduit.

Storage types are (NEC 422.13) but I would not consider an instant water heater to run for 3 hours. EVen I don't take showers that long even if the hot water never runs out.