27 kw tankless water heater

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LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
To add, I haven't installed more tankless water heaters than I have installed. Allow me to 'splain:

A few years ago, a new, green (-ish) company called me about wiring the ones they wanted to sell. I explained I'd have to see each existing service and loading to price the work, and if it was feasible at all.

In almost every case, the customers weren't happy when they heard they'd need service upgrades, especially for the 28kw units, which they were told were "large enough for even the biggest families."

The worst was a stuffed 200a CH panel, supplying the house as well as two 100a sub-panels, one for a recent basement apartment with full kitchen, the other a 4-car garage with an upstairs apartment.

I told them they would absolutely need an upgrade, and I couldn't believe they hadn't had the main trip already. The husband later admitted to me that it had on a holiday or two. No big surprise there.

The company stopped calling me rather soon after. The few I've done for myself were ones I installed myself, including the plumbing. It's really no harder than replacing tank water heaters. I haven't done a gas one.
 

JOHNEO99

Senior Member
Well I studied International Trade not electric and if you read the whole thread you may or may not decipher that I was more curious if these elements all ran at the same time because technically I think 3- 40 amp breakers would be fine if not ran simultaneously. I really didn't think it through as far as I could of but hey sometimes this happens. I thank you for the vote of confidence. Yes I am licensed by the national test.



I talked to the distributor because I was worried about the lights dimming. I have read about this on the interwebs but he insists it wont be a problem in this scenario but now I am wondering again.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I talked to the distributor because I was worried about the lights dimming. I have read about this on the interwebs but he insists it wont be a problem in this scenario but now I am wondering again.

I'll admit I've never wired a tankless either but I have a VERY hard time believing the lights won't dim. I'd tell the customer your opinion on this too if it were my install. The manufacturer can say all they want but when the lights start dimming(if the main doesn't trip first!) you can bet you'll be in the customers crosshairs as well....

They need to stick with the storage type...
 

JOHNEO99

Senior Member
I'll admit I've never wired a tankless either but I have a VERY hard time believing the lights won't dim. I'd tell the customer your opinion on this too if it were my install. The manufacturer can say all they want but when the lights start dimming(if the main doesn't trip first!) you can bet you'll be in the customers crosshairs as well....

They need to stick with the storage type...



I may just do this. He says they have installed over a hundred of these and he is "in love" with this unit.

What makes you think this would it trip a 125a breaker?
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Turns out she has a 150 amp panel with 2/0 ran from the meter(200amp) to the panel. Sometimes you just gotta look yourself.

2/0 Aluminum? So the ampacity of the wire is 135A, and 310.15(B)(6) allows the 150A breaker. If your existing connected load is 37.5A you're in good shape, and should stop on the way home to buy a lottery ticket, because it is wildly implausible, since you're at around 30A without any electric appliances.

Think about this. 310.15(B)(6) allows a higher breaker to be used than normal due to the load diversity of a dwelling unit. You are about to dedicate 75% of the available power to a single appliance. Your load diversity just flew out the window.

Yes I am licensed by the national test.

What national test? :-?

They need to stick with the storage type...

Bingo!

What makes you think this would it trip a 125a breaker?

It won't trip it's 125A breaker. If they dare to turn any lights on, or run the dryer, or anything else, it will trip the 150A main.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I talked to the distributor because I was worried about the lights dimming. I have read about this on the interwebs but he insists it wont be a problem in this scenario but now I am wondering again.
Of course, he does. That's what they told customers in my situation above.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Thanks Chris

I mean I know how to do simple ohms laws but I was thinking the same thing about how they may not run simultaneously.

They changed this heater from 1-125 to 3-40amp breakers recently and I'm not sure why. I cant find the install pdf for this unit yet.Hopefully all three elements don't run at the same time for better efficiency or more consistent heating or something.

Who is "they" that changed the 125A to 3 40A breakers. If this has already been installed and wired, what are you trying to accomplish here. Did the condo owner call about checking this out or what? Sounds like there is already a problem with tripping breakers or lights dimming. This all sounds strange to me.
 

JOHNEO99

Senior Member
Who is "they" that changed the 125A to 3 40A breakers. If this has already been installed and wired, what are you trying to accomplish here. Did the condo owner call about checking this out or what? Sounds like there is already a problem with tripping breakers or lights dimming. This all sounds strange to me.

It hasn't been installed and the client is my mother in-law lol. She lives in one unit and rents the other unit. That statement was incorrect. I read 125A on the spec sheet then in the install manual it says 3-40 amp breakers. I caught that after the post.
 
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