I am trying to understand how add this water heater load to my All electric Residential Load calc. This Electric Tankless water heater use 3 x 40A breakers. Brand new house , I suppose it is been review by the Engineers but this Water heater is bumping up my numbers way over my main breaker . Any Idea how a brand new house was designed this way?
ELECTRIC WATER HEATER
- Thread starter ING23
- Start date
Looks like 4 40 amp breakers, not 3. What is the KW rating if the heater? It will go into the load Calc at 40% of that, but even that is going to add about 50 amps or so on its own. Maybe it fits, but show your load calc. Many people end up not liking tankless electric water heaters because of flickering lights and they still may not be powerful enough if two showers are going at once.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
.... and only 1 kitchen GFCI??
I see 2…
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
In my opinion, those four 40a breakers should be in their own 200a panel, perhaps with one or two other line-to-line loads. I have upped a 200a to 320/400a just for a tankless with the same 4 x 40s.
ptonsparky
Tom
- Occupation
- EC - retired
I just read a paper on these water heaters and the POCOs supply. The case under study required a doubling of the transformer feeding the house. 25 to 50 KVA. VD was still noticeable, but livable. The paper suggested that POCOs are adjusting what they will provide and will add costs to compensate for theses WH demands.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I always discouraged homeowners from choosing electric. The gas ones IMO are better
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
What method are you using for calculating the load? It is pretty amazing what the nec will allow on a 200 amp service.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
No. Or rather, I do have one idea: someone didn't know what the @#$%! they were doing.
I'd almost go so far as to say these things should be banned. Heat pump water heaters are more energy efficient.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
That whole panel is a mess. Why would anyone start off fresh with too few spaces for the loads? The panel is using quads and twins right off the bat. Looks like a 30 space panel, and should have been a 40. Actually, with the four 40's, it should have been a 400A service with two panels.
ramsy
Roger Ruhle dba NoFixNoPay
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
Are all those 2-Pole locking mechanisms typically needed for appliances?
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I don't see why a dryer would need one, and the HVAC should have a disconnect outside. The oven and cooktop probably need the lock as they are hardwired.
ramsy
Roger Ruhle dba NoFixNoPay
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
If fuse box is within sight, does lockable OCP avoid HVAC disconnect?
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
The panel would have to be outside to be "within sight".
ramsy
Roger Ruhle dba NoFixNoPay
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
Op is in Las Vegas, which was on 2017 NEC, until 3/23/23 adoption of 2021 IBC (using 2020 NEC).
Las Vegas appears to adopt codes without amendments, including AFCI's, not found in Op's photo of fusebox.
Notice labels for kit/bath breakers to GFCI outlets, but Bedroom breakers not labeled to AFCI outlets.
Unqualified & deliberate construction defect are typically ignored during occupancy, especially remodel outlets, when furnishings may block access to inspection points.
Virgin real-estate may be unmolested, but plenty of track home defects pass inspection, and nothing avoids tax assessors & AHJ's more than property sales.
Custom home builders may be the last bastion of good construction.
Last edited:
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
My point was simply that a competent person doesn't install a 150A water heater on a 200A service for a single family home. You get a different water heater or a different size service.
Another way to put it is that most people don't bother to actually do load calcs for new single family homes, and just spec a 200A service. And most of the time that works out fine. But not with an electric on demand water heater.
I agree that the other details suggest that this wasn't the only aspect of the electrical that was rushed and sloppy.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I just did a load calc using 32 amps x4 for the water heater or 30,720 watts. I used 4,000 sq.ft added the typical range, dryer, microwave, dw, etc. I used 10000 watts for the a/c unit. I came up with 183 amps using the optional cal and 238 using the standard
Yes , this is in Henderson NV, the OP photo is not an isolated house, this is a Town house and like this , could be 60 or maybe more house with the same water heater. This is the first time I see a Tankless water heater like this one on a dwelling unit. I understand all your concerns, but my question was .. how to deal with this kind of appliance on a Load Calc.
Attachments
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Are you familiar with the optional calculation...
Honestly , no