mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
New Water heater circuit too small
- Thread starter brother
- Start date
- Status
brother
Senior Member
like the others said, 2000 watt technically would be too much per NEC.
water heaters are continuous loads per NEC.
a 2000/120v = 16.66666667
16.67 x 1.25= 20.833
need a minimum of 25 amp breaker and # 10 copper for 2000 watt heating element at 120volts.
So the 3000/120v = 25 amps
25 amps X 1.25 = 31.25
minimum breaker and branch circuit size, 35amp. # 10 cannot be on a 35 amp breaker (cannot meet the exception like motors etc..), so would need # 8 thhn/thwn copper wire on 35 or 40 amp breaker.
No room to pull larger wire (barely got number #12 currently there) because of other circuits in the box and conduits etc.. They should have called us, electricians, when they first walked the job, but that wasn't the case and ordered the right size (wattage) water heater that would be COVERED under the WARRANTY (that they seem to be crying about now)Now this nonsense is happening.
Thanks for the responses.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
That also means there's no room to pull another hot #12 and use 240 volts.
(re-identifying a white wire is a violation in conduit, and there's a nonzero chance some other circuit shares this white wire)
Is that a common size combination? I’d expect anything that big to have a pair of 4.5 KWs.
ptonsparky
Tom
- Occupation
- EC - retired
Certainly not for an above the ceiling one, like the one in the OP.
kwired
Electron manager
- Location
- NE Nebraska
In reality probably not very often. NEC still says you must consider them to be continuous load. 422.13.
kwired
Electron manager
- Location
- NE Nebraska
That also depends on how cold the start is. Where I am municipal water is warmer just from sitting in the piping system vs what the water coming directly from the aquifer is. If on a private well you usually have colder incoming water as a general rule. Mine is around 55F once you have purged the lines of warmer water. Municipal water could easily be 10 degrees warmer when there is low demand on the system. Or at my last place the incoming water was a little shallow in depth near the street as they had taken some dirt off top back when they paved that street. In really cold winters the frost level got closer to that depth you could tell the incoming water was colder and it did burst the line one year.
kwired
Electron manager
- Location
- NE Nebraska
4.5 kw you would think would be what is commonly stocked in a 240 volt rating anyhow. Other ratings likely cost more simply because of volume sold on that particular model and also normally be a special order.
For a 120 volt unit you possibly could have a 3000 watt unit, but even that is too much for 10 AWG supply conductor needs to be less than 2880. I once had roughed in 10 AWG as is typical for a WH then customer comes up with a 120 volt unit. Don't remember what wattage was but do remember I simply moved the white to the neutral bus in panel, and just used one pole of the 30 amp breaker I already had for it, so must have been 2880 or less. I do remember inspector looking at my local disconnect, white was ok to disconnect if simultaneously disconnecting, he got out his black marker and began to mark the white conductors, I had to tell him it was a 120 volt unit and that is why it was not marked.
Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
One would need to consider derating as well since its raceway with other conductors in it.
My first thought was cable not raceway.
Maybe run a new MC cable.
Thanks for the math lesson.
Now in English please.
I'll get out my conversion calculator.
How did you get 160 kilograms. With small of elements. Volume effects calculated time at zero flow.
kwired
Electron manager
- Location
- NE Nebraska
IIRC one liter of water has a mass of 1 kilogram. Dissolved content I imagine can change this some.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
kwired
Electron manager
- Location
- NE Nebraska
Step up/step down and spend more than what the WH costs just so you can use the existing conductors?
Some guys like to step over dollar bills so they can pick up nickels.
brother
Senior Member
I personally have never had to do the calculation for the heating of water per kilogram etc.. Thanks for the math info. We let the plumbers decide how big of a water heater to install in a place. We just let them know what circuit size would be needed. Good info to know, I was curious how the past old engineers came up with the continuous load calculation for water heaters.
As for the water heater circuit issue, I think they might just go with the changing of the heating element because that would be the cheap and easy route, even though it voids the warranty.
Lesson on how NOT to do a job. Make sure you have qualified people (electricians etc..) to walk it with you and to turn off the circuit at the panel if they want the electrician to connect the wiring. Another (minor) code violation they had was that they didn't have a local disconnect at the water heater, or a lockable breaker at the panel.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
If getting new conductors to the installation is prohibitive (for whatever reason) then you should consider alternatives.
Once the cost of the alternatives is considered, then maybe pulling the proper conductors isn't so prohibitive.
FWIW if a step up were considered, I would change the heating element to match, not use step up/down.
Jon
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
A 3000 watt heater at 120 volts is about 25 amps. It should surprise no one that it ran all these years without any issues on a 20 amp ocpd.
Bottom line. It does not meet code. If whomever is footing the bill wants it to meet code, it is going to cost some money.
I don't know how you can claim that it's a 3-hour heat up time because you don't know what the temperature of the water coming in is or what the setting is.
The calculation is simple. It takes 1 btu to raise the temperature of 1 pounds of water 1 degrees F. 3000 Watts is a little over 10,000 btu per hour. Three hours would be about 30,000 btu. Thirty gallons of water is about 250 pounds so in three hours you could raise the temp of the water by about 120 degrees.
Bottom line. It does not meet code. If whomever is footing the bill wants it to meet code, it is going to cost some money.
I don't know how you can claim that it's a 3-hour heat up time because you don't know what the temperature of the water coming in is or what the setting is.
The calculation is simple. It takes 1 btu to raise the temperature of 1 pounds of water 1 degrees F. 3000 Watts is a little over 10,000 btu per hour. Three hours would be about 30,000 btu. Thirty gallons of water is about 250 pounds so in three hours you could raise the temp of the water by about 120 degrees.
Last edited:
Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
For fun we could consider VD and re run the numbers for a 20 amp breaker/ #12 thhn branch circuit. Let go with a 6 (5%)volt drop @120v, 2000w 120v rated element. 
Now are we good with no derating?
I do know 3% on branch is recommended.
Just fun math for those in the field why thing work when the should not according to the book.
Now are we good with no derating?
I do know 3% on branch is recommended.
Just fun math for those in the field why thing work when the should not according to the book.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I think the watt rating is at 125 volts too so at 114 volts you are looking at about 21 amps.For fun we could consider VD and re run the numbers for a 20 amp breaker/ #12 thhn branch circuit. Let go with a 6 (5%)volt drop @120v, 2000w 120v rated element.
Now are we good with no derating?
I do know 3% on branch is recommended.
Just fun math for those in the field why thing work when the should not according to the book.
Tulsa Electrician
Senior Member
- Location
- Tulsa
- Occupation
- Electrician
Did some quick checks. All I could find is 120v rated.
I did say fun math.
Then we can add, what the max length would be for the VD @6 v
With 6 CCC in raceway.
I did say fun math.
Then we can add, what the max length would be for the VD @6 v
With 6 CCC in raceway.
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