non simutanious water heater load

[Dbronx]

Jumper,

The water heater is single phase 208 volt, I'll check the name plate and get back to you in a day stay tuned

thanks

They make them and I bet a donut that is what the OP has.

http://www.miamiwaterheater.com/pdf/CommElecLightDuty.pdf

 

[Dbronx]

Augie,

The referance to 5000 watts and 4000 watts came from the tag on the elements. I will take some pictures and post them later

thanks

What voltage does the nameplate indicate ?
A common rating on an element is 4500 watt at 240 volts.. If you are using these on a 208 volt system your current will be less.
(also, double check your nameplate.. a 5000/4500 is highly unusual)

(david, I was typing as you posted..sorry.. same info basically)

 

[kwired]

My point was that they make small units even with 480V. I would have expected a lot larger units with 3 phase 480V. I have wired a 26 or 28 kw unit that was 3 phase so I know they make them bigger.

Point taken. Wasn't trying to hurt any feelings or anything like that.:angel:

 

[Dbronx]

With all the posts about amprage this WH is non simultaneous operation. What is the chances that both elements will be on at the same time and for how long. If my amp reading are don't change I would use 16amps X 125% = 20 amps for onr element, if both activated simultaneous would a 40 2P be sufficient

The calculated current of 16.3 amps and the measured value of 14 amps are not that much different.
16.3 amps at 208 volts would be less than 15 amps if the utility voltage is low and there is voltage drop between the service and the heater.
If the heater is only 95% of the nominal wattage, which is an entirely reasonable tolerance, then that is 14.25 amps, or within reasonable instrument error.

I would measure the actual voltage at, or close to the heater terminals.
If it is only drawing 14 amps on a generous 208 volts, then it may be faulty or wrongly marked.
If the actuall supply is about 190 volts, then 14 amps is about what should be expected.

 

[Dbronx]

Charlie B,

I concur, I will use a bit of tact when I converse with the inspector thanks for reinforcing my thimking.


QUOTE=charlie b;1401348]That, at least, is an error on the part of the inspector. Put a disconnect rated at 4000 amps in this application, if you like. That might prove unnecessarily expensive, and perhaps a bit awkward looking. But the only code requirement is that the disconnect be rated at least as high as the rating of the circuit in which it is installed. [/QUOTE]

 

[Dbronx]

How Does Voltage Effect Electric Tankless Water Heater Performance?
The wires that carry electricity from the electrical panel throughout the rest of a home or business are designed to carry a specific amount of voltage to each location they service. For instance, typical residential electrical wall outlets are wired with 110 volt. Appliances within a new home are typically wired with either 220 or 240 volts. Older homes and apartments may be wired with 208 volts. The stated ability for the amount of kW each electric tankless water heater can produce is based on a specific voltage.What is the effect of installing a tankless water heater rated at a Specific voltage to LOWER VOLTAGE?Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them. Basically, this means the capacity of the heating element or kW of the heating element drops.Example: The ECO 27 tankless water heater has three (3) heating elements rated at 9KW @ 240V. If the element is rated at 9KW @ 240V and you install to a 208V power supply, then this 9KW element will only put out 0.75 of its? rated capacity. (9 x .075 = 6.7) in this case this 9 kW element will become a 6.7 kW, thereby reducing the Temperature Rise and Outlet Temperature of the unit.
Following is the conversion from higher Voltage to Lower Voltage:
230V multiple KW by .92
220V multiple KW by .84
208V multiple KW by .75
IF kW is rated at:
5.5 KW at 208V becomes a 4.1 KW
6.0 KW at 208V becomes a 4.5 KW
9.0 KW at 208V becomes a 6.7 KW

 

[Dennis Alwon]

So this is a tankless water heater? I am more confused now then before. If it is tankless then you would have both elements on at the same time. As stated above 9kw at 240V is 6.76 at 208V. That means you need 32.5 amps

 

[infinity]

So this is a tankless water heater? I am more confused now then before. If it is tankless then you would have both elements on at the same time. As stated above 9kw at 240V is 6.76 at 208V. That means you need 32.5 amps

I was going to comment but now I'm waiting for the nameplate photo's.

 

[kwired]

If it is tankless the specs in the op says it holds 120 gallons:?

 

[readydave8]

If it is tankless the specs in the op says it holds 120 gallons:?

yes, that's a big tankless tank.

 

[Dennis Alwon]

If it is tankless the specs in the op says it holds 120 gallons:?

My guess it is a water heater with a tank but he posted info not realizing it was for a tankless setup.

 

[Dbronx]

No it is not a tank less water heater. That is part of the quoted paragraph that illustrates 240 volt heating elements on 208 volts, and how the watt will be lower. With a lower wattage the amperages would be lower. The main point I was trying to draw attention to was the under voltage formulas below that, and to show where I got the information from. I often copy passages and save for later reference. I must find where I got that information from, I did not read the Forum bylaws thoroughly .I may have committed a Mike Holt Forum violation I apologize.

So this is a tankless water heater? I am more confused now then before. If it is tankless then you would have both elements on at the same time. As stated above 9kw at 240V is 6.76 at 208V. That means you need 32.5 amps

 

[Dennis Alwon]

I may have committed a Mike Holt Forum violation I apologize.

Why is that. You have written that you are an electrician so I am not sure why the apology.

With resistant heat the amperage goes down when the voltage is decreased however with other loads the the amperage increases when the voltage drops. A motor will take more current to run on 120V then would the same motor on 240V. With resistant heat the element would just get hotter as the voltage goes up and thus increases the current.

R= V^2/Watts

If the voltage is 240 volts squared then we have 57600
Square the voltage at 208 and we get 43264

The ratio of43264/57600 = .75 So as your info stated 9000 watt units at 240 V is only 9000*.75= 6750 watts