Hot water tanks

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Big Guns

Member
Good Morning

If you have a 80 gallon electric hot water tank @ 208 volts with two elements @ 4500 watts a piece non simultanious. do figure the amps @ 4500 watts or 9000 watts.
 

e57

Senior Member
It should have a min OCP - max OCP listed on the data plate...

So the question is: 3 Phase or single phase? Anyway I would do it at 9000VA - unless there is something else that should be known.
 
Good Morning

If you have a 80 gallon electric hot water tank @ 208 volts with two elements @ 4500 watts a piece non simultanious. do figure the amps @ 4500 watts or 9000 watts.
For non simultanious useage just go by one element like your qoute stated so go with 4500 watts or 4500 va.

That is the key word if it was simultanious then you will have to go with 9000 watts or 9000 va.

Merci,Marc
 

e57

Senior Member
I kinda question the 'simultaneous' part - on a water heater??? Say Upper and lower at a cold start.... Does it have some sort of interlocked dual thermostat??? It might be 'non-continuous'????
 
E57.,

You did bring up good point so let me make it clear on this one.

Ok ., for the simultaneous operation it mean it will useally have single thermosat to control both heating element in the water heater.

For non simultaneous operation yes there is interlock thermosat on upper element plus there is a lower thermosat as well so when the water heater tank is cold the upper element will come on first and heat the upper half first when it get warm up to the point the thermosat call the heat off it will do two functions one is turn off the upper element and the interlock will change the circuit connection to the lower lower element. { sorta like DPDT switch }

And yeah all the water heater do have limit switch that useally located at the upper element { if have dual element tank } otherwise at lower element location { single element tank }

that item that what I describe it will work with both single and three phase two element water heater tanks { three phase multi elements will use single thermosat with contractor }

Oh yeah the other thing the water heater can be contionuis useage due if used alot of hot water.


Merci,Marc
 
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e57

Senior Member
Thanks Marc....

Just googled '3 phase water heater schematic' and found some - example on page 16 of 16 Which has 3 phase and single phase schematics - I get it now... ;) So then - if it is interlocked - it would act as a single 4500VA load - I've seen a few other thing likes it - but the 208 threw me - 3 or single - I was thinking 3 phase "V" set up (Like an open V transformer) there is one on that page too...
 
Sure anytime E57.,:cool:

by the way not too often you will run into three phase with two heating element set up unless this is found in commercal location. { they useally are a specail order item IIRC } and yes they run in open delta format with this set up and keep in your mind the B phase will have higher current drawage if both elements are on.

Typically 1.73 X amps on other two phases.

Merci,Marc
 

e57

Senior Member
yes they run in open delta format with this set up and keep in your mind the B phase will have higher current drawage if both elements are on.
Thats why I questioned it. ;) You know... Often we get only some of the info - and sometimes can give a wrong answer based on that. Sometimes we get all the info - and still the wrong answer if it is missed if presented the wrong way...

Merci - Mark ;)
 

mcclary's electrical

Senior Member
Location
VA
Nobody mentioned the size, as far as I know, that's what determines it, not the thermostat.

A WH less that 125 gallons in considered continous duty.

A wh more than 125 is considered non continous.

4500 watts, continuous, makes you run a #10 for the load
 

Dave58er

Senior Member
Location
Dearborn, MI
A WH less that 125 gallons in considered continous duty.

A wh more than 125 is considered non continous.
I believe it's 450 L (120 gal). ;)

A small distinction but I do remember a post from a while back where someone had come across a water heater on a job that was something like 121 gallons and thought it was a odd number.

But apparently it was manufactured with 422.13 in mind, so that it just crossed the threshold into non continuous.
 

mcclary's electrical

Senior Member
Location
VA
I believe it's 450 L (120 gal). ;)

A small distinction but I do remember a post from a while back where someone had come across a water heater on a job that was something like 121 gallons and thought it was a odd number.

But apparently it was manufactured with 422.13 in mind, so that it just crossed the threshold into non continuous.


So true, again my memory failed me.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Had a similar situation recently. I checked out the Rheem site and found this http://globalimageserver.com/fetchDocument.aspx?id=7522ff8d-b9a6-420d-ba77-3263d7148f76. (check out pages 8 and 20 of this PDF) The heating elements are interlocked so that they can't both operate at the same time. In my case I had (2) 4500 watt elements, non-continuous with a 3 wire outlet. Customer currently has a 2-pole 20 amp circuit to the heater that the plumber installed (replaced). It won't pass inspection and I've already told them they'll have to replace the wiring and disconnect. Will the wiring burn up before they decide that I'm right. :confused: Who knows;)
 

mcclary's electrical

Senior Member
Location
VA
Had a similar situation recently. I checked out the Rheem site and found this http://globalimageserver.com/fetchDocument.aspx?id=7522ff8d-b9a6-420d-ba77-3263d7148f76. (check out pages 8 and 20 of this PDF) The heating elements are interlocked so that they can't both operate at the same time. In my case I had (2) 4500 watt elements, non-continuous with a 3 wire outlet. Customer currently has a 2-pole 20 amp circuit to the heater that the plumber installed (replaced). It won't pass inspection and I've already told them they'll have to replace the wiring and disconnect. Will the wiring burn up before they decide that I'm right. :confused: Who knows;)


If it's 240 volt,and non continuous, the 20 amp circuit is big enough
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
If it's 240 volt,and non continuous, the 20 amp circuit is big enough
Not the way I read the chart. It requires a 25 amp circuit so the next highest trade size breaker is 30 amps and # 10 wire. If you do the math 4500/240= 18.75 amps. 80% of a 20 amp breaker is 16 amps so you'll have to go to the next size up the way I see it.
 

jumper

Senior Member
Not the way I read the chart. It requires a 25 amp circuit so the next highest trade size breaker is 30 amps and # 10 wire. If you do the math 4500/240= 18.75 amps. 80% of a 20 amp breaker is 16 amps so you'll have to go to the next size up the way I see it.
Actually 25 amps is a standard sized breaker, 240.6. We use a 30 amp for convenience.
 

mcclary's electrical

Senior Member
Location
VA
Not the way I read the chart. It requires a 25 amp circuit so the next highest trade size breaker is 30 amps and # 10 wire. If you do the math 4500/240= 18.75 amps. 80% of a 20 amp breaker is 16 amps so you'll have to go to the next size up the way I see it.


I'm not talking about the chart. I'm talking NEC. The op said non continous.

Why can't I load a 20 amp breaker past 16 amps? Pleaase provide code article.
 
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