Change 208 circuit to 240

Status
Not open for further replies.
N

ncgreenplumbing

Member
Location
United States
I have a point of use water heater that is rated for 208 and want to replace it with one rated for 240. Can anyone explain how this would be accomplished? My limited license does not cover this work, but I need to explain to the customer in general terms what needs to be done and how involved it would be.

Thanks.
 
ncgreenplumbing said:
I have a point of use water heater that is rated for 208 and want to replace it with one rated for 240. Can anyone explain how this would be accomplished? My limited license does not cover this work, but I need to explain to the customer in general terms what needs to be done and how involved it would be.

Thanks.
Click to expand...

What is the voltage at the building? If it is 208v technically you cannot put a 240v heater in but it will work. It just wont get to its full potential--
 
ncgreenplumbing said:
I have a point of use water heater that is rated for 208 and want to replace it with one rated for 240. Can anyone explain how this would be accomplished? ... I need to explain to the customer in general terms what needs to be done and how involved it would be. ....
Click to expand...
Following Dennis' post

Assuming:
there are no motors,
the heater is a resistive load only,
the supply is 208V,
the existing conductors are sufficient for the new heater
and the inspector does not catch fire while walking by **:roll:​

Connect it.

The heat output will be Nameplate X (208^2)/(240^2) = about 75% of nameplate watts.

** Note: This is not an inspector flame. It is just a comment that it is not going to cause an electrical hazard.

ice
 
You could put in the 240 and replace the elements with 208 ones. Elements are pretty inexpensive.
 
If an inspector wanted to turn it down he could based on the nameplate being incorrect for the voltage of the unit. 110.4
 
iceworm said:
Following Dennis' post

Assuming:
there are no motors,
the heater is a resistive load only,
the supply is 208V,
the existing conductors are sufficient for the new heater
and the inspector does not catch fire while walking by **:roll:​

Connect it.

The heat output will be Nameplate X (208^2)/(240^2) = about 75% of nameplate watts.

** Note: This is not an inspector flame. It is just a comment that it is not going to cause an electrical hazard.

ice
Click to expand...

I want to change it to 240v because I'll get higher output with the same amperage breaker and wire size.
 
ncgreenplumbing said:
Most point of use water heaters do not have replaceable elements and those that do are not cheap.
Click to expand...

I must be old school. Never seen one without replaceable elements. I've replaced a lot in my long history of being a cheapskate and doing it myself. New world, I guess.
 
meternerd said:
Why is there a 208 heater installed now? Am I the only one who's confused (not unusual for me)?
Click to expand...
Nope

ncg - let's try again.
The existing heater namepalte says 208V?

The new heater nameplate says 240V?

The building existing voltage is 240?

You are going to keep the same CB and wire?

You are buying a 240V heater that will draw the same current as the existing 208V heater?

ncgreenplumbing said:
I want to change it to 240v because I'll get higher output with the same amperage breaker and wire size.
Click to expand...
If the answers to the five questions is "Yes to all", then: No. Regardless of the nameplate numbers, if the current is the same and the applied voltage is the same, the heat output is the same.

ice
 
All else being equal, a 208V heater of a given wattage will actually heat better than a 240V heater of equal wattage when connected to the same supply. Your only issue with running a 208V heater at 240V might be the fact that you're changing elements more often than you change underwear.

Assuming both are 4kW units:

4kW @ 208V = 19.23 amps = 10.82 ohms
4kW @ 240V = 16.67 amps = 14.40 ohms

Now, connected to a 208V supply:

10.82 ohms @ 208V = 19.23 amps = 4000W
14.40 ohms @ 208V = 14.44 amps = 3004W

Then, connected to a 240V supply:

10.82 ohms @ 240V = 22.18 amps = 5323W
14.40 ohms @ 240V = 16.67 amps = 4000W
 
ncgreenplumbing said:
I want to change it to 240v because I'll get higher output with the same amperage breaker and wire size.
Click to expand...
No you won't, not when it comes to heating water anyways.

You can't mix and match inductive loads with resistive loads. Even when you try, in the long run, the answer is the same..... if I give you 208 M&M's in an hour it is always less than if I give you 240 M&M's in an hour.
 
ActionDave said:
No you won't, not when it comes to heating water anyways.

You can't mix and match inductive loads with resistive loads. Even when you try, in the long run, the answer is the same..... if I give you 208 M&M's in an hour it is always less than if I give you 240 M&M's in an hour.
Click to expand...
I think what you really mean is motors and maybe multi voltage ballasts. There is no reason that all inductive (or capacitive for that matter) loads would increase current as voltage decreases.
Maybe a better comprehensive term would be "constant power" loads?
 
Last edited:
GoldDigger said:
I think what you really mean is motors and maybe multi voltage ballasts. There is no reason that all inductive (or capacitive for that matter) loads would increase current as voltage decreases.
Maybe a better comprehensive term would be "constant power" loads?
Click to expand...
I might....I'm not 100% sure, but I trust you. Keep in mind I never went to school for electrical, I backed into it one day pouring concrete at an electrician?s house and stayed longer than the rest of the crew.

In the case of the OP he wanted to use 240V elements on a 208V system.....that ain't gonna do what he wanted, that much I do know.

When it comes to motors (ballasts too) everybody says, "More voltage, less amps". But they leave out the part that you reconfigure the windings from parallel to series...kw is the same.
 
Actually the important, and counter intuitive for some, thing about motors is that if you stay within the allowed range for a given wiring configuration (which might include both 208 and 240) the current will still increase as you drop the voltage as long as the load on the motor is constant.
Sometimes it helps to understand the reasoning or physics behind the behavior, sometimes you just need to remember the result. :)
 
Status
Not open for further replies.
Top