Electricalhelp
Senior Member
- Location
- NJ
What breaker size would I need to install if I have 208V or 240V Single Phase service
6000W/208V = 29A
6000W/240V = 25A
6000W/208V = 29A
6000W/240V = 25A
Breaker Size for 6000W Electric Patio Heater
- Thread starter Electricalhelp
- Start date
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Is there a fan in it, too? (If this is a test question, what's your answer?)
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I will give you the hint that you're describing two different heaters. Any given unit will have a lower current on a lesser voltage.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
As Larry stated your math is incorrect. If this is a single heater designed for either voltage you need to find the resistance first and then find the current.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Given a 4800 watt heater at 240V then we can calculate the resistance-
240*240/4800 = 12 ohms
Now the same heater at 120V
P = V*V/ R
P= 120*120/12 = 1200 watts
so yes the wattage is 1/4 the 4800 watt element. So the 4800 watt heater at 240 will draw 20 amps while the same heater at 120v will draw only 10 amps and not be as hot...
240*240/4800 = 12 ohms
Now the same heater at 120V
P = V*V/ R
P= 120*120/12 = 1200 watts
so yes the wattage is 1/4 the 4800 watt element. So the 4800 watt heater at 240 will draw 20 amps while the same heater at 120v will draw only 10 amps and not be as hot...
Electricalhelp
Senior Member
- Location
- NJ
The unit is a radiant heater so I don't see a fan on the specifications.
But they way I approached the problem was, since Power was given, I have to assume it will be the same for 208V or 240V.
Since the specifications only gives the Watt for 240V at 6000W.
So if Power Output can't change, I would size the breaker as
(6000W/208V)*125% = 36A so next size breaker is 40A.
But they way I approached the problem was, since Power was given, I have to assume it will be the same for 208V or 240V.
Since the specifications only gives the Watt for 240V at 6000W.
So if Power Output can't change, I would size the breaker as
(6000W/208V)*125% = 36A so next size breaker is 40A.
- Location
- Connecticut
- Occupation
- Engineer
The power can't stay the same if a different voltage is applied, as others have pointed out. A 6kW, 240V heater would output 4.5kW if 208V is applied to it.
A 40A circuit would be fine.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Do you now understand that that is not true? For resistive loads, such as the heater in question, the resistance is constant, and the power is not. The related math is described above.
For other types of loads, motors being one, it is the value of power that is constant. A motor will draw more current from a 208 volt source than it would from a 240 volt source. Here is the math:
* P = V times A. (Let's ignore the square root of 3 that appears in 3-phase calculations, as it would cancel out anyway.)
* Since P is constant, then V times A is also constant. Therefore, (V1) x (A1) = (V2) x (A2).
* For the present example, (208) x (A1) = (240) x (A2).
* That equation will only work out if A1 is larger than A2.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You're assumption is incorrect. If you're using the 240 volt heater on 208 volts you amperage would be 4500/208=21.6 amps so a 30 amp circuit is all that is needed.
Not enough information given. It could be designed to use full power at both voltages.
If the element has a center tap, it could be connected to the neutral on 208 to yield the same power as it would connected to 240 line to line (no neutral connection required).
We had a thread previously about an oven that was designed this way.
If the element has a center tap, it could be connected to the neutral on 208 to yield the same power as it would connected to 240 line to line (no neutral connection required).
We had a thread previously about an oven that was designed this way.
kwired
Electron manager
- Location
- NE Nebraska
True, but then it should be identified as 120/240 volts and/or 120/208 volts. Since it is identified as straight 240 volt there probably is no center tap.
In the OP, no voltage ratings of the device were given. Only the wattage.
Then the poster speculated on the current draw at both 208 and 240.
powerpete69
Senior Member
- Location
- Northeast, Ohio
- Occupation
- Professional Electrical Engineer
By using a factor of 1.25 you could guess 35A or 40A for the 208V system. Either one will likely work and would require a #8 wire for either case.
By using a factor of 1.25 you could guess 30A or 35A for the 240V system. Either one will likely work and would require #10 wire for the 30A and #8 wire for the 35A.
However, the better approach would be to either read the owners manual or the nameplate on the unit. It should state the recommended MOCP (Maximum Overcurrent Circuit Protection) also known as the manufacturers recommended breaker size.
The comments on the resistance staying the same and the lower power from the 208V is all true. I agree with all that. Again, nameplate and manufacturers recommendation is always best.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
- Status