240 or 120 Volt?

[LD1]

Where to begin:confused2:

The 240V hookup uses half the amperage and since watts equals ohms times amps times amps, using 240V gives you less wattage lost in the wiring to the heater...1/2 the amps and 1/4 the watts. It also reduces voltage drop since volts is amps time ohms...1/2 the amps and 1/2 the voltage drop which means slightly more output from the heater. Using 240V also balances the load on your service, using 120 might add load to the heavier loaded hot leg or it might add load to the lighter loaded hot leg..without an amp meter, you probably won't know. Balanced loads are always better. As far as cost, you pay by the watts used regardless of 120V or 240V so not having the higher watts load in the wire itself would mean you are getting more heat where you want it and less where you don't want it. Without actually doing the math, I'm not sure if using the 240V would save you money overall on your power bill, but it definitely is more efficient! Using 240V might allow you to use a smaller (less expensive) gauge conductor when wiring it up.

You are mostly correct, except the first line. Watts does NOT equal ohms times amps times amps:confused2:. Watts is simply volts times amps:thumbsup:

Higher amps (120 volts) = higher electric bill

WRONG

No, higher amps at 120 is the same electric bill as lower amps at 240. You are paying for watts, not amps. volts times amps equal watts

CORRECT

There is a slight savings in using 240 rather than 120. This is due not only to the lower resistive losses in the wiring but also lower internal losses in the equipment. In a resistance heater, this won't make any difference but 220 motors, etc are more efficient than 120v.

SPOT ON MAN. 208/220/240 is more efficent at delivering the power where it is needed vs 110/120. Plus a smaller wire can be used.

I was wondering someone opinion on this one
NEW Soleus Electric 5,000 W Portable Garage Shop Heater | eBay
The amp rating is 21 amps...
would you use a 20 or 30 amp breaker? Never seem 21 usually they will say 20 or 30 amps,as most ads do.
One reason I ask is i have a 20 right now..Figure id use the 20 and see if it blows and then upgrade to the 30.if needed..

Hey Kenney we couldnt even make the switch to METRIC LOL But I like your thought on that

They would probabally suggest a breaker size in the instructions. But IF it pulls 21A, a 20A breaker is NOT going to be enough. Plus, you size the breaker to the wiring. The machine will pull what it will. I would follow the advise in the directions, but it probabally recomens 30A breaker and 10ga wire minimum.

So to conclude, I also vote for a 220/240 unit. IF you can even find a 5000w 120 unit, the thing would pull about 42A and require a 50A breaker and 6guage wire, and would cost fractionally more to run due to ineffeciencies. VS a 220 heater @ 21A w/10ga wire and a 30A breaker. The cost difference between 50' of 10ga and 6ga is probabally about $50 also.

 

[ducks13]

More efficient? Depends upon your defination of efficiency. Is you use the defination of power out divided by power in the efficiency (that is what is in a physics book) is the same at 120 and 240 if you increase the wire size appropriately. It is more economical to circuit at 240 rather than 120 due to the reduced wire size required.

Motor more efficient, not necessarily? Take a look at this cut sheet on a 120/240V motor Products: AC Motors: L3351: Baldor Electric Company, a leader in energy efficient electric motors, linear motors and adjustable speed drives industry Note the efficiency is the same regardless of the voltage.

As for the circuit size for the heater, the National Electrical Code (NEC) requires that branch circuits for heaters the conductor ampacity and rating of the overcurrent device (breaker) must be 125% (because, as someone else mentioned, typical breakers are only rated for 80% of their rating if the load lasts more than 3 hours and heaters commonly operate for more than 3 hours without shutting off long enough for the breaker and wire to cool off) of the load. So take 21 x 1.25 = 26.25 and the next standard breaker is 30 amps and you need #10 wire. You are welcome to try the 20A circuit but it will probably trip in 15-45 minutes and it is certainly not the safe thing to do.

 

[Mace Canute]

Where to begin:confused2:

Originally Posted by Mace Canute View Post
The 240V hookup uses half the amperage and since watts equals ohms times amps times amps, using 240V gives you less wattage lost in the wiring to the heater...1/2 the amps and 1/4 the watts. It also reduces voltage drop since volts is amps time ohms...1/2 the amps and 1/2 the voltage drop which means slightly more output from the heater. Using 240V also balances the load on your service, using 120 might add load to the heavier loaded hot leg or it might add load to the lighter loaded hot leg..without an amp meter, you probably won't know. Balanced loads are always better. As far as cost, you pay by the watts used regardless of 120V or 240V so not having the higher watts load in the wire itself would mean you are getting more heat where you want it and less where you don't want it. Without actually doing the math, I'm not sure if using the 240V would save you money overall on your power bill, but it definitely is more efficient! Using 240V might allow you to use a smaller (less expensive) gauge conductor when wiring it up.

You are mostly correct, except the first line. Watts does NOT equal ohms times amps times amps:confused2:. Watts is simply volts times amps:thumbsup:

mmmmmmmm I think I am correct. Have a looksee at this...

 

[LD1]

mmmmmmmm I think I am correct. Have a looksee at this...

I guess you are correct:confused2: It has ust been awhile since I used all them other formulas. But the easiest is volts x amps IMO, because those are both known by looking at the tag on the heater:thumbsup:

 

[Travelover]

I guess you are correct:confused2: It has ust been awhile since I used all them other formulas. But the easiest is volts x amps IMO, because those are both known by looking at the tag on the heater:thumbsup:

It is true that watts = (volts x amps). But volts = (amps x resistance).

So watts= (amps x resistance) x (amps), which is the same as (amps squared) x resistance.

 

[KennyG]

Motor more efficient, not necessarily? Take a look at this cut sheet on a 120/240V motor Products: AC Motors: L3351: Baldor Electric Company, a leader in energy efficient electric motors, linear motors and adjustable speed drives industry Note the efficiency is the same regardless of the voltage.

Your example is a 120/240 motor so it is not optimized for 240 operation. Although the manufacturer is listing the same efficiency, it will actually use a little less electricity on 240 due to reduced internal heating. It will also probably last longer on 240 for the same reason.

The real difference comes when you design motors for a specific voltage. At a given horsepower, a 240 motor can be built lighter and will start much easier and run cooler. The efficiency difference is not earthshaking, but it is real. In an industrial situation, 120 v motors are usually limited to fractional horsepower motors and not just because the wiring is smaller.

 

[JB4310]

If it's rated 21 amp (That's 240 right?) then you will need a 30 amp breaker and 10 gauge wire to keep it within code. and safe.

I'm no electrician but that's what I believe. I've got an equivalent electric heater in my shop and it has performed flawlessly for 10 years.

Quark from Granger, see upper left in this picture. set it to a low setting just to keep the plumbing from freezing when I'm not there and it maintains perfectly.
This is a small shop, (basically built like a cape house) but it heats 3 rooms on the first floor and prevents plumbing in basement and bathroom from freezing.

JB

 

[jonyyuma]

JB, nice heater, much safer than the chill-chaser floor type. Correct on the 30 amp breaker and #10 wiring.. Plus the plug on the cord to prevent exchanges on a 21 watt unit?

 

[chopped]

Thanks so much Ive really getting an education here.adn another question im finding some heater that say 240/208 V So the 240 is wired the same as 220?

 

[Mace Canute]

So the 240 is wired the same as 220?

Actually, it's ALWAYS 240V nominal. If you meant is 208V wired the same as 240V then yes it is. The difference comes from the transformer. 208V is associated with three phase power from a transformer that has the secondary in a wye configuration where each of the three hotlegs has 120V to neutral/ground and 208V between any two of them.

I'm going to add something here that always bugs me. People refer to their electrical service as being 110V or 220V (or even worse as a 120V/220V service...it CANNOT be 120V/220V) but it isn't, it's 120V/240V, and here's the reason why.
Your basic voltage control at substations, regulators etc is always based on 120 volts. You might have a substation with a 72,000V or 138,000V line feeding it and the transformer might be putting out 25,000V but when we adjust the transformer for output voltage, it's ALWAYS done based on 120V. At the substation transformer, that might be set at 123 or 124 volts to offset voltage drop through the power lines but down the line residential voltage should ideally be 120V to neutral/ground and 240V phase to phase (single phase power).