SPA -- replacing a 120V heater with 240V heater

[Ignoramus31846]

I have a very old spa.

It has a 120V circuit for everything, the pump and heater.

I had to do some repair on it yesterday. The heater was not heating, which, as I realized, was caused by a crimp that worked itself loose. Which I recrimped.

It seems to work, but still, the low power heater is very slow to heat the spa at 120V.

The heater is switched on and off with a power relay (contactor).

The question that I have is this. Would it be sensible to add another circuit to this spa, supplying 240VAC, that would power the heater only. The old control system and pump would still be on 120VAC, but the contactor would switch 240VAC going to the heater.

I would use a GFCI breaker on that 240V line, just like I have on the

120V line.

The only issue that I have with this possible change is that instead of one breaker disconnecting the spa, there are now two. It may present a possible hazard to someone attempting to repair the spa, as they could turn off one circuit and forget to turn off another, leading to possible electric shock.

Any thoughts?

i

[Ignoramus31846]

Oh, and I realize that I would need a bigger contactor. No problem here.

i

[trader4]

It's hard to recommend doing this without seeing it, knowing your skill levels, etc. Essentially, you are modifying a std power pack, which is likely UL listed, and turning it into something else. Another problem is if say a future owner or even you calls a service guy, who now has a kludge to deal with and may not service it.

If you do do it, I would install a 240V GFCI that becomes the single breaker for the whole SPA. You can then use 240V off that for the heater, 120V off that for the rest of the SPA. That's how my spa is set up. Also make sure that all metal bonding of the spa is maintained.

[trader4]

Voltage does matter. The same heating element will produce 4 times the power at 240V, compared to 120V, which is exactly what he wants, so the water heats faster. Many water heating elements are made that are rated to run at either voltage, they just produce more heat at the higher voltage.

Almost certainly yes. SPAs that heat at 120V take just about forever to warm up. Even with 4X the heat, it still takes hours. Some small spas are sold in virtually identical config for 120V or 240V, the only diff being that 240V goes to the heater.

You would, in effect, be

[Doug Miller]

That's because a heater that delivers, say, 1200W at 240V is *not* the same as a heater that delivers 1200W at 120V. A heater operated at 240V delivers four times the power as _the_same_heater_ operated at 120V.

Try again.

Suppose the heater delivers 1200 watts at 120V. Thus it draws 10 amps, and, by Ohm's law V = IR, its resistance is 120 volts / 10 amps = 12 ohms.

Now push 240V through the same heater. Again, V = IR, where V = 240 volts and R = the same 12 ohms... thus I = 20 amps.

Now calculate the power... P = IV where I = 20 amps and V = 240 volts... P =

4800 watts.

[Bud--]

To heat the water faster you would need a higher wattage heater. The same wattage heaters will draw half the amps at twice the voltage. Otherwise voltage doesn't matter.

Could the spa handle higher heat production? You would, in effect, be re-engineering the spa. I personally would be very unlikely to change parts on a spa given potential safety problems. And if it is UL listed now it wouldn't be after.

bud--

[Ignoramus31846]

Sure, yes, I would definitely install a new heater instead of the old one. The old one is rated 4000W at 208 volts (weird rating for a household heater). Since it is running at 120 volts instead of 208, it only produces 120*120/208/208*4000 watt or 1,300 watts.

I think that it could, the water flow through the heater is very substantial. There is also a overheat prevention device on the pipe that encloses the heater.

i

[Ignoramus31846]

Here's where I am confused. How do 240V GFCI breakers work? By comparing currents going through two legs? If so, how can I power 120V devices, that would naturally give off some current to neutral, and yet not trip the GFCI?

i

[trader4]

There are two types of 240V GFCI. One only checks the current flow between the two hots. It will trip if you try to use it with a neutral and pull 120V off one leg. The other type includes neutral protection and compares all the current flow. That's the one you want.

[Don Young]

If you look carefully you may find that your heater element also has a 240 volt rating. It is common for elements to be rated for both 208 and 240 volts.

Don Young