Instant hot

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aftershock

aftershock

Senior Member
Location
Memphis, TN
Has an insta hot tripping a breaker. Went and looked at it. 12/2 MC on a 20 amp 208/v circuit. 20 amp 2 pole breaker, 20 amp single receptical and cord.

Nameplate under the cover shows to be a 9500 watt @ 240 volts.
Im gonna need to run number 8 and place on a 50 amp breaker.
Being that the panel which the circuit will be coming from is 208/v, will there be a problem with this?
 
9500/240*125%=49.479
9500/208*125%=57.091

This has me thinking as well. At 208/v Im looking at having to run #6. Or am I not calculating right?
 
9500 watts at 240 volts would be 7135.56 watts at 208. 7135.56 / 208 = 34.51amps.

(9500 / 240? * 208?) or (9500 * 0.7511)
 
480sparky said:
9500 watts at 240 volts would be 7135.56 watts at 208. 7135.56 / 208 = 34.51amps.

(9500 / 240? * 208?) or (9500 * 0.7511)
Click to expand...

Ok, so Im back to #8 on a 50 amp breaker. I wish I did more with heating elements so I could experiance more on those calculations.

Maybe I should study more, but I was always more of a hands on person.

Thanx.
 
hardworkingstiff said:
@ 240-volt = 9500 watts
@ 208-volt = 7136 watts

That's about a 25% drop in power consumption.

When it didn't trip a breaker, it heated the water sufficiently?
Click to expand...

Im not really sure if it heated the water sufficiently. I just did an amp test on the circuit after turning on the water (never checked the heat of the water) then turned off the water and the circuit. Then I popped the cover to find the nameplate/sticker. At that point when I found the wattage and voltage I informed the boss of what we needed to do.
 
aftershock said:
Ok, so Im back to #8 on a 50 amp breaker. I wish I did more with heating elements so I could experiance more on those calculations.

Maybe I should study more, but I was always more of a hands on person.

Thanx.
Click to expand...

Rick, The "secret" to remember in this type situation is that the only thing that is "constant" is the resistance of the element. Thats why the other calcualtions differed from yours. As shown 9500 watts at 240 is not still 9500 watts at 208. Voltage and current varied, but resistance is a constant.
 
why 125% ?

i was under the impression that was only if the load would be on Continuous for 3 hours or more.
an insta hot will only be on for 10 minutes at most i would think

that would be more like a #8 on 40 amp
 
aftershock said:
Im not really sure if it heated the water sufficiently. I just did an amp test on the circuit after turning on the water (never checked the heat of the water) then turned off the water and the circuit. Then I popped the cover to find the nameplate/sticker. At that point when I found the wattage and voltage I informed the boss of what we needed to do.
Click to expand...


Maybe the original installer thought since it was a 20amp 2-pole, he had 40 amps (20x2)
jester.gif
 
augie47 said:
Rick, The "secret" to remember in this type situation is that the only thing that is "constant" is the resistance of the element. Thats why the other calcualtions differed from yours. As shown 9500 watts at 240 is not still 9500 watts at 208. Voltage and current varied, but resistance is a constant.
Click to expand...

Thanx, Im gonna try and remember this for the next time I run into a situation like this.

One other thing that I thought I remembered reading in a thread on here. You cant get 240 from 3 phase right? For some reason I remember reading that, I could be wrong. When me and my partner went to the breaker panel and I saw the 3 phase breakers I told hime to open it up and check the voltage with his DMM and it showed 212/v.
 
izak said:
why 125% ?

i was under the impression that was only if the load would be on Continuous for 3 hours or more.
an insta hot will only be on for 10 minutes at most i would think

that would be more like a #8 on 40 amp
Click to expand...

I had thought the 125% was for any heating element. A water heater will not run continuously for 3 hrs but it has to follow that calculation.
 
480sparky said:
Maybe the original installer thought since it was a 20amp 2-pole, he had 40 amps (20x2)
jester.gif
Click to expand...


I know who the installer was. He was on the other end of the DMM. Aparently he saw that the cord (which was already on the unit) was 20 amps and went from there. I told him to always look for and check the nameplate/sticker.
 
There is no requirement for overcurrent protection of heating elements to be sized to 125% if they will not run for 3 hours or more.

and yes, you can get 240 volts on a three phase system.

its called a 120/240volt Delta High Leg (Wild Leg)
where phase to phase will all be 240v +/- , two phases to grounded conductor will be
120v +/-, and one phase to grounded conductor will be about 210v +/-
 
aftershock said:
I had thought the 125% was for any heating element. A water heater will not run continuously for 3 hrs but it has to follow that calculation.
Click to expand...

If the heating element runs for 2 hours, 59 minutes and 59.999 seconds, it is not a continuous load. If this is a instant-hot water heater, then it will only run when the faucet is turned on. Who runs hot water in a faucet for more than 3 hours?
 
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