25 amp breaker for # 10 wire

[Dennis Alwon]

I think Dennis wins the prize on this one. Give the man a cigar. :grin:

I only want Cuban. Then I'll sell them to someone who smokes.:grin:

 

[dicklaxt]

I agree with Dennis based on 422.11(F)(3)

dick

 

[DaveBowden]

Thanks Dennis for the 422.13 guidance. I appreciate the knowlege I gain from this site.
To make sure I understand, the calculated load is 16.25 amps. The branch circuit must be rated at 125 % of this = 20.3 amps. 422.11(E)(3) applies to the 16.25 amp load = 24.4 amps not the 20.3 amps @ 150 % = 30.5 amps. Right?

 

[Dennis Alwon]

Thanks Dennis for the 422.13 guidance. I appreciate the knowlege I gain from this site.
To make sure I understand, the calculated load is 16.25 amps. The branch circuit must be rated at 125 % of this = 20.3 amps. 422.11(E)(3) applies to the 16.25 amp load = 24.4 amps not the 20.3 amps @ 150 % = 30.5 amps. Right?

Correct... 150% of the appliance rating- that is 16.24 *1.5= 24.4. I had a typo in my last part of the other post- I had 15.25 instead of 16.25....

 

[hardworkingstiff]

Dennis

Dennis

You are "THE MAN" Dennis (for this thread anyway ).

Thanks.

 

[jrohe]

I agree with Dennis. The load of the 240 volt water heater, when connected at 208 volts is calculated by:

4500 watts * (208^2/240^2) = 3380 watts/208 volts = 16.25 amps.

I presume the storage capacity of the water heater is 120 gallons or less, so 422.13 applies. Therefore, 16.25 amps * 125% = 20.3 amps. The next standard size breaker is 25 amps and you would need #10 wire (Copper TW).

Per 422.10(E)(3), the branch circuit rating can not exceed 150% of the appliance rated current. We have already established the rated current of the water heater, when connecting to a 208 volt system, is 16.25 amps. Therefore, the branch circuit is not permitted to exceed 16.25 amps * 150% = 24.4 amps, rounded up to 25 amps.

 

[jetlag]

Correct... 150% of the appliance rating- that is 16.24 *1.5= 24.4. I had a typo in my last part of the other post- I had 15.25 instead of 16.25....

Im not sure I agree with all this I would keep the 30 amp breaker, 422.11 E is refering to the appliance name plate rating which is 4500 watt at 240 v eguals 18.75 amp x 150 % = 28.12 next size is 30 amp. The code says nothing about you have to figure your own name plate rating if connected to a different voltage than stated on name plate even though that is the actual 3800 watt as connected. I would still argue the name plate rating is 4500 watt since the heater name plate doesnt give the dual voltage 208/240 seperate wattage. I will bet you the element itself shows the 208 and 240 wattages if it has ever been replaced but thats not the appliance name plate rating in my opinion

 

[Jim W in Tampa]

I would leave it at 30 so if when they replace element with a true 4500/ 208 it is ready. Is no hazard just lower voltage resulting in lower load. Kinda nit picking for nothing

 

[jetlag]

I would leave it at 30 so if when they replace element with a true 4500/ 208 it is ready. Is no hazard just lower voltage resulting in lower load. Kinda nit picking for nothing

I give jim the the cuban cigar , since the name plate doesnt show 208 , a person could connect to 120 v and not be any worse violation than 208 if it is a violation at all , and yes it will get hot eventually I know because during storm I got some hot water from a 120 v generator by moving one of the hot on breaker to neutral. So every one is saying I should have changed the breaker to 9.37 x 150 = 14.07 or 15 amp ? I will be sure to do that next time till storm passes LOL

 

[Jim W in Tampa]

I give jim the the cuban cigar , since the name plate doesnt show 208 , a person could connect to 120 v and not be any worse violation than 208 if it is a violation at all , and yes it will get hot eventually I know because during storm I got some hot water from a 120 v generator by moving one of the hot on breaker to neutral. So every one is saying I should have changed the breaker to 9.37 x 150 = 14.07 or 15 amp ? I will be sure to do that next time till storm passes LOL

I had small trailer many many years ago and put in water heater 20 gal 240 on 120. Was better than ice cold water but not much

 

[Jim W in Tampa]

I give jim the the cuban cigar , since the name plate doesnt show 208 , a person could connect to 120 v and not be any worse violation than 208 if it is a violation at all , and yes it will get hot eventually I know because during storm I got some hot water from a 120 v generator by moving one of the hot on breaker to neutral. So every one is saying I should have changed the breaker to 9.37 x 150 = 14.07 or 15 amp ? I will be sure to do that next time till storm passes LOL

Dang, and i don't smoke. Well at least not that brand. Can i get it in 420

 

[jetlag]

I had small trailer many many years ago and put in water heater 20 gal 240 on 120. Was better than ice cold water but not much

maybe I should not have said hot, it would if covered with insulation enough, the low wattage is not a lot above the heat loss thru the WH, You could have gotten a 120v element to install in the WH you know , will heat the 20 gal just fine

 

[Jim W in Tampa]

maybe I should not have said hot, it would if covered with insulation enough, the low wattage is not a lot above the heat loss thru the WH, You could have gotten a 120v element to install in the WH you know , will heat the 20 gal just fine

back then i was not an lektican or plummer

 

[jetlag]

maybe I should not have said hot, it would if covered with insulation enough, the low wattage is not a lot above the heat loss thru the WH, You could have gotten a 120v element to install in the WH you know , will heat the 20 gal just fine

oops i will probably get blasted for saying put 120v element in a 240 volt name plate appliance

 

[One-eyed Jack]

I had small trailer many many years ago and put in water heater 20 gal 240 on 120. Was better than ice cold water but not much

Your recovery rate would have been low but 120 degrees is 120 regardless of how long it took to get there. 1500 watt elements were the norm 40 years ago. This was back when we had the time to wait for the water to get hot.

 

[eprice]

Okay let's assume that the heater is listed for 208 volts-- not sure why it wouldn't be....

As the OP states the wattage, using ohm's law, at 208 volts=3380. Divide by 208 and we get 16.25 amps.

Now go to 422.11(E) -- the ocpd cannot be larger than 150%-- 15.25 equal 24.4 amps. Thus, IMO a 25 amp breaker is req as (E)(3) allows you to go to the next standard size from 24.4-- that is a 25 amp breaker.

422.11(E)(3) requires a maximum of 150% of the rated current. This water heater is rated at 4500 Watts @ 240 volts. I would say that the water heater is rated at 18.75 amps. Just because we apply a lesser voltage doesn't cause it to loose its ability to handle 18.75 amps. 150% of 18.75 amps is 28 amps. Next size up is a 30 amp breaker

 

[hardworkingstiff]

422.11(E)(3) requires a maximum of 150% of the rated current. This water heater is rated at 4500 Watts @ 240 volts. I would say that the water heater is rated at 18.75 amps. Just because we apply a lesser voltage doesn't cause it to loose its ability to handle 18.75 amps. 150% of 18.75 amps is 28 amps. Next size up is a 30 amp breaker

I knew I should have gone to Law school. :grin:

 

[Dennis Alwon]

You all can argue this all you want. I don't care what the rated voltage nameplate states. If we use that then the water heater is non compliant on 208v. If we accept that 208V will not hurt anyone or anything because it is resistance heat then IMO, you need to use the nameplate that would be there for 208V. You can't just use one part and not the other. If 208V is used the nameplat would not be 4500 watts.

Do I think this is an issue to have a dp 30 on the circuit--- no not really esp. since the voltage will vary at 208. For instance if the voltage fluctuates to 212 then we would be over 25 amps with 150%.

Look at the code section cited and get the meaning of what they want not necessarily what it states. Obviously the code does not want more than 150% OCP for the nameplate--- pretend the nameplate is 208v and then figure it out. I believe the 25amps is what the code is looking for here.

If the heater stated 240v at 4500 but will allow voltages between 200-250 then what would you do? I would put a 25 amp breaker and call it a day.

 

[growler]

422.11(E)(3) requires a maximum of 150% of the rated current. This water heater is rated at 4500 Watts @ 240 volts. I would say that the water heater is rated at 18.75 amps. Just because we apply a lesser voltage doesn't cause it to loose its ability to handle 18.75 amps. 150% of 18.75 amps is 28 amps. Next size up is a 30 amp breaker

As usual you get at least two different opinions of how the overcurrent protection can or could be calculated. Some folks think that a 25 amp breaker would be required and others think that a 30 Amp breakers would still be legal.

But there is only one size breaker that satisfies both arguements. and that's a 25 amp breaker because it meets all requirement no matter how you choose to look at the situation.

 

[jetlag]

422.11(E)(3) requires a maximum of 150% of the rated current. This water heater is rated at 4500 Watts @ 240 volts. I would say that the water heater is rated at 18.75 amps. Just because we apply a lesser voltage doesn't cause it to loose its ability to handle 18.75 amps. 150% of 18.75 amps is 28 amps. Next size up is a 30 amp breaker

Cigar for e price also , sorry dennis I think you are losing the cigar smoke it quick lol