25 amp breaker for # 10 wire

[eprice]

Look at the code section cited and get the meaning of what they want not necessarily what it states.

I think what they want is a breaker sized small enough to interrupt the current before the internal parts of the appliance are damaged. Based on the nameplate, the internal parts of this water heater are sized so as to be able to conduct at least 18.75 amps for several hours at a time without adverse affect. If we apply 208 volts instead of 240 the sizing of the internal parts and what current they can conduct without adverse affect does not change.

 

[eprice]

If the heater stated 240v at 4500 but will allow voltages between 200-250 then what would you do?

I would say that the internal resistance of the water heater is around 12.8 ohms based on the 4500 Watts at 240 volts. Since the water heater can safely operate at 250 volts, It has the capacity to conduct at least 19.5 amps under operational conditions, so that would be the rated current if none is given by the manufacturer.

 

[Dennis Alwon]

If we apply 208 volts instead of 240 the sizing of the internal parts and what current they can conduct without adverse affect does not change.

That may be true but I don't think that is the intent of the section. Like I say argue away- I made my statement and I would a 25 amp breaker. I see no problem with a 25 amp breaker even at 240V so if questionable why not just use the 25 amp breaker.

 

[charlie b]

There is no sense in debating a point for which we have no factual information to use as a starting point. Show me a photo of the nameplate, or send me a PDF of the installation instructions, and we can go from there.

The only thing given was 240 volts and 4500 va. From that, and that alone, I infer that a 30 amp breaker is appropriate, and that installing this heater in a 208 volt system is a violation. Any arguments that employ 208 volts in their reasoning are meaningless, unless and until we see the actual manufacturer's information.

 

[iwire]

That may be true but I don't think that is the intent of the section.

What do you think is the intent of 422.11(E)(3) is?

I see it's intent as eprice seems to.

That said I also agree with Charlie that without more info it is all guessing.


Me, I would run 10 AWG with a 30 amp breaker as that is how we always do it. :grin:

 

[jumper]

There is no sense in debating a point for which we have no factual information to use as a starting point. Show me a photo of the nameplate, or send me a PDF of the installation instructions, and we can go from there.

The only thing given was 240 volts and 4500 va. From that, and that alone, I infer that a 30 amp breaker is appropriate, and that installing this heater in a 208 volt system is a violation. Any arguments that employ 208 volts in their reasoning are meaningless, unless and until we see the actual manufacturer's information.

The OPs water heater might be different, but this a pretty standard name plate.

View attachment 5015

 

[jetlag]

That may be true but I don't think that is the intent of the section. Like I say argue away- I made my statement and I would a 25 amp breaker. I see no problem with a 25 amp breaker even at 240V so if questionable why not just use the 25 amp breaker.

The section is protecting the internal parts if you use the 4500 watt name plate rating at 150% , the reason we need to adress this is the person going all over town turning down WH with a 30 amp breaker needs to be corrected, It is costing people a lot of money to call out an electrician , he probably got the idea from hearing about the violation on a WH that had a lower name plate rating, I heard some things about AHJ s turning some down, and requiring the 25 amp. Some WH only have 3500 watt rating and thats how it got started.

 

[Dennis Alwon]

I totally agree with Charlie also. If the unit is marked 240 V and is installed at 208 it is a violation. I am totally unsure what the problem could be but I don't know enough to argue. My point was if 208 was appropriate then I believe we have to compensate for that. I don't expect you to agree and that's fine.

I think the intent is to limit the OCPD to 150% of the current if it is not marked--- well it is not marked at 208V so it isn't marked. That was my whole point so now-- what is the problem with connecting resistance element to a lower voltage than marked? Obviously the lower you go the longer it will take to heat but....

 

[Npstewart]

Without having a code book handy, I think the water heater is only continuous if it is 125 gallons or more.

Practically speaking, if the water heater runs for more than 3 hours, someone needs to cut down on the showering time.

 

[growler]

one of our regular customers who manages several apartment buildings.
One of their tennants had called POCO to have them install an energy management device on the water heater in their apartment.

It is costing people a lot of money to call out an electrician , he probably got the idea from hearing about the violation on a WH that had a lower name plate rating.

Very few people will be affected by this. Anyone in a residential area will have 240V power and no problems. The apartment complex and their installer or maintenance staff started this by installing a water heater not rated for the correct voltage.

Instead of asking them to replace the water heater they are only asking that the breaker size be reduced to the calculated wattage of the element at the operating voltage (208V).

When they change out this heater the next time hopefully to one with the correct nameplate rating the will just have a head start by already haveing the correct breaker.

 

[Dennis Alwon]

Without having a code book handy, I think the water heater is only continuous if it is 125 gallons or more.

Practically speaking, if the water heater runs for more than 3 hours, someone needs to cut down on the showering time.

I agree that a water would rarely run continuously however here is the article.

422.13 Storage-Type Water Heaters.
A fixed storage-type water heater that has a capacity of 450 L (120 gal) or less shall be considered a continuous load for the purposes of sizing branch circuits.

 

[brother]

The POCO person was wrong. Start at 422.10(A). The branch circuit rating cannot be less than the marked rating of the appliance. In your case, the marked rating is 4500 VA at 240 volts, which is equivalent to 18.75 amps. So the breaker has to be at least 18.75 amps, but this article does not give a maximum breaker rating.

Next, go to 422.11(A). If the water heater had been marked with a maximum breaker size, then you would have to meet that requirement. But it is not so marked. So here again the code does not give a maximum breaker rating.

Next, go to 422.13. You didn't give us the water volume of the heater, but I think it is a good bet that we have to consider it a continuous load. That makes the minimum breaker rating 18.75 times 1.25, or 23.4 amps. So a 25 amp breaker will satisfy the code. But here again this is a minimum rating. Nothing prohibits us from using a higher rated breaker, so long at the conductor can handle the current that the breaker will be able to pass along.

Finally, go to 240.4(D)(7). Presuming your answer to hardworkingstiff's question is "yes," then tor a #10 copper, the maximum breaker rating is 30 amps.

What about NEC 2011 422.11 (E)(3) for maxium breaker/ocp size. maxium of 150% of the rated appliance or the next size up if it doesnt correspond to a standard breaker size.

 

[charlie b]

What about NEC 2011 422.11 (E)(3) for maxium breaker/ocp size. maxium of 150% of the rated appliance or the next size up if it doesnt correspond to a standard breaker size.

I think you haven't read the rest of the discussion yet. We have already moved past that point.

 

[eprice]

The OPs water heater might be different, but this a pretty standard name plate.

View attachment 5015

From an inspectors perspective if the water heater has this name plate and is supplied by a 208 volt circuit: If I see a 25 amp breaker in the panel, obviously I should pass the installation. If I see a 30 amp breaker in the panel and #10 conductors, I think I should pass that as well.

I don't see a maximum current listed on the name plate, so I have to make a judgment call. The water heater is suitable for use on a 240 volt circuit at 4500 watts. From this I can infer that the internal parts of the water heater are rated for 18.75 amps. The fact that it is also listed for use on a 208 volt circuit doesn't change that fact. I would have a hard time coming up with a reason to fail a 30 amp breaker in a 208 volt installation of this water heater.

 

[jetlag]

From an inspectors perspective if the water heater has this name plate and is supplied by a 208 volt circuit: If I see a 25 amp breaker in the panel, obviously I should pass the installation. If I see a 30 amp breaker in the panel and #10 conductors, I think I should pass that as well.

I don't see a maximum current listed on the name plate, so I have to make a judgment call. The water heater is suitable for use on a 240 volt circuit at 4500 watts. From this I can infer that the internal parts of the water heater are rated for 18.75 amps. The fact that it is also listed for use on a 208 volt circuit doesn't change that fact. I would have a hard time coming up with a reason to fail a 30 amp breaker in a 208 volt installation of this water heater.

I agree 100% , There are a lot of 40 gal WH out there with a 3500 at 240 and 2700 at 208 name plate. I have a fairly new one myself. The AHJ around here turned down several 3500 with 30 amp breaker but gave no reason why.That is where the 25 amp got started and there are those through word of mouth or what ever going around declairing WH can only be on a 25 amp . Some how along the way the reason for the 25 amp got all lost.

 

[brother]

I think you haven't read the rest of the discussion yet. We have already moved past that point.

Your right, I did not read all the posts, a bit long for me. LOL can someone give a direct link for me? feeling lazy today.

 

[Dennis Alwon]

From an inspectors perspective if the water heater has this name plate and is supplied by a 208 volt circuit: If I see a 25 amp breaker in the panel, obviously I should pass the installation. If I see a 30 amp breaker in the panel and #10 conductors, I think I should pass that as well.

I don't see a maximum current listed on the name plate, so I have to make a judgment call. The water heater is suitable for use on a 240 volt circuit at 4500 watts. From this I can infer that the internal parts of the water heater are rated for 18.75 amps. The fact that it is also listed for use on a 208 volt circuit doesn't change that fact. I would have a hard time coming up with a reason to fail a 30 amp breaker in a 208 volt installation of this water heater.

Logic sounds okay but if it was listed 208/240 and 3380/4500 then your logic disappeas because that same heater would now req. 25 amps at 208V. Do you agree?

My point is there is a difference code wise but maybe not logically.

 

[jetlag]

I agree that a water would rarely run continuously however here is the article.

I want say this is a "totally incorrect statement ", but continuous load does not mean the water runs all the time , it means an element is on,, at 8 or 10 gal a min this happens very quickly . after the water is cut off the elements are still on for the recovery period and if water is used before the elements cut off again it starts all over.

 

[Dennis Alwon]

I want say this is a "totally incorrect statement ", but continuous load does not mean the water runs all the time , it means an element is on,, at 8 or 10 gal a min this happens very quickly . after the water is cut off the elements are still on for the recovery period and if water is used before the elements cut off again it starts all over.

So you think a water heater will run for more than 3 hours as a norm? You know it should say the water heater not the water---

 

[eprice]

Logic sounds okay but if it was listed 208/240 and 3380/4500 then your logic disappeas because that same heater would now req. 25 amps at 208V. Do you agree?

Well, I'm not convinced that the 208/240 3380/4500 name plate establishes separate rated currents for the two acceptable voltages. Rated current is not stated on that name plate. What it tells me is that the water heater can be used at 208 volts or 240 volts and that it will provide 3380 watts of heating if used at 208 volts and 4500 watts of heating if used at 240 volts. As an inspector, I'm not sure it provides adequate basis to turn down an installation of this water heater supplied by a 208 volt, 30 amp circuit using #10 conductors.