Electrician Talk banner

water heater

8K views 57 replies 10 participants last post by  Speedy Petey 
#1 ·
Is there any problem with fusing a 3380w @ 208v 1p water heater at 20 amps? It comes up to be 20.3 with a 1.25 demand factor.I know your allowed to increase the demand factor. This was a debate I had with an inspector who demanded it to be sized at 25amps. If I remember correctly your allowed to drop a minor fraction of an amp.
 
#3 ·
What about this:

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.
 
#4 ·
220.5 (B). Where calculations result in a fraction of an ampere that is less that 0.5, such fractions shall be permitted to be dropped.

I believe it is compliant to connect a 4500 watt 240 volt heater to a 20 amp circuit at 208 volts. I've done it many times, never been busted for it yet.

But if an inspector ever questions it, I know what my argument will be

Rob
 
#5 ·
Sorry, I didn't do the math at first. The "demand factor" referenced in the OP is the continuous load 125% I was talking about.

Provided the heater is rated for 208V use I see no problem in violation in this.
 
#6 ·
IMO there is a problem as far as the NEC is concerned, but in reality, I don’t think it makes much difference at the end of the day.
Since 422.10 doesn’t reference 220.5 allowing you to drop fractions of an amp when sizing branch circuits for appliances, I believe that code wise at 208V, you would still need #10 wire with a minimum 25A OCP.
I think this is also indicated in 422.10 since 16.25A would be more than allowed at 100% continuous operation on a 20A circuit.

However, I will say that I don’t feel that these fractions of an amp really seem like enough to warrant the extra expense of larger conductors, etc., although I admit I always use #10 for these domestic water heaters anyway, but that is only because my name is on the permit.
 
#8 ·
Since 422.10 doesn’t reference 220.5 allowing you to drop fractions of an amp when sizing branch circuits for appliances, I believe that code wise at 208V, you would still need #10 wire with a minimum 25A OCP.

I disagree. Art. 422.10 or any other article does not have to reference 220.5(B). I actually don't know an article that does reference so by your account it is a worthless article. 220.5(B) stands alone and comes into play here.

I think this is also indicated in 422.10 since 16.25A would be more than allowed at 100% continuous operation on a 20A circuit.
Again 16.25 amps drop the .25 and you are still good at 80% of 20 amps.

However, I will say that I don’t feel that these fractions of an amp really seem like enough to warrant the extra expense of larger conductors, etc., although I admit I always use #10 for these domestic water heaters anyway, but that is only because my name is on the permit.
This part I agree with and I would also use #10 but the code does allow #12, IMO.
 
#9 ·
The water heater is considered a continuous load, if it is 120 gallons or less; therefore, your conductors need to be rated 125% of the rated load. At 4500 watts, that's 23.4 amps, you would need to use a 30 amp breaker and #10 wire. As far as the OP is concerned, that is so borderline, I would go ahead and pull #10s and put it on a 30 amp breaker; better to design a robust system and avoid potential nuisance trips.
 
#12 ·
The op is talking about a 3800 watt element at 208 vlolts.

Now I will ask the OP if the element is rated 3800 at 208 or at 240 volts? This will make a difference. If the element is rated 3800 at 240 volts then it will be less at 208 volts
 
#13 ·
It took this inspector and entire electrical department 3 days to get back to my boss with an ok. They could not find any reason besides the fact that "they didnt feel it was right" to make us change it. By the way, this is the worst inspector anyone could encounter. Ive dealt with him many times and hes just one of those SOB's that come to a site to fail you , not to inspect the job.
 
#15 ·
IMO, the inspector was right, but either just didn’t know why he was right or didn’t think that a fraction of an amp was going to be that big of a deal in this case.

As I see it, in addition to 220.3, Table 220.3, and 422.11[E],... 422.13 also gives you a hint via the fine print note that the end result will be that you will be using 422.10 and the actual appliance rating to size your branch circuit conductors for storage type water heaters and not Art. 220.
 
#17 · (Edited)
I'm sort of lost in this whole discussion. The exception under 220.3(b) indicates the circuit for the HW heater should be calculated on the amperage rating of the HW heater, not using a 125% "demand load" factor. As a purely resistive load on a dedicated branch, I can agree that there may be a disconnect between the branch circuit voltage (208) and the wattage rating which could be at 240, but I also think the amperage at 208 volts could push the ampacity limits of a #12 wired circuit especially if that circuit is also exposed to ambient heat conditions.

To me, it is the borderline ampacity that makes me prefer to err on the side of caution and use #10 on a 30 amp circuit.

By the way, IF the wattage is at 240 volts, then the actual amperage at 208 volts would be something like 14 amps and a 20 amp branch should be okay. I wouldn't do it myself, but that's because I never figured winning an argument with an inspector was worth it.
 
#18 ·
KayJay makes a good point; 422.13 says WH's shall be considered a continuous load, and the FPN refers to art. 422.10, which "specifies the ratings of branch circuits capable of of carrying appliance current...", thus seperating WH's from the run of the mill branch circuit.
 
#19 ·
And I see it a bit differently. The fact that 220.5(B) allows us to drop decimals below .5 makes the load not greater than the appliance load plus 125%. I see your point but for calculation purposes 220.5(B) , IMO, gives us this freedom for any circuit. If art. 422.10 stated that 220.5(B) does not apply then we would have a different story.

By the way, IF the wattage is at 240 volts, then the actual amperage at 208 volts would be something like 14 amps and a 20 amp branch should be okay. I wouldn't do it myself, but that's because I never figured winning an argument with an inspector was worth it.
That was the point I was making earlier.

BTW I still do not see how 422.11(E) changes things
 
#23 ·
Based on what? Bob's method ? :) That is a blanket statement. Suppose 3 phase was involved with a 4500 watt element. Are you saying that #10 is required? It has already been stated that a water heater rated at 240 volts and 3380 watts wired to a 208 system would not require #10.

This thread is not about what most of us would install but what the code requires.
 
#28 ·
I agree, and I would also wire it with #10 just to make sure someone didn't upsize it but we do have to be careful throwing in a 30 amp breaker with the #10 wire. Just because 30 amps equates with #10 it is not always legal to put a 30 amp breaker in as William has mentioned.

William1978 said:
The max OCP you can put on the water heater that the OP is talking about would be 25a.
 
#31 ·
Lost me again. The OCP is for the circuit, not the hot water tank. Is there some confusion about the OCP for the circuit versus some sort of fused disconnect at the hot water tank?

If a 30 amp breaker is illegal for a #10 wired circuit, then I sure installed a lot of circuits that should have been turned down.
 
#32 ·
Lost me again. The OCP is for the circuit, not the hot water tank. Is there some confusion about the OCP for the circuit versus some sort of fused disconnect at the hot water tank?

If a 30 amp breaker is illegal for a #10 wired circuit, then I sure installed a lot of circuits that should have been turned down.

If you used a fuseible disconnect with 25a fuses then you could use a 30a breaker on the #10 for the circuit. But why not use a 25a breaker and be done with it.
 
#34 · (Edited)
because the breaker is for the circuit, not the hot water tank. A fused disconnect would be for the hot water tank, not the circuit.

I can understand a fused disconnect for an air conditioner unit or other motorized device, but I can't see it for a hot water tank.

Good point. I guess we need to know the amperage on the nameplate. A 25 amp breaker would be the next common size.
 
#42 ·
"The water heater element is part of the circuit. If I ran a #4 copper to the unit I would not be allowed to use an 80 amp breaker on it. or do you think one could?"

As are the lead wires which come with the hot water tank and they are #10, so no, I wouldn't run #4 and use an 80 amp breaker.

However, I might run #4 on an 80 amp breaker feeding a disconnect fused at 25 amps feeding the hot water tank.
 
#45 ·
As are the lead wires which come with the hot water tank and they are #10, so no, I wouldn't run #4 and use an 80 amp breaker.
I believe the lead wires from the water heater are #12. You got the correct answer but not the correct logic. Micromind's post below yours has it correct with art. 422.11(E)(3).[/quote]
 
#43 ·
I believe 422.10 (E) (3) is trying to address this very issue. It's talking about overcurrent, and says "Not exceed 150% of the appliance rated current......the next higher standard rating shall be permitted."

So, in accordance with this paragraph, you could not have #4s with an 80 amp breaker as the only protection of a 3380 watt water heater at 208 volts.

Rob
 
#48 ·
Oh and, the hot water tank I just looked at, a regular residential on 240 volts, has #10 lead wires.
The internal wiring installed by the manufacturer of the listed water heater is not subject to the requirements of the NEC. However, the OP’s situation was brought up previously at a code seminar.
Others may not agree, but it appears to be the most logical conclusion.

As soon as you open NEC 220, why does Table 220.3 immediately divert you specifically from branch circuits directly to over current protection when referencing storage type water heaters?
It was determined that is to bring to your attention that the OCP in 422.11[E] is also based on the appliance rated current, not the branch circuit rated current as sized in 220.

Fractions of an amp are not dropped when sizing min OCP from appliance rated current as they can be when sizing branch circuit conductors in 220.5.

3380W / 208V = 16.25A appliance rated current X 125 % = 20.3A min OCP.
125% min and 150% max. = 20.3A min or 24.37 max.
422.11[E] allows using the next higher size rating if 150% doesn’t coincide with a standard size, which would be 25A max OCP.

This just happens to coincide exactly with the branch circuit requirements of 422.10 as referenced in the fine print note to 422.13.

This normally wouldn’t be a problem, but with "Small Conductors" as in the OP’s case, this creates a situation where your min OCP will be larger than allowed for the min size branch circuit conductors sized in 220 based on Table 310.16.
Table 310.16 refers you to 240.4[D], which states 20A max on #12 Cu unless modified by Table 240.4 [G].
The only section of 422 modified in Table 240.4[G] is motor operated appliances, which doesn’t apply to this installation. The end result is minimum sized branch circuit conductors of #10.
Once your required branch circuit conductors are larger than #10 this situation goes away, since 240.4[D] would no longer be an issue.

If this same listed water heater were rated at 240V being connected to 208V, you would still size your branch circuit conductors and OCP based on the 240V nameplate voltage and appliance rated current, not at 208V. So at 240V it would have a rated current of 18.75A and the minimum size branch circuit conductors in this situation is also #10 with 25A min OCP.
Just because the supply voltage is 208V doesn’t mean you can use anything but the marked nameplate value of 240V. You would either need to have a 208V unit or one with a dual 208V/240V rating to be able to use the 208V value for sizing these.

 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top