Three Questions About 10-2

[Speedy Petey]

If you install a HD water heater which always has 4500 watt upper/lower elements on a 12/2 20 amp breaker, it will blow the breaker every single time.

No. Not at all.

4500 watts @ 240v is 18.75 amps. A 20A breaker will hold all day.
This is NOT to say that this is a "legal" installation. We all know it is not.

 

[Bob NH]

If you install a HD water heater which always has 4500 watt upper/lower elements on a 12/2 20 amp breaker, it will blow the breaker every single time.

I saw a 4500 Watt water heater on a 12/2 circuit with 20 Amp breaker that never tripped in two years of service.

The current measured about 18.5 Amps. The calculated current is 4500 Watts/240 Volts = 18.75 Amps. It isn't to code but it will work unless you get a supply well over 240 Volts or the breaker is in a very hot panel.

 

[Sponsor]

 

[sbrn33]

You guys should not with mess with Speedy on this one as he is right. You can control the WH with one pole but if it is out of site from the breaker or your jurisdiction requires a disconnect closer, you need a 2 pole disconnect.
If Molo wants to try to save a little energy he should maybe think about a water heater timer or something like that, although the little bit he might save is probably not worth the expense. Scott

 

[Dunbar Plumbing]

I used to be the plumbing contractor who did the installs for HD when they started out with GSW's, then moved to Richmond, then GE.

Some of the other installers would put these in on 20 amp circuits and the company would lose money because we had a responsibility to either upgrade the service or cancel out the install. They constantly tripped out whether within a few days or months later....suggesting the amp demand on a breaker with a hair's difference in tripping is not safe.

From a liability/profit factor we had to install on 10-2, problem solved.

In my stint with the company we had installers incorrectly install those heaters, about 8 heaters....all of which had to have electrical upgrades to rectify the problem.

I'm not an electrician but we all know *I hope* the following:

Breakers are not designed to be consistently brought up to their maximum protection...they actually hum when they are about to trip and I've seen breakers malfunction and not protect.

Some breakers *mfg* can be more sensitive than others...if there is high demand pulling from other breakers at that same time....it can have a bearing on this. I've seen where an electric furnace with individual breaker trip out a water heater breaker at the same time for no reason.

Like I stated, I'm no electrician but I've witnessed the above situations countless times. I'll replace a breaker and make sure the wiring is correct, anything else goes to a higher power. *licensed electrician*

The both of you agree though it is NOT code to run on 20.

 

[Speedy Petey]

Problem is some folks know just enough to be dangerous.

They know how to figure out the amperage; 4500w÷240v= 18.75A.

Cool, 20a circuit...... right?

WRONG! They don't know the codes regarding things like this.

Math is one thing, codes are another.

 

[Abikerboy]

Correct me here if Im wrong...BUT...I have a brand new switch box, and a new switch still in the pack that I bought to replace the switch to my outdoor flood lamps. Reading the printing on the switch, it is rated at 30 amp/125vac. 600 volt flash (I think thats the insulating value...never seen "flash" rating before) Now if Im correct, and you run 240 volt through that switch, the amperage rating goes down as the voltage goes up, so wouldnt that mean that the 30 amp switch is now good for only 15 amp? Double the voltage, cut the amperage in half. Sounds like something that could be unsafe to me.

 

[Speedy Petey]

No, your theory is flawed. The "Double the voltage, cut the amperage in half" theory is not always true. It depends on the load.

Besides, how are you going to put 240v through a single pole switch?

 

[Jadnashua]

Contacts that can handle 30A, except for possible arcing, handle 30A regardless of the voltage. By using it on a higher than specified line voltage, you lose a good portion of the safety factor, but from a current standpoint, it doesn't matter.

 

[JWelectric]

Problem is some folks know just enough to be dangerous.
They know how to figure out the amperage; 4500w÷240v= 18.75A.
Cool, 20a circuit...... right?
WRONG! They don't know the codes regarding things like this.
Math is one thing, codes are another.

To help explain what Petey has posted;

210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

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.

Here are two code articles that apply to water heaters. 210.19 states that all continuous loads must have a factor of 125%

422.13 states that a water heater is a continuous load.

Doing the math based on the size of the element in the water heater;
4500w÷240v= 18.75A. we are now required to add another 25% to the load or
18.75A times 125% which would equal 23.43 amps.
Using Nonmetallic cable the requirement in 334.80 that the 60 degree column be used to size the conductors we would be required to use a #10 conductor.
The overcurrent device would be code compliant if a 25 amp breaker was installed.

The use of 30 amp breakers on water heaters has become common place due to an allowance found in 422.11(E);
(E) Single Non–motor-Operated Appliance. If the branch circuit supplies a single non–motor-operated appliance, the rating of overcurrent protection shall:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or
(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.
I have a 40 gallon water heater in my basement that has been on a 20 amp breaker with #10 NM cable for a little over two years and used daily that has not tripped.

 

[Abikerboy]

No, your theory is flawed. The "Double the voltage, cut the amperage in half" theory is not always true. It depends on the load.

Besides, how are you going to put 240v through a single pole switch?

Ok, guess I learned something here on the amperage theory. Lol! All I know is that the switch in my hand is rated at 125 volt, so I would never be brave enough to put anything higher through it anyway!


How would you put 240 volt through a single pole switch? That, someone will have to explain to me! I know that by breaking one hot on a 2 wire (no nuetral) circuit, you can, in theory turn off the water heater, and yes it will work, but now you have a live wire at each terminal on the switch, and the wiring inside the wall and the water heater is still holding current even with that switch off....not something I'd feel very safe with!

 

[Jadnashua]

Got your terms wrong....current is actual power flow. If you break one lead, you won't have any current flow unless the circuit is short-circuited somehow. You'll have voltage (potential) there, but no current.

They do make double-pole toggle switches, I have one to shut off my air handler. It breaks both legs, which does remove all potential to the thing. It doesn't draw that much current (no backup heaters), so it's only a 15A, fairly common switch.

While not an exact analogy, think of voltage sort of like pressure and current as the volume/time. You can use a pressure-washer and have really high potential (pressure), but not get all that much volume through the small nozzle. Change that over to a fire hose, and the current (volume/time) will be greater, but the pressure (voltage) won't be anywhere near as high.

 

[Speedy Petey]

I know that by breaking one hot on a 2 wire (no nuetral) circuit, you can, in theory turn off the water heater, and yes it will work, but now you have a live wire at each terminal on the switch, and the wiring inside the wall and the water heater is still holding current even with that switch off....not something I'd feel very safe with!

THAT is why the switch is rated at 125v and not 250v. They do not want voltage present at both terminals. There are SP switches rated at 250v and 277v.

 

[Abikerboy]

oops...boo-boo'd again! Lol! I do know the terminology, and shouldve known how to better word it. I have had electrical and electronics classes, and at one time even had the papers I needed to get my electrical certification. I misused the term in it's meaning; correct thinking voltage is electrical pressure, amperage is the amount of electricity flowing through an electrical load. What I meant to say, and to explain, you have two hot wires on a tru 240 circuit, with no nuetral, so when you flip off that switch, breaking one of the hot wires, that water heater may not heat, BUT, you have a live wire on both terminals of that switch! Now, if someone turns that switch off, and decides to try to replace an element or a t-stat, then you WILL have current flow because even though you've broken the circuit, you still have power in the heater! Not like breaking a hot wire on a 110 circuit, where the hot is dead, and the neutral wont matter anyway since it's at earth potential!

 

[Speedy Petey]

What I meant to say, and to explain, you have two hot wires on a tru 240 circuit, with no nuetral, so when you flip off that switch, breaking one of the hot wires, that water heater may not heat, BUT, you have a live wire on both terminals of that switch! Now, if someone turns that switch off, and decides to try to replace an element or a t-stat, then you WILL have current flow because even though you've broken the circuit, you still have power in the heater!

That is why, as we have been saying ALL along, a single pole CONTROL switch CANNOT serve as the required service disconnect.
You still need a DISCONNECT even though you have a switch to control the heater.
Understand?

This is a rare type of installation, but some folks do have this.

 

[Abikerboy]

That is why, as we have been saying ALL along, a single pole CONTROL switch CANNOT serve as the required service disconnect.
You still need a DISCONNECT even though you have a switch to control the heater.
Understand?

This is a rare type of installation, but some folks do have this.

My understanding wasnt that he wanted it as a required disconnect, but that he wanted to turn the heater off when it wasnt needed, like for instance, in a summer home or something. Sorry if I read that wrong. I was just trying to make my example for a situation...say if he has a problem he cant fix, and he calls in someone to help him, and that person says "go turn the heatr off", so he turns the switch off, thinking that he has now cut power to the heater. WRONG!!!! I would hate to be the guy working on it! In my house, if someone tells me to turn the water heater off, I go flip the breaker, and ALL power is off on both lines into that heater. That wouldnt be the case with a single pole switch, whether it's designed for 240 or not! If the breaker or fuse panel is within reach, why not just turn the breaker off, or remove the fuse if you want to disconnect the heater during times of non-use? Ive been told a zillion times that it doesnt hurt the breaker to turn it off and on, and even if it did wear out the breaker, then the breaker would just trip constantly. Otherwise, go buy a box like I have on my central air. It has a plastic bar type thing in it...pull it out, turn it upside down, and stick it back in, and the power is off! My other suggestion would be a timer switch...got one on my heater. Turns the heater on a 6:00 am, off again at 9:00 am, on again at 7:00 pm, and off again at 9:00 pm. You can set the times you want it on or off, but for me, this program gives me hot water for a shower in the morning, and for dishes and a load of laundry in the eve, plus the tank holds the water hot enough that if Im here all day, I still have enough hot water for whatever.

 

[Speedy Petey]

My understanding wasnt that he wanted it as a required disconnect, but that he wanted to turn the heater off when it wasnt needed, like for instance, in a summer home or something.

That was my interpretation as well.

If you tell someone to turn something off (as opposed to doing it yourself), and you start to work on it without confirming that it is indeed off, you deserve any consequences.
"You" being anyone.

 

[Molo]

It hasn't been stated if code requires a disconnect.

whats the code on this?

TIA,
molo

 

[JWelectric]

It hasn't been stated if code requires a disconnect.

whats the code on this?

TIA,
molo

III. Disconnecting Means
422.30 General.
A means shall be provided to disconnect each appliance from all ungrounded conductors in accordance with the following sections of Part III. If an appliance is supplied by more than one source, the disconnecting means shall be grouped and identified.

422.31 Disconnection of Permanently Connected Appliances.
(A) Rated at Not Over 300 Volt-Amperes or 1/8 Horsepower. For permanently connected appliances rated at not over 300 volt-amperes or 1/8 hp, the branch-circuit overcurrent device shall be permitted to serve as the disconnecting means.

(B) Appliances Rated Over 300 Volt-Amperes or 1/8 Horsepower. For permanently connected appliances rated over 300 volt-amperes or 1/8 hp, the branch-circuit switch or circuit breaker shall be permitted to serve as the disconnecting means where the switch or circuit breaker is within sight from the appliance or is capable of being locked in the open position. The provision for locking or adding a lock to the disconnecting means shall be installed on or at the switch or circuit breaker used as the disconnecting means and shall remain in place with or without the lock installed.

 

[Speedy Petey]

It hasn't been stated if code requires a disconnect.

And you haven't yet explained your intentions.

Are you looking to turn the heater on and off occasionally, or are you looking to kill power completely to work on it?

 

[Molo]

The thought was to be able to turn it off if it was malfunctioning, but if it was malfunctioning, or you wanted to turn it off to leave for a few days, or to service it, iT SEEMS THAT IT WOULD BE best to go to the breaker anyway.

molo