An easy test question, "whoops I'm wrong"

[Josh.E]

I'm studing for the masters test in GA. About a month ago they mailed me a "Candidate Information Bulletin". In this bullentin there are 3 Sample Questions. 1 of which I got wrong, and it still bothers me. It took me longer to read the question than it did to answer it, but once again I was wrong.
Here is the question:
What is the current draw of a 230 volt quick recovery residential water heater that has two 3000 watt elements?
Please tune in with an answer and why?
This question bothers me so much because I have delt with much harder questions and if I do get them wrong I understand why, but if this question appears 100 times I would answer it quickly and miss it 100 times.

 

[Zifkwong]

Re: An easy test question, "whoops I'm wrong"

26 Amps.....no?

 

[augie47]

Re: An easy test question, "whoops I'm wrong"

current draw? I'd say 13 amps

 

[jimwalker]

Re: An easy test question, "whoops I'm wrong"

6000 divided by 230

 

[jimwalker]

Re: An easy test question, "whoops I'm wrong"

hang on i changing answer to 13
quick recovery is mis leading

[ February 12, 2006, 01:22 PM: Message edited by: jimwalker ]

 

[augie47]

Re: An easy test question, "whoops I'm wrong"

 

[jimwalker]

Re: An easy test question, "whoops I'm wrong"

They love to try and trick you

 

[roger]

Re: An easy test question, "whoops I'm wrong"

Jim, it is not tricking people, it is just another piece or part of an exam, which is to read and understand what is being asked.

In the real world, hearing or reading things wrong is probably one of the most common reason for failures and added expense of a project.


Roger

 

[LawnGuyLandSparky]

Re: An easy test question, "whoops I'm wrong"

13 amps. Only one element fires at a time.

 

[DaveTap]

Re: An easy test question, "whoops I'm wrong"

Hi Josh,
The answer is 13 amps... Why? Because if you've ever studied the thermostat on an electric water heater... it only turns on the elements one at a time. I first figured it out the hard way... after replacing a thermostat. But then I'm from Chicago... we don't have electric water heaters.

 

[infinity]

Re: An easy test question, "whoops I'm wrong"

I'd say 25 amps. Calculations are figured using the nominal voltage which would be 240 volts. A fast recovery HWH would use two elements at the same time. 6000/240=25 amps. Am I close?

 

[Josh.E]

Re: An easy test question, "whoops I'm wrong"

13 is correct. Of course my answer was 26. By most of you getting 13 it tells me you guys know how to translate quick recovery. I've been doing electrical work for about 15 years and did not realize that quick recovery ment one fired at a time. Honestly, I would think just the opposite I would reserve the term emergency or back up if the second element was never on with the first. Anyway, it is kinda of spooky to think I might have a test full of these type questions. They don't test your knowledge of the code or of calculations, or do they. Is quick recovery a term often used in you guys areas? Any other things to look out for?

 

[LawnGuyLandSparky]

Re: An easy test question, "whoops I'm wrong"

"Fast recovery" is a sales gimmick. In a 30 gallow WH, 3000 watt elements might be considered fast recovery, where 2500 watt elements would be included in normal recovery models.

 

[augie47]

Re: An easy test question, "whoops I'm wrong"

"quick recovery" is used commonly in this area.
the top element turns on 1st to heat the smaller portion of water in the top of the tank. once thats heated the thermostat switches to the lower element to heat the balance of the water. water is drawn from the top, filled from the botttom, so a small suppy of hot water is available "quickly".

 

[LawnGuyLandSparky]

Re: An easy test question, "whoops I'm wrong"

Isn't that how all dual element water heaters work?

 

[haskindm]

Re: An easy test question, "whoops I'm wrong"

That is the way dual element water heaters work. That is why most jurisdictions require that a candidate for a Master Electrician license have some experience. There are many things for which the electrician is responsible that are not in the code book, basic electrical theory, following the directions included with the listing a labeling of a product, where to install smoke detectors, where a bath fan is required, and whether or not layin fluorescent fixtures need to be supported independent of the ceiling grid come to mind. I bet you will never forget the answer to that question.

 

[Onitram]

Fast recovery is misleading, both heaters are on same time to start heating. and maybe one will go off after water reaches certain temperature.

 

[tshea]

Re: An easy test question, "whoops I'm wrong"

Best explanation of an electric water heater operation:

the top element turns on 1st to heat the smaller portion of water in the top of the tank. once thats heated the thermostat switches to the lower element to heat the balance of the water. water is drawn from the top, filled from the botttom, so a small suppy of hot water is available "quickly".

13.04 Amps


Most of the larger (52 gal) EWH I've seen have 4500W elements.

 

[jwelectric]

I am totally surprised at some of you.

3000 X 125% = 3750
3750/ 240 = 15.625

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.

 

[al hildenbrand]

Re: An easy test question, "whoops I'm wrong"

What is the current draw of a 230 volt quick recovery residential water heater that has two 3000 watt elements?

JW, the question is about current drawn by the element, not the sizing of the circuit.

But allow me to add another slight spin.

If the heater element is rated at 230 V and is subject to "calculated current" based on the NEC 220.5 nominal voltage of 240 V, the important thing to remember is that the only thing that stays constant in the element is its resistance. The Wattage changes with the voltage change.

A "rated" 3000 W 230 V element has a resistance of 17.64 Ohms and a current of 13.04 A.

Change the voltage to 240 V on that "230 V element" and the current climbs to 13.6 A and the Watts rises to 3264 W.

I.E.:

3000W @ 230V implies 3000 W ? 230 V = 13.04 Amps

And: 230 V ? 13.04 A = 17.64 Ohms.

Raise the voltage to 240 Volts and: I = 240 V ? 17.64 Ohms = 13.6 Amps

At 13.6 Amps and 240 Volts the "3000 Watt" element puts out 3264 Watts.

IMO, what is missing in the question (maybe it is said elsewhere in the Test Rules) is a statement of the voltage placed on the heating element. Maybe it is 208 Volts.

The real world installation of the water heater element is going to subject the element to voltages all over the place.