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spikesnet 10-20-2008 09:10 AM

multimeter question
 
I need to test an element in my hot water heater and I was told to do this I need to:
  1. Turn off power at the Electrical Service Panel and post a sign warning others not to turn it on.
  2. Remove the access panel on the electric water heater.
  3. Disconnect one of the element wires and set a multimeter to RX1000 (resistance times 1,000). Touch one probe to an element mounting bolt and the other to each element terminal screw, in turn. If the tester displays anything but infinity (open circuit), replace the element.
The problem is my digital multimeter I have doesn't have RX1000. What it has under the headphone looking icon is 20, 2000, 20k etc.

Here is a diagram of what my meter has:

http://www.cyberpoet.net/ebay/centech.html

Can I complete the steps above with this meter? If I use 2000 will that work or will thought make the results different?

Right now when I put it on 2000 and turn it on the screen displays a number 1.

Billy_Bob 10-20-2008 10:59 AM

I read on the following link toward the bottom that your element should be about the following...

15.5 ohms for 3500 watts
13.0 ohms for 4500 watts
10.0 ohms for 5500 watts

http://www.plumbingstore.com/elements.html

Let's see... How do I explain this????

If you have a light bulb, there is a wire inside you can see. This wire makes an electrical connection. If the wire is connecting, the light bulb works! Same with a water heater element. It too needs to have the "wire" inside making an electrical connection, then it can heat.

BUT if you have wires connected to the two electrical connections on the element and try to measure "ohms" (or that there is a connection), you could be reading something else connected to the wires like the other element on the water heater.

Therefore it is necessary to disconnect one wire. So disconnect one wire from the element, then read between the two "electrical connection" screws. Do this with your meter set to 200. Then you should get a reading like the above if the element is good. If there is no reading, then the "wire" inside the element is broken and it will not heat.

Another test is to see if there is a "short circuit". This is between one of the electrical connections and a "mounting screw" on the element. This would mean the wire inside the element is "touching" the metal case around it (dangerous/replace). Set your meter to 2000, then you should get the same reading on your meter as when the test probes are not touching anything (no connection).

Billy_Bob 10-20-2008 11:18 AM

P.S. The way a water heater works is that first (when water cold) the top element turns on and heats the water in the top of the tank. Then when the water in the top reaches the temperature selected on the thermostat, the upper thermostat turns off the upper element and switches the electricity to the lower element.

Then the lower element kicks on and heats the water in the lower portion of the water heater until the water reaches the temperature selected on the lower thermostat.

Usually the lower element is what runs most of the time unless you use all of the hot water in the tank.

Because of the "switching" needed by the upper thermostat, the upper and lower thermostats are different.

Also warm/hot water comes out from the top of the tank, then there is a "tube" inside the water heater which directs the cold water to go to the bottom of the tank. This is called a "dip tube".

J. V. 10-20-2008 11:21 AM

The element resistance (ohms) will be very low, but well above zero. Set your meter first to the 200 ohm scale. Remember the scale is determined by the decimal point. So you can get the same reading on multiple scales, just the decimal point location will be different. But you need to know what the resistance should be first, right?

Use the formula (voltage squared divided by watts). This will give you the resistance reading you want to see. The watts will be listed on the element and the voltage will be determined by the voltage your water heater uses. Usually 240 volts. Measure the voltage with your meter and use this reading. A couple ohms up or down is fine.

I would not test this element with the power on. This is dangerous, and should only be performed by a qualified person.


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