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How to Repair a Water Heater and Oven Circuit Feedback Condition


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Summary: Electrical Circuits Question: Hi Dave, I recently went from a gas range to an electric wall oven. It is a Maytag 3.6kW@240V that I bought used.


Water Heater and Oven Circuit with a Voltage Feedback Condition



Water Heater and Oven Circuit with Voltage Feedback Conditions

Hi Dave, I recently went from a gas range to an electric wall oven. It is a Maytag 3.6kW@240V that I bought used.

It is on a segregated circuit with #12 copper wire, 3 wire installation, with a 20A breaker. It has operated for several months without problem until a few days ago, when the breaker tripped while preheating the oven. I reset it and it immediately tripped again.

The panel is in the basement, and I noticed that the water heater had just kicked on because of the noise it makes when first starting. The water heater has 2 3800W elements also on a segregated circuit with 10/2 wire with a 30A breaker.




It has never had any problems other than scale and lower element burnout. When I shut off the water heater, the oven worked just fine. Can you think of a reason these appliances on separate circuits would effect each other?
Thanks-
Steve.

Hi Steve - Great Question.
I am assuming that both the oven and water heater are on dedicated 240 volt circuits, each being served by their own 2-pole circuit breakers. If this is true - then I would shut off the circuit breaker and look for a loose connection or burnt wire, possibly where the wiring connects to the heating elements. Sometimes the controls will wear out as well, but make sure that all of the connections are ok. If the wiring and connections look ok, then I would check the circuit breaker and make sure that there is a reading of 240 volts between the two terminals. If this reading is not correct then there is a possibility that the breaker is bad or has a connection problem with the buss of the panel. All of these connection checks should be made with the circuit power OFF.

The process of elimination is the best way to troubleshoot starting with the most vulnerable parts of the electrical device. A check of the connection where the oven power is being supplied at the junction or splice would be good to check as well.
Let me know what you find out.
Dave

From: Steven N
Dave, I haven't tested it yet, but It seems you hit the nail square on the head. The wire from the lower heating element was loose at the water heater thermostat. It probably loosened the last time I changed out the element. I appreciate your help very much,. if you have time, could you explain to me why this would impact the oven circuit?
Thanks,
Steven N

Combined conversation between Steve and Dave:

Steve:
1 - Are you saying that even though an obvious problem was identified, I may still have a problem which needs to be corrected?

Dave: Possibly, however it is hard for me to tell from here. As stated initially - these two circuits should operate independently of each other under normal conditions. If you were to remove the loose wire from the water heater, insulating it with electrical tape to keep it safe, and try to duplicate what occurred before, then yes - you may in fact have another problem which sounds like a feed-back. If you find that you cannot duplicate the problem with the oven buy performing this test then it was just a coincidence. If the original problem occurs again while the water heater is wired correctly then it is possible that there is a problem with the oven wiring.

Steve:
2 - Is it possible that the loose water heater wire was the only source of the problem?

Dave:
If you wish, perform the test as mentioned above and see what happens.
If the original condition repeats itself then there is an additional problem. I would be surprised if there is a feed-back occurring because typically a feed-back would affect other circuits as well, but bit all depends on what is really occurring and where with respect to the all the electrical circuits.

I would be interested to know if your service is fed from a main panel of a sub-panel. Please understand that it is difficult for me to troubleshoot from my remote position, so I am offering suggestions based upon my experience and typical conditions which are commonly found.
Thanks,
Steve

Hi Steve -
The water heater and oven circuit should not affect each other at all, with one exception. If there is a problem with the main breaker or sub-main breaker that feeds the panel which supplies power to these two circuits then there will most likely be what is known as a feed-back.

A feed-back commonly occurs through other 240 volt large appliances especially when they are off there by creating a path for electricity to feed back through the heating elements of the 240 volt large appliance.

Here is a typical Voltage Feed Back scenario:
A main breaker has a bad connection on one of the 240 volt incoming legs of main power. Because the panel has circuits feeding from two legs of 120 volts each, the circuits being fed from the defective side can actually pull power through a 240 volt appliance. In most cases, the voltage will be around 94 volts due to the 240 volt appliance having a heating element which acts as a resistor which allows the power from the working side of the service to back feed the deficient side of the service.

This condition can cause a lot of potential problems within the service and the electrical components being fed. A condition such as this needs to be identified and corrected asap. The above scenario may in fact be happening with your service, and this happens more during the hot summer months due to expansion and contraction of electrical connections and heavy electrical loads being placed on large circuits.

This condition can be identified by an electrician who would measure the incoming voltages and the voltages of each circuit leaving the panel, then measuring the voltage at each dedicated circuit and branch circuit. When an abnormal or low voltage reading is identified then the process would be to examine the circuit back to the panel or source until then problem is discovered.

The problem could be a loose or burnt splice or connection or possibly a burnt or faulty breaker. Some times it is something as simple as a 240 volt breaker that has one side tripped in the off position, even when it appears to be in the on position. Every once and a while the problem may be identified on the electrical utility primary side of the service which would then require the attention of the electrical utility company.

I hope this helps you.
Dave



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