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Downgrade and Disable Breakers

Hello all,

Thank you for you time.  I have an electric tankless water heater.  I only have a 200 amp panel in my home and this water heater is wired for 120 with 3x40 amp breakers.  I have been told by several folks this should never have been put in my house and could cause potential damage to our home.  Becuase of the draw of the water heater we have flickering lights when its on and the breaker has tripped if we run the dryer or oven at the same time as the hot water.  My plan is to remove this and put in a 55 gallon tank electric water heater.  I know that this will require only one 30 amp breaker.  I have some questions about how to accomplish this myself safely.

I believe that I can replace the breaker (40 amp) that will support the new water heater with a 30 amp breaker and not have to change any wiring as you can downsize wire but not upsize.  Is this correct?
For the other two 40 amp lines that will not be used, what is the best way to decommission those?  I know I can get blanks for the panel, but wanted suggestions for best practice.  I can cap the wires themselves or possibly pull them, the water heater is on the same wall as the panel.

Thank you again for any and all suggestions.  I consider myself a fairly competent around the house handy man but a very, very novice electrician.  I can upload some pictures later if that might help and provide any more info.

Re: Downgrade and Disable Breakers


The best thing is to use natural gas water heater(s). The suggestion is correct. Tankless water heaters are not nearly as good as folks think they are. There are many things that need to be inline first before even considering that device. Using a wire size larger than recommended is one of those things. You can Never use any wire smaller than the calculated load of a device. This would be why your are having issues of the panel not self balancing. You can use wire that is larger than the minimal recommended standard in the NEC, or required for any device. If the manufacture requires number 12 AWG copper for say a dedicated microwave circuit, you can use number 10 or evne number 8. Number 8 would be overkill, but nothing wrong with number 10, other than you will have a little difficulty in getting the wire under the screws unless you use a commercial grade 20 or 30 amp receptacle. But I would never, ever use number 14 any where in a residental or commercial structure. Even though the NEC says I can.

I cannot comment on your skills or experience. Anytime that a circuit is not being used, remove the breaker(s) and cut out the wiring from the source and destination. There is nothing wrong with wiring remaining in areas that a person cannot access. Cut it out every where you can see it. If your panel has very few available slots, then you need to go above the minimal required wire size. Depending on the length from the panel, I would suggest at least a number 6 AWG copper. That way the resistance will be low. I almost bet the you used a minimal wire size for that tankless unit, which I bet you use number 10 or number 8 AWG. Should have used at least number 6 AWG copper, or better yet, number 4 AWG copper off each breaker. I always use the same size wire for the neutral, even though the NEC says one can use something smaller than the feeders. Never use aluminum as a branch circuit. I would never use aluminum as a feeder from the pole. I pulled 2 sets of 4 each of 750 mcm from the pole to supply 800 amp service to my house, even though the meter is less that 500 feet from the pole and less that 750 feet from the transformer. So using a larger wire size is better than using the minimal listed in the NEC. The NEC is a minimal starting point. It sounds like your range and dryer have wire that is too small for the length and load. You would be better off changing the wiring on those devices as well. Have you performed a load calculation on your electrical system? Sounds like that is needed.

I suggest installing a disconenct at the water heater just for ease of maintenance. There is nothing wrong with doing that. This is another one of those steps for going above the minimal standard.


Handy Andy In Mt Airy NC

Re: Downgrade and Disable Breakers

Thank you very much for all the info.  I will review more thoroughly and post back later.  Was out of town for the weekend and then had some trouble getting to my account.  Thanks again!

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