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Mike, Master Electrician
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Experience:  Licensed Master Electrician - OnQ Certified Data Voice Audio Video Installer
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Tankless hot water heater flickering the lights. Can you use

Customer Question

Tankless hot water heater flickering the lights. Can you use an AC Capacitor on each leg of the 220 to eliminate the flicker? Specs of water heater: 220v 60amp, real pull of 51amps. On a scope you can see the water heater chopping the top off the sine wave on about every 5th or 6th high.
Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) Flickering lights is an indication of a loose wire connection, usually a hot wire. Since the H2O heater resides on a separate circuit than the lighting, this suggests a loose hot phase connection either at the meter socket or at the lugs of the main breaker. Lighting circuits are a separate circuit than the H2O heater. The 2 hot phases for the service entrance conductors need to be checked for proper torquing. Also double check the H2O branch circuit connections/terminations.

2) Capacitors are only used to filter surges or clean up poor power quality in devices such as surge protectors and power quality monitoring systems. A cap is not going to resolve the problem:)

3) On a properly wired 120 and/or 240 volt AC system, an oscilloscope should show a fairly clean sine wave.

Customer: replied 1 year ago.
There are no loose connections, and the grounds are solid. Even installed a new ground for the meter base. Took the main wires out of the box cleaned them and put anti oxidizer goop on them. (yes the mains are aluminum) The power company replaced the transformer and meter. Sine wave at the meter still shows the tops of the waves getting cut off as the water heater reduces the load under low flow. If the water heater is under full load-no flicker.
Expert:  Kevin replied 1 year ago.

Thanks for the replies.

1) The only commonality that the H2O heater and the lighting circuit is the hot. The H2O heater does not have a neutral, so that eliminates that possibility.

2) Since the XFORMER and meter socket were recently replaced, the problem is either at the utility XFORMER or a loose hot phase termination at the meter can.

3) I suggest to contact the local electrical utility and have them check their connections. They can also install a power quality monitor at the meter can to confirm the cause of the problem if within their transformer.

Expert:  Kevin replied 1 year ago.

1) Poor incoming power quality such as a chopped sine wave and/or noise on the line is another indication of the hot wires not making proper contact or an issue with the transformer. The LOAD side lug connections at the meter can be temporarily removed and the utility can place a scope or power quality monitoring device on the LINE side of the meter to confirm if the problem is the utility.

Customer: replied 1 year ago.
Maybe i did not make that clear:
Utility installed in XFORMER just for me on a new pole. They ran all new wire from XFORMER to the meter base on house.
Utility says "we have done all we can do." They had monitor on the meter side for a week." Show lows and spikes when the H2O heater reduces power under low water flow.
Power coming from the XFORMER looks good.
Customer: replied 1 year ago.
new XFORMER just for me
Customer: replied 1 year ago.
At this point I am just trying to reduce the flicker. I switched to all LED lights, and that helped. but still makes you twitch when running hot water.
Expert:  Kevin replied 1 year ago.

1) Well, utility companies have been known to make mistakes. Been down this road before:)

2) Your lighting system requires a neutral conductor for the 120 volt circuits, yet the H2O heater is a 240 volt circuit which does not require a neutral connection. Flickering lights indicate a loose hot wire and dimming lights indicate a loose neutral wire. Thus the only commonality between the lighting circuit and the H2O heater are the hots.

3) Since the H2O heater only requires 2 hots and the flickering stops when the H2O heater is under full load is due to the contacts expanding. When the H2O heater is not under full load, the contacts (terminations) contract. In any electrical circuit, amperage flow causes terminations to expand as the conductors heat up and a reduction in amps or no amps flowing cause the terminations to contract when cooling down.

4) In fact, the H2O heater technically does not even require a ground connection. The ground on the H2O heater is only for safety reasons. Electrically speaking, the H2O heater will work correctly with or without a ground. The neutral conductors are the grounded conductors and the hot wires are the ungrounded conductors. Therefore, I don't see how a potential grounding issue can be caused by the H2O heater which flickers the lighting circuit?

I will opt out of the question and place it back to the open board. Perhaps another expert here has a better idea than I do. No need to reply back to me. You will be notified once another electrician picks up the question.


Customer: replied 1 year ago.
Thank you
Expert:  Wayne Roberts replied 1 year ago.

Do you have a 200 amp service?

Customer: replied 1 year ago.
Expert:  Wayne Roberts replied 1 year ago.

Look at the position of the breakers in the panel, the water heater should be closest to the main lugs and definitely before the lights.

Customer: replied 1 year ago.
There are no lights on the side of the box, but there are other unused 220 breakers above it in the box.
Expert:  Wayne Roberts replied 1 year ago.

Well, this seems to be a common issue. These tank-less water heaters have caused a lot of people similar headache. What gauge wire is coming out of the tank-less heater breaker? If the water heater is less that 75 ft away it can be #6 copper. Any more than 75ft #4 copper.

Customer: replied 1 year ago.
It's about 4 feet, #6, The setup is a 60 amp breaker with #6 copper coming down to another switch box 4 feet away with a60 amp breaker in it. I can send pic if needed.
Expert:  Wayne Roberts replied 1 year ago.

Everything you can provide in the way of information would be most appreciated. I was thinking voltage drop...but that is a very short distance and the wire # ***** within code. Are there sub panels? As in your main panel feed another 100 amp panel?

Expert:  Wayne Roberts replied 1 year ago.

I would scour for any loose connections as well, if you can... remove the cover from the tank less and just kind-of probe its components looking for anything loose or amiss. But it doesn't hurt to double check everything.

Customer: replied 1 year ago.
There are no sub panels fed from this main panel. There is a panel that is wired off the top of this panel.Pics coming
Customer: replied 1 year ago.
there should be 3 pics
Expert:  Wayne Roberts replied 1 year ago.

Are the lights controlled by the same panel as the tank less or are they in the panel on the right?

Expert:  Wayne Roberts replied 1 year ago.

And, are the dimming lights plugged into a receptical?

Expert:  Wayne Roberts replied 1 year ago.

If the offending lights are controlled by the right panel we then must determine how that panel is fed.

Customer: replied 1 year ago.
Well the lights that are flickering are on the left leg of box the H2O heater is on, and on the two breakers below the H2O heater.
The lights that are flickering are ceiling and wall mount lights, with incandescent bulbs and LED bulbs.
Customer: replied 1 year ago.
not noticed it on any of the lights on the right panel, but will check it right now.
Customer: replied 1 year ago.
It's there on the lights on the right panel but very faint.
Expert:  Wayne Roberts replied 1 year ago.

Well, I can tell you whats happening and how to try and eliminate the problem. However, most people only get limited results. You have to rearrange the breakers in the panel to balance the load across both phases. This and putting the H2O heater breaker as close to the lugs as possible may eliminate or reduce the problem. Beyond this all i can say is you can upgrade service or supplement power with solar or wind. The heater is simply a power hog. As far as the sine wave goes, i'm not sure. That is very interesting. I can offer no more help to you so im opting out boss. Good luck, and be safe!

Customer: replied 1 year ago.
k, thanks
Customer: replied 1 year ago.
video of the lights on the far right panel.
Expert:  Kevin replied 1 year ago.

One question that needs to be confirmed:

1) Did the lights flicker prior to the utility company replacing the transformer, the meter and the service entrance conductors to the meter can?

2) Is the tankless H2O heater a new installation or was this previously installed prior to the utility company work?

3) Can you temporarily shut OFF all of the branch circuit breakers in the home with the exception of the problem lighting circuit and the H2O heater breakers? Turn the H2O heater to Full Load and then to minimal load a few times. Do the lights still flicker with no other circuit breakers in the ON position?

Customer: replied 1 year ago.
1: Yes, oh my they flickered way worse than they do now.2: The H2O heater is was replacing a tank water heater (that had no flicker) Once the new tankless was installed, we had flicker so I sent that unit back and got a replacement. It did the same thing so I sent it back and got a totally different brand. (same results)3: Not sure i have tried this in this setup. I will do it and post shortly.
Customer: replied 1 year ago.
Okay, The lights on the same leg as the H2O heater still flicker.
It did seem to help the lights on the other legs, and other panel to not flicker as much. But alas, they still flickered.
Expert:  Kevin replied 1 year ago.

OK, Thank you for confirming that.

1) Here is how your panels are configured:

The panel on the left is your main panel. The middle panel is a sub-panel that is being fed from the main panel. The smaller 70 amp panel connected to the H2O heater is also a sub-panel being fed from the main panel. Thus you have 2 separately installed sub-panels of which both are fed off of the main.

2) Can you provide me with a breakout of the quantity of lighting circuits that flicker in each panel?

How many in the main panel and how many in the middle sub-panel flicker?

Customer: replied 1 year ago.
I can try: It is a very very big house. 6100 sqf 7 bed 5 bath. Before I type all that up, I am going to try and balance the load on the legs. I will post tomorrow the results.
Expert:  Kevin replied 1 year ago.

1) Since you are familiar with what a hot leg is, are you comfortable in "rolling" 1 or 2 of the flickering lighting circuits over to other known working single pole breakers of the same amperage in the main panel or middle sub-panel?

We need to determine if the lighting flickering is being caused by one hot phase or both of the hot phases and if the flickering will follow or go away when "rolling" the lighting circuit or circuits over to the opposite phase.

Keep in mind that the lighting circuits only reside on (1) one hot leg, yet the H2O heater takes 2 hot legs. The $64K question is, does the flickering stop or does it follow when a lighting circuit is "rolled" from 1 hot phase to the other hot phase?

As you are probably already aware of, your main panel contains 2 hot phases which originate from the transformer and tandem thru the meter and onto the lugs on the main panel. The double pole feeder breakers to the other 2 sub-panels also contain the same 2 hot phases.

2) If you have a "clamp-on" amp meter and when the home is under Full Load (all possible electrical items in the ON position) light, TV, radio, microwave, dryer, washer, pumps, etc are all in the ON position. In other words, fire up every possible load in the home simultaneously. Then the clamp-on amp meter can quickly confirm if the 2 hot phases are close to being balanced. Both phases won't have identical amps under full load but should be somewhat close.

The amount of amps on the neutral service entrance conductor at the main panel will be the difference in amps of the 2 hot phase amp Highest Hot phase (-) subtracted from the lower hot phase will = the total neutral current under Full Load.

3) There is no hierarchy as to the position/location of a double pole circuit breaker in any panel. The voltage (120VAC each side) is evenly distributed on both sides of the hot bus bar from the main breaker thru the hot bus bars and onto to a double pole breaker. What does matter is if the phase amps are close to being balanced when under full load.

Reply back to me when you have an opportunity and we can take it from there............Thanks...........Kevin:)