Lights Flash When Water Heater is Turned On - Why?

[cigar7]

There are 2 LED lamps (total less than 80W), on a Panasonic 300w dimmer switch, turned on at full power, that blink when I turn on the shower water heater, 4500w. These lights are on a separate circuit wired to the breaker panel, 2.5mm copper wire, into 20A breaker. The water heater is on a dedicated circuit and breaker, no other appliances are on the circuit, and it has ground wire, 2.5mm copper wire, into a 20A breaker, grounded to rebar of the condo building. The breakers are NOT adjacent to each other in the panel. If I remember correctly, incandescent lamps also dimmed briefly, when the water heater was turned on. The Bticino panel has 232v AC supplied, with a 63A RCBO main breaker.

Why do the lights blink? What can I do to stop the lights from blinking?

[bankruatsteve]

Your mains supply might be on the edge. If your neighbors lights also blink when you turn on the shower - yeah, that might be it. If that's all that happens, I wouldn't worry about it.

[ignis]

Why do the lights blink?

Is a good question, and have been asking that myself for past 12 years, only for me it is the main TV that blinks... had the house built in 2003, so nothing is that old. + the same since day 1

block of 6 light switches, the garage, hall and stairs = TV blinks on and off, the other 3 nothing......... another block of 3 switches all outside lighting, just one makes the TV go on and off, another block of 3 in the dinning room just the one for the kitchen makes the TV in the livingroom blink... ? why ?

old projector TV, and present Plasma TV [now about 6 odd years old] ..... but my LED monitor 32" TV on the same circuit has never blinked

[cigar7]

Your mains supply might be on the edge. If your neighbors lights also blink when you turn on the shower - yeah, that might be it. If that's all that happens, I wouldn't worry about it.

I live in a condo. About 2 years ago, the main service was upgraded from the electric distribution room for the floor to my condo rooms. New copper mains wire, not sure of the gauge but much thicker than the old ones, a new 63A breaker in the distribution room and new panel and all new breakers in my room.

I can run 3 AC units (45,000 BTUs), 2 4500W water heaters, 2 fridges, 2 electric kettles, 2 toasters, 2 TVs, 2 electric irons, about 10 lights, all at the same time, no breakers popping. When the lights blink, the original issues, 70% of these electric devices are off. Does it really sound like a mains issue?

[RichCor]

Sound like an issue with the 'dimmer' on the circuit starving the bulbs.

Do, or would, the same bulbs 'blink' if they weren't behind a 'dimmer' when you turn on the 4500w shower water heater?

Or, would an incandescent bulb dim down if it was swapping into place in the 'dimmer'.

I'd also suggest checking both the shower heater circuit path and the 'dimmer' circuit path to verify that both are wired securely and correctly (Phase Live, Neutrals and Grounds) to the panel terminals.

Then again, a Google search for Dimmable LED Bulbs Blink shows this is a common occurrence.

LEDs require so little power compared to traditional bulbs, and even the 'dimmable' bulbs have issues with some 'dimmers'. Some companies sell "dimmer bypass" which appears to be a resister "dummy load" designed specifically to increase the power consumption to keep the bulbs from flickering.

You also might want to read this c|net article (found as part of that Google search):

Which LED bulbs are best for built-in dimmers?

Shopping for dimmable LEDs, but concerned about buzzing, flickering, and other annoyances? We're here to help.

c|net | by Ry Crist | June 16, 2014

"Modern dimmers (the kinds you'll find on the shelf at your DYI store) won't actually raise and lower the voltage for smooth dimming, but will instead flash the power up and down at unnoticeably high speeds to create the illusion of dimming.

[Crossy]

We have some regular lamps on dimmers which do odd things on normally un-noticeable mains blips (they are actually the heaters in our chick brooder).

Try replacing the dimmer with a regular switch, or replace one of the lamps with an ordinary bulb in case the dimmer doesn't like the LEDs.