Voltage Drop from High Current Load

Not.

No idea at all. It could be a problem. It could not be a problem. You should hire somebody with proper test equipment and power distribution experience (an electrician) to test the house wiring when this heater engages.

Sounds like it's just loading of that leg. Not a major deal, but can be annoying.

My microwave's fan and light would power on for about one second whenever my Aero Garden would turn on its grow lights. It took a few times before we realized our house wasn't haunted. A little circuit detective work tracked down the effect.

Your tankless is probably not on a different circuit, but I don't know what country you are in. A 240VAC appliance in the US uses both legs of incoming power, so is essentially sucking juice from the whole house (like you assumed). Depending on how sensitive to incoming power your rope lights' power supply was, they were just indicating a sag better than anything else (like you thought).

Depending on if her kitchen is up to code (NEC), there are specific requirements for certain appliances, the number of receptacles per area, how many on a branch, shapes of counter tops(!), etc.

NFPA 70 (the NEC), Article 210.50 under section III, Required Outlets gives all of the details.

You can view the NEC for free (as you can most NFPA documents) here. You will need and account, but it's well worth the effort.

By dedicated, I meant that it has its own 240v breaker in the main panel, so it is probably causing a slight voltage drop on the incoming power upstream of the main panel.

I suspect that it is just such a relatively large current load that is regularly switching on and off(usually 3 or 4 second cycle) that it is more noticeable than other large loads.

Florida, USA

Dimming lights indicates undersized wire, a poor connection, or overloaded circuits....as long as your circuit breakers are properly sized, and in proper working condition, they should trip if a dangerous rather than just annoying situation presents itself.....The average load for a microwave is around 10-12 amps, and should be on a separate 20amp circuit, as well as the toaster oven and refrigerator....I always like to oversize the capability of the wire in reference to the circuit breaker, in this case rather than 12 single strand I would use 12 thhn, stranded higher temp wire...this allows some leeway for degradation of connection over the years...doesn't hurt to use some conductive grease as well.....You should have a minimum of 150 Amp service coming in to the house....

All good points.

You have mentioned all possible causes . If there is loose contact in the main service cable connection from the OH distribution to the meter or under sized cable is used for the service connection similar problem of voltage drop can happen. So needs through check up by experienced professional.

Take a look at a Kill-O-Watt meter. Very handy tool for the price.

I have one of those. It doesn't work on high voltage and/or amp devices. I have a clamp on ammeter for that.

If your heater is on it's own breaker in the panel then you either have a loose terminal on the panel bus or an undersized drop wire from your utility.

You have a meter...measure the voltage on the panel bus while the heater is doing its thing.

Then tighten all the terminals and repeat measurement.

If the voltage drop disappears or diminishes significantly then you are good to go.

If there is no change and the drop is more than say 3% call the utility to come and have a look.

An understandable comment until one realizes that the possibly loose terminal screw maybe might be connected to the power grid with no disconnect between screw and power grid. To tighten this screw might require working hot.

....and your point is?

OP can protect himself by repeating this mantra..

"One flash and you are ash" repeat continuously as you meditate on the job.

I can assure you that I do have enough knowledge to be aware that terminal screws are potentially connected to the grid. (I was an industrial electrician several decades ago. I've forgotten a lot, but some of the more important basics have stuck in my brain so far. If I've forgotten that kind of detail, I might as well check out. Reminds me of an elderly acquaintance who was afraid of Alzheimer's. She considered putting a bottle of poison on the mantle with a note that said, "If you can't remember what these are, take them.")

My point is that I'm not going to recommend to somebody that is clearly not knowledgeable on how to work hot to work hot. You may not give a $#!t about human life that's not your own but I do.

According to your description, most of the voltage drop is in the utility system. The transformer is too small or it is too far away and the secondary conductors are too small. The flicker you are seeing is more of a nuisance than a problem. You should get the utility to check it out.

One thing you can check is to see where that drop might be coming from.

I'd first look at the AC at the main lug/breaker before and after the microwave comes on, Major drops there suggest problems before the panel.

Maybe an IR thermometer to check for poor connections?

That's all I've got.

Upgrade your connection from utility.

The reasons to both the problems i.e. your and your step daughter are similar but may be/ may not be the same. Over all issue seems to be Votage drooping called regulation. May be this is due to the lower incoming voltage from source it self. Might be you have low voltage issue in your area ( It is common in INDIA). It yes then that is the issue and whenever yoiu switch on heavy power drawing appliances there will be a drooping effect . The gravity of effect depends on electrical vicinity of the two circuits - affecting and addected. If that not be the case then it could be the faulty wiring or shorting of wires somewhere. The leakage is not heavy enopugh to trip the MCCB or blow the fuse but in the longrun i.e in the corse of time this may develop and result in burning of wores and tripping of MCCB/ Blowing of fuse. Get them checked. If fault is SMALL in source the problem settles after a few secas or max a minute ( TOO MUCH) OF SWITCHING ON THE heavy lpower appliance.. else it may sustain through out the period appliances is in service. In any case better get it attended - at least by measuring source input voltage to your premises.

This problem exists in many countries.When applying to utility for power connection the load is normally small but later additions like water heater/AC etc increases the load for which the voltage of utility drops may be due to small cable from utility.If utility lay larger cable making room for future additions it will be ideal.

yeah, This could also be a cause but chances are grim... can't be ruled out. This is because of high current in and resistance of the wire/cable. with thewires generally available in market, for house hold wiring ( of standard makes) - this isuue should normally not cropup.

Normally the load increases on every consumer's premises,therefore sometimes even transformers & feeeders(primary & secondary) need upgrading. Utility should take measurements of V,I,pf,Hz etc regularly to study the growth of load.

It could be a problem for any electric motor such as a HVAC unit or refrigerator.

If the voltage is dipping too low especially during the starting sequence, the motor cannot produce enough torque/HP to drive the load.

This will result in excessively high amperage and can cause severe damage to the motor(s) over a short period of time if not corrected.

Have the voltage level checked by a competent electrician to find out what you are faced with.

FYI: Normally the voltage dip is caused by the utility transformer that supplies the dwelling being too smal and/or being overloaded.

hey sharpstick,

you want to be of course careful with potentially lethal line voltage, but what's wrong with measuring the voltage drop between the fuse box and the outlet?

if yer high impedance DMM is giving you spurious or irrelevant readings, try parallelling it with a 5W 3K3 resistor long enough to get a real reading (it'll get hot rapidly)

...or just open a hot water tap and load the line with the heater's element.

Could be a good thing. When the lights brighten, you know the food is cooked.