Is there a safe, long term way to monitor actual voltage going through an outlet? I can check with a voltmeter, but it would be ideal to have an ongoing display -- even better to collect historical timestamped data.

We have kilns in the garage, all wiring has been done professionally and to code. Recently both kilns are not firing to temperature and one of the troubleshooting steps is checking the voltage while running. We might not be getting the needed voltage during peek times.

I'd like to have a continuous read-out of the live voltage if possible. It seems like it would be possible to have a device that is plugged into the outlet and the kiln plugs into it, but I'm not sure if something like this exists.

I'm also in contact with both the city (municipal power) and our electrician.

  • 1
    Is your power service large enough to power more than one kiln(you said kilns)? If everything is nice and tight and nothing defective then voltage in should stay the same unless trying to use too much power. There should be monitors made for what you want, but might be expensive for the size needed.
    – crip659
    Commented Dec 11, 2022 at 15:03
  • 1
    @crip659 Only one kiln runs at a time. We have plenty of service (got that upgraded) and everything necessary was re-done a few years ago. No problems up until recently. A friend had a similar issue and had to have a buck-boost installed. I'm thinking long-run since even if we solve this current problem, the voltage is literally a make or break scenario for kiln firings and losing a ton of work (or having it be reduced quality) is a big deal, especially if it keeps happening. Knowing the voltage is running correctly for the duration of a firing (12-18 hours) can help with troubleshooting.
    – MikeJansen
    Commented Dec 11, 2022 at 15:18
  • 2
    Probably the simplest solution is to get a voltmeter attachment for an inexpensive laptop computer, and have the computer monitor and record the voltage.
    – Hot Licks
    Commented Dec 11, 2022 at 15:24
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    Short term: Some DMMs can do min/max/average over a period of time, e.g. Fluke 87V MAX. There are single-phase recorders, e.g. Fluke VR1710, that can record the data for subsequent analysis on a PC. You can rent power analyzers from various sources, though it may be hard to find a single-phase device. If the stars aligned the city or electrician might be willing to loan you a suitable device. Long Term: Search <your favorite search engine> for line voltage monitor recorder with alarm for devices that can record and notify you of problems when they occur.
    – HABO
    Commented Dec 11, 2022 at 16:00
  • 1
    @HABO Can make this an answer since it does answer the question if there are monitors.
    – crip659
    Commented Dec 11, 2022 at 16:18

2 Answers 2


I have panel meters that report Voltage, amperage, wattage and either Hz or Power factor which were nice enough when new, but I cannot recommend the things as both expired in not terribly long. They were a supposedly quality brand name, (Murata) purchased from a reputable electronics supplier, (Mouser) not "weird stuff from ebay" and were "RU" listed as components.

I built one into the junction box for my well circuit, and replaced it with the other one when the first died and I hadn't gotten to the project I bought that for yet.

They provided a constant display which could either be one of the readings or cycle through all 4, and they first became unresponsive to the buttons to change what reading you saw, and then the displays just went dark, with no serviceable parts. In the end, the only useful bits left are some current transformers that cost far more than just buying a current transformer.

While power monitors that record are available they are usually cost-prohibitive for mere mortals. These days a video camera pointed at a voltmeter might be a reasonable approach to that on a budget.

The NEMA 14-50 kill-a-watt seems to be niche that someone should fill, based on some searching, though a kill-a-watt would not really solve your problem without a video recorder.


This is a possible workaround, though perhaps not a complete answer. If the internal wiring is in good shape, you can just monitor one side of the split phase for voltage drop. If there is any voltage drop from the utility, it will show up on both sides of the split phase, so you'll see it on a 120v circuit as well. Assuming you already have a 120v outlet on the same panel, get a Kill-A-Watt or similar plug-in voltage monitor, then point a cheap security camera at it. You won't get a logged set of data precisely, but you will get timestamped voltage. Multiple the visible figure by two to get your 240v equivalent reading. Again, this assumes your inside wiring is in good shape, and that your loads are at least mostly balanced.

  • Problem is, it would be 50-50 on if you'd catch a failing leg this way Commented Dec 12, 2022 at 5:24
  • @ThreePhaseEel fair point, though there's probably an outlet on the other side to check another day. Just looking for the cheapest safe and decent path.
    – KMJ
    Commented Dec 12, 2022 at 6:42

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