Dimming lights when I run power tools

your tool could be too big.









twss

The outlet I normally use it on is 110 on older copper 12/2. Everything else is 12 or 14.

They dim initially, on lighter stuff like the angle grinder or heat gun. Constant flicker when I start getting into something heavy with the cutoff saw and welding machine. With the bigger draw stuff, it has shut off my cable box a couple of times when I turn them on. The shop panel is on a 60A breaker coming off of the main box.

What I can't figure out is why it would do it when I'm just using a 7.5A grinder from a house plug.

Measure your incoming line voltage. Right now mine is 250/125VAC. If you're below 220/110 that could be the problem. If so, contact power company about raising their line voltage or changing taps on your transformer.

Alright, I'll talk to the power company guys when they come by to straighten my telephone pole. Had to sign a ROW paper for them to come do that, so I don't guess getting them to run new lines will be easy. It's just annoying as hell that I've got to watch what I have on just to use a power tool

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It's just annoying as hell that I've got to watch what I have on just to use a power tool

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My house was built in the 1950's, I had to make sure the fridge wasn't running its compressor before using the microwave.

The lights dim no matter where I plug stuff in

Voltage sag at the lights is the direct cause for the dimming (obviously).

The voltage sag itself is caused/exacerbated by a couple of issues, most likely either an undersized transformer or voltage drop (which is a result of the additional current you draw when you run relatively large loads like a welding machine or power tools).

Voltage drop is caused by the resistance in the wire from the transformer all the way to the point of the system where you're seeing voltage sag, as well as by the total amps you are drawing at any given point. This includes the service conductors to the house and any conductors from there to additional panels and then on to the lights themselves. The resistance in the wire is increased when the wires are either small or they run a long way.

So, you have a couple of options:
Increase the wire size from the pole to your panel
Increase wire size from the panel to the lights
Increase XFMR size

Also, if your 100A shop panel is sub-fed through your 200A main panel, you could up the wire size from the main to the sub panel (or find a shorter route, which is unlikely). I would check the available voltages at the panels and at the lights with a meter to see what voltage your system is actually maintaining when the power tools are not in use. If they're low to begin with, I would think you probably are looking at voltage drop issues in the cables.

Also, IF the XFMR has adjustable taps on it (i don't know what kind the utility uses, but it's worth asking because it makes for an easy fix if so) you could ask them to adjust the tap setting on the XFMR to account for your long runs. This would change the nominal voltage on the XFMR secondary side, usually in 2.5% increments. For example, if the XFMR is single phase, 7200V:220V, moving the XFMR tap up would change the voltage to 7200V:225.5V.

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The problem is that the lights even dim for a second when I use my 7.5A angle grinder from an outlet in the front of my house. I can also make it happen when I use a 10A heat gun or hair dryer from an interior outlet. Just barely dims when my AC kicks on.

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Then you're having voltage sag issues at both panels. Probably correct in your assessment that the power line coming to the house is too small. The XFMR tap thing would still work though if the XFMR has movable taps. Otherwise it's probably a wire size thing, but the XFMR could be undersized. Need to get the XFMR size and a load check on your incomer to be sure though.

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Sounds like you have a supply problem. Call the power company. If they give youthe run around call the public service commission.

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No if the power company tells you to frick off then call whichever local news station that likes to take on shite like this....believe me the power company does not want bad publicity even if they have a monopoly.

Start with your extension cords for your tools, they may be too long or too weak. 18 g cords are just too small for most heavy tools but people buy on price and then buy them too long.

Next I would look at the circuits you are plugging in to. You may have too many in series sharing the breaker. I prefer to have a dedicated 20 amp breaker circuit on my bench just for tools.

Not sure of all the effects it may have but perhaps your ground is bad, check it at the breaker box, it will be a solid wire going down to the ground and attached to a rod that should be inserted 4-8' into the soil.