220v & dimming lights

Ty G

Well-known member
I now have two 220 volt machines, a 2 hp bandsaw and a 3 hp tablesaw.  When I turn a machine on, the lights slightly dim for about 2 seconds while motor cranks up, then once motor gets going, all is fine.  The three hp tablesaw is a little more noticible than the 2 hp bandsaw. Will this hurt or damage the motor over time?
Sounds like you have the machines and lights on the same circuits. Best to separate them in case you blow a fuse or circuit breaker and end up in the dark while in the middle of a cut on the tablesaw. It's normal for fractional hp motors to create a momentary electrical surge and voltage drop on startup. Even if your lights are independent of the machines' 220 volt feeds, your entire electrical service could be near or at load capacity and may need to be looked at by a licensed electrician. What can be more harmful to motors is running on a lower voltage than they were designed for. If your electrical load is creating enough of a continuos voltage drop, your machines' motors will work less efficiently and over time could suffer from constant heat build-up due to the overloaded condition created by a reduced voltage. Also make sure that the 220 volt feed wires are of sufficient gauge and make them as short as possible. I use #10 wire for my 220 volt feeds. Again, a good electrician can help you out.

I would be more concerned about safety.  It sounds like you are using a very small gauge of wire or running it a great distance.  Check the amperage requirements of your tools.  Using too  small of a wire gauge can cause excessive heat  which can be a problem.  

jim vojcek
I agree something is wrong with your electrical system. As others have mentioned most likely a run that is to long from the source, and under sized. I normally turn on my 3hp dust collector, then my 5hp planer, while the lights and radio are on, no flickers, dimming or drop in sound on the radio.

Since my shop is on the opposite side of the house from my service entrance I put a 100amp service in for the shop. I installed a dedicated circuit for each of my stationary machines. I put each wall on it's own circuit, and the lights on thier own circuit.

I think lights should always be on thier own circuit, cause the last thing I want if I trip a breaker is for the lights to go out while the machine is winding down.

I also put an outlet hooked up to my lights (and marked it so) and plug my glue pot into this. So that way I don't forget to turn off my glue pot when I leave for the night.
Thanks all for the detailed help.  I did some measuring and figuring today.  The path of my electricity right now is this, from the meter pole to the house breaker, then to a small barn breaker, then to my shop, a total distance of 325 feet.  I can pull the buried wire and rerun it to another large shed that is connected to the meter pole, the total distance that route is 220 feet.  Less distance and not sharing the house power.  I did email the motor company Leeson and they replies that the dimming would do no harm.  But, for safeties sake and other reasons you guys brought up, I feel I need to do the rerunning of the wire.
Thanks again, Ty
You might want to have your power co. check the connections from the pole to the house.            Good Luck/Ed

Before you go changing wires that involves buried conductors, I suggest you pause and reconsider.

1. I agree completely with the recommendations others have made for separate breakers, and adequate extension cords. I would start by double checking your wires that run to the tool for adequate size.

2. You said the lights dim slightly as the motor starts and then are O.K. I am not persuaded that your description is sufficient to take action, or to know what action to take. You may not need to take any action depending on what "slightly" means.

3. If you are considering altering permanantly installed wiring; wires that feed service boxes, distribution boxes, or even hard-wired fixtures like outlet boxes,it seems prudent to first check what you have.  I don't know where you live, who did the wiring, how old it is and how strictly the National Electric Code is/was enforced on your wiring, but if the wiring is well done and meets code requirements I do not expect you will see much of a gain by changing a particular wiring run as the wires should have been sized to match the voltage drop to the length of run in the first place. Before you start changing things, check to see exaclty what you have matches code for wire sizes. You can get info on code requirments on wire sizes lots of places that has been interpreted for Harry Homeowner, and all of your wires are probably marked with size information. Of course if you live on an old rural farm that was never really wired to Code, and that has been  "rewired" by the occupants over time, all bets are off.

Hello Ty, I believe all of the above responses to be excellent. I will put in my 2c. I am not an electrician but a general contractor. Before I did anything drastic, I would call a local reputable electrician, explain what you have, have them look at the existing situation and then have them make any recomendations. The hour that they  will charge you for may be money well spent.
incandescent lights are sensitive to a voltage drop when you start a large load. this is pretty normal behavior, I'd have to see how much the lights dim.

last time i checked the NEC allowed a max voltage drop of 5% from your main breaker. In your case the meter socket/house breaker  to the end device (table saw)

If you are getting a voltage drop your getting to much impedance, (resistance for AC) increasing the wire size can improve this. The larger the wire the less impedance the conductor has.

You house/street may have lower voltage then normal, this coupled with the long wire runs to your shop makes the problem worse. I've seen suburban house voltage vary form 95 to 128 volts.  Call the power company and talk to them.

If it makes you feel nervous, please call a qualified electrician.
Not becaue I am soliciting electrical contracting work, but to give you some perspective on the basis for my comments, in my County, it is possible to obtain a permit to wire one's own dwelling if your are willing to study the National Electric Code and sit for a written exam. The exam is less rigourous that that required to do wiring for hire for others, but gives a good "grounding" in safe wiring practices. Having done that successfully is the basis for whatever expertise I may have acquired.

My guess is that for a barn or something you probably have a single 30 amp run (10 guage wire). This is pretty typical for an out building used as garage, and in NY would meet code in most situations. For the distance you have there will be a 3 or 4 amp drop, and there is probably a another 1 amp drop due to connections. So for your machines you should be fine power wise, but you should not have your lights dimming, especially the bandsaw. For a 2 hp machine on 220 max draw should be less than 15 amps, your lights, if you have a lot of them, should draw no more than 2 amps, radio, fan, wall clock, glue pot, etc., another 2 amps. So worst case 19 amps. Your lights should not be dimming. The 2 incandesents over my bench don't dim when I power up my planer with the DC running (8 hp total).

Check your wiring to see if it's aluminum. If so there should be a special grease on the connectors to keep the aluminum from corroding. In a shop the grease could get full of dust and dry the grease out. A lot of home fires have been blamed on aluminum wiring, which is why it can no longer be used in NY for anything less than a main run, and is coded oversized (i.e. where the math calls for 8 guage, you have to use 4 guage). If you have aluminum for you source swap it out for copper.

I agree with what kerry and farms posted. If there are no obvious problems (loose wires, corrosion, moisture in a box) call an electrician. It probably is just current drop due to distance. If everything is safe, which it probably is, the electrician can let you know what you need to do to have adequite power. And If it's not safe, you'll be really glad you called him. The $100 or so it will cost will be much cheaper than redoing something that isn't a problem.