Lights Dimming?

[Adam Cavaliere]

So I am throughly confused right now as to why lights are dimming when I turn on one of my tools.

I just moved into a new house and this is my first experience with a subpanel.

The subpanel is running off of a 60 amp circuit breaker on a main panel which is rated for 200 amps.

My bandsaw is hooked up to a 15 amp circuit breaker on the 60 amp subpanel.

All of the wiring inside the house is coming off of the main panel. The garage is only hooked up to the subpanel.

When I turn on the bandsaw, the lighting in the house slightly dims for a second. Any ideas as to why? Any ideas on how to remediate this?

[Paul Stoops]

What is the HP rating of your bandsaw motor? Does this occur when you turn on another tool? What else is hooked into that 60 amp circuit? Are you turning on a DC when the bandsaw motor turns on?

[Adam Cavaliere]

I am just setting up the shop, so the bandsaw is the only thing that is being turned on. I have not tried another tool. It is only a 14" bandsaw.

There is technically a heater on that 60 amp line, but it wasn't running at the time.

At most there was 600W of lighting running and the 14" bandsaw.

Also, interestingly enough, the lighting in the shop (on another 15 amp circuit) does not flicker or get affected by the bandsaw being turned on.

[Steve Meliza]

I have a similar setup except that my lights are from the sub panel too. Pretty much any 120V 1.5HP motor load turned on will cause a slight dimming of the lights for just a moment. I don't think there is any getting around it without installing some monster capacitors.

[Rod Sheridan]

Hi Adam, let's do some basic calculations assuming your bandsaw motor draws 10 amperes at full load.

Depending upon the motor, the starting current could be in the 70 to 150 amperes range for a second or two.

Adding 70 to 150 amperes load to your electrical service will cause the voltage to dip, in proportion to the increased current.

So your band saw motor starting current is causing the voltage to dip, on the supply carrying that bandsaw.

If your kitchen lighting is on that same pole, it will dim, your shop lighting may be on the other pole and it won't experience the voltage reduction.

Regards, Rod.

P.S. Convert your bandsaw to 240 volts and the voltage reduction will 1/4 of the percentage it is now.

[Carl Beckett]

And when that surge hits, all of the current gets redistributed via 'path of least resistance'. Meaning that its easier for it to route to the bandsaw or garage lights, than it is for it to route to the house lights. It doesnt necessarily have to be two different poles.

Its ironic - because it likely means larger wires and easier path to the garage lights than it means to the main lights.

Another explanation might be the type of light? Are there differences in the type of light in the house vs the garage? Some lights might tolerate a voltage drop more easily than others (Im imagining a flourescent, with a ballast/transformer having the ability to hold better than a pure incandescent)

[Stephen Cherry]

One way to think about it is with a plumbing analogy. If you have tubing that is too small in your house, when someone flushes the turlet while you are in the shower, the water goes hot.

It's about the same thing with the wires. If you try to get too much juice through the wires, the voltage drops. Also, everyone thinks about what size wire is good for a certain number of amps. This prevents heating and fires. There is also the length issue; as the wires get longer, the resistance goes up, causing greater voltage drops during an inrush.

[Adam Cavaliere]

Hi Adam, let's do some basic calculations assuming your bandsaw motor draws 10 amperes at full load.

Depending upon the motor, the starting current could be in the 70 to 150 amperes range for a second or two.

Adding 70 to 150 amperes load to your electrical service will cause the voltage to dip, in proportion to the increased current.

So your band saw motor starting current is causing the voltage to dip, on the supply carrying that bandsaw.

If your kitchen lighting is on that same pole, it will dim, your shop lighting may be on the other pole and it won't experience the voltage reduction.

Regards, Rod.

P.S. Convert your bandsaw to 240 volts and the voltage reduction will 1/4 of the percentage it is now.

Here is a diagram of how the wiring is laid out:

Drawing1.jpg

[Dan Hintz]

Adam,

I'm going to take a stab at it and say the workshop lights are on one phase, and the bandsaw and kitchen lights are on the other... hence, the kitchen lights dim when the bandsaw kicks in, but not the workshop lights.

[Bruce Wrenn]

Adam,

I'm going to take a stab at it and say the workshop lights are on one phase, and the bandsaw and kitchen lights are on the other... hence, the kitchen lights dim when the bandsaw kicks in, but not the workshop lights.

Instead of phase, the word should be "other side of neutral." A three wire service has a hot, neutral and another hot in addition to a ground, all of which are SINGLE phase. I have a 1/2 HP water pump that dims only some of the lights when it kicks in. There is no 14 ga stuff anywhere in my place.

[Stephen Cherry]

Instead of phase, the word should be "other side of neutral." A three wire service has a hot, neutral and another hot in addition to a ground, all of which are SINGLE phase. I have a 1/2 HP water pump that dims only some of the lights when it kicks in. There is no 14 ga stuff anywhere in my place.

All just what you want to call it, but there are two phases with respect to neutral or ground in a "single phase" supply- the two hots are 180 degrees out of phase to each other when referenced to ground, if they were not when you measure between the hots with a juice meter you would get 0 volts, and there would be no reason for the juice to flow.

[Rod Sheridan]

Thanks Adam, that's what I understood.

As I said, I expect that your bandsaw and kitchen lights are on one pole, the shop lights on another............Perfectly normal occurence.......Rod.

[Ole Anderson]

And you might notice a bit more dimming with the bandsaw than other tools as you need to spin up those 2 heavy wheels, so the high starting current lasts a bit longer than with other tools. Probably just a flicker with your TS.

I understand the phase thing, I just wish it worked out that convention said that 120 is single phase, 240 is two phase and three phase wye or delta is, well, three phase. It would just make sense in discussions like this. I mean 240 is two 120s out of phase with each other, so it would make sense to call it 2 phase. I'm sure an EE could chime in with a full discussion as to why it is not 2 phase.

[John Lifer]

So, I agree with the above posters, kitchen lights and BS are drawing power from same side of the main panel. Solution is to live with it, or if motor can be changed to 240V change it and add receptacle if you don't have one, or at the sub panel (assuming it has 240 coming in) change wiring sides for the outlet you are using. If only 120V coming in, you would have to change at the main breaker, this may make your garage dim, but your SO may not give you as much grief if her lights are not dimming One thing to look at is to see if your main box is evenly distributed. In other words, are there close to the same number of breakers on both sides.

[Carl Beckett]

As I said, I expect that your bandsaw and kitchen lights are on one pole, the shop lights on another............Perfectly normal occurence.......Rod.

Laughing at myself Rod. By 'pole', I took this to mean the physical pole at the street and couldnt understand what you meant!

'Leg' worked better for me. Or 'phase', or spelling it out as 'other side of neutral' got me clued in.....

In any event, a highly likely culprit.

If he just switched which side the bandsaw breaker was snapped into, would this be a simple way to test this theory?