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deadant
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I have a outbuilding that has a subpanel that gets it power from the main panel at my house. I was doing some work in the outbuilding when I noticed that things didn't seem right. When I started the saw I noticed that the lights got brighter. And when I stoped the saw the lights got dimmer. Considering that this is opposite of what would normally happen, does anyone know what would cause this.
 
Posts: 1 | Location: usa | Registered: 10-19-05Reply With QuoteEdit or Delete MessageReport This Post
frankvan
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You're right, that's not what one would expect to happen. As the load on a circuit is increased there would normally be a voltage drop proportional to the product of the current draw and the resistance (or impedance) of the line. We have several electrical engineers on these boards besides myself, but I can't imagine any set of conditions that would explain what you report. Not being able to check out the conditions, perhaps you might try to furnish all the relevant facts you can observe. How far is the sub panel from the main? What kind of lighting is in the remote building? Fluorescent, incandescent, how many? Do some things stop or flicker or go out, and does the brightening of the light (lights) remain bright or gradually dim when the saw is started? Is this when the saw is idling and does the effect increase when the saw is loaded; sawing material? In the meantime, let's see if any of the other guys weigh in on this mystery. And welcome to AnswerPool. Smile
 
Posts: 6887 | Location: Baltimore, MD, U.S.A | Registered: 06-03-02Reply With QuoteEdit or Delete MessageReport This Post
bedstor
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Reading through this the only conclusion I come to is somehow the Low amperage circuit is drawing on a High amperage circuit as well perhaps wired across both circuits
Check the fuses that they have the correct value fuse or fuse wire I'm not familiar with the ratings in the US I'd say no more than 15 amps,and a 13 amp fuse in the tools plug tops.
If it has the thick 30 amp fuse worst still a fuse wire that has been folded over several times(A fire risk) they'll never blow they'll get very hot and ignite Mad
Last but not least the Old Favorite Bad Earths or Grounding switch off the supply and Inspect All the Grounding points but on the Fuse box and on the tools if possible take them off and clean the contact with the terminal(with steel wool) and tightly secure it and see if that improves matters? Could be a greasy or loose connection at the root of this?
That's my best Ideas (Not a Household electrical engineer ) Plenty of troubleshooting experience on Auto electrics over 20 years
 
Posts: 13157 | Location: 6 miles west of Wigan UK | Registered: 06-05-02Reply With QuoteEdit or Delete MessageReport This Post
frankvan
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One other thought occured to me since yesterday. If the motor driving the saw is a capacitor-start, induction-run, or (very unlikely) a synchronous motor, the starting of the unloaded saw (very little starting torque required), together with a rather long distance from the main service, if the voltage drop at the remote location is otherwise rather high --- assuming a combination of all those things -- it could be the case that the starting of the saw actually IMPROVES the power factor. Again this is based on several assumptions, but the fact is that if capacitance is introduced in an otherwise inductive circuit, or inductance in an otherwise capacitive one (rarely present) the power factor could be better. Power factor is a measure of the degree by which the voltage and the current in an alternating current circuit rise and fall in unison with one another.
Not being able to examine the site, of course, this is pureely conjecture. I assume 220/110 @ 60 Hertz AC. If you are in the UK or Europe the frequency would be 50 Hertz but otherwise in the same ball-park. Let us know if you find the real answer to this mystery. So far, I don't think it sounds dangerous, just unusual! Confused
 
Posts: 6887 | Location: Baltimore, MD, U.S.A | Registered: 06-03-02Reply With QuoteEdit or Delete MessageReport This Post
Professor
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quote:
Originally posted by Frankvan:
We have several electrical engineers on these boards besides myself, but I can't imagine any set of conditions that would explain what you report...In the meantime, let's see if any of the other guys weigh in on this mystery. And welcome to AnswerPool.
I'm only an amateur electrician and wannabe EE. I, too am completely baffled by the situation. The good news is that Frankvan has asked all the right questions. Smile

And let me join others in welcoming you to AP, deadant.
 
Posts: 1967 | Location: U.S. | Registered: 06-03-02Reply With QuoteEdit or Delete MessageReport This Post
Walks On Water
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This is just a guess.

I am wondering if what your seeing is the light dim on the initial start up locked rotor load and once it gets running the amps drop off and the light returns to it's normal brightness.

In other words, the saw may draw 10 amps running but could be draw as much as 50 amps or more starting depending on the motor.

If not then you have me stumped also. I am not an electrical engineer, I am a practical engineer.
 
Posts: 1587 | Location: Cleveland, OH. US of A | Registered: 06-03-02Reply With QuoteEdit or Delete MessageReport This Post
bunkboy
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Only a change in current through the bulbs will cause them to brighten or dim. The only thing that could possibly brighten a bulb first is a stored charge awaiting a discharge path, such as the capacitor Frankvan suggested. It is totally harmless as long as you don't use your body for a discharge path. The worst that could happen is a burned out bulb or a thrown breaker, both of which immediately stop the current.

If you have reason to suspect that your subpanel was a homemade job, all you have to do is make sure that your breaker ratings match the guage of the cable (cables are labled). I think the only real danger is a buildup of heat around cables and outlets that allow too much current. Most subpanels that I've seen are 60 amps drawing from a 200-amp box, and the grounding at the main box is sufficient (should be one grounding pole buried in the dirt and one hooked to the water supply).

(You could also go to your local Lowes or Home Depot or Eagle and ask for a three-prong outlet tester. They cost about $2 or something like that. You just plug them into each outlet to make sure they are wired properly. They have a guide labeled to the top, very easy to use. If you're brave enough to open the outlet and try to work on it, be sure to turn off the breaker, test it with the tester to insure the power is off, and then open it up.)
 
Posts: 239 | Location: Great lakes area | Registered: 11-07-05Reply With QuoteEdit or Delete MessageReport This Post
WoodStoneSteel
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Hmmm! Does your subpanel have a neutral that returns to the primary panel or have they wired in a UFER ground?
 
Posts: 1 | Location: San Diego | Registered: 03-19-07Reply With QuoteEdit or Delete MessageReport This Post
donaldekliros
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quote:
Originally posted by frankvan:
One other thought occured to me since yesterday. If the motor driving the saw is a capacitor-start, induction-run, or (very unlikely) a synchronous motor, the starting of the unloaded saw (very little starting torque required), together with a rather long distance from the main service, if the voltage drop at the remote location is otherwise rather high --- assuming a combination of all those things -- it could be the case that the starting of the saw actually IMPROVES the power factor. Again this is based on several assumptions, but the fact is that if capacitance is introduced in an otherwise inductive circuit, or inductance in an otherwise capacitive one (rarely present) the power factor could be better. Power factor is a measure of the degree by which the voltage and the current in an alternating current circuit rise and fall in unison with one another.

Frankvan:

I beleive that you have given this person the only logical answer that is possible fo this kind of situation.

DEK

Not being able to examine the site, of course, this is pureely conjecture. I assume 220/110 @ 60 Hertz AC. If you are in the UK or Europe the frequency would be 50 Hertz but otherwise in the same ball-park. Let us know if you find the real answer to this mystery. So far, I don't think it sounds dangerous, just unusual! Confused
 
Posts: 696 | Location: St. Louis Missouri, USA | Registered: 06-03-02Reply With QuoteEdit or Delete MessageReport This Post
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