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Old 12-07-2008, 10:53 AM   #16
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lights dimming when using the vacuum


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Originally Posted by Marvin Gardens View Post
Physiologically some people are more attune to light changes than others. I have the same issue with very slight dimming of lights when I turn on my high amperage devices. My wife and others can't see it but it is real noticeable to me.
I would not worry about the slight dimming of the lights when running high amperage devices. It's pretty normal in every house I have even been in.
I agree, while I am very aware of it, others I know and discuss this with never even notice.

Jamie

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Old 12-07-2008, 11:02 AM   #17
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lights dimming when using the vacuum


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Originally Posted by Speedy Petey View Post
I disagree. Dimming is simply voltage drop and most of the time it is just normal. Rarely is it a "poor connection".
I see this in brand new homes wired beyond code.

My own home is wired with all #12, even the lighting, and quite a few circuits. I still get a dip in the ceiling lights when the fridge or A/C kicks on, and they are totally unrelated circuits.
I guess it depends on how much dimming we are talking about, the only way to really know if it is a problem would be to check voltage drop.

My line of thinking is poor connections = more resistance = more voltage drop.

I understand the ac causing a system wide dip, but a fridge? My fridges both only draw about 1.3 to 1.5a while running, if there inrush is 6x that, we are still only talking about 9a. I applogize, I don't mean to sound disagreeable with your information, it is just in contrast to what I have observed.

When you say dip in the lights, are you speaking of just a very momentary flicker or something longer than a fraction of a second?

I think I am going to have to get a fluke RMS clamp that can do inrush capture.

Jamie
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Old 12-07-2008, 12:40 PM   #18
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lights dimming when using the vacuum


Jamie, did you happen to measure your available voltage on that circuit that you tested your chop saw on?

I'd like to see 3 readings:

1) no load at all
2) all lights lit as described
3) #2 + chop saw running

Report your findings here ....
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Old 12-07-2008, 03:57 PM   #19
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lights dimming when using the vacuum


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Originally Posted by kbsparky View Post
Jamie, did you happen to measure your available voltage on that circuit that you tested your chop saw on?

I'd like to see 3 readings:

1) no load at all
2) all lights lit as described
3) #2 + chop saw running

Report your findings here ....
I say use a known heavy load where I is linearly proportional to V. Hair dryers, toasters, with nameplate data.

No motors, no lamps, no computers, no TVs.
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Old 12-07-2008, 11:43 PM   #20
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lights dimming when using the vacuum


Quote:
Originally Posted by kbsparky View Post
Jamie, did you happen to measure your available voltage on that circuit that you tested your chop saw on?

I'd like to see 3 readings:

1) no load at all
2) all lights lit as described
3) #2 + chop saw running

Report your findings here ....
118.6 at se (running a bit lower than normal). Porch circuit no load 118.6. Dedicated 20a on porch 118.6 no load. Porch circuit with 75 watt bulb, 118.5 +/-.1.

I will try it with the chop saw, it is a bit late and I didn't want to get people round here too angry. So I tested with a 1200 watt load, heat gun. Both the porch circuit with lighting and the dedicated 20 showed right about 2volts less, 116.7 -116.9 range.

When it was pluged into the same circuit as the porch lighting, I noticed no dimming, and after testing it several times, turning it on and off, I did see a very small very fast fraction of a second flicker - barely preceiveable.

I tested my longest circuit, a run of about 80 feet to my upstair bar / kitchenette area. It had a 3 volt =/- .2 to .3v drop.

With the bar circuit upstairs or the porch circuit, when on a isolated circuit, without lighting, even with a heavy load, there was absolutly no preceiveable change in lighting on other household circuits.

What kind of voltage drop do you normally see with a 10a load?

Jamie
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Old 12-07-2008, 11:49 PM   #21
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lights dimming when using the vacuum


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Originally Posted by Yoyizit View Post
I say use a known heavy load where I is linearly proportional to V. Hair dryers, toasters, with nameplate data.

No motors, no lamps, no computers, no TVs.
Plain analog heat gun, name plate @120 watts.

You said something to the effect that more than a 4v drop indicates a problem. Would this be a 4v difference from the se or a 4 volt at the outlet when a load is applied vs no load?

Jamie
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Old 12-08-2008, 08:09 AM   #22
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lights dimming when using the vacuum


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Originally Posted by jamiedolan View Post
Plain analog heat gun, name plate @120 watts.

You said something to the effect that more than a 4v drop indicates a problem. Would this be a 4v difference from the se or a 4 volt at the outlet when a load is applied vs no load?

Jamie
Seems to me there is an NEC requirement that the voltage doesn't drop more than 5% from panel to the last outlet (at what current?).
5% of 120v is 3.6v. At 10A this would be 0.36 ohm, equivalent to 72' of #14 copper (144' loop distance), at a 20C conductor temp.

NEC table 310-16 sort-of-tells me that 10A in #14 gives ~ a 10C rise in conductor temp, so you can then figure out the higher resistance in this conductor due to current heating,

R at 30C = R at 20C x [(235 + 30)/(235+20)] = 0.36x1.04=0.37, 4% higher.

but we're only looking for approximate values here.


Last edited by Yoyizit; 12-08-2008 at 08:44 AM.
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