Im currently an electrical estimator, I hold a journeymans card and Im taking the masters Nov,15 in Orlando Fla. My Boss ask me a few questions about his lights dimming when large loads are turned on, about a month or so ago there was a good forum presented on here but I cant seem to find it. Any help in finding this forum or professional advice will be greatly appreciated.Thanks again in advance!!!
Lights Dimming when large loads turned on.
- Thread starter butch
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Lights Dimming when large loads turned on.
When you start a large load, the high current passing through the service transformer causes a large voltage drop internal to that transformer. As a result, the voltage on the secondary of the transformer will be lower than normal. This will cause all lights (and all other loads as well) to have a lower voltage. That is why the lights go dim. Since this type of issue usually arises when a large motor is started, and since the high starting current lasts only a short time (less than one second), the resultant dimming of lights will also last a short time.
That is what is happening, but does it answer your question? If not, what type of information are you looking for? Are you trying to solve a specific problem at a specific location? There are many ways to address the problem, but they depend heavily on the type of facility, the type(s) of lighting loads, the type(s) of motors, and the nature of the service (both the transformer and the upstream grid). Could you clarify your question?
When you start a large load, the high current passing through the service transformer causes a large voltage drop internal to that transformer. As a result, the voltage on the secondary of the transformer will be lower than normal. This will cause all lights (and all other loads as well) to have a lower voltage. That is why the lights go dim. Since this type of issue usually arises when a large motor is started, and since the high starting current lasts only a short time (less than one second), the resultant dimming of lights will also last a short time.
That is what is happening, but does it answer your question? If not, what type of information are you looking for? Are you trying to solve a specific problem at a specific location? There are many ways to address the problem, but they depend heavily on the type of facility, the type(s) of lighting loads, the type(s) of motors, and the nature of the service (both the transformer and the upstream grid). Could you clarify your question?
G
Guest
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Re: Lights Dimming when large loads turned on.
Large is relative. In a dwelling when say a furnace or washing machine turns on lights may not dim, but when a microwave or A/C compressor kicks in the lights will dim. The effect can be reduced by making home runs for those "large" loads, but it's nearly impossible to eliminate the dimming effect. That's my experience-- speaking residentially. A microwave is "large", but a washing machine, furnace, or refrigerator may be "small".
Large is relative. In a dwelling when say a furnace or washing machine turns on lights may not dim, but when a microwave or A/C compressor kicks in the lights will dim. The effect can be reduced by making home runs for those "large" loads, but it's nearly impossible to eliminate the dimming effect. That's my experience-- speaking residentially. A microwave is "large", but a washing machine, furnace, or refrigerator may be "small".
A
a.wayne3@verizon.net
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Re: Lights Dimming when large loads turned on.
Just my 2 cents.....Last week one of our builders
had a home close and when they moved in the h/o
was vacuming before movers came in.They complained that the light dimmed terribly.I went there and yes the lights did dim really bad.I put an amprobe on the circut and with lights on 6.5 amps,start the vacum it spiked to 23 amps and settled to 13.9 amps.I looked at the vacum a new one by the way and the sticker said 12 amp motor.solutions were simple either get a smaller vacum or plug in a 20 amp circuit.This is one reasson I dislike 14 ga.But to the owner of the company $$$ is a priority :roll:
Just my 2 cents.....Last week one of our builders
had a home close and when they moved in the h/o
was vacuming before movers came in.They complained that the light dimmed terribly.I went there and yes the lights did dim really bad.I put an amprobe on the circut and with lights on 6.5 amps,start the vacum it spiked to 23 amps and settled to 13.9 amps.I looked at the vacum a new one by the way and the sticker said 12 amp motor.solutions were simple either get a smaller vacum or plug in a 20 amp circuit.This is one reasson I dislike 14 ga.But to the owner of the company $$$ is a priority :roll:
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