Motors and dimming lights

Originally Posted By: jonofrey
This post was automatically imported from our archived forum.



The lights of the masterbathroom dimmed momentarily every time the hydro-therapy tub motor was kicked on. I understand that the motor will draw more amps on start up than once it is running and this can rob amps from other devices on the circuit.


My question is:

Is this just a nuisance or is there more to it?


--
Inspection Nirvana!

We're NACHI. Get over it.

Originally Posted By: bbadger
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jonofrey wrote:
My question is:

Is this just a nuisance or is there more to it?


99% chance it is just a nuisance.

The short instant that the power is applied to the motor but it is not yet rotating is called locked rotor.

The locked rotor current is quite high, six times running current would not be unusual.

A motor that takes 10 amps running could easily draw 60 amps at start up, the instant the motor starts turning the current falls rapidly.

With this high of a current draw it is difficult to wire building in a way that it goes unnoticed.

The human eye is very good at noticing a just a few volts of drop on an incandescent lamp.

I was just working on a 500 HP electric motor yesterday, if this motor was brought on line directly it would dim the entire area around this facility.

Its running current is about 600 amps @480 volt 3 PH, it's locked rotor current would be about 3600 amps. ![icon_eek.gif](upload://yuxgmvDDEGIQPAyP9sRnK0D0CCY.gif)

The way around this is the use of a speed control to wind it up slowly, in this case about 5 minutes to get this motor and the fan it drives up to speed.

It would be possible to use a 'soft start' device on a small motor like that in the hydro tub but they are expensive.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: jonofrey
This post was automatically imported from our archived forum.



Thanks Bob.



Inspection Nirvana!


We're NACHI. Get over it.

Originally Posted By: jtedesco
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Was the motor recently installed and was it connected to a circuit that is already loaded?


If the utility companies connection is not connected the the drip loop properly there could also be a problem there too.

![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



Joe must you find fault with everything?


Is nothing normal?

One can only wonder how the entire country is getting by without you riding shotgun on every inspection. ![nachi_sarcasm.gif](upload://6HQh6KbNiD73gqTNQInjrR2zeJw.gif)

When was the last time you actually worked with tools and not a book.

Its called street smarts and you can not find it in a book.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: jonofrey
This post was automatically imported from our archived forum.



Joe,


I guess the answers are yes and yes. One year builders warranty inspection. All the neutral conductors were terminated under single screw terms on the neutral bus. I assumed that the tub motor was connected to the lighting circuit but I don't know that for sure.

The system ground clamp was loose but I tightened it since I was there and had a screwdriver.


--
Inspection Nirvana!

We're NACHI. Get over it.

Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



bbadger wrote:
Joe must you find fault with everything?

Is nothing normal?

One can only wonder how the entire country is getting by without you riding shotgun on every inspection. ![nachi_sarcasm.gif](upload://6HQh6KbNiD73gqTNQInjrR2zeJw.gif)

When was the last time you actually worked with tools and not a book.

Its called street smarts and you can not find it in a book.


Bob:

What did I say this time to upset you?


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



jonofrey wrote:
Joe,

I guess the answers are yes and yes. One year builders warranty inspection. All the neutral conductors were terminated under single screw terms on the neutral bus. I assumed that the tub motor was connected to the lighting circuit but I don't know that for sure.

The system ground clamp was loose but I tightened it since I was there and had a screwdriver.


Thanks John: That may have been some of the problem.


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



jtedesco wrote:
[Bob:

What did I say this time to upset you?


Why, could you tell I was upset? ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)

Nothing in particular, just the normal doomsday attitude.

My general attitude is that the glass is half full and it contains a tasty drink.

IMO, your general attitude is the glass is half empty and it is dangerous.

Then again I had just come in from working in the sun, I might have been delirious.

To each their own.

Bob


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: bsmith
This post was automatically imported from our archived forum.



What if the light dims when the motor starts and then stays dim until the motor is turned off?



Bill Smith


www.SmithHomeInspection.com


“The difference between stupidity and genius is that genius has its limits.” A. Einstien

Originally Posted By: rcooke
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It could be the suppliers fault I did a home last week 200 amp service fed from the road with # ten I guess some time ago it had a much smaller service and has been upgraded maybe more the once . It could be a simple as upgrading the incoming lines.


There are also other things that could cause it to many homes on too small a supply transformer . To far away from the transformer .


It is some times impossible to get the full answer here as many things can be part of the problem . I to find it hard to inspect from a picture as you do not get all the information .


Thanks Joe Tedesco I sure do appreciate your feed back much appreciated . From A retired Sparky started the trade in 1951
In Canada some things are done just a little differently


--
Roy Cooke Sr.

http://Royshomeinspection.com

Originally Posted By: bbadger
This post was automatically imported from our archived forum.



bsmith wrote:
What if the light dims when the motor starts and then stays dim until the motor is turned off?


That I would be concerned with, for the reasons Joe T brought up and other issues.

In that case I would probe deeper or hire someone to probe deeper.


--
Bob Badger
Electrical Construction & Maintenance
Moderator at ECN

Originally Posted By: jtedesco
This post was automatically imported from our archived forum.



Thanks Roy! Experience is always the best teacher!


I am familiar with the CEC, and have written articles in CodeWatch discussing some of the rules which are a lot easier to understand.

![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)


--
Joe Tedesco, NEC Consultant

www.nachi.org/tedescobook.htm

Originally Posted By: bsmith
This post was automatically imported from our archived forum.



Bob-


Thanks for your reply. The light dimmed only in one room (which I suspect was on the same circuit as the motor). The motor was a small pool pump which seemed to be plugged into a general use 15 amp circuit. Could the cause of the dimming be as simple as the motor drawing too much current from that circuit?


--
Bill Smith
www.SmithHomeInspection.com
"The difference between stupidity and genius is that genius has its limits." A. Einstien