Voltage Drop - Dimming Lights

[MA_PE]

I have a question regarding dimming lights when for example a blow dryer is turned on. I am assuming this is a voltage drop problem. The house in question is fairly large with what is supposed to be a 200 amp service. There are (2) 200 amp panels each consiting of 30 circuits. We have already made sure that all of the terminations are tight. It is a service lateral with what looks like XHHW #2 Aluminum service entrance conductors and the length of the service lateral is approximately 180 feet. From what I can see #2 Aluminum is only rated for 100 amps. I think the conductor size and length of the service lateral are what is causing the problem. Anyone have any ideas on this? If more information is required please let me know.

Thanks

 

[480sparky]

Is the hair dryer a real-life example, or just a hypthetical question?

If it's real life, I'd check to see if the circuit the hair dryer is on is the same as the lights first.

Loose connections either on both circuits (assuming there's two involved) and in the service may cause it.

The real culprit may be the (seriously undersized) #2 on a 400a service.

 

[Jljohnson]

Is the hair dryer a real-life example, or just a hypthetical question?

If it's real life, I'd check to see if the circuit the hair dryer is on is the same as the lights first.

If 480 is on the right track and this is a real-life example I would venture a guess that the hair dryer is at leat 1500 watts and is being used on a 15 amp bedroom general use receptacle instaead of the typical 20 amp bathroom GFI circuit. 12.5 amps load on a 15 amp circuit will cause the remaing loads to dim almost every time, even if the circuit is designed properly. The # 2 service lateral could well be the culprit also. Is the lateral an UG feed or ASCR cable in open air or are you talking about the feeder behind the POCO metering. If the former then it may not be undersized at all, according the local POCO's standards.

 

[quogueelectric]

Some of the utility guys have suggested that certain light dimming may be caused by overloaded transformers out at the pole. How many houses are being served at this location?

 

[iwire]

I have a question regarding dimming lights when for example a blow dryer is turned on. I am assuming this is a voltage drop problem.

Is it really a problem or just an irritant?

What I am saying is this, it does not take much voltage drop to an incandescent lamp for our eyes to detect it.

I suggest putting a meter on the circuit and see what the real voltage drop is before I went to far trying to fix it what may not really be an issue.

 

[480sparky]

Well, let's do some math here.

400a service with #2 aluminim..... Let's assume the circuit with the dryer is wired using the same 'logic.

#2al = 10 'wire sizes too small' for 400amps.

So a 20a circuit should have...... Lesse: 10 wires sizes smaller than AWG 12 would be...... AWG 22 (cu). 640 cmils, if I'm reading the chart right.

Pop Quiz Time! What is the ampacity of AWG 22 copper?

 

[iwire]

The real culprit may be the (seriously undersized) #2 on a 400a service.

400a service

I am not sure it is a 400 amp service.

The house in question is fairly large with what is supposed to be a 200 amp service.

I think you are assuming based on this.

There are (2) 200 amp panels each consiting of 30 circuits.

Myself? I would break out a meter before assuming anything. :smile: