Voltage Sag


  #1  
Old 03-08-01, 10:23 PM
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I have installed a new service Entrance meter pack (this includes a 125amp breaker)outside, and a new 125amp main breaker Square D QO load center inside. I have rewired a 1950 home with new circuits. My problem is many of the individual circuits, i.e.garbage disposal or refrigerator or heating motor for a water system, when in a run mode, dim the lights of seperate circuits throughout the house. Note: The Refrigerator, garbage disposal and heater motor are on individual 20amp circuits.

This will happen with just one of the loads running, say the garbage disposal and all other loads in the house will be off, except the lights in the kitchen (seperate circuit) and they will dim for a few seconds, when i first turn on the disposal.

Someone tell me i am over looking something.

Bill
 
  #2  
Old 03-10-01, 07:26 AM
Wgoodrich
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We should go with the obvious first. If this doen't localize the problem then we can do some calculations.

What size feeders from the Utility connection to the main breaker in the inside panel? What size feeders is the Utility Company feeding you with? How far is it from the Utility transformer to your main panel outside then how far is it from you main panel out side to the main panel inside? How many square feet is your house? Do you have electric heat or central air?

Answer these questions then confirm that these circuits you mentioned with motors are actually single dedicated circuits, this would make a big difference in our advise to you.

Get back in with us with the above info. Then we may be able to pinpoint where your problem is.

Wg

 
  #3  
Old 03-13-01, 12:20 PM
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Voltage sag reply

I installed a 1/0 AWG.THHN cable from the roof top Conduit sevice hood down to the utility meeter box with a 125amp C/B, this is a 12 ft. run. The cable from the load side of that 125amp C/B to the line side of the Main C/B in the, load center(inside the house) is 30 ft. of 1/0 AWG. XHHN. There is no marking on the utility cable from the Power pole (at the street) to the Service hood (at my roof) this connection was provide by PG&E Utility Co., but it looks to be smaller then the 1/0 AWG. THHN cable.

My House is 1850 Sq. Ft.

The home heating, except for a small single phase circulation water pump, is Gas. No A/C in the house.

Also, the water heater, clothing dryer, stove and oven are Gas.

There are no 240 volt loads in the house.

The loads with motors (garbage disposal, refrigerator, and water circulation pump are on single phase sources on individual dedicated circuits.

Bill
 
  #4  
Old 03-13-01, 04:15 PM
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Bill;
any motor will "spike" when first started, this is normal, and ballparked around 6 times the nameplate rating. This happens too quickly to trip your dedicated breakers, but you will notice this in your lights, mostly incandesant.

This should be a momentary phenomenon, not something that lasts over a second.

if you have access to an amprobe,( analog ,with moving vain galvometer, not digital) put it on the disposal, or other motorized appliance and see.





 
  #5  
Old 03-13-01, 04:42 PM
Wgoodrich
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Try and take off the panel cover and touch the test leads form line one to the neutral bar and then a second test from line two to the neutral bar. Use a sweep style volt meter on a setting as close to 120 settings on the meter as you can. Do these two tests while turning on your motorized appliances that cause the dimming of the lights. This should tell us if your voltage is starving on the lines coming in or not. Come back in and tell us what you find on the change of voltage during starting of these appliances on the main feeders measured from each feeder to the neutral bar of the panel. While you are at it estimate the length of wire from you meter to the Utility transformer.

Waiting on info

Wg
 
 

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