pulsating lights


Old 01-18-01, 08:59 AM
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2 questions 1)How do you calculate the"Demand Load" for my
home ??
2)Everytime my washing machine goes into it's "wash cycle"
EVERY light in the house PULSATES.What gives ?? I have
a 100 amp service. It splits into 2-50 amp sub-panels.
50 amps for the main house and 50 amps for an addition that
was done about 10 years ago. Do I need more than a 100 amp
service??? An electrican at work told me to check and tighten all the NEUTRAL leads.Could the neutrals be wired
wrong??? This is not a big problem(at least I don't think
it is)just annoying. Help,Tim
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Old 01-18-01, 12:01 PM
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A good guess would be that your lights that are pulsating are on the same sub panel or even same branch circuit. When the motor is taxed by the agitater in your washer changing directions your motor increases and decreases total amps applied to that common conductor. don't see a hazard, just an irritation as long as you are not oversizing your breakers or fuses and they are not blowing or kicking off.

Hope this helps

Old 01-18-01, 12:19 PM
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To figure a demand load of a total house thus sizing the minimum amp rating required for a main service size see below.

Multiply the square footage of the house times 3 volt amps [watts]. Add to that 1500 volt amps for the laundry and 3000 volt amps for the kitchen. Now take that total and subtract 3000 watts from that total and multiply that answer by 35%, then add back in the 3000 volt amps. This gives you the total general lighting load.

Now to calculate the heat and air conditioning. Find the larger of the two loads [heat or air conditioning] throw out the smallest load and add the largest load to the general lighting load from above as your running total.

Now to calculate the fastened in place appliances. Make a list of all appliances using their name plate rating in amps. All appliances fastened in place will be added in here except your range, dryer, and heat or air conditioning. This is all appliances connected with a romex connector and not with a receptacle and plug. Now add all these fastened in place to get a total amp load.

Remember to convert amps to watts [ amps times volts = watts].

Now take that total watt load of fastened in place appliances and count how many appliances you have. If you have three or more add 100% of that total to your running total from above. If you have more than 3 fastened in place appliances then multiply that total watt load by 75% and add this total instead of the 100% total to your running total.

Now find the largest motor in amps and multiply that amps times the voltage and then that answer times 25%, and add that answer to your running total.

Now if you have one electric range then add 7000 watts to your running total. If you have two electric ranges in the house then add 11,000 watts to your running total instead of the 7,000 watts.

Now if you have an electric dryer then add 5,000 watts to your running total.

Now take the total answer to your running total and divide that answer by 240 volts.

That answer if your demand load required to size your main service to your house. Remember your minimum main service size can be no smaller than 100 amps. If your answer lands between 101 and 125 amps then your minimum service size would be 125 amps. If your answer lands between 126 and 150 = 150 amps. If your answer lands between 151 and 200 =200 amps. If your answer lands between 201 and 225 =225. Etc.

This is an approximate format for calculating your demand load that came out of my feeble old brain without looking up the Codes found in Chapter 2 of the NEC. There may be a few minor inaccuracies but should give you a pretty close shot at your minimum service size required to serve your dwelling.

Hope this helps

Old 01-18-01, 12:45 PM
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I'll digest the "Demand" info later.If I increased the total AMP service,increase the sub panel AMPS and
ran a dedicated circuit for the washer,might that solve the problem ??? Thanks again WG. Tim
Old 01-18-01, 03:10 PM
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It might, but your guessing. Would you want to guess whether your kid could swim to shore in a lake then throw him in to see? Same values at stake. Your family sleeps in this home and are defensless while they sleep. Worth guessing, I wouldn't. I would do the calculations, then you will know. You can calculate the load of a sub panel by adding all the loads on that sub panel. Receptacles count as 180 Volt amps and all light bulbs as the bulb is rated in volt amps or watts. Check the name plate rating on your appliances. Add it all up. You should have a panel capable of carrying at least 125% more than the total connected load.

Branch circuits are calculated same as above.

Good Luck

Old 01-18-01, 03:59 PM
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Question I know!

I experience the same annoying problem! We bought a new top-of-the-line whirlpool gold catalyst/senseon set of laundry appliances in the past 6 months. The washing mashine causes the circuits on the same phase to pulse. The opposite phase leg does not experience the same problem much if at all. Apparently this is a problem unique to some of the Whirlpool/Kenmore washing machines?

Does anybody else out there have this problem? or experienced it somewheres?

I'd be interested to know if there is a solution too!

green jacket
Old 01-18-01, 04:51 PM
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Pulsing of lights when a motor starts or changes in heavy loads is a common event especially when lighting is on the same circuit as the motor. Washers are especially prone to this experience if the washer is a back and forth twist type of agitation. Usually the pumping agitation style is so fast the pulsing of the lights are less noticable.

Pulsing of lights is just a bounce of electrical current. Usually not a hazard, just an annoyance.

To cure the problem two items are viable. Washer on a single circuit and the service feeders plenty big enough to obsorb the bounce of the electricity.

If you put the washer on a single circuit the bounce is limited to that circuit and thus not registered on the other branch circuits if the feeders are large enough for the service to obsorb. The feeders are the only area still in common with the washer motor if washer on a single circuit.

Also an overloaded transformer at the utility company pole can cause this at times also.

Old 01-19-01, 05:59 PM
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The City of Davis website has a page online which may help you digest what Wg said for calculating your electrial load http://www.city.davis.ca.us/city/plannbld/pdf/load.pdf Print the form and fill it out.
It's an Adobe Acrobat document so you will need a reader available free online.

Phil H
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