Power surge

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Re: Power surge

Of course Jim is correct that sometimes things will fry.

My point has been that I have dealt with lost neutrals many times and out of these times more often then not once I fix the lost neutral everything runs fine just as it did before the incident.

IMO it is a myth that losing a neutral guarantees destruction of electric equipment.

I spend much of my time in office environments that have 100s of office cube wall partitions, 90% of the time these are 4 wire multiwire circuits. Many times the installers of this equipment (not electricians) do not properly plug in the wiring harnesses and you loose the neutral, the PCs connected do funky things but hardly ever "smoke".

I can tell you that those surge suppression strips that you often see do smoke quite well when a neutral is lost though. :D

Bob
 
Re: Power surge

Wayne, the issue is not whether it is damaging or not, it's pointing out the fact that "one" load will never see "full" leg to leg or phase to phase voltage in a lost neutral scenario, it could be close but that's it. Now let's say we're equal at center of the series, what would the lost neutral do?

Roger
 
Re: Power surge

And in a typical home with mom,dad,2 1/2 kids and a dog.We likely have several loads,maybe 3 tv's ,sterio,frig,ceiling fans.The chances of it being perfectly balanced are slim but 40% and 60% are within reason.Should the neutral come loose we would see some dimming and flashes but most everything could tolerate this for a while.Hopefully they notice and call sparky.Now if they just let it go because money is tight, then sometime within a few days (or sooner)the system will get too far unbalanced and stuff starts burning.
Think of this as a possibility.
1.Family functioning about normal at 5 pm,typical loads.Neutral opens
2.Kids go to bed and computers,tv,lights,turned off.Now maybe tv in living room on and dads on computer,and a few lights.We might still be somewhat balanced.
3.Hour later parents go to bed.
Load now might only be a few night lights 7 watters.Load almost nothing (we won't get into the ground rods helping )
4.At 11:43 the fridge tries to come on.With neutral open it instantly burns night lights out.With no complete circuit it doesn't run ,but also won't burn up.We now have 2 loads fridge and 1 night light on 1 leg and nothing on other leg.
5.In morning when they wake up late because alarm clock fried,they reach over and turn lamp on.Dam there goes another bulb.
Your now are about to burn up things one by one.
At the panel on leg (a) is a fridge thats been ready to start for hours and on leg (b)we start getting loads that burn up instantly,and reopen the circuit.
My point here is if everything came back on at same split second there would be no problem,but that's not likely how it will go.
On a test board this looks easy,2 resisters ,1 burns open the no current thru either.
Most of the calls i get over neutrals have already taken some things out.If they were lucky they lost a few bulbs,and some cheap stuff.Some have fuses internal and saves the item.

[ February 18, 2004, 02:15 PM: Message edited by: jimwalker ]
 
Re: Power surge

Jim, how do you see more than "two" resistors in Ed,s drawing?

Go back to my first post in this thread and read it very slowly and closely, notice the word "TWO".

Now, being that you are back to the house question, how many of these loads you mention
3 tv's ,sterio,frig,ceiling fans.
Click to expand...
would see full voltage, or even 237V,? :roll:


Roger

[ February 18, 2004, 03:32 PM: Message edited by: roger ]
 
Re: Power surge

"On a test board this looks easy,2 resisters ,1 burns open the no current thru either."
I only mentioned 2 :confused:

As to the house,with a non running motor ,just what impedance will that be to a 60 watt bulb ?
The bulb will not last more than a second at 237 or probably even 200 volts.Does anyone have an ohm reading value for a non running frig.Very low i am sure.The bulb is about 240 ohms, frig maybe 10 ohms. bulb would see about 230 volts for a split second then burn out.Ceiling fans in series with frig motor,would think fan is far smaller load so burns up but might last a few minutes.In real life conditions we care about the damage and not actual voltage.Yes you are right in that it can not be the full 240 volts.Real close but not 240. If thats your point i agree with you
 
Re: Power surge

Roger if it's close to a balance load the result of the lost neutral would be nothing until a heaver load like a motor tried to start up.

By Bob: I can tell you that those surge suppression strips that you often see do smoke quite well when a neutral is lost though
Click to expand...
This is kind of funny as if you have enough surge strips (the type with MOV's) on both leg's of the panel they will kind of automatically balance the voltage in the event of a lost neutral think about it as the voltage rises the MOV's do there thing and start applying more resistance thus keeping the circuit balanced somewhat. Now the reason you don't see the damage a lost neutral does is in offices and other industrial type buildings there is more redundant grounding and more surge suppressing being used. So I agree you won't see as much damage. but I have and it sometimes can wipe out all the electronics in a house. I have posted several story's of things like this happening. The worst one was when the POCO hooked the drop back up to the transformer with out looking at the drop at the house end. It was and older house and didn't have a water ground or a ground rod. It was an elderly man who lived alone on a fixed income and had no insurance. a bunch of got to gather and found some radios and a TV and VCR to get him by until he could get a settlement from the POCO.

[ February 18, 2004, 08:21 PM: Message edited by: hurk27 ]
 
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