[Boatanchors] Storm Damage to Electronics

[WA5CAB at cs.com]

Ron,

I assume that when you say "neutrals were broken", I presume that you mean 
that the neutrals broke first, then the lines.  

This could be like the case we had once when an electrician we had hired 
ran 120/240 VAC service to an office trailer inside of one of our workshops.  
He ran the service without copper neutral, claiming later that the conduit 
should have been all that was needed.  After he finished, someone went inside 
the trailer and turned on a light switch.  Nothing happened.  For whatever 
reason, he left that switch on and turned on another group of lights.  Both 
groups came on but the lights in one group were noticable brighter than 
those in the other.  There were more lamp tubes in the dimmer group than in the 
brighter one.  One group was on one side of the 120-0-120 service and the 
other group were on the other side.  So they were in series across 240 volts.  
Unfortunately, instead of stopping right there, with no damage done yet, he 
then turned on one of the photo processors (the reason for the trailer).  
One light group essentially went out and the other went super bright and 
started blowing ballasts.

Anyway, when you disconnect the neutral in a 120-0-120 (120/240) volt 
system, the loads on each side are placed in series across 240 VAC.  If both 
groups of loads are identical, nothing much happens.  But if one side has a 
lower total parallel resistance than the other, the higher resistance side with 
get higher than 120 volts across it, by the ratio of the resistances.  
Actual 240 volt loads should not be affected.  But it is common in for example a 
heat pump for the high current part (heater elements for example) to be 
across the full 240 but the controller only across one of the 120's.

In a message dated 11/04/2011 17:04:59 PM Central Daylight Time, 
ronhunsi at ptd.net writes: 
> All,
> 
> Maybe you can help me understand some damage to the electronics of my 
> neighbors.
> 
> During the recent northeast snow storm ten neighbors, all on one PPL 
> transformer, lost power.  Power was lost because branches pulled the 
> electric services from both halves of a duplex (semi-detached house).  
> At the same time that the power was lost, there was a voltage spike that 
> blew out all kinds of solid state devices (Yeah, I know, if they had 
> tubes...).  What were lost were things that are always on (stoves, 
> furnaces, heat pumps, microwaves) or "on" even when they are turned 
> "off" (TVs, principally).   There were reports that the lights suddenly 
> became brighter and that there was a sizzling noise.
> 
> The story is that, when the two services were pulled from the walls, the 
> neutrals were broken and the spikes were the result.
> 
> Would someone please explain why the voltage spiked when the neutrals 
> were lost?
> 
> Thanks,
> 
> Ron
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480