Scary Electrical Problem

Thanks to all of you who answered my question about the neutral bus
which got hot -- including those who got into a debate about whether
holes drilled in metal expand when heated or not. :-) Most of you seem
to agree that the high heat was due to resistance caused by loose or
corroded wires.

If anyone is interested in seeing a photo of the bus and wires, I have
temporarily posted one at #

BTW, only two of your replies reached my ISP's News server. I did not
find the rest of the 23 replies until I did a Dejanews search.

Thanks again.

Paul

Sent via Deja.com #
Before you buy.

so if the hole is a square one, would it get bigger?

--
email:

...
the

Re. all comments about bearings; the bearing is built around the "hole" the
hole is NOT a hole in the sense of the original post ie. drilled and tapped.
But please let's not go back to square one with this thread.

Digger, AKA Grumps (old and crusty)
All errors; spilling, grimatical, ore tieping intenshunal.

My father heated steel tire rims, forced them onto wooden wagon wheels, then
quench cooled them in a water tank.

He THOUGHT the hole got bigger with heat. BUT what did he know? Today of
course he would expand the hole in the rims using dry ice. <G>

He is not well bred that cannot bear ill breeding in others. Franklin, 1734

Aha... I knew running hot water on a stuck jar lid to make it open was only
an old wive's tale... yeh right!!

DH

Sorry George, but this is one of the most common questions in basic
engineering "Properties of Materials". The thermal expansion
differential of the surface of a hole is found by analyzing the
surface of the plug that came out of the hole.


"George E. Cawthon" <GeorgeC-B> wrote:

Not true; the holes get larger because the circumference gets longer.
Obvious with a wire ring or donut, but harder to visualize with a plate
and a drilled hole, however, for the hole to get smaller the inner surface
molecules or grain or whatever would have to compress...

If I have a bolt stuck in something, and I heat the something, will the
bolt be stuck tighter? Or will it come free?

Hmm, well, perhaps the guy who has to heat an interference-fit
bearing to get it to slide down on a shaft? Or the guy who heats a
crankcase bearing boss so that the interference-fit bearing will
drop down in the hole. Yeah, that's the ticket.

John

--
John De Armond
johngdSPAM@bellsouth.net
#
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"

I believe that would depend on the coefficient factor and whether any external
magnetic flux was present, also the ambient temperature of the evnvironent
altitude and crresponding atmospheric pressure. In other words WHO gives a
rat's __?

Digger, AKA Grumps (old and crusty)
All errors; spilling, grimatical, ore tieping intenshunal.

...
Some bearings are assembled on machine shafts (such as used in lathes)
merely by using a bearing heater to expand them. They are then placed on the
shaft and allowed to cool. Cincinnati Milling and Grinding once made a lathe
chuck of dissimilar metals where the inner diameter of the outer ring was
actually smaller than the outer diameter of the part it was to assembled on.
This was accomplished by heating the outer ring, while chilling the inner
piece until they assembled, then letting all return to ambient temp. The
outer ring contracted, the inner part expanded and the metals actually fused
together.

I do, when George makes an a**hole observation like this one. Any
apprentice knows how to shrink fit a bearing on a shaft. You heat the
bearing, apply dry ice to the shaft, slip the bearing on the shaft, let
things cool and heat up and voila, you got an interference fit.
Hugh

Say what?
Hugh

Nope, sorry, but good guess.

--
John De Armond
johngdSPAM@bellsouth.net
#
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"

Sorry, Barbara, but the part about the holes is not true. Metal expands
in all directions, so the holes actually get smaller with heat.

--

Have not had this happen but my neighbour had a 27' Class C and every time
he plugged it in the breaker would kick out for the circuit it was plugged
in to. I started to check and found out the manufacturer had run the "shore
power" wire from the main panel and had not tightened the clamps where it
enters the box, then had secured it with "nyloclips" but only after the wire
was pulled so tight the outside insulation on the cable was out past the
clamp and the insulation on the individual wires got cut one the sharp edges
of the knockout in the box...

Mo

It is a good idea to check and tighten all electrical connections soon after
purchase of a new MH. AND do this each few years after. The conductors "cold
flow" like a wax candle in the sun much slower of course.

When loose resistance increases -- thus your smoke.

If the insulator in the panel is carbonized scrape off the carbon -- it is a
conductor and can smoke again. Cut back the affected wires and splice in new,
clean the screw, and the terminal, lubricate with silicone and reassemble
tightly. Check in a month and then at one year.

He is not well bred that cannot bear ill breeding in others. Franklin, 1734

On Fri, 21 Jul 2000 05:52:31 GMT, in message

<<..>>

I've seen it happen before, though it is reasonably rare (I've
seen it happen in buildings, as well). Most likely it was a loose or
slightly corroded neutral connection- once it started to heat, it went
downhill from there.

The good news is that -most likely- if you hadn't been there,
the connection would have gotten worse and worse until the power just
went off. The insulation on the wire is (I think) self extinguishing,
and the box itself would contain any threat of fire.
This is one of the points about a UL listed device- they test
not whether a device works well, but whether when it fails, it does so
in a relatively benign way.

When you fix it- be sure to go back to good wire, and replace
the neutral buss.

--
Chris Bryant
Bryant RV Services- DeLand, Florida mailto:
On RVing- TV about RVs, by RVers #

It is more than likely that one of the wires is loose and was arcing.
Tighten all connections until you find the one which is loose, and then
check the rest just to be sure.

--
Lon VanOstran
Williamston, MI
FMCA, Good Sam Life, SKP, NRA Patron

You had a loose / bad connection which caused heating. Once this starts
it's all down hill after that. I have actually had a fuse block at a
household AC box disintegrate it got so hot. Multi conductor aluminum
cables that are frequently used in high amperage circuits can be especially
troublesome, even more so if used in fixtures not designed for aluminum.
It's a good idea to check all electrical box connections once every few
years as routine maintenance.

Al

Yesterday evening I was sitting at the dinette table in my motorhome
addressing an envelope that I was about to mail. The motorhome was
plugged into a properly wired and tested 30 amp receptacle. I was
running the air conditioner, and the refrigerator was running on 120 v.
AC. No other 120 v. appliances were in use. All of a sudden, I
thought that I smelled something burning. It smelled like an
electrical fire. I looked down at the Magnetek
converter/charger/distribution panel under my seat. I felt the circuit
breaker panel, and it was hot! While I was looking at it I saw a little
wisp of smoke rising. I immediately turned off the air conditioning
unit and went outside and cut off all electricity going to the motor
home.

Today, I removed the panel that surrounds the six 120 v. circuit
breakers. Some of the insulation of all six white wires which were
connected to the negative or common bus was melted and black.
Evidently, the whole common bus had become extremely hot. I hate to
think of what might have happened if I had not smelled the melting
insulation on those wires. (The circuit breakers did not open, either.)

Has anyone had this happen to them before? Do any of you electricians
have a theory as to what happened? This is the first time I had any
problem with the 120 v. electrical system in my 1993 motorhome.

Sent via Deja.com #
Before you buy.