From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Dirty CG Power Damage
Message-ID: <637gev0d31sb31jse3c4qp9skddv91dfp5@4ax.com>
Date: Thu, 12 Jun 2003 02:43:12 -0400

On Wed, 11 Jun 2003 19:20:31 -0700, "Alan Robinson" <alr@bmi.net> wrote:


>
>John.
>    Using two light bulbs as you state will only work if the
>'floating neutral' problem is affecting several sites at a
>campground. If the neutral problem is *only* in the wiring for
>your pedestal, the two light bulbs will light equally - because
>they are in series between the two hot legs - even if neutral
>isn't connected at all. You would need to use widely different
>sizes of bulbs - like one 40W and one 150W - to give
>unmistakeable results.

But then maybe the neutral can be open in the RV plug or cord and YOUR setup
would miss it or....  At some point we play the odds.  The odds are the open
neutral will be on one of the heavily loaded feeders, probably the pole drop.
If the problem IS at the pedestal, the problem is not nearly so severe because
only under extreme circumstances will the RV load one pole enough to actually
do damage.  This is a "soft neutral".

A couple of years ago I conducted a study on almost this same topic for a
local utility.  The utility was interested in determining why they were
suffering so many open neutrals and what the solution might be.  Most of the
opens occurred at the crimp joint where the utility neutral ties to the
customer neutral.  Second was open neutrals in the meter base.  A distant
third was in the breaker panel followed by misc conductor damage such as the
homeowner drilling into the drop line.  We concluded that the major problem
was due to the use of non-precision, non-calibrated crimp tools.  The utility
changed over to a calibrated powder-driven crimp tool which solved most of the
problems.  A note to the electrical inspectors to request that they check the
tightness of the meter base wire clamps and to verify anti-oxidant compound on
the aluminum wires hopefully will address most of the rest of the problem.

I don't expect this utility to be much different than most.  It is routine to
allow the transformers and drops to run overloaded during the peak load.  This
combined with improperly crimped or treated splices leads to relatively
frequent neutral failures, much more often than leg failures.  We don't know
why but my opinion is that the neutral, being fully exposed to the weather,
traps and holds more moisture than the other conductors.

If you wanted to be very paranoid, you could check the voltage between the
ground and neutral with no load.  Very unlikely to be zero with an open
neutral.  More likely to read some voltage between several volts and 120
volts, depending on where the break is, how much interconductor capacitance
there is and how much leakage to ground there may be.

I made the decision to worry about the most likely faults and not to worry
about the rare ones.  I place pedestal failures in the rare category. I probe
the 30 amp socket with my little meter that I keep in the cord box.  One probe
on the metal box, the other in the hot, ground and neutral.  If I get 120
volts, zero and almost zero I'm happy.  To tell the truth I've never found bad
power on a true pedestal.  Only bad one I found was in a very old CG that had
nothing more than water resistant outlet boxes sticking out of the ground on
conduit stalks.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Dirty CG Power Damage
Message-ID: <vdchev0bfjkorp21mleb6h6nu1savuf4s9@4ax.com>
Date: Thu, 12 Jun 2003 13:10:54 -0400

I've been sitting here for the last half hour or so pondering this.  I haven't
come up with anything that would handle all possible power faults and be
idiot-proof.  That is, work well enough that some bozo with a sue-happy
personality could plug it in and blindly rely on it.

What does occur to me is a monitor that could be installed in the RV that
would continuously monitor the incoming power and isolate the RV when it goes
out of bounds.  This would still be somewhat complex, as it would have to
monitor trends and distinguish between momentary excursions caused, for
example, by an AC starting and serious problems.  It would be doable.  A
fairly fast contactor coupled with suitably rated arc tubes and MOVs to clamp
the voltage until the contactor could open would do the trick.  Might even
include the facility to momentary load each leg and measure the result before
closing the contactor when power is applied.

The big question is, would enough people buy the thing to make development
worthwhile?  Developing the heuristics would require a LOT of field work and
long term data logging.

On Thu, 12 Jun 2003 06:31:23 -0400, "Steve Wolf" <w8iz_news@w8iz.com> wrote:

>Obviously there is a market for a device that plugs into a 50 amp
>receptical and, via a series of LEDs, advises if the pole is
>properly wired.
>
>We had a floating neutral at work that would affect things once
>in a blue moon.  The sides were well balanced.  Finding it was a
>real chore.
>

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Dirty CG Power Damage
Message-ID: <q030fvc3er4ord6njved5vltm5sn421rdj@4ax.com>
Date: Wed, 18 Jun 2003 02:58:58 -0400

On Sat, 14 Jun 2003 02:14:13 GMT, Don Murray <don@murrayranch.com> wrote:


>I put some pictures on my website of a homemade device for finding
>bad/open neutrals at customers' service entrance panels. (I didn't make
>it. We had the electrical techs make several of these up for our
>department to try out.) It uses a 1500W heating coil with fan and two
>volt meters. You can switch the load from one hotleg to the other and
>see the voltage swing on the volt meters. The one in the picture uses a
>meter base that we can plug in where the watt/hour meter on your house
>is. Or it can be switched to be used with the two leads with the red
>ends. The green neutral lead can be moved around in the panel to find
>where the neutral is bad. Something like this could be made up with a
>50A RV pigtail and no need for a meter base. If there is more than a one
>volt difference in the hotlegs then the neutral is suspect.
>
>I'm not sure with the light bulbs if you would see a one volt difference
>on the hotlegs.

Slick.

While your 1 volt difference criteria is valid at a meter base, it won't work
with a campground power supply where significant loads on one leg or the other
come and go pretty much at random.

Now that this thread came up and I mentioned that I'd never experienced bad
power at a CG, you can guess what just happened.  Yep, rotten power at the
Fall Creek Falls State Park campground here in TN.

Even though the weather was mild, I noticed that the digital meter in my rig
was reading about 108 volts in the middle of the afternoon.  It had been 123
volts the night before when we pulled in.  The pedestal was one of those combo
20 amp, 30 amp and 50 amp jobbies so I took my DVM out and probed the 50 amp
jack.  One side held solid at about 120 volts while the other one swung a few
volts either way as ACs turned on and off.  Apparently the bozos who wired
this CG loop (either state employees or low bid electricians, I imagine) hung
all the 30 amp sockets on the same leg!  No bad neutrals or any of that stuff,
just a grossly unbalanced distribution loop.  I can just imagine how this loop
will be when every slot is filled and the temperature outside approaches 100.

John