Index Home About Blog
From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Installing a shore power outlet...
Date: Thu, 21 Sep 2000 12:09:39 -0400

James Gemmill wrote:

> Speaking of GFI, whenever I plug, 15 amp adapter,   in an RV park the
> circuit breaker blows. When I use the thirty amp plug this does not
> happen. Is this typical of RV connections?

Yup.  I've had  years of grief with this with my concession
operations too.  Most commercial food service gear has enough
leakage through the heating elements to trip the 5 ma GFIs.  Yet the
ill-advised code (or at least the interpretation of the code by most
inspectors) requires GFIs for temporary power at special events.
That's why I learned to travel with my "power crash kit" as I called
it.  It contains a 60 amp, 120 volt (cut a 240 breaker apart) for
every major brand of breaker out there.  I can quickly open the box,
pull their breaker and stick mine in for my outlets.  I also carry
some heavy duty industrial grade outlets mounted in boxes with
pigtails coming out.  If the event wiring is sub-standard, I'll use
my own outlets too.  I've started gradually converting over to 30
amp RV plugs for the added ampacity and the convenience of being
able to buy prefabricated cords.  I find that I can pull 60 amps
through an RV plug OR an industrial 20 amp convenience outlet-type
plug and 10 ga wire with an acceptable amount of heating. (Safety
nazis save your breath.  This is temporary event wiring and unless
you do special events, you'll not know what you're talking about)

Our town made an ill-fated attempt to start a summer street festival
a couple of years ago.  Since my restaurant is right off the square
and I was to set up a food booth, and since I wanted to not have
power problems on my home turf, I volunteered to manage the
temporary power installation.  I had a set-to with a typically
closed minded electrical inspector who absolutely insisted with no
wiggle room that all temporary outlets have GFIs on 20 amp max
breakers (ALL concessionaires want at least 30 amps.)  The light
bulb finally came on and I figured a way around him and the 20 amp
problem.  I simply had RV outlets installed in each temporary outlet
and then pre-installed adapters.  30 amp, non-GFI outlets for
everyone.  This worked great. I've seen the idea copied at other
area events.

Anyway, back to RVing.  The only reliable solution is to carry an RV
to convenience outlet adapter and use it where there are 30 amp
outlets.  And if you're going to be in one place for awhile, you
might consider a "power crash kit" of your own :-)  (I will now don
flak jacket and duck in the face of angry camp ground owners
everywhere :-)

John


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: electrical problem
Date: Tue, 14 Nov 2000 17:34:32 -0500

LOCOMOTIVE2506 wrote:
>
> GBinNC wrote:>
> >I keep my Class B plugged into a dedicated 15-amp GFCI circuit (mostly
> >to keep the battery up between trips). Does this GFCI provide ample
> >protection for the the entire vehicle (assuming, of course, that the
> >wiring is in good shape), or do I need to install GFCIs in the van
> >too?
> >
> >I have this thing about getting shocked...
>
> I believe that you can still get shocked even with a GFI installed
> depending on what loads are applied and how the circuits are wired.
>
> In an RV, the hot wire (black), the return wire (white), and the ground
> wire (green) are all kept isolated from each other. The function of the
> GFI is to trigger and shut off the hot wire if it detects a few
> milliamps of current flow in the green wire.

That is not how a GFI works.  The GFI measures any imbalance between
hot and neutral current.  Normally via a longitudinal transformer
followed by a simple rectifier and trip logic.  The leakage current
does NOT have to flow through the green wire.  Indeed most shock
current does NOT flow though the green wire.  As long as the GFI
itself is properly functioning and the neutral connection is intact,
it is impossible to get seriously shocked on a protected circuit.

> If there are no loads on the output of the GFI and the wiring is
> reversed then there is no current flow but, if you happen to touch
> something, say the chassis and it is wired wrong then you become the
> load between the chassis and earth. At that point, if you have wet shoes
> or touch both the chassis and the earth or a water pipe with bare hands,
> then you become the load. Current sill then flow through you. The GFI
> will then trip if that current flowing is over the 3 or 4 milliamp range
> that it takes to trigger it. Yes, you will feel a pretty good shock
> prior to the GFI tripping.

It doesn't matter to the GFI whether the hot and neutral leads are
reversed.  Any leakage to ground will still appear as a difference
between the hot and neutral and will trip when the leakage reaches 5
ma.  Five ma can be felt but for an ordinary health person, will do
nothing more than startle them a bit.

> I don't know of a sure fired way to prove that every thing is safe short of
> taking a good AC voltmeter and sticking one lead into the  dirt by the RV and
> the other lead on the chassis of the RV. If you measure anything above 5 volts
> or so then things are probably amiss someplace.

This is a very unreliable test because it can indicate a false
negative.  That is, indicate nothing when there is something.  It
can also give a false positive if there is a surface ground
potential - not uncommon in dry weather with high density housing
and less than optimal earthing.  The only absolute method of
checking the chassis potential available to most people is to
measure between the ground/neutral buss in their breaker panel and
the chassis.

John



From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: electrical problem
Date: Wed, 15 Nov 2000 05:32:16 -0500

LOCOMOTIVE2506 wrote:

> Wil Sill wrote:>Not long ago, locomotive2506@aol.com (the familiar loco weed)
> wrote
> >the following demonstration of the idea that a little knowledge, when
> >combined with some myths & complete untruths and spouted by a moron,
> >can be dangerous:
>
> Hi Will, nice to hear from you again. Hope you are having a wonderful day.
>
> >To the contrary, a GFI monitors the balance between hot & neutral.
> >Current flow in the green wire is not monitored because it is
> >irrelevant.  That wire exists entirely for safety reasons,
> >specifically for the purpose of carrying fault currents to ground.
>
> Will, look up the following
> site:http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html#c1

This web page is absolutely incorrect.  Pretty embarrassing to see
this degree of error on a university site.

>
> You are somewhat correct in stating that the the GFI monitors the balance
> between the hot & neutral. But since there are only three wires, any misbalance
> has to flow through the green ground wire. If you don't believe this,
> disconnect a green wire from the GFI and test it. You'll find it won't work.
> The reason is that to test the "balance" of current, they run the green wire
> current through a torrid core in the GFI. When that current gets hight enough,
> it triggers a Silicon Controlled Rectifer or TRIAC, depending upon the mfgr,
> which then pulls in a current breaking relay. Yes, the green wire is very
> important in spite of what you say.

This is again absolutely wrong.  The ground wire plays NO role in
the function of a GFI.  I've been interested in GFIs ever since I
was assigned the task of evaluating the then-new units on the market
for TVA.  Believing that a picture is worth a thousand words, I
chose to write up WHY you and that web site are wrong in an acrobat
article.  This article can be found on my web site here:

http://personal.cha.bellsouth.net/cha/j/o/johngd/files/rv/gfi.pdf

This file is somewhat large at 1/4 megabyte because I left the
pictures at a fairly high resolution. In this article, I dissect an
actual GFI and analyze its circuitry.  This is essentially the same
circuitry as what was in the very first units I examined 25+ years
ago.  About the only difference is that this one uses dual
differential longitudinal transformers to make the unit more immune
to external EMI.

Even without this article, it should be obvious to anyone with a
little thought why it is silly to think that the GFI needs the green
wire to function.  If that were true, then the unit would become
inoperable if the green wire became disconnected or cut.  A wholly
unacceptable condition.  A basic principle is that if power can get
through the GFI, then the GFI must protect from faults.  To have it
any other way would mean that someone somewhere would wire the thing
so that it would not work.

Similarly, it would be unacceptable for the GFI to malfunction if
the neutral and hot leads were to become reversed.  The GFI must
protect during any operating mode where power can get through the
unit and that includes reversed polarity.

John




From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Tripping GFCI
Message-ID: <p87nduk144l02vq631encc3guo09f9l2o5@4ax.com>
Date: Fri, 10 May 2002 06:43:33 -0400

On Thu, 09 May 2002 20:01:08 -0400, heydave
<davesch@nospam.ourplace.cnchost.com> wrote:

>Is there anything obvious to check inside the trailer in an attempt to
>isolate the cause of the GFCI tripping before I take it back to the
>dealer?  It would be nice to go there at least armed with some idea as
>to what might be wrong.

Couple of things. The GFI could be tripping on improper neutral-ground
interconnect in your rig.  That has little practical safety implication but
you can fix it easily enough if that's the problem.  To check: flip all the
breakers and plug the rig in.  If the GFI trips, you have a pretty good clue.
Pop the lid off the breaker box in the rig and look to see if the neutral
(white) and ground (green) wires are interconnected in any manner.  Running an
ohmmeter check from neutral to ground on the RV cord plug is another check.
Should be no continuity.

If you have a generator with a transfer switch (manual or automatic), it could
be wired wrong. The switch should switch both the neutral and hot legs because
most generators connect neutral and ground together internally.  That's proper
when the generator is operating.  If the transfer switch only switches the hot
leg, the generator will cause the neutral-ground interconnect.

If your neutral/ground is OK, the most likely problem is sneak leakage,
probably either in the converter, refrigerator or other appliance.  If the
electric element in the refrigerator has become leaky, it would shunt enough
current to ground to trip the GFI.  With the rig only 2 years old, this is
unlikely.

A second source of leakage current can be the converter.  If it is a
switchmode unit, it likely has an input line filter.  This filter, if against
one end of its tolerance or defective, will shunt some small bit of current to
ground.  It is also not uncommon to see mfrs put small capacitors between the
hot leg and ground, and the neutral leg and ground to shunt off RFI.
Depending on the size, these can shunt enough line voltage to trip a GFI.

Any three wire appliance in your rig could also leak enough current to ground
to trip a GFI while remaining perfectly safe.

Finding any of this will be a process of elimination.  Flip all the breakers,
then close each on back in until the GFI trips.  Figure out what is fed from
that breaker, then disconnect each load until the GFI does not trip.  The
device that causes the trip may not be defective.  It might just be the straw
that broke the camel's back, contributing the last little bit of accumulated
leakage that causes the GFI to trip.

This is the reason that trying to make an RV live on a GFI outlet is a bad and
frustrating idea.  Also the reason the code doesn't require GFI on 30 amp RV
outlets.  The GFI has to be so sensitive (5 ma max imbalance in current
between hot and neutral) to prevent harmful shock that it is practically
impossible to feed multiple loads because almost all appliances leak a little
current to ground. Doesn't take much to add up to 5 ma. That's why you don't
see whole house GFI.  The spec was originally written and intended to protect
point loads - a single outlet, hair dryer, shaver, etc.  As is typical when
the safety nazis cut loose, the original intent has been distorted and abused,
both in subsequent code revisions and in the public's minds.

The proper architecture is for your RV to be fed like any other sub-panel
(isolated ground and neutral, no GFI) and then individual GFIs applied where
they're appropriate inside the rig.

What I'd do is yank that GFI outlet out and install a proper 30 amp RV outlet*
and be done with it.  If you feel vulnerable, check (or have checked) your
ground resistance and make sure your rig has GFIs where they're needed -
around the sink and in the bathroom.  An informal, non-quantitative check of
ground integrity is to take your DVM, connect one end to your ground rod near
your meter and the other lead to the RV frame.  If you see less than about
10-15 volts AC, you're fine.

If you need to plug in both your RV and conventional 120 volt loads, you can
a) get an external GFI outlet box and install a 30 amp RV plug for ordinary
loads, b) install an expansion box and install both a 30 amp outlet and a 20
amp GFI outlet or c) if you can live with the way things have always been (no
GFI), simply install the 30 amp outlet and use a 30 amp RV to 20 amp
conventional adapter.  Personally, I'd do c) unless I needed to plug the RV
and other loads at the same time, whereupon I'd do b) but with a conventional
outlet.

John

*it is both legal and safe to feed a 30amp outlet with a less than 30 amp
circuit.  As long as the circuit breaker is sized to protect the wiring
connected to it, the labeling on the outlet doesn't matter.  You can install a
30 amp outlet on a 15 amp branch.  You'll of course, only get 15 amps.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Newbie question re power GFIs
Date: Sat, 14 Jan 2006 12:29:28 -0500
Message-ID: <0dbis191j85v6un55ekteske30147mnavd@4ax.com>

Steve, I think the design of GFIs is OK, the problem is that they're
being horribly misused, much of this misuse is being forced by the
unregulated safety nazis on the code committees.

This is an example.  A GFI should be pushed out as close to the load
as possible.  The reason is to minimize stray leakage and capacitance
coupling eating into the 5ma of current imbalance allowed by the
design spec.  Feeding downstream outlets with the GFI causes all
subsequent leakage of the wiring, outlets and appliances to add toward
that 5 ma.  If the wiring and outlets have, say, 1 ma of leakage and 4
appliances are plugged into the several outlets, each with 1 ma of
leakage, there's your 5ma.

It is not at all unusual to see a few ma of "leakage" from electronics
that have EMI filters or discrete capacitors from the hot leg to
ground.  Individually, they're not a problem but have them add through
several outlets and spurious trips are inevitable.

As cheap as GFIs are now, there is no excuse to feed multiple outlets.
Make each outlet that needs protecting a GFI.  The move to put GFIs on
risky appliances such as hair dryers is an excellent move.  That GFI
sees ONLY the leakage from that one appliance and nothing else.

Another horrible application is forcing GFIs on RV and outdoor event
20 amp outlets.  That causes all the leakage of all the wiring in the
RV to work against the 5 ma limit.

As I witnessed in person from participation in the Section 600
revisions a couple of years ago, the problem is that the code is now
driven by two factions.  One are the irresponsible "safety at any
cost" safety nazis.  The other, worse, IMHO, are the manufacturers who
make changes to sell more product.  The GFI situation is an
unfortunate one where the two factions come together and we become the
losers.

John

On Sat, 14 Jan 2006 09:57:53 -0500, "Steve Wolf" <news@w8iz.com>
wrote:

>In addition to what Eisboch said below, if you have a dead outlet without a
>GFI, check backwards, toward the breaker panel.  If you have a tripped GFI
>in a previous outlet, it could very well be the cause of the outlets
>downstream being without power.
>
>GFIs are a technology that, while a good idea, aren't really "there" yet.
>They need more work; they need to be designed better.  Unfortunately, once
>sucked into the black hold of "standardization" the design is not likely to
>improve or it will improve very slowly.  The National Electrical Code has a
>habit of killing technologies such as these.
>
>Steve
>www.wolfswords.com under the motorhome link
>
>> A GFI is not the same thing as a circuit breaker.  A standard circuit
>> breaker trips when the current draw exceeds its rating.  A GFI (ground
>> fault interrupter) compares the current flowing through the "hot" leg and
>> the neutral leg.  If there is a difference, it trips. The difference would
>> be due to leakage or a grounded neutral lead that allows the ground lead
>> to carry current.
>


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Can I use two 30A outlets to feed a 50A cord?
Date: Mon, 18 Jun 2007 13:31:10 -0400
Message-ID: <gkfd735tf3ksn9hhc9r9inhbkdhjjeo619@4ax.com>

On Mon, 18 Jun 2007 15:39:05 GMT, Jud Hardcastle
<I5i5changethistodash5rbo@xemaps.com> wrote:

>In article <ogsc73h0p1nn7isjmi8vekjsm95emhvd3o@4ax.com>, no@never.com
>says...
>>
>> Figuring this out from the outside will be tricky.  If you apply a load to one outlet
>> and measure the CHANGE in voltage from both the loaded and unloaded outlets then you
>> can get a clue.  If the voltage CHANGE is practically identical then they're probably
>>
>> lots of good stuff snipped...
>>
>Thanks John for the best summary I've ever seen on this recurring
>subject--too bad usenet doesn't allow for "stickies" this would
>certainly qualify.

Thanks.

>
>Guess I need to experiment with that change in voltage method. I bought
>one of those 2x30 to 50 adapter "boxes" from CW last year but have yet
>to use it--every post I've used has one 30 and one 15/20 but the 15/20
>is on a CFI that everyone says will trip. The "change in voltage" test
>would at least tell me if it would work if the GFI was bypassed.

About GFIs.  RV pedestals - One of the dumber applications of the gadgets yet.

If you don't mind doing a little "midnight wiring", here's how to quickly defeat the
GFI but still have it appear to work.  Kill the power, pop the cover and remove the
GFI.  Move the wires from the "line" to the "load" side (most all modern GFIs have
both terminals.)  Put everything back together, turn on the breaker and enjoy your
uninterrupted power.  The "test" button still works and the trip button pops, it just
doesn't do anything. :-)

This GFI NEC madness has invaded the special events world.  For the last few years,
outlets provided for exhibitors and concessionaires have been crippled with GFIs.
Commercial restaurant gear leaks a little current to ground - just the nature of the
beasts after crud builds up internally.  Of no consequence since this stuff is
designed to be hard-wired and grounded (duh) except that it reliably trips GFIs which
were never designed for such applications.

I've gotten very good at doing the wire swap that I described above.  I do have to
suppress a sly grin when every other concessionaire is fighting power problems and
I'm truckin' along, cookin' on high :-)

For events that I did regularly, I could sometimes get the sponsors to install 30 amp
RV outlets, not because they're particularly good outlets but because they're exempt
from the NEC madness.  That's the only outdoor 120 volt outlet (among common types at
least) that can be installed without GFIs and escape the safety nazis' scrutiny.

John


From: John De Armond
Newsgroups: alt.energy.homepower
Subject: Re: Parallel generators
Date: Thu, 06 Sep 2007 21:44:50 -0400
Message-ID: <qka1e3d9j6hrbke7b9qmhs9ed8m2bbvik4@4ax.com>

On Thu, 06 Sep 2007 15:19:07 -0000, philkryder <alt.google@Kryder.com> wrote:

>On Sep 6, 7:40 am, Neon John <n...@never.com> wrote:
>> On Thu, 06 Sep 2007 04:02:51 -0000, philkryder <alt.goo...@Kryder.com> wrote:
>> >John -
>> >does this mean that you disagree with the more recent GFI models with
>> >Bonded Neutral?
>> >Your points make a lot of sense (at least to me).
>>
>> Are you talking about the neutral fault detection that trips if the neutral and
>> ground become connected aft of the GFI?
>>
>> Yeah, I disagree with that.  I'm not really sure what problem this "feature" is
>> alleged to solve.  All I've seen it do is cause more nuisance trips.
>
>John - Yes, I think that is it - though the exact details of the new
>GFI machines aren't completely clear to me.

The way it works is this.  There is a second toroidal inductor around the hot and
neutral lines.  It is driven by the 60 hz signal and is the primary of a transformer.
The neutral is the one turn secondary.  Ignore the hot lead for this discussion.

The neutral and ground are bonded together at the breaker.  If they get connected
together aft of the GFI then a complete circuit is formed, neutral->ground->breaker
ground->breaker neutral->neutral.  Current flows in this loop, induced by the second
toroid.  The main sensing toroid detects this as imbalance current and trips the GFI.

It's hard to imagine any credible (not fictitious products of some safety nazi's
imagination) scenario where connecting the neutral and ground together causes any
hazard.  I'm not sure what they were thinking (scratch that, they weren't thinking)
when they came up with this "feature".

>
>Could you describe specifically how you ground a generator at a
>jobsite or somewhere it will only be for a day or two?
>How do you verify the quality of the ground?
>Do you connect it directly to the ground lug on the gen head? or do
>you also connect to the generator frame?

I don't ground it.  I leave the neutral floating.  If the generator has the neutral
and green wire connected internally then I separate it.  The green wires and the
third pins are still there but they don't do anything.

In the rare event that some other consideration (such as noise on amateur radio
equipment being powered by the generator) requires earth grounding then I connect the
earth ground (green wire) and the generator chassis (via the grounding lug that most
of 'em have) to a known good earth ground, usually a ground rod.

John


 






































































































































































































Index Home About Blog