[Johnson] Fused Line Cord Plugs - Roy's diatribe

[Roy Morgan]

At 04:00 PM 1/8/04 -0800, Cal. N6KYR wrote:
>Hi Roy and Co:
>Has there been an actual recorded incident of someone getting "capped" 
>using the 2 wire fused plug?

Not that I know of.  Likely very few widows have kept on with the deceased 
ham's mailing lists.  (But plenty of fellows have had "hot chassis" from 
the old method of line bypassing.)

>To date, I have had multiple amounts of EFJ "fused plug" items and quite 
>frankly (or quite luckily), I have had no problems to date. Cal. N6KYR.

Quite possibly you will not have any trouble, but if you do, your wife (the 
newly made widow) will be very upset.

You fall into attitude category 1, 3, or 4 as I describe below.

For the record, ONCE AGAIN, here is my diatribe on these deadly devices:


Roy's Diatribe on Fused Line Cord Plugs and Line Cords and RF Bypassing

Fused Line Cord Plugs:

Under no circumstances should you ever use a fused line cord plug, 
period.  It can kill you in a variety of ways.  The Johnson company put 
them on Rangers, Valiants, and other equipment.  I have a Heath VHF-1 6- 
and 2-Meter transmitter with one on it.  That will be the first thing to go 
when I start returning it to serviceable condition.

I have written imaginative but quite serious descriptions of some of the 
many ways fused line cords can make a widow out of your wife.  I want to 
re-write that thing and put in back into circulation, but that will have to 
wait for another day.

In summary, however, the way to make your wife a widow is as follows:
1) The equipment with the fused line cord plug suffers an internal short 
such as in a transformer or RFI bypass capacitor, with the short circuit 
more or less to the chassis.
2) ONE of the line cord plug fuses blows.
3) You unplug the thing, remove it from the operating stainon, move it to a 
work bench, and the ground you *might* have had on the chassis is removed.
4) You plug it back in and haplessly insert the unpolarized plug so the 
intact fuse puts line voltage on the chassis.
5) You reach for the power switch, the current kills you and your wife 
becomes a widow.


This is a sure-fire topic to generate much traffic on any mailing 
list.  People's attitudes seem to fall into four groups:

1) "Originality forever." To hell with the fact that it may kill me or 
someone else, I will use the original deadly fused line cord.

2) "But of course."   Safety in line cords is easy to understand and worth 
paying attention to.

3) "Hmmm..."  I'm glad to know about all this (but I may not DO anything to 
prevent my death or that of any other hapless and innocent person.)

4) "Problem?  What problem?  There's no problem here." Duuuhhhh!

Be safe, live long. Do not use fused line cord plugs.
Install a three-wire grounded line cord.



Line cords and how to install one safely:

(in US standard line cords):
GREEN is safety ground, and should be tied directly to the chassis.
In European (IEC) cords, the safety ground is Green/Yellow.

BLACK is "hot" or "line" - it goes directly to the rear of the fuse holder, 
the terminal farthest from the outside of the fuse holder where the cap is 
installed.  The terminal on the fuse holder nearer the chassis or panel 
goes off to the switch and should go nowhere else.  If you use an open 
clip-style fuse holder under the chassis, use either end of it.

WHITE is "neutral" and goes UN-fused to the system, e.g. power transformer 
primary.  Do not put a fuse in both power cord lines. This can lead to a 
dangerous situation, though it's less likely to be dangerous with a three 
wire grounded line cord than with the deadly fused two-wire un-polarized 
line cord plug.

On the line cord wall plug,
  - the round, longer pin is green
  - the larger flat pin is neutral
  - the narrower flat pin is line or hot.

Note that European color coded line cords have different colors..  Here 
they are:

LINE            (US) Black  =  (EU)  Brown
COMMON   (US)White  =  (EU)  Blue
GROUND    (US) Green     (EU)  Green/Yellow.


(begin extract from message by Bob Nickels)
From: "Robert Nickels" <w9ran@oneradio.net>
Subject: [Johnson] Fused Plugs
...
A good source of replacement 3-wire power cords are those used by computers
and peripherals, but most of them use the European color designations   For
years, the colors of individual conductors in cords for use in North America
have been black for line, white for neutral, and green for earth (ground).
But in order to harmonize worldwide standards,  two major UL equipment
standards, UL 1950, Information Technology Equipment, and UL 2601, Medical
and Dental Equipment, started several years ago to require the more
traditional European conductor color coding: brown for line, light blue for
neutral, and a  combination of green and yellow for ground.

The color conversion is as follows:

LINE            (US) Black  =  (EU)  Brown
COMMON   (US)White  =  (EU)  Blue
GROUND    (US) Green     (EU)  Green/Yellow

(end extract from message by Bob Nickels)

Older HP and other test equipments were equipped with an oval line cord 
connector and matching cord.  The Belden/Volex 17280 power cords are 
apparently the normally-connected cord.  In all of them, the offset 
(center) pin is chassis ground.  There is a version with reversed line and 
neutral. When working with these equipments and line cords, do take time to 
sort out hot from neutral so you retain the safety aspects of the fuse 
connection.


RF Bypass caps should be installed as follows:

One from Line to Neutral, after the fuse.
One from neutral to chassis.

Do not install one from line to chassis and neutral to chassis as was 
normally done years ago.  This causes a danger of fire should the line to 
chassis cap short but not draw enough current to blow the circuit breaker, 
and this arrangement also causes the chassis to be at half the line voltage 
if the safety ground is not present (such as in a two-wire outlet used with 
an adapter, or in an outlet improperly wired or faulty.)

There are currently available "Safety" capacitors meant for line bypass 
applications. You can tell them from normal caps in the catalogs because 
they cost about 5 times as much as normal caps.  If you take apart computer 
power supplies or junk TV sets, you will wind up with one or two from each 
unit.

Fuses:

The topic of fuse installation and choice of fuse type and rating is a 
complicated one, but here are some points to consider:

  1) For normal equipment, put one fuse only, in the Hot wire of the line 
cord as near as practicable to the point where the line cord enters the 
equipment.  The black, Hot wire of the line cord runs directly to the tip 
of the fuse holder.

In equipment such as the Valiant transmitters that are made with extensive 
RFI filtering on all leads exiting the case, you may not want to add a rear 
chassis skirt mounted fuse holder. In other radios that never did have a 
fuse, such as the Hallicrafters S-20R, adding a fuse holder would ruin the 
originality of the set.  In these cases, mount an open fuse clip below the 
chassis, possibly using an existing screw or transformer mounting bolt.

Some military equipment was built with a fuse and possibly a switch section 
in both wires of the line. This was done  where the equipment was to be 
used aboard ship or in other places where the power circuits were floated 
from ground for safety and reliability reasons.  (This situation also 
applies generally in Sweden and some other European countries.)  If the 
equipment is in good condition you can leave it as it was built but make 
sure you have a good three wire grounded line cord and that your outlet 
grounds are properly connected.

Note: the three-terminal MS series, "Amphenol" type connectors used by the 
military on such equipment as the CV-591 and CV-89 were installed with (at 
least) two different pin arrangements.. Be very careful that you dope out 
what you have when working on equipment of this sort. Mis-matching the cord 
to the equipment could lead to trouble.

2) The Hot or line wire of the power cord goes directly to the rear of the 
fuse holder, the one farthest from the outside of the fuse holder where the 
cap is inserted.  The terminal on the fuse holder nearer the chassis or 
panel goes off to the switch. This reduces to the absolute minimum the 
amount of conductor inside the equipment that is not protected by the 
fuse.  And it reduces the chance of a shock when you are installing or 
removing the fuse.

3) The "cold" or neutral side of the line cord should NOT be fused.  The 
Green, safety ground wire should never be fused.

4) Follow manufacturer's specs for the type and rating of the fuse.  Beware 
of low voltage fuses that may fit the fuse holder you have. Fuses rated at 
32 volts may not properly protect you and the equipment in normal line 
voltage situations.  If you don't know the ratings needed, make a guess at 
the rating and use smaller and smaller fuses until they blow from time to 
time.. then increase the rating a bit.


GFI and Hot Chassis Troubles:

The R-390 series of receivers, among others, was built with robust line 
filters. The arrangement of the capacitors places half the line voltage on 
the chassis if the chassis is not grounded.  This is NOT because the line 
filter capacitors are leaking or shorted, it is normal voltage division 
behavior of the circuit as installed.   If the chassis is grounded, enough 
current flows in the safety ground wire to unbalance the two line currents 
and trip many ground fault interrupter devices.  Old style methods of 
bypassing both wires of a two-wire line cord to the chassis can do the same 
things.  Steps to correct these troubles include:

1) Remove the line filters or line bypass capacitors connected in the old 
style and either leave them out or install bypasses as above.

2) Use an isolation transformer or a "Sola" type constant 
voltage  transformer (most of which have isolated secondaries).  Note: most 
"Variacs" or variable voltage transformers do NOT provide any 
isolation.  Some that do apparently exist but they are rare.  Further, 
fuses in these things may be in the input wire only and not in the variable 
voltage output wire.  This can lead to overloading the low voltage turns of 
your transformer.  Both input hot and output hot should be fused.

3) Use properly grounded three wire line cords with non-GFI protected power 
circuits.


Outlet Safety Testers:

Most home stores and electrical supply houses can sell you a small gadget 
to test your outlets with.  They have a number of neon lamps that indicate 
proper functioning or various fault conditions. The cost is less than $10 
and is one of the best investments in your safety you can make.  Even 
"licensed professional electricians" can and have made mistakes wiring up 
houses, and time and wear can open up safety grounds that were installed 
properly in the beginning.  You owe it to yourself, your family, and later 
occupants of your house to buy and use one of these very helpful gadgets.


Think safety.
Install proper grounded line cords.
Live long.


(end of diatribe)



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan@nist.gov --