Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Neutral connected to chassis?  (Read 550 times)
KE2KB
Member

Posts: 127




Ignore
« on: December 04, 2008, 07:16:44 PM »

Hi all;
It has been brought to my attention by a discussion in an electrical DIY forum that newer audio and video equipment is being manufactured with the neutral (wider blade) of the 2-wire plug connected to the chassis and all external connectors.

The equipment I have at home is all 10+ years old, and measurements with an ohmmeter have shown me that none of my equipment is wired this way.

I am befuddled as to why UL would allow such a configuration to be sold in the U.S., given our earth referenced power system.

There are two instances I can site that would be potentially lethal to someone coming between one of these devices and an earth ground.

1) The neutral wire between the device's cord and the main electrical panel is broken.
The device would not function, but anyone coming between the chassis and a grounded object would then become the missing neutral wire, and receive a potentially lethal shock.

2) The hot and neutral are reversed at the receptacle or somewhere along the line, causing the chassis of the connected equipment to become live.
Anyone coming between it and a grounded object would also be subject to a potentially lethal shock.

If this is really the case, as has been stated by one member of the DIY forum, as he has made measurements on his equipment and confirmed the connection, then we should all be using GFCI receptacles wherever such equipment is connected.

I don't know if this applies to any amateur gear, but if it does, we should all take the necessary steps to protect ourselves.

I would appreciate any comment on this.

Thanks

Frank
Logged
N4CQR
Member

Posts: 566




Ignore
« Reply #1 on: December 05, 2008, 06:13:51 AM »

Years ago (abt 1979 I think) many TV sets were wired this way. GE especially. Typical internal stickers said "WARNING Hot Chasis" We used a isolation transformer (B&K-something I can't remember) for safety during service.

I see people replace a cord cap on a lamp and pay no attention to the polarity. And in a number of cases I have seen the hot side of the line connected to the base threads rather than the socket's center contact.
Same goes for extension cords.
Logged
AA4PB
Member

Posts: 12672




Ignore
« Reply #2 on: December 05, 2008, 10:20:29 AM »

I haven't seen any equipment wired with the EXPOSED metal chassis connected to the neutral wire of a two-wire cord. Years ago it was common to have the neutral connected to the chassis but the chassis was inside a non-conductive enclosure, supposedly isolating the chassis from the user. An EXPOSED metal chassis or case should always be connected to the grounding conductor of a 3-wire power cord and not to the neutral.
Logged
K1CJS
Member

Posts: 5871




Ignore
« Reply #3 on: December 06, 2008, 08:51:45 AM »

I don't see that being done, I see the power cord wiring being connected to a transformer with maybe one or two traces on the circuitboard being at a 120 volt potential--even in the modern picture 'tube' type TV sets.  Of course, most of the units being manufactured today have no exposed chassis, and are plainly marked 'No user serviceable parts inside'.

I haven't seen an example of the neutral wire being connected to an exposed chassis for many years.

Logged
WA9SVD
Member

Posts: 2201




Ignore
« Reply #4 on: December 22, 2008, 04:57:17 PM »

N4CQR on December 5, 2008       Mail this to a friend!
Years ago (abt 1979 I think) many TV sets were wired this way. GE especially. Typical internal stickers said "WARNING Hot Chasis" We used a isolation transformer (B&K-something I can't remember) for safety during service.

I see people replace a cord cap on a lamp and pay no attention to the polarity. And in a number of cases I have seen the hot side of the line connected to the base threads rather than the socket's center contact.
Same goes for extension cords.
 
--------------------------------------------------

    At one time, it WAS common with "isolated" chassis equipment, where the user had no possible (under normal use) contact with the chassis.  But it's not standard NOW, and foolish, whether for a manufacturer or a "DIY" enthusiast.

    But normal lamp sockets (such as for table lamps) do NOT have exposed surfaces that are or can be connected to either side of the line cord so there should really be no significant difference as to how they are wired.  (Of course, wiring errors can pose a hazard to even the best designed systems.)
Logged
WB6DGN
Member

Posts: 584




Ignore
« Reply #5 on: January 01, 2009, 05:13:10 PM »

Anybody remember the old "AC/DC" table (broadcast) radios?  These old radios were usually five tube radios where the total series heater voltage equaled about 117 volts and the line cord was also connected directly  to a half wave rectifier (usually Selenium, but sometimes a 35W4 tube) and ground.  This in the days before the polarized AC plug!  Because there was no transformer, the set could be used on a normal 117volt AC line or on 120volt DC mains.  It was, however, a disaster waiting to happen.  I often wonder how many electrocutions resulted from the use of those radios.  To top it off, MANY had UL certification on their label!  As a kid, I wired a high impedance microphone into the audio amplifier to make a PA system out of it.  The mic. had a metal case and when it "zapped" me, I'd just flip the AC plug around to the other position.  No big deal!  It was a few years before I understood enough to realize the danger in what  I was doing.
Tom
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!