[alpha_uma]

Does anyone remember when manufacturers started using two-prong power plugs
for TVs? For that matter, did they ever use three-prong plugs for TVs? What
are the advantages and disadvantages--from a safety perspective, not from
the cost-cutting perspective?

They did that to the simple toasters a long time ago. Are they doing the
same to microwave ovens, or have they done it already? How safe is it
really? Are they simply assuming that all households would have been wired
with electrical ground fault protection these days?

Thanks

 

[Beachcomber]

I've never seen TVs with 3 prong plugs. Not even the old "transformerless"
tube TVs, although they used interlocks to prevent one from opening the
back while powered on, and they were at the time the only devices with
one blade wider than the other so the chassis was (hopefully!) at the
neutral's potential. (now most 2 prong plug devices have the wide blade)


Every microwave I've seen, including older ones, had 3 prong plugs.

TV's generally have no exposed metal parts to shock the user and
in-effect are the equivalent of double-insulated when it comes to
safety issues, hence the two-prong polarized plug. Commercial video
monitors may contain conductive rack mounts or metal frames and are
almost always grounded.

For a microwave oven, the grounding of interior conductive cage is an
essential part of the shielding from microwave leakage and also serves
as an electrical safety ground for the appliance. These are always
grounded with 3 prong plugs. Not having a proper ground on a
microwave oven might lead to a re-radiation problem under certain
conditions.

Just a note about your terminology which I am sure you understand but
some readers may not. There is a difference between being wired with
"Ground" protection and "Ground Fault Protection". "Ground"
protection (in the form of 3 prong receptacles) is something that has
been required in the US since the late 50's - early 60's for most
places. "Ground Fault Protection" is a relatively new requirement
that takes the form of a GFCI device, either at the breaker, on a
receptacle, or sometimes on the power cord of an appliance itself.

Beachcomber

 

[alpha_uma]

I have never seen a regular TV with a 3 prong plug. I have a "monitor" with one
but it was sold as an industrial unit.

Me neither, or at least not I do not recall having seen one myself. However,
all computer monitors that I have bought so far (all rated for residential
use) have 3-prong power plugs. Does that mean computer monitors are less
"doubly-insulated" than TVs? After all, many of the computer monitor
manufacturers are the same companies that make TVs.

In fact most old 50s era tube TVs actually had the chassis connected to one
side of a non-polarized plug. That will wake you up if you lose a knob and
touch the stem.

LOL. Does wonder to the hair too. Wonderfully lax electrical codes back
then?

The same is true with consumer toasters and other kitchen appliances. They all
seem to be 2 prong although the ones made since the Johnson administration do
have polarized plugs. I think most are double insulated these days.

Speaking of power plug and power socket "polarization", is it a world-wide
practice? I know they do so in N. America. Do they do that in Europe and
Asia? Other parts of the world?

My Philips electrical kettle comes with a 3-prong plug. But I think I have
seen some electrical hot pots (for boiling water or heating soup stuff) use
2-prong plugs (I don't know if they are rated as "double-insulated" or not,
though). Wouldn't that be dangerous (if the user is not protected by CFCIs)?

How trustworthy is "double-insulation" for toasters, really?
Al-U

 

[alpha_uma]

It's fine until you stick the fork in there to retrieve a stuck begel.

LOL.

But wait a minute. Are toasters these days stamped with the "double
insulation" rating or not? If "yes", then according to the standards of
"double insulation", shouldn't the bread-slice chamber of the toaster be
isolated from the live main power of the device? Not that I would want to
stick a fork in there, but has anyone tried rescuing a bagel with a fork and
live to tell it?

Al-U

 

[alpha_uma]

My Philips electrical kettle comes with a 3-prong plug. But I think I have
seen some electrical hot pots (for boiling water or heating soup stuff) use
2-prong plugs (I don't know if they are rated as "double-insulated" or not,
though). Wouldn't that be dangerous (if the user is not protected by CFCIs)?

<snip>

Sorry for the typo. I meant GFCIs.

 

[SQLit]

Does anyone remember when manufacturers started using two-prong power plugs
for TVs? For that matter, did they ever use three-prong plugs for TVs? What
are the advantages and disadvantages--from a safety perspective, not from
the cost-cutting perspective?

They did that to the simple toasters a long time ago. Are they doing the
same to microwave ovens, or have they done it already? How safe is it
really? Are they simply assuming that all households would have been wired
with electrical ground fault protection these days?

Thanks

Double insulated tools are usually 2 pronged. All of my old power equipment
has 3 prongs. The weed eater and my mower do not, just 2 prongs. I doubt
that microwaves or anything that draws a lot of power over time will ever
have 2 prongs. I guess hair dryers and curling irons are exempt cause they
are never plugged into an non-GFCI outlet. (They never met my ex)

 

[alpha_uma]

Just a note about your terminology which I am sure you understand but
some readers may not. There is a difference between being wired with
"Ground" protection and "Ground Fault Protection". "Ground"
protection (in the form of 3 prong receptacles) is something that has
been required in the US since the late 50's - early 60's for most
places. "Ground Fault Protection" is a relatively new requirement
that takes the form of a GFCI device, either at the breaker, on a
receptacle, or sometimes on the power cord of an appliance itself.

Yes, I should NOT have used the potentially confusing phrase "electrical
ground fault protection" to mean "GFCIs". After all, there are different
ways and levels of protection to decrease the possibility of an electrical
fire or electrocution. For the sake of completeness, the commonly used ways
(that I'm aware of) in house wiring are:

(1) Fuse box (probably obsolete?)
(2) Circuit breaker
(3) Ground wire via 3-prong receptacles
(4) GFCI (ground fault circuit interrupter)

Are there other practised ways? Any known studies that compare the
effectiveness of (4) vs (3) (assuming the presence of (2) in each) in saving
lifes? Basically, I'm just curious whether or not manufacturers of
electrical/electronic equipment are increasingly more in favor of achieving
the "double insulation" rating than utilizing (3) via 3-prong plugs.

Al-U

 

[alpha_uma]

<snip>
Double insulated tools are usually 2 pronged. All of my old power equipment
has 3 prongs. The weed eater and my mower do not, just 2 prongs. I doubt
that microwaves or anything that draws a lot of power over time will ever
have 2 prongs. I guess hair dryers and curling irons are exempt cause they
are never plugged into an non-GFCI outlet.

(They never met my ex)

LOL. AFAIC, Murphy's law trumps all other rules. Sooner or later, someone
will stick a fork in the toaster or put a spoon in a microwave oven, and
someone will use a blow-dryer while the sink or tub is full of water. I
guess it is a good thing that the new codes require GFCIs be installed in
bathroom circuits.
Al-U

 

[Rowbotth]

We had an old Admiral TV that Dad bought in the mid to late 1950s. A
little 12" unit that had a picture that was only surpassed by satellite
images of modern times, by the way.

This thing had a metal case with a 2-prong plug, and it was eventually
installed in the basement of our house some 20 years later.

I learned very quickly that the knobs were plastic and were safe.
Touching the case of the TV was a very dangerous occupation - not enough
charge to do any physical damage, but enough to make you ay attention to
the plastic parts of the TV. (I still recall the tingle running up my
arm!)

On a wooden floor, no tingle. But on that d*&^#d cement floor, watch
out.

HR.

 

[Anthony Guzzi]

TV sets {'monitors'} with grounded cords are typically for "institutional"
duty; likely with a telltale odd lot of other assorted video/audio connectors.

My TV, VCR, and component DVD player all have two prongs, and then all
of my Stereo equipment has a two prong too. They're all polarized, with
one blade being bigger than the others though.
On the other hand, ALL of my computer has 3 prongs. CPU, Monitor,
Printer. Although, they all also use interchangable power cords that
can be detached from the unit, those cords with three holes that look
like an inverted plug, I've noticed a ton of devices that use those
standard cords, because all have the transformer in the device itself
instead of on a brick for a cord.

 

[Don Kelly]

LOL.

But wait a minute. Are toasters these days stamped with the "double
insulation" rating or not? If "yes", then according to the standards of
"double insulation", shouldn't the bread-slice chamber of the toaster be
isolated from the live main power of the device? Not that I would want to
stick a fork in there, but has anyone tried rescuing a bagel with a fork and
live to tell it?

Al-U

See those nice glowing heating elements. See the absence of any 1200watt,
120/120V isolation transformer built into the toaster. The toaster elements
are electrically hot and if you stick your fork in the toaster while
touching a grounded sink or whatever- you can be in for a nasty surprise.
The little wires holding the toast and other exposed metal parts are
insulated from the heating elements. Attempts are made to make things fool
proof but not damnfool proof.

 

[Andrew Gabriel]

Me neither, or at least not I do not recall having seen one myself. However,
all computer monitors that I have bought so far (all rated for residential
use) have 3-prong power plugs. Does that mean computer monitors are less
"doubly-insulated" than TVs? After all, many of the computer monitor
manufacturers are the same companies that make TVs.

I don't think anywhere else much in the world uses US TV's, but the
same monitors are used the world over, and hence conform to more
different country's safety standards.

Speaking of power plug and power socket "polarization", is it a world-wide
practice? I know they do so in N. America. Do they do that in Europe and
Asia? Other parts of the world?

The UK does, but most of Europe doesn't (in some parts of Europe,
neither mains conductor is guaranteed to be near ground potential).
The UK socket outlet (and it's round pin predecessor which is also
polarised) are still used by most former British Empire/Commonwealth
countries too.

My Philips electrical kettle comes with a 3-prong plug. But I think I have
seen some electrical hot pots (for boiling water or heating soup stuff) use
2-prong plugs (I don't know if they are rated as "double-insulated" or not,
though). Wouldn't that be dangerous (if the user is not protected by CFCIs)?

How trustworthy is "double-insulation" for toasters, really?

Double insulated appliances are common in the UK, but it's difficult
to make double insulated appliances with high power heating elements,
so those aren't common. You won't find a double insulated toaster in
the UK (not that I've ever seen anyway, nor anywhere in Europe AFAIK).

 

[Andrew Gabriel]

For a microwave oven, the grounding of interior conductive cage is an
essential part of the shielding from microwave leakage and also serves

It can't be -- the impedance of the ground connection at 2.4GHz
will be so high as to be completely useless. The shielding operates
simply as a microwave reflector and doesn't need to be grounded for
this purpose.

 

[alpha_uma]

See those nice glowing heating elements. See the absence of any 1200watt,
120/120V isolation transformer built into the toaster. The toaster elements
are electrically hot and if you stick your fork in the toaster while
touching a grounded sink or whatever- you can be in for a nasty surprise.
The little wires holding the toast and other exposed metal parts are
insulated from the heating elements. Attempts are made to make things fool
proof but not damnfool proof.

Yes, of course the toaster heating elements are electrically hot, and
therein lies the danger. That is the main reason for my skepticism/sarcasm
(in my previous message) on any toaster attaining any "double insulation"
rating. For example, my toaster (with a 2-prong power plug) does not seem to
have a "double insulation" rating--no "concentric square" symbol that I can
see.

Inside a toaster, the nichrome wires, which wrap around mica sheets, and
which carry the current from the power plug, do not have much (physical)
clearance to the

bread slice chamber,

which, IMHO, should be viewed as an

"user accessible" area with many exposed metallic parts.

My thinking is that I would feel more comfortable treating the typical $12
toaster as a device which barely passes "basic insulation". And since
toasters usually come with only a 2-prong plug these days, we can't even
classify it as a Class I device. But I could be wrong as I only have a
cursory understanding of electrical safety standards. So, I'll ask, again,
if anyone has seen a toaster with a "double insulation" rating.

Another thought. Why don't they use a (electrically) non-conducting sheath
for the toaster like the kind they use for the electric stove to shield the
nichrome wires? Too costly?

Al-U

 

[Jimmie]

Does anyone remember when manufacturers started using two-prong power plugs
for TVs? For that matter, did they ever use three-prong plugs for TVs? What
are the advantages and disadvantages--from a safety perspective, not from
the cost-cutting perspective?

They did that to the simple toasters a long time ago. Are they doing the
same to microwave ovens, or have they done it already? How safe is it
really? Are they simply assuming that all households would have been wired
with electrical ground fault protection these days?

Thanks

Dont remember TV sets ever being 3 prong and I was a TV tech in the
seventies.