Hello!

I found a description of a series light bulb circuit on the net at
http://www.vintage-radio.com/project...-limiter.shtml
and there's a statement which confused me a bit:

"Note that the lamp is in the live side of the mains supply, not the
neutral.
This is for safety, so that the neutral side (and the chassis in AC/DC
sets)
stays close to earth potential no matter how much voltage is dropped across
the lamp."

Now I built an isolation transformer into a box with a lamp socket connected
to a bypass switch, i.e. if the switch is open both socket pins are
disconnected.

However, I put the lamp socket into the return wire, not the live wire,
because I want to use differently rated bulbs (quick exchange) and the
socket, if empty, is a great place for children or other innocent people to
poke their fingers in. So, even if the switch is closed connecting the lamp
in-circuit, accidentally touching the fixture should be safe.

For us in Germany it's possible to put a 230V plug into a live socket both
ways round, so we're not sure which wire is actually live. That's why I use
an LED to indicate wrong polarity; it lights when my intended neutral is
live in respect to earth ground, so I can simply change plug orientation.

For this reason I don't understand the statement above. If I've got an
appliance which uses only two wires I'm pretty sure that no point of the
chassis is directly connected to either (because any of them might be on
live voltage). In fact, most of these contain a transformer or SMPS and the
secondary side 0 potential is usually connected to the chassis.

And if I've got an additional earth ground this is the one usually connected
to metallic parts. So according to my thinking I should be quite safe
putting the lamp into the return wire.

Am I making a mistake and should I better put the lamp into the live side?
Are there devices in other countries which use a fixed setup of
live/neutral?
Or am I simply already too tired to understand?

Any help is greatly appreciated (my life may depend on it ;-)

Regards, Leo

Location of series lightbulb - Hot side or Neutral side.

I'd agree that it would be better to be in the Hot side since then
the equipment would be operating under conditions closer to normal
with the Neutral of its circuitry at Neutral/Ground potential. The
return of the measuring equipment can be near Ground potential.

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Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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"Leo Meyer" writes:

Hello!

I found a description of a series light bulb circuit on the net at
http://www.vintage-radio.com/project...-limiter.shtml
and there's a statement which confused me a bit:

"Note that the lamp is in the live side of the mains supply, not the
neutral.
This is for safety, so that the neutral side (and the chassis in AC/DC
sets)
stays close to earth potential no matter how much voltage is dropped across
the lamp."

Now I built an isolation transformer into a box with a lamp socket connected
to a bypass switch, i.e. if the switch is open both socket pins are
disconnected.

However, I put the lamp socket into the return wire, not the live wire,
because I want to use differently rated bulbs (quick exchange) and the
socket, if empty, is a great place for children or other innocent people to
poke their fingers in. So, even if the switch is closed connecting the lamp
in-circuit, accidentally touching the fixture should be safe.

For us in Germany it's possible to put a 230V plug into a live socket both
ways round, so we're not sure which wire is actually live. That's why I use
an LED to indicate wrong polarity; it lights when my intended neutral is
live in respect to earth ground, so I can simply change plug orientation.

For this reason I don't understand the statement above. If I've got an
appliance which uses only two wires I'm pretty sure that no point of the
chassis is directly connected to either (because any of them might be on
live voltage). In fact, most of these contain a transformer or SMPS and the
secondary side 0 potential is usually connected to the chassis.

And if I've got an additional earth ground this is the one usually connected
to metallic parts. So according to my thinking I should be quite safe
putting the lamp into the return wire.

Am I making a mistake and should I better put the lamp into the live side?
Are there devices in other countries which use a fixed setup of
live/neutral?
Or am I simply already too tired to understand?

Any help is greatly appreciated (my life may depend on it ;-)

Regards, Leo

"Leo Meyer" wrote in message
...
Hello!

I found a description of a series light bulb circuit on the net at
http://www.vintage-radio.com/project...-limiter.shtml
and there's a statement which confused me a bit:

"Note that the lamp is in the live side of the mains supply, not the
neutral.
This is for safety, so that the neutral side (and the chassis in AC/DC
sets)
stays close to earth potential no matter how much voltage is dropped
across
the lamp."

Now I built an isolation transformer into a box with a lamp socket
connected
to a bypass switch, i.e. if the switch is open both socket pins are
disconnected.

Which side of the tranny is the lamp ??
If you put it in the secondary it will reduce the "finger" hazard also the
ground for instruments I imagine.

--
Regards ............... Rheilly Phoull

Leo,
I think you are correct & agree the statement is confusing.
Ultimately you don't need to trust your life to web sourced advice.
I suggest you power your device via a "leakage current detecting breaker".
Alternatively, simulate the silly child manoeuvre & put your finger where it
should not be.
If you are in good health & are carefull not to make a circuit across your
chest you should be safe even if "stung"
Pete


"Leo Meyer" wrote in message
...
Hello!

I found a description of a series light bulb circuit on the net at
http://www.vintage-radio.com/project...-limiter.shtml
and there's a statement which confused me a bit:

"Note that the lamp is in the live side of the mains supply, not the
neutral.
This is for safety, so that the neutral side (and the chassis in AC/DC
sets)
stays close to earth potential no matter how much voltage is dropped
across
the lamp."

Now I built an isolation transformer into a box with a lamp socket
connected
to a bypass switch, i.e. if the switch is open both socket pins are
disconnected.

However, I put the lamp socket into the return wire, not the live wire,
because I want to use differently rated bulbs (quick exchange) and the
socket, if empty, is a great place for children or other innocent people
to
poke their fingers in. So, even if the switch is closed connecting the
lamp
in-circuit, accidentally touching the fixture should be safe.

For us in Germany it's possible to put a 230V plug into a live socket both
ways round, so we're not sure which wire is actually live. That's why I
use
an LED to indicate wrong polarity; it lights when my intended neutral is
live in respect to earth ground, so I can simply change plug orientation.

For this reason I don't understand the statement above. If I've got an
appliance which uses only two wires I'm pretty sure that no point of the
chassis is directly connected to either (because any of them might be on
live voltage). In fact, most of these contain a transformer or SMPS and
the
secondary side 0 potential is usually connected to the chassis.

And if I've got an additional earth ground this is the one usually
connected
to metallic parts. So according to my thinking I should be quite safe
putting the lamp into the return wire.

Am I making a mistake and should I better put the lamp into the live side?
Are there devices in other countries which use a fixed setup of
live/neutral?
Or am I simply already too tired to understand?

Any help is greatly appreciated (my life may depend on it ;-)

Regards, Leo

On Fri, 21 Nov 2003 22:24:49 +0100 "Leo Meyer"
wrote:

However, I put the lamp socket into the return wire, not the live wire,
because I want to use differently rated bulbs (quick exchange) and the
socket, if empty, is a great place for children or other innocent people to
poke their fingers in. So, even if the switch is closed connecting the lamp
in-circuit, accidentally touching the fixture should be safe.

If you're working on the device, I think you should be more worried
about a possible hot chassis than a errant finger in an open socket.

I agree with the need to have several light bulbs available, but even
with your switch, you could still leave the light bulb installed.
There's no real reason to remove the bulb just because you've decided
it's safe to bypass it.

In my case, I don't have a bypass switch, I just have a screw-in type
fuse which I install instead of a light bulb.

BTW, with a bulb installed in the hot side of the line, the upper edge
of the base threads will be at least somewhat hot. I was careful to
wire the hot side of the line to the center terminal of the bulb, but
there's still enough juice available at the shell to hurt or even
kill.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Alternatively, simulate the silly child manoeuvre & put your finger where it
should not be.

Silly advice. As in "I *think* it's safe."

Not only are we unsure of the persons qualifications/knowledge, what
about the others, the novice out there reading this forum.
Irrespective of the intentions, I wouldn't suggest this to anyone.

__ __ __ __ __
Regards, Chris
[spamblock used]

DaveC writes:

On Fri, 21 Nov 2003 20:16:29 -0800, Jim Adney wrote
(in message ):

BTW, with a bulb installed in the hot side of the line, the upper edge
of the base threads will be at least somewhat hot. I was careful to
wire the hot side of the line to the center terminal of the bulb, but
there's still enough juice available at the shell to hurt or even
kill.

How can this be so if the shell of the socket is at neutral potential (only
one or two volts with respect to ground)?

Because the light bulb is in series with a load that will drop some
voltage and the shell of the bulb is on the Hot side of the load.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.

DaveC writes:

On Fri, 21 Nov 2003 20:16:29 -0800, Jim Adney wrote
(in message ):

BTW, with a bulb installed in the hot side of the line, the upper edge
of the base threads will be at least somewhat hot. I was careful to
wire the hot side of the line to the center terminal of the bulb, but
there's still enough juice available at the shell to hurt or even
kill.

How can this be so if the shell of the socket is at neutral potential (only
one or two volts with respect to ground)?

Because the light bulb is in series with a load that will drop some
voltage and the shell of the bulb is on the Hot side of the load.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.