Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here? This cannot be normal. For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?

Any ideas or info would be appreciated. Thanks.

DMT

ineedcoffee wrote:

Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here?


Yes. A lot.


This cannot be normal.


Yes, it is.


For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?


No. How would _YOU_ isolate the chassis when the RF connectors are
grounded to the chassis without causing other problems, and keep the
price reasonable? How will you pass the strict EMI requirements if the
RF can radiate out of the case?


Any ideas or info would be appreciated. Thanks.


That is normal capacitive leakage in the power supply. If you put a
1 Kohm resistor across your voltmeter you will see almost nothing.


Do things the right way. You are supposed to hook up all of the RF
cables BEFORE you plug it in. Then the chassis is grounded, and there
will not be enough voltage for you to feel anything.



--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

On May 9, 8:41*pm, "Michael A. Terrell"
wrote:
ineedcoffee wrote:

Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. *This cable box has no ground prong. *When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. *For ground, used both my hot water base board and the neutral
and ground from the receptical. *The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. *When it is connected
to the box, the voltage on the case of course disappears. *Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here?

* *Yes. A lot.

*This cannot be normal.

* *Yes, it is.

*For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. *Does this sound right?

* *No. *How would _YOU_ isolate the chassis when the RF connectors are
grounded to the chassis without causing other problems, and keep the
price reasonable? *How will you pass the strict EMI requirements if the
RF can radiate out of the case?

Any ideas or info would be appreciated. *Thanks.

* *That is normal capacitive leakage in the power supply. *If you put a
1 Kohm resistor across your voltmeter you will see almost nothing.

* *Do things the right way. You are supposed to hook up all of the RF
cables BEFORE you plug it in. Then the chassis is grounded, and there
will not be enough voltage for you to feel anything.

--http://improve-usenet.org/index.html

Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account:http://www.usenettools.net/ISP.htm

I figured I was making some incorrect assumptions. Just for the fun
of it, I tried an ammeter with a resistor and some current did flow
but it was only 1/10 of one milliamp. I'm glad to know that nothing
is wrong. Thanks for taking the time to answer.

Regards

DMT

ineedcoffee wrote:

On May 9, 8:41 pm, "Michael A. Terrell"
wrote:
ineedcoffee wrote:

Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here?

Yes. A lot.

This cannot be normal.

Yes, it is.

For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?

No. How would _YOU_ isolate the chassis when the RF connectors are
grounded to the chassis without causing other problems, and keep the
price reasonable? How will you pass the strict EMI requirements if the
RF can radiate out of the case?

Any ideas or info would be appreciated. Thanks.

That is normal capacitive leakage in the power supply. If you put a
1 Kohm resistor across your voltmeter you will see almost nothing.

Do things the right way. You are supposed to hook up all of the RF
cables BEFORE you plug it in. Then the chassis is grounded, and there
will not be enough voltage for you to feel anything.

--http://improve-usenet.org/index.html

Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account:http://www.usenettools.net/ISP.htm

I figured I was making some incorrect assumptions. Just for the fun
of it, I tried an ammeter with a resistor and some current did flow
but it was only 1/10 of one milliamp. I'm glad to know that nothing
is wrong. Thanks for taking the time to answer.

Regards

DMT


You're welcome.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

ineedcoffee wrote:

Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here? This cannot be normal. For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?

Any ideas or info would be appreciated. Thanks.

DMT

Is it possible that the shield of the cable is not grounded where it
enters your home?

JAM

Leo Marx wrote:
ineedcoffee wrote:
Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here? This cannot be normal. For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?

Any ideas or info would be appreciated. Thanks.

DMT

Is it possible that the shield of the cable is not grounded where it
enters your home?

JAM
This is quite normal for any equipment having a
powersupply interference filter.
You might feel a slight trickle of current,
but once you apply all cabling before you apply
power, you will be oke.
Almost all computers, printers, etc have it.
There are two small capacitors from each of
the main power wires, to the frame, to suppress
radio interference.
That means you see about half the mains voltage at the
case, but at a very high, safe impedance(although it tickles).
Once you connect and ground things you wont feel a thing.

Leo Marx wrote:

ineedcoffee wrote:

Voltage question for some electronics repairs techs...

After feeling electricity when connecting two cable wires via a
coupler, I traced the source back to my Scientific Atlanta 8300HD
cable box. This cable box has no ground prong. When all wires expect
the power are disconnected, my meters reads 48 V AC from the case to
ground. For ground, used both my hot water base board and the neutral
and ground from the receptical. The outlet polarity is not
reversed.

When touch ground and the box with my hands, I can intermittently feel
slight tingling, about the strength of a dying 9 V on the tongue.

I've also verified the cable wire is grounded. When it is connected
to the box, the voltage on the case of course disappears. Obviously
it cannot source much current, since this is effectively shorting a
voltage source to ground.

The cable company has had two other boxes out, and both have the same
symptoms.

Am I missing something here? This cannot be normal. For a two
pronged appliance, I assume the case should be electrically isolated
from both the hot and the neutral. Does this sound right?

Any ideas or info would be appreciated. Thanks.

DMT

Is it possible that the shield of the cable is not grounded where it
enters your home?


If the shield was not grounded there, it is grounded at the CATV
amplifier, so you would not see 48 VAC. I already explained the case,
and how to deal with it.


--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm