I believe I now understand your product's nature. First, it is
not ITE, i.e. not under IEC 60950. Technically, it falls outside
the "letter" of the LVD which refers to the voltage "rating" of
the equipment. However, I feel it falls within the "intent" of the
LVD. Here's why:
In use, the device may have 250V or so differential between internal
parts. Can this result in a shock hazard? Yes. Can this result in
a fire hazard? Maybe, depending on the power delivered to a fault
which could result in ignition.
If no harmonized standard exists for this type of "test" equipment,
you will probably have to use a TCF to demonstrate how the user is
protected against electric shock, and what prevents a possible fire
hazard.
Only my opinion........
George Alspaugh
"Gary Labadie" <glabadie%acromag....@interlock.lexmark.com> on 06/11/98
04:52:00 AM
Please respond to "Gary Labadie"
<glabadie%acromag....@interlock.lexmark.com>
To: cnj%dolby.co...@interlock.lexmark.com
cc: emc-pstc%ieee....@interlock.lexmark.com (bcc: George Alspaugh)
bcc: George Alspaugh
Subject: RE: Isolation versus IEC1010
The issue arises because our instruments are for the industrial
environment. They interface to low level sensors such as a thermocouple,
RTD, magnetic pickup, flowmeter, etc. These are very low level signals
in the 0 to 10VDC level or less typical. The output is also a low level
signal in the 0 to 10VDC or less. For high performance and accuracy, we
electrically isolate the input from the output and prevent ground loops
from happening. In our installations, without isolation between the
sensor and the control room equipment, the ground potentials are always
different and if you don't isolate the signals become corrupted. The
industrial environment always is an electrically noisy environment and
isolating circuits is a way to help control the noise. It is not always
necessary, and there are products that don't isolate input to output.
There are hundreds of applications where the device won't work without
isolation. But does the fact that isolation is included affect whether
the Low Voltage Directive applies? I can make very strong arguments both
ways that non-isolated devices are more hazardous than isolated devices
due to the industrial environment they are installed in and vice versa.
Example 1: Isolated device input to output
My sensor input is isolated from the output and grounded at the field
sensor. My output signal of 0 to 10VDC is grounded at another point in
the control room. Both signals are below 10VDC. However, the ground
potential between input to output could be 250VAC. Does the Low Voltage
Directive apply?
Example 2: Non-isolated device from input to output
My field sensor is grounded and connected to my input port. My output
signal is grounded at the control room. Both signals are below 10VDC and
input common is electrically connected to my output common. The ground
potential at the sensor is 0 volts. THe ground potential at the control
room is 250VAC with respect to the sensor ground. Hence a ground loop is
set up and a 250VAC potential exists between the two points and current
is flowing. Does the Low Voltage directive apply now? Or is should the
end-user known better that they created this ground loop and hence now
could be considered a hazard.
Example 1 and 2 occur on a daily basis in the industry. Everyone has
different opinions at this point. But the fact that the Low Voltage
Directive applies or not when isolation is present has a major impact on
the manufacturers product.
Best Regards,
Gary Labadie
Marketing
Acromag, Inc.
30765 Wixom Rd. Ph: (248)624-1541 ext. 205
P.O. Box 437 Fax:(248)624-9234
Wixom, MI 48393 Email: glaba...@acromag.com
-----Original Message-----
From: James, Chris [SMTP:c...@dolby.co.uk]
Sent: Thursday, June 11, 1998 3:43 AM
To: 'Gary Labadie'; emc-pstc
Subject: RE: Isolation versus IEC1010
The directive says "designed or adapted for use with......" the
voltages ranges you state.
If you product is not intended for use with such voltages then I do not
see you need to seek approval (LVD) irrespective of what you rate the
isolation.
Having said that if you state a rated isolation then you need to be sure
you meet it.
How is your unit powered? Sounds like an external wall brick adaptor -
this will of course need to comply.
Chris
> -----Original Message-----
> From: Gary Labadie [SMTP:glaba...@acromag.com]
> Sent: Wednesday, June 10, 1998 8:08 PM
> To: emc-p...@ieee.org
> Subject: Isolation versus IEC1010
>
> I would like to get the consensus on the following concept.
>
> The low Voltage directive applies to products that use 50VAC or 75VDC
> and
> higher signal levels basically up to 1000VAC. Now, If a product's I/O
>
> and power signals do not exceed 24Vdc anywhere, does the low voltage
>
> directive apply. Here's the catch, the unit contains electrical
> isolation between input, output and power signals. The electrical
> isolation rating is specified as 250VAC continous.
>
> Some argue, that since the unit is isolated and has an isolation
> rating
> the Low voltage directive applies because the isolation specification
>
> exceeds 50VAC. You can also argue that within the scope of the Low
> Voltage directive that the I/O and power signals are below the
> directives
> requirement and hence do not apply if you don't consider whether the
>
> product has electrical isolation or not.
>
> Does the fact that electrical isolation is included into a product,
> affect whether the Low Voltage Directive may or may not apply?
>
> Best Regards,
>
> Gary Labadie
> Marketing
>
> Acromag, Inc.
> 30765 Wixom Rd. Ph: (248)624-1541 ext. 205
> P.O. Box 437 Fax:(248)624-9234
> Wixom, MI 48393 Email: glaba...@acromag.com
