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Safe low voltage

R

Raveninghorde

Jan 1, 1970
0
I need to make a mains powered test jig with at least a 60V dc output.
My memory tells me that 65Vdc is OK

I've just grabbed my copy of IEC 61010-1 to check and note it is well
out of date but it says 70V dc.

I looked a wikipedia

http://en.wikipedia.org/wiki/Extra-low_voltage

which says:

"The International Electrotechnical Commission and its member
organizations define an ELV circuit as one in which the electrical
potential of any conductor against earth (ground) is not more than
either 50 volts RMS (70 volts peak) for alternating current, or
ripple-free 120 volts for direct current under dry conditions."

120Vdc sounds wrong for parts that an operator can touch.

So what is the current safety standard for operator accessable
voltages?
 
R

Rich Grise

Jan 1, 1970
0
Raveninghorde said:
I need to make a mains powered test jig with at least a 60V dc output.
My memory tells me that 65Vdc is OK

I've just grabbed my copy of IEC 61010-1 to check and note it is well
out of date but it says 70V dc.

I looked a wikipedia

http://en.wikipedia.org/wiki/Extra-low_voltage

which says:

"The International Electrotechnical Commission and its member
organizations define an ELV circuit as one in which the electrical
potential of any conductor against earth (ground) is not more than
either 50 volts RMS (70 volts peak) for alternating current, or
ripple-free 120 volts for direct current under dry conditions."

120Vdc sounds wrong for parts that an operator can touch.

So what is the current safety standard for operator accessable
voltages?

According to http://www.i-spec.com/IEC_60950/glossary.html ,
"Hazardous Energy Level

A stored energy level of 20J or more, or an available continuous power level
of 240 VA or more, at a potential of 2V or more.

Hazardous Voltage

A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does
not meet the requirements for either a Limited Current Circuit or a TNV
Circuit."

This was the first of "about 97,600" results on
http://www.google.com/search?hl=en&...erator+accessible+voltages&btnG=Google+Search

It might be different in different countries.

Hope This Helps!
Rich
 
R

Raveninghorde

Jan 1, 1970
0
According to http://www.i-spec.com/IEC_60950/glossary.html ,
"Hazardous Energy Level

A stored energy level of 20J or more, or an available continuous power level
of 240 VA or more, at a potential of 2V or more.

Hazardous Voltage

A voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does
not meet the requirements for either a Limited Current Circuit or a TNV
Circuit."

This was the first of "about 97,600" results on
http://www.google.com/search?hl=en&...erator+accessible+voltages&btnG=Google+Search

It might be different in different countries.

Hope This Helps!
Rich

Not a lot:)

I'll order the up to date IEC standard tomorrow. £234 or about $375.
Expensive at half the price.
 
U

Uwe Hercksen

Jan 1, 1970
0
Raveninghorde said:
I need to make a mains powered test jig with at least a 60V dc output.
My memory tells me that 65Vdc is OK
Hallo,

the value of a safe voltage depends, is it used in a dry or wet area,
what parts of the operators body may get contact to the voltage, the
safe voltage for childs is lower, persons with a thick horny skin at
their hands would tolerate higher voltages. If the voltage may contact
the body at the chest or back near the heart the safe voltage is much lower.
Here http://en.wikipedia.org/wiki/Extra-low_voltage
you find less than 120 V ripple free DC in a dry area

Bye
 
J

Jasen Betts

Jan 1, 1970
0
I looked a wikipedia

http://en.wikipedia.org/wiki/Extra-low_voltage

which says:

"The International Electrotechnical Commission and its member
organizations define an ELV circuit as one in which the electrical
potential of any conductor against earth (ground) is not more than
either 50 volts RMS (70 volts peak) for alternating current, or
ripple-free 120 volts for direct current under dry conditions."

120Vdc sounds wrong for parts that an operator can touch.

Indeed, 36V DC has been fatal in at least one instance.
So what is the current safety standard for operator accessable
voltages?

Slot-cars and model trains run at about 12V, and _some_ people find
contact with that unplesant.

Those halogen lamps with exposed wiring also seem to use 12V bulbs
(but probably AC)

Apple's magsafe chargers may have exposed 16.5V contacts.
 
Slot-cars and model trains run at about 12V, and _some_ people find
contact with that unplesant.

Testing a 4.5 V or 9 V battery with your tongue can be a bit
uncomfortable, if the battery is still fully charged :).
 
N

Nemo

Jan 1, 1970
0
I need to make a mains powered test jig with at least a 60V dc output.
My memory tells me that 65Vdc is OK

I've just grabbed my copy of IEC 61010-1 to check and note it is well
out of date but it says 70V dc.

I looked a wikipedia

http://en.wikipedia.org/wiki/Extra-low_voltage

which says:

"The International Electrotechnical Commission and its member
organizations define an ELV circuit as one in which the electrical
potential of any conductor against earth (ground) is not more than
either 50 volts RMS (70 volts peak) for alternating current, or
ripple-free 120 volts for direct current under dry conditions."

120Vdc sounds wrong for parts that an operator can touch.

So what is the current safety standard for operator accessable
voltages?

I've had to design to IEC61010 too and my understanding is that:

any current is OK (for electrocution purposes) up to 42.4V dc or the
equivalent AC. My suspicion is that this level was chosen because there
are a lot of 24V AC power buses in industrial equipment, with a 10%
tolerance. That just happens to be 42.4V peak. Note that high currents
begin to impact choice of connectors, wire etc which must be rated by a
recognised body as fire-safe at that current.

Above that voltage you need to limit the current, OR use special
connectors which are inaccessible to standard fingers; and there are
further complications if the area is wet, etc.

I've not designed medical stuff, but I think the limit on things
attaching to (or perhaps implanted in) the body is just 6V, which gives
you an idea of how sensitive our bodies can be in the wrong conditions.
 
R

Raveninghorde

Jan 1, 1970
0
I've had to design to IEC61010 too and my understanding is that:

any current is OK (for electrocution purposes) up to 42.4V dc or the
equivalent AC. My suspicion is that this level was chosen because there
are a lot of 24V AC power buses in industrial equipment, with a 10%
tolerance. That just happens to be 42.4V peak. Note that high currents
begin to impact choice of connectors, wire etc which must be rated by a
recognised body as fire-safe at that current.

Just received the 2010 standard. For normal conditions it states 33V
rms, 46.7V peak and 70V dc.
 
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