# RE: [SI-LIST] : Number of GND/Power pins in a connector ?

From: Bob Davis ([email protected])
Date: Tue Mar 28 2000 - 00:06:04 PST

Gents,

The 42.4V is the RMS value with a peak at 60V (42.4x1.4142). The DCvalue is
60Vdc which defined as Safety Extra-Low Voltage (SELV) under IEC 950 Clause
2.3.2 and Clause 2.3.3. As it is set there most of the world telephones are
at "48V" which is usually 50.4V (4x12.6V) nominal and 55V (4x13.75V) in a
system under charge. In most cases the Telephone system of a country is not
a hazardous voltage, which would require all the protection we must use for
the 120/240V systems up to the 600V systems. Remember the "12V" automotive
battery is really 12.6v and the automotive system charges the battery and
maintains the electrical system at 13.75V in normal use. 24V aircraft and
trucks are at 27.5V under normal conditions etc.

Try thinking about running the telephone lines in ROMEX.

This definition is for secondary circuits, isolated from the mains. Several
countries do not accept this and have local exceptions.

Cheers,

Bob Davis

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Rick Brooks
Sent: Monday, March 27, 2000 7:44 AM
To: [email protected]; Jim Leng
Subject: Re: [SI-LIST] : Number of GND/Power pins in a connector ?

Jim,
is this correct, that the highest voltage allowed under UL for SELV is
42.4V?
Also, is the wattage limit 15 watts?

- Rick

At 06:35 PM 03/24/2000 -0800, you wrote:
>>>>

In the US, the UL ELV limit is 42.4V. They used to look the other way at
telco battery voltage, but no longer,

Regards,

Steve

At 07:31 PM 3/24/2000 +0000, you wrote:

Check out your electricity safety standards! The only way you are
going to get into trouble with 48 volts is by putting it in your mouth or
some other stupid place.

Building sites use 50-0-50 volts centre tap grounded for the simple
reason that it is safe for what is one of the most hazardous places to be
working from any point of view.

Independant of country and their perceptions of risk, if a person
becomes the unwilling subject of gravity, fire, electricity, radiation, high
pressure substances let loose then the result is the same. Not a lot of
people understand this point, especially politicians.

----- Original Message -----
From: <mailto:[email protected]>Kai Keskinen
To: <mailto:'[email protected]'>'[email protected]'
Sent: 24 March 2000 18:49
Subject: RE: [SI-LIST] : Number of GND/Power pins in a connector ?

When the backplane carries nominal -48V, there is a danger of
personnel accessing what is considered a hazardous voltage in some regions.

I don't see any reason from an EMI or SI point of view for having
either male or female contacts on the backplane.

Cheers,

Kai Keskinen
Equipment and Network Interconnect
Nortel Subsystems and Performance Networks (NSPaN)
(613)-765-3506 (ESN 395)

<mailto:[email protected]>[email protected] -----Origina
l Message----- From: Nerheim, Max [SMTP:[email protected]] Sent: Friday,
March 24, 2000 1:21 PM To: '[email protected]' Subject: RE:
[SI-LIST] : Number of GND/Power pins in a connector ?

Maybe it could also be a carry-over from UL/TUV safety requirements:
If you have a male pin with power on some pins it is more susceptible to be
shorted out.

-----Original Message----- From: [email protected]
[<mailto:[email protected]>mailto:[email protected]] Sent:
Friday, March 24, 2000 9:29 AM To: '[email protected]' Subject: RE:
[SI-LIST] : Number of GND/Power pins in a connector ?

The usual reason to use male pins on the daughter card is because it
is much easier to protect the male pins with a shroud, or connector
placement on the pwb. Having male pins on the motherboard makes them very
susceptible to damage during assembly and handling. Bill Gaines Sr.
Engineer, Electronic Packaging, Aerojet, Azusa 626-812-2199 m-f 7-3:30
626-969-5772 fax [email protected] 626-849-2324 pager

> ---------- > From: Lum Wee Mei[SMTP:[email protected]] > Reply
To: [email protected] > Sent: Thursday, March 23, 2000 3:18 PM > To:
[email protected] > Subject: Re: [SI-LIST] : Number of GND/Power
pins in a connector ? > > Since we are in this question, I would like to add
one : > > Is there a preferrence to use female connector on a board? I was
told that > male connector is not prefer because the pins may acts as
antenna loops > when the board is left alone. > > Can someone enlighten me
on this subject? > Thanks. > > > > Scott McMorrow wrote: > > > Stuart, > > >
> "It depends" is the correct answer. > > > > The best way to size the
number of ground and power pins in > > a connector is to simulate the
regions on either side of the > > connector. The connector model should be
fully coupled for > > all pins including power and ground. You should grid
the ground > > and power planes around the connector edge and within the > >
grid include the decoupling capacitors. A connector swath > > should be
simulated with data transmitted in both directions > > (if bidirectional)
and driven by worst case driver edge rates into > > transmission lines which
are referenced to the non-ideal power > > and ground grid. Multiple data
patterns should be simulated > > for worst case pattern sensitivity. > > > >
These sorts of simulations will answer several questions: > > > > How much
data skew and jitter is caused by connector crosstalk, > > and return path
effects for each ground/power pattern? > > > > What happens when a signal is
referenced to a ground plane > > on one side of the connector and to a power
plane on the > > other side? > > > > How much noise is induced by data
switching into the ground and > > power grids on either side of the
connector? > > > > What is the worst case instantaneous voltage differential
> > across the ground pins on either side of the connector? > > > > What is
the worst case instantaneous voltage differential > > across the power pins
on either side of the connector? > > > > And for bonus points: > > > > If
you have accurate modeling of the power switching currents of > > the
devices on either side of the connector, you can simulate the > > worst case
connector and plane noise due to power transients > > and data switching
transients. > > > > Depending on the edge rate and the quality of the
connector you > > may find that although you need few power and ground pins
to > > facilitate clean power delivery, you may need many more power > > and
ground pins to facilited clean signal delivery. > > > > regards, > > > >
scott > > > > -- > > Scott McMorrow > > Principal Engineer > > SiQual,
Signal Quality Engineering > > 18735 SW Boones Ferry Road > > Tualatin, OR
97062-3090 > > (503) 885-1231 > >
<http://www.siqual.com>http://www.siqual.com > > > > Stuart Adams wrote: > >
> > > How do I calculate the number of ground and power > > > pins I need in
a board-to-board connector. > > > > > > The number of grounds is a function
of switching > > > current and how many signals will switch at the same > >
> time, correct ? > > > > > > More grounds is always better but what about
power pins ?? > > > > > > If one or two pins are sufficient to carry the max
steady > > > state current and my board is well bypassed with bulk and > > >
ceramic caps, is there a need for alot more power pins ? > > > > > > --
Stuart > > > > > > **** To unsubscribe from si-list or si-list-digest: send
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