"AC Inductive Load PF"

[Andre Majorel]

Saw this in the specs of a momentary switch :

Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?

--
André Majorel <URL:http://www.teaser.fr/~amajorel/>
"After 15 minutes, I wanted to marry her. After a half hour, I completely
gave up the idea of snatching her purse." -- _Take the Money and Run_

 

[Lostgallifreyan]

Andre Majorel <cheney@halliburton.com> wrote in
news:slrngkc9o1.445.cheney@atc5.vermine.org:

Saw this in the specs of a momentary switch :

Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?

PF might be power factor. Not sure about L/R.

 

[Lostgallifreyan]

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9B7565A9E6395zoodlewurdle@216.196.109.145:

Andre Majorel <cheney@halliburton.com> wrote in
news:slrngkc9o1.445.cheney@atc5.vermine.org:

Saw this in the specs of a momentary switch :

Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?


PF might be power factor. Not sure about L/R.

A bit of Gooling suggests that L/R is just inductance over resistance, in
analysis of the inductive load the switch is meant to be used for.

 

[Peter Dettmann]

On Mon, 15 Dec 2008 04:08:13 -0600, Lostgallifreyan
<no-one@nowhere.net> wrote:

Lostgallifreyan <no-one@nowhere.net> wrote in
news:Xns9B7565A9E6395zoodlewurdle@216.196.109.145:

Andre Majorel <cheney@halliburton.com> wrote in
news:slrngkc9o1.445.cheney@atc5.vermine.org:

Saw this in the specs of a momentary switch :
Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?

PF might be power factor. Not sure about L/R.

A bit of Gooling suggests that L/R is just inductance over resistance, in
analysis of the inductive load the switch is meant to be used for.

That is exactly right, as consider a dc suppy to an inductive relay
coil, the operating switch has to be able (reliably) to break the coil
current. But being inductive, there is a much greater amount of
arcing at the switch contacts. So a contact, or switch must be rated
for its voltage, current carrying capacity, and its load breaking
ability (especially when there is inductance in a DC circuit).
And of course, the greater the L/R ratio, and higher voltages, then
greater arcing will occur, to the extent that the contact nay not be
able to break the arc at all if it does not have an adequate rating.

Peter

 

[Eeyore]

Peter Dettmann wrote:

Lostgallifreyan <no-one@nowhere.net> wrote:
Lostgallifreyan <no-one@nowhere.net> wrote
Andre Majorel <cheney@halliburton.com> wrote

Saw this in the specs of a momentary switch :
Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?

PF might be power factor.

Yup.

Not sure about L/R.

A bit of Gooling suggests that L/R is just inductance over resistance, in
analysis of the inductive load the switch is meant to be used for.

That is exactly right, as consider a dc suppy to an inductive relay
coil, the operating switch has to be able (reliably) to break the coil
current. But being inductive, there is a much greater amount of
arcing at the switch contacts. So a contact, or switch must be rated
for its voltage, current carrying capacity, and its load breaking
ability (especially when there is inductance in a DC circuit).
And of course, the greater the L/R ratio, and higher voltages, then
greater arcing will occur, to the extent that the contact nay not be
able to break the arc at all if it does not have an adequate rating.

Nice to see it so well explained. I've never seen L/R specified before but I'm
not into heavy power where it's likely a more significant issue.

Graham

 

[Lostgallifreyan]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote in
news:4946DA1A.5EBACE58@hotmail.com:

Nice to see it so well explained. I've never seen L/R specified before
but I'm not into heavy power where it's likely a more significant issue.

Actually, you might. You're into audio amps, right? Toroidal transformers
are a classic switched inductive load. The main reason it's not much of an
issue is that it's cheap to overspecify a switch on that scale. Or more
likely, easy to just do what others have done. Which is not easy if you're
switching a new design of industrial motor...

I liked that explanation too. Helps to clarify it. Closest I knew of this
before is that a coil of thin wire won't arc so bad because its own
resistance is a strong factor in what happens when the circuit is broken. But
large amplifiers have windings just heavy enough to be important to consider.
Though a few tests of a real switch are as good a way to find out as
calculations, maybe. If a 1A current switches with a crack like a 10A current
I'll use a 10A switch.

 

[Jamie]

Andre Majorel wrote:

Saw this in the specs of a momentary switch :

Note: AC Inductive Load PF = 0.6 - 0.7
DC Inductive Load L/R = 7 msec

I suppose I should be ashamed, but... Someone care to tell me
what "PF" and "L/R" mean here ?

Power Factor?

http://webpages.charter.net/jamie_5"