An aside related to delayed fuses.
Two issues with the subject came up when I was an intern a few decades ago.
The fuses were used in ELV circuits so could be touched in application. In
use, they got too hot to touch, so said the safety folks. Tasked with finding
a lower touch temp fuse to use. Samples from every vendor and some never heard
of. Found one, half the resistance, and temp. But unknown source so lots of
testing to evaluate performance.
Then found that the in-rush current at each turn-on affected the delay
mechanics. The fuse used a little solder cup and spring to make connects, and
each in-rush caused a slight slip. 5-10 turn on's and it would open. Power
supply engineers found a way to limit in-rush current to avoid the condition.
Saw this in-rush issue over and over in the following decades.
Bill Owsley
EMC First LLC
On Wednesday, March 2, 2022, 05:44:09 PM EST, Douglas E Powell
<[email protected]> wrote:
Very nice, thanks.
Now I may need to convince my client to stop using Slow Blow on international
shipments.
-Doug
Laporte, Colorado USA
LinkedIn
(UTC -07:00) Mountain Time (US-MST)
On Wed, Mar 2, 2022 at 3:34 PM Scott Aldous
<[email protected]> wrote:
Hi Doug,
As the link Rich provided from Littelfuse indicates, the international symbols
come from IEC 60127-1. See the last page of this preview, section 6.1.
On Wed, Mar 2, 2022 at 2:22 PM Richard Nute <[email protected]> wrote:
Here is some info:
https://www.swe-check.com.au/pages/learn_fuse_markings.php
https://www.littelfuse.com/~/media/files/littelfuse/technical-resources/documents/reference-documents/littelfuse_5x20mm-iec-fuse-cap-marking_guide.pdf
Rich
From: Brian Kunde <[email protected]>
Sent: Wednesday, March 2, 2022 1:08 PM
To: [email protected]
Subject: Re: [PSES] Fuse designations
I do not know where the information I have originally came from, but I got this
and have been using this for over 30 years:
FF = Very Fast Acting
F = Fast Acting (Common)
M = Medium Time Lag
T = Time Lag (Common)
TT = Long Time Lag
I got this from Bud Lang who was our Safety Guru at Heath Kit many years ago.
The Other Brian
On Tue, Mar 1, 2022 at 5:33 PM Douglas E Powell <[email protected]> wrote:
All,
Over the years, I've seen various ways people include a caution or warning, in
their user documents or product labels, for replacement fuses. Similar to:
"replace only with same type and rating of fuse"; followed by a code:
T1.6AH250V. And for those who may not understand the code, they may sometimes
add in parentheses some variant of "(1.6 Amp time-lag, ~250V, high breaking
capacity)".
So now to my question, US manufacturers sometimes use the phrase "SLO-BLO" or
"Slow Blow" instead of Time-Lag or Time-Delay. Are these terms commonly used
internationally and if so, are they clearly understood?
I took some time to look up SLO-BLO and found it's a registered trademark for
Littelfuse going back to 1957, and it has been continuously renewed since that
time.
Incidentally, a German Engineer once told me the way he would designate a fuse
type for a variety of tripping characteristics was in this order from very slow
to very fast: TT1.0A250V, T1.0A250V, 1.0A250V, F1.0A250V, FF1.0A250V.
Thanks, -Doug
Douglas E Powell
Laporte, Colorado USA
(UTC -07:00) Mountain Time (US-MST)
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