There are times where products can not afford a 14c fuse but they can
afford the consequence of that fuse not being there even less. If there
is a product safety issue and someone is hurt as a consequence, can you
defend your decision with a less than friendly lawyer grilling you? As
much as we all hate product liability lawyers, sometimes their threat
makes us think through the consequences of our decisions.
Looking strictly from a product liability standpoint, by putting a
fusible link, you are acknowledging that you believe that a safety
device is needed. Then you go ahead and put in something really
inadequate -- you just lost the case. If it can be shown that you put
in something that you knew (or ought to have known) to be inadequate
just to save money, you are looking at punitive damages. If you do not
put a fuse, you can have the position that a safety device was not
necessary (provided that that is a reasonable decision based on the big
picture of the design). You now have a position where you can at least
make a stand, though if someone has already been hurt, you are starting
from a bad position.
If you really can not afford a real fuse, then design the product
without one. A feel good "fusible link on the PCB" that will blow at
some unknown current after an unknown time, with the unknowns depending
upon the batch of boards and the manufacturing process, does you no good.
Regards,
Hamid
Butcher, Bob wrote:
Thanks for the reference, that is just what I needed. I am pushing for a
real fuse, but may be forced to add a fusible link to the PCB due to the
excessive cost of a 14 cent surface mount fuse!
Bob
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Brad Velander
Sent: Friday, November 04, 2005 10:48 AM
To: Protel EDA Discussion List
Subject: RE: [PEDA] How do I design a fusible link into a PCB?
Bob,
If you have not already found it, check out WWW.ULTRACAD.COM
Doug Brooks has studied and written several articles on this
subject. >From my own personal experience many many years ago, the
fusible link is not very reliable. It is only good as an absolute
disaster stopping link that may blow at 3 amps or may not blow until you
reach 10 amps (we were trying to make it a 3 amp link). It may hang in
there for 3 minutes at 8 amps as well. So don't expect any fine
tunability, too many variables and variances for great accuracy.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
#14 - 1925 Kirschner Road,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Butcher, Bob [mailto:[EMAIL PROTECTED]
Sent: Friday, November 04, 2005 9:30 AM
To: [email protected]
Subject: [PEDA] How do I design a fusible link into a PCB?
I want to add a narrow circuit trace to a PCB design to act as a fuse.
It should operate with 1 Amp of current continuously and open if the
current exceeds a higher value (2-5 Amp). This project is very cost
sensitive and a 15 cent fuse may be too much. I have the guidelines for
conductor heating vs cross section, and it appears the conductor would
need to be less than 10 mils wide on a 1 Oz copper board. Does anyone
have experience with this subject?
Bob Butcher
[EMAIL PROTECTED]
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