When to use Fuse or Auto Reset breaker
Submitted: Wednesday, May 25, 2011 at 09:53
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KenInPerth
Hi all
Pondering issues as I do, I was thinking about "when should you use a fuse and when should you use an auto reset (thermal) breaker".
I am assuming there are some "best practices" that apply to the use of one over the other.
My assumptions are:
1. if the circuit had the chance of developing a hard fault (say something cuts into a cable) then you would want a fuse to blow and that would be the end of it - especially if this is a take off direct from the battey.
2. if the circuit is a high current circuit that could have transient overload (say a winch jamming) then the auto reset breaker would be the choice there??
As always I look forward to your responses.
Ken
Reply By: Member Al (Sunshine Coast) - Thursday, May 26, 2011 at 11:29
Thursday, May 26, 2011 at 11:29
Hi Ken,
The reason for any protection, fuse or circuit breaker, is to disconnect a circuit where the current is exceeding a safe value and so avoid further damage and possibly fire. The application of an automatically resettable circuit breaker is normally restricted (in industry and domestic applications) to incorporation within appliances where an overload, as distinct from a fault, may occur. This may for example be a portable tool or battery charger. It is not a good idea to use auto-resettable protection with unsupervised loads as the repeated re-application of the supply may cause further damage than the original fault.
I would consider it best to be made aware of a fault by a blown fuse or opened manually-resettable circuit breaker than to have an auto-resettable breaker continue to repeatably apply power until the battery was flat or something worse occurs.
My preference is for manually resettable breakers where the circuit is rated above 10 Amps and appropriate fuses where the circuit is rated below 10 Amps.
I am not at all sure about protection for
winches where the current is up to several hundred Amps. A circuit breaker capable of this would be very expensive and of questionable protective value. Some
winches may incorporate protection by means of internal thermal sensing which controls the contactor (solenoid) but otherwise it is left to the operator to judge if the motor is reaching its temperature limit. A fusible link (really just a high-rated fuse) could be used in the winch supply cable to protect against a short-circuit but may
well not discriminate between maximum winch current and a short-circuit. I would prefer a manual isolator installed at the battery to be closed only when actually using the winch. This has distinct advantages against catastrophic short circuit and possible fire in the event of a front-end collision.
AnswerID:
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Follow Up By: KenInPerth - Thursday, May 26, 2011 at 11:57
Thursday, May 26, 2011 at 11:57
Great info and explanation.
As you say, and when I was thinking about using auto reset breakers, I started to come to the conclusion that they would not be very good if there is a hard fault "downstream" and it kept re-applying the power. Worst case would come to a fire somewhere in the vehicle.
The Winch was probably a bad example from me but I will heed your points about isolation of such high current stuff.
Ken
FollowupID:
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Follow Up By: Member Al (Sunshine Coast) - Thursday, May 26, 2011 at 13:01
Thursday, May 26, 2011 at 13:01
No Ken, I think your raising the issue of winch protection was good and useful.
I don't want to get too deeply into engineering detail but overload or even short-circuit protection can be difficult with high-current circuits on very low voltage (12V) supplies. Which is why vehicle manufacturers do not protect starter motor circuits.
Mind you, some offered isolators may not serve the requirement. A winch isolator needs to be capable of continuously handling 200 to 500 amps. The "Key Switches" on offer usually do not meet this. Jaycar advertise a "500A" switch but the fine print says "120A continuous" and Supercheap advertise a "1000A switch" with a fine print of only 100A continuous! Probably neither of these would reliably serve winch duty.
Probably the "screw-down" variety of isolator where a knob screws-down a
bridge onto a contact surface would be best. (Illustration below) However even here quality would be an issue.
Image Could Not Be Found
I should point out that not having a winch, I have not tested such winch isolators so my comments are based on engineering theory only. It would be good to hear from those with experience in this.
FollowupID:
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Reply By: snoopyone - Friday, May 27, 2011 at 22:21
Friday, May 27, 2011 at 22:21
Heres what Tekonsha say about the Overload indicator on a Prodigy.
Attention: Technical Support
From:
Subject: Prodigy error codes
When a Prodigy comes up with an Overload code o.L What would cause this please as the manual doesnt give any indicaton. Thanks
Thank you for contacting Technical Support. In response to your email, the OL code is present mainly because there is a problem somewhere along the electric brake wire. I would inspect the trailer wiring looking for broken wires, or spots where wires could have wore through as
well as inspecting brake magnets for possible failure. If you have any questions or need further assistance feel free to write back or contact us at (888) 785-5832.
Technical Service Agent
Cequent Performance Products, Electrical Division
101 Spires Parkway
Tekonsha, MI. 49092
(888) 521-0510
Monday-Friday 8:00 AM-4:30 PM Eastern Time
From: TekonshaWebsite@tekonsha.com [mailto:TekonshaWebsite@tekonsha.com]
Sent: Thursday, May 26, 2011 2:45 AM
To: Tech Support
Subject: Tekonsha® Website : Contact Form Message (Technical Support)
The following message has been sent from the Tekonsha® website:
AnswerID:
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