[PSUBS-MAILIST] Motor Protection

[irox via Personal_Submersibles]

For those interested, there is a paper "Grounded vs Ungrounded Electrical Systems for Use in Manned Submersibles" by Kenneth Privitt (son of Doug Privitt, maker of Nekton and Delta submersibles): 
https://www.privitt.com/mydocs/MTS_Journal.pdf

He makes the case that if a sub's electrical system 50v or less than it is okay to use a grounded system. 



-----Original Message-----
From: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: May 21, 2024 8:37 AM
To: <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] Motor Protection

Use a resettable breaker and not a fuse wherever possible. Protecting any single equipment circuit demands a single breaker which may be anywhere in the circuit, as you don't have a "live" side and a "grounded" side on the equipment. On a submarine, your hull / chassis / earth connection(s) should not be referenced to the battery negative (as is the case with automotive systems), but rather should float. A short circuit failure within a piece of equipment that produces an overcurrent but does not also create a ground fault should trip that breaker regardless of position.

Ground faults (continuity between the hull and either battery terminal) are a separate matter, and need to be monitored for and acted on independently of any individual circuit overcurrent fault. A failure within a piece of equipment which does also create a ground fault could conceivably do so from either side. A short circuit failure through the equipment circuit which produces an overcurrent should be interrupted by the equipment's own breaker. A failure which simply creates a ground fault at the equipment should not produce an overcurrent since there is (ideally) no return path to the battery (unless you have two simultaneous ground faults to opposite battery terminals that act to create a circuit). Any such ground fault must be detected so that you can act to isolate it.

If you do happen to have a short circuit through a ground fault because a return path to the battery exists for whatever reason, that overcurrent should ultimately be interrupted by the breakers / fuses protecting the battery (one device at each battery terminal).

Sean




-------- Original Message --------
On May 21, 2024, 05:14, Jon Wallace via Personal_Submersibles < personal_submersibles at psubs.org> wrote:
Hey gang, I'm curious what the general consensus is regarding fuse/breaker protection on both pos/neg legs of the propulsion motor or if protection on just the positive side is enough.
 
Jon



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