[PSUBS-MAILIST] grounding question

Mon Dec 9 00:34:23 EST 2013

Actually, the isolated system's handy dandiest attribute is its inability to electrocute the owner/operator. Low voltage is less an issue for that. The Nektons are all grounded systems, for instance (24 or 48 volt), and ABS certified. But you wouldn't get any one of those subs certified today. Beyond that, and once you step up to 120 or 240 volts, then you are pretty much holding the reins on a potential DC welding machine. You don't want to turn it into an electric chair. Thus all my soap boxing on fuses and isolation capabilities in the little subs.

And of course Alec is quite right about corrosion and so on. You want to control high resistance shorts to ground in any case, and they are lots easier to track when they don't exist at all under ordinary circumstances (that is if your popped fuse isn't clue enough to track the problem).

Under normal ops, anodes will serve admirably in the protection of dissimilar metals. Additionally, anodes serve as a pretty good indicator of the general health of your electrical system. If you have buzzy little shorts, the anodes will turn to sponge on you in short order. See that, get the multimeter out and plan on a long night.

As to the risk of fire, I suspect that's as much about proper assembly and maintenance as anything else, but Sean is absolutely right about the risk of arcing. I've had two fires while diving, both on isolated systems (and both isolatable systems, luckily). What you don't want is cheap connectors or crappy installation or unfused/unbreakered circuits, or false grounds where you might get those magic blue electron streams zapping back and/ or forth. The mathematics for that unhappy occasion are simple. High 02 atmosphere + electrical arcing = Bad juju.

Vance

-----Original Message-----
From: brian <brian at ojaivalleybeefarm.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Mon, Dec 9, 2013 12:04 am
Subject: Re: [PSUBS-MAILIST] grounding question

Seems like you would be grounding your hull anyway if you're running a propeller shaft from the motor through a thru hull to the outside ;   Unless the motor housing is electrically insulated from any part of the motor  

-----Original Message-----
From: "Alec Smyth" <alecsmyth at gmail.com>
Sent 12/8/2013 8:02:59 PM
To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] grounding question

Yep, the K boats are just like any others in this regard... one does NOT connect either battery terminal to the hull. In addition to what Sean mentioned, I believe the main reason hulls are never grounded, not just in subs but in any metal hulled vessel, is to prevent corrosion due to stray currents. 

Best,

Alec

On Sun, Dec 8, 2013 at 10:51 PM, Sean T. Stevenson <cast55 at telus.net> wrote:

I don't know anything about the K-boats specifically, but the ABS rules specifically state that all subs are to use isolated electrical systems (battery negative not connected to hull). Safety grounds (component chasses, connector shells, cable screens, etc.) may be safety grounded to the hull, but there should be no electrical continuity between any battery or power supply terminal and the hull. The idea is that this significantly reduces the risk of electrical fire, as a loose wire contacting the hull (or any other short circuit, such as a carelessly handled wrench) - even your positive battery cable, will exhibit no potential to arc.
Sean

brian <brian at ojaivalleybeefarm.com> wrote:

Hi All,
              On the K boats where does one normally connect the ground to the sub?  

Brian

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