<html><head></head><body><p dir="ltr">Perhaps I misunderstand. Chassis continuity to hull is a good thing. You just don't want to tie your power supply common (battery negative) to it.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On June 29, 2015 7:56:32 AM MDT, James Frankland via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div dir="ltr"><div>Hi sean,</div><div><br />The battery negative is NOT connected to the hull. Only the chassis of this new item.</div><div> </div><div>But thinking about it, I suppose it does create a permanent connection to the negative terminal. The negative wire on the compressor is connected to the negative bus on the boat, which is creating a permanent connection to the hull via the mounting bracket. </div><div> </div><div>Damn, i'll have to insulate it somehow, before Sat.</div><div> </div><div>Regards</div><div>James</div></div><div class="gmail_extra"><br /><div class="gmail_quote">On 29 June 2015 at 14:46, Sean T. Stevenson via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>></span> wrote:<br /><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><p dir="ltr">Your electrical system should not be negative
grounded, meaning that the battery negative should not be common with the hull / chassis as it would be in an automotive system, for example. The reason for this is in part to do with galvanic corrosion, since this avoids regular currents and nonzero potentials through structural elements, and in part to do with arc safety, since a single fault or operator error which connects either battery potential to the chassis will not produce a short circuit current through the battery in this case. That said, SAFETY grounds, which include AC ground and most chassis ground and cable shield connections which are confirmed not in common with the supply DC negative, should indeed be connected through the hull (either locally or through a dedicated ground point) in order to serve their intended function: providing a short path to earth-ground potential in the event of a fault that might otherwise energize
equipment / chasses that could be hazardous to personnel, and serving as a connection to an "infinite" charge sink to reference cable shields to for effective noise rejection.</p>
<p dir="ltr">A negative connected chassis on a DC powered compressor can be accommodated, as you surmised, by isolating that chassis from the hull, and additionally should be isolated from the operator / cabin (via enclosure?), because the chassis in that case does not represent the safety ground potential, and is thus akin to a large bare conductor at the battery negative potential. Alternatively, you could look at modifying the unit to break the negative-chassis connection, running that negative to the battery and grounding the chassis.</p>
<p dir="ltr">Sean</p>
<br /><br /><div class="gmail_quote"><div><div class="h5">On June 29, 2015 6:48:15 AM MDT, James Frankland via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>> wrote:</div></div><blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid"><div><div class="h5">
<div dir="ltr"><div>Hi All,</div><div> </div><div>Ive made a real point of making sure that nothing at all is electrically connected to the hull of my boat. Everything is wired to and from the battery and insulated from the hull.</div><div> </div><div>However, ive recently fitted a new item, a Cornelius compressor which Hank gave me. Ive realised that the negative terminal on the unit is the chassis of the compressor, which is bolted to brackets on the hull, so its actually connected to the hull of the boat as well. </div><div> </div><div>The hull of the boat is not connected to the negative battery terminal.</div><div> </div><div>I don't think there is an issue there with galvanic corrosion, but im not sure.</div><div><br />I could insulate the compressor from the mounting bracket and hence insulate it from the hull, but it will be a bloody pain and im diving this weekend so don't really want to start changing it now.</div><div> </div><div>Thanks<br
/>James</div><div> </div></div>
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