Possibly magical negative feed

[funkfunk]

Ahoy,

I am continuing a phase of "figuring out what multiple generations of owners (with very little understanding of dc electrics) have done on top of a 1980s electrical system".

This is a friends boat and the wiring is a nightmare that I'm slowly bypassing and/or tracing and figuring-out to a point that a) my head doesn't explode b) the boat doesn't burn down c) electrical systems work correctly.

Ive just accompanied this friend on a passage and had the joy (sarcastically) of seeing the lights flicker with the autopilot and to hear the watermaker vary it's pump sound based on similar overloading or voltage dropping that is going on.

All of these devices and more are wired into a 1980s Marinetic panel. A wee glance tells me the positive feed is far too small-a-gauge, I've run all the loads through a calculator and with the 12ft round trip have come out with an advisable 4AWG wire size (currently its a 10AWG). All good, easy fix. However when I look at the negative 'busbars?' (not sure if that really sums them up, they're more like terminal blocks with joiners all the way down), but on the two in the (unfortunately bad) photos I've attached, one of them being very main indeed, I cannot trace any main feed back to the main negative busbar at the shunt.

The two photographed negative joint-terminal blocks are not joined together either (they should be!), however the devices connected to them are all working, not as well as they should, but as if by magic. I would love to rewire the entire boat and therein remove wall and cabinet panels that are hiding and obstructing a lot of the tangle of wiring that may explain how these devices are getting back to base, but alas I am not authorised to (yet!).

My only guess is that there is a connection to the engine negative (or ground?) somewhere that is linked to these joint-terminal blocks that is completing the circuit (substandardly), although that doesn't explain the mystery of the smaller block which is only connected to devices (except that some of those are radios with ground connections perhaps). My mind wants to explode thinking about the implications.

What I want to do to get the systems running correctly is to run correct gauge positive and negative feeds (there is an appropriate fuse for the main positive line in the cabinet). I would run one 4AWG wire to the main negative joint-terminal block, then join the smaller one to it with 8AWG. My concern is unknown but there around ground loops or something that could go awry if I do this and there is already a negative feed in somewhere I cant see.

I hope this is somewhat readable and appeal to the hive mind as to thoughts and yay or nay on the caution and action to run these main power feeds.

Many thanks in advance,

Jordan

[JoeRobertJr]

Hi, Funkfunk,

I feel your pain. Sometimes, you just want to rip it all out and start over. I was repairing faulty engine control wiring early this year, and ended up doing just that - a complete rewire. But for the main breaker panel, I have been cleaning it up incrementally as I work on individual circuits.

If I digested your description correctly, I think you want to know if there is a risk in connecting the two ground terminal blocks together. Your goal is to improve the current carrying capacity of the ground wiring. I understand your concern to be that the smaller terminal block does not have an obvious connection to ground.

One step to take before connecting them, is to take voltage readings across those two ground terminals with various loads on and off. If the difference is always small (under one volt), that confirms your suspicion that you are dealing with just an inadequate ground. If you get a large difference, maybe that small ground terminal is not actually a ground terminal after all.

You mentioned a concern about creating a ground loop, by which I think you mean having your new connection in parallel with some hidden connection. That is not a problem, as long as these two terminal blocks really are both intended to be ground terminals.

Best wishes with your friend's boat!

[funkfunk]

Howdy JoeRobertJr,

Thanks for the reply and the empathy! I have reread my original post and have realised there are some ramblings which made my question more difficult to understand than it already was. You have done well to digest what you have, cheers!

Just to clarify a bit;

I'm coming from an electrical background of off-grid DC in van conversions, I appreciate the ABYC standards and use those in the jobs I do. Getting an opportunity to work on a boat was cool (until I discovered a snake's honeymoon and worse), but I realised there are some foundational differences between automotive and marine 'grounding'.
From what I understand in this monohull I'm working on, there's a bug chunk of copper in the keel that certain ground points are connected to (via distribution methods I haven't seen, guessing for AC or perhaps the motor..?), and that (in the case of this boat at least), most or all of the DC circuits are generally grounded back to the negative terminal of the battery or not at all, i.e just positive and negative. There is an extra circuit of 'galvonic isolation', which I gather is used on metal housings of seacocks and device chassis or suchlike which contact the water..(?), I'm not entirely sure but don't think this circuit will be affecting any DC circuits I'm working on. Please correct me if I'm wrong or muddled about any of that.

So my main question is less around the risk of joining the two negative terminal blocks together (although I will double check with multimeter as youve suggested, cheers!), it is more that I have to assume that these terminal blocks are getting back to the negative post on the battery somehow, both of them in a way I can't see (although the smaller one is easier to trace wires from). From the performance of the circuits being powered I can see there is voltage drop due to incorrect wire gauge somewhere (and overloaded circuits), although I really should get the multimeter on each one of those circuits to see just how much. Because these circuits performance interacts with each other, I can assume (and observe) their common power feed is the first point to address.

From your reply do I understand that adding a second (let's assume) negative feed from the main negative busbar (which is indeed obvious, correctly wired and located close to the battery) to these (post-confirmation) negative terminal blocks won't likely cause any issue? Indeed that would be a parallel connection to negative.. Im definitely tempted to try!

An interim concern is if indeed these circuits are all being jammed through far-too-small a wire through their common power supply, wouldn't that create quite a risk of heat and therefore fire? The fuse for the main positive feed into the cabinet is 100A and far too large to protect the 10AWG wire from the combined loads on the other side.. eek.

Many thanks

[funkfunk]

p.s. apologies for the spelling errors, (autocorrect) I'm typing laboriously on a touchscreen. On this touchscreen device I also don't seem to be able to find the 'edit' button for my posts.

Cheers

[funkfunk]

Update:
Have tested various circuits with various loads across those negative terminal blocks and indeed both are showing similar voltage with a matter of 0.04 volts of difference at a maximum.

So this does confirm that both terminal blocks are negative and I haven't got much to lose hooking them up with some appropriately gauged wire even if it's in parallel to an existing inadequately gauged connection to negative?

Cheers,

Jordan

[JoeRobertJr]

I'd be comfortable connecting those two terminal strips directly.