Engine block as ground bus?

[Ddog]

I’m upgrading my DC system and am wondering if I should gather all my grounds into a proper bus. The existing system has all grounds (11or so) attached to bolts on the engine block, then one cable to the start battery and one to the house. It’s worked fine forever but is there a downside I’m not aware of?

 

[rslifkin]

Using the block as ground is fine. Or you could run them to a bus and then a single cable to the block. I'd go for whatever gives the best cable layout and shortest runs.

 

[rgano]

To have all the grounds labeled and co-located on a single buss with single cable to the engine's mass would satisfy my organized mind.

 

[hytedin]

Though such would work, everything I e read in prep to install a new inverter and other devices indicated not using the engine for such. It certainly should be grounded and bonded, but to a central bus which everything else is individual grounded to to avoid grounding loops—including grounding your alternator separately from the engine.

I guess it depends on what electrical needs you have.

 

[C lectric]

NO. Although people do that it is NOT recommended. All grounds should be run to a proper buss to which the engine is also connected.

Doing it the other way can exacerbate any dc leaks through the engine, the shaft and the prop if a connection starts to fail.

By using a proper buss any potential leakage will be minimized.

 

[Comodave]

I would use a proper ground bus bar. Cable the engine to the bus bar. In addition to the reasons stated above there will be less vibration on the cables since most will go to the bus bar and not the engine.

 

[socalrider]

Yeah, not a great way to save $100. Go ahead and spring for a proper ground bus like this one:

https://www.amazon.com/gp/product/B000MMDL6Q/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Besides the vibration & incessant minor fluid leaks (if you have a FL120 like I do) your're bolting to steel rather than tin plated copper, so over time corrosion will create resistance at your connections. I imagine it'd be a pain connecting & re-connecting if you are tracing faults, etc. if you're turning bolts on your engine versus a nice strong bus bar.

 

[DennisB1]

The goal is to keep the voltage drops low on each connector interface. The blue seas bus blocks us a 3/8 inch stud on the larger ones and at max two cables per stud. (see prior response reference) Most marine installations use two wires rather than ground through the engine block like automotive installations. Starter motors, alternators need low resistant ground with the high amperage so us a good bus block. Clean all the connections. Use dielectric grease on all the connections and torque the nuts properly to get good clamping force. Also use the proper size cables for the amp loads and cable lengths.

 

[angus99]

The goal is to keep the voltage drops low on each connector interface. The blue seas bus blocks us a 3/8 inch stud on the larger ones and at max two cables per stud. (see prior response reference) Most marine installations use two wires rather than ground through the engine block like automotive installations. Starter motors, alternators need low resistant ground with the high amperage so us a good bus block. Clean all the connections. Use dielectric grease on all the connections and torque the nuts properly to get good clamping force. Also use the proper size cables for the amp loads and cable lengths.

Good advice but wouldn’t conductive grease on the mating surfaces of the connections be better? Dielectric is non-conductive, IIRC.

 

[DennisB1]

When you coat two cleaned metal surfaces then spread a film of dielectric grease and clamp/torque the bolts and squeeze the parts together you form a low resistant bond path. The surface make direct contact metal to metal contact as the grease flows outward during the squeezing process. The grease provides a long term seal and maintains the low resistant path preventing moisture and contaminants to cause surface corrosion which would start increasing electrical resistant which is bad. So the dielectric is the correct material. You are not using the grease as a conductor only the direct metal to metal contact.

 

[catalinajack]

The same would be accomplished, even better, with Kopr Kote.

When you coat two cleaned metal surfaces then spread a film of dielectric grease and clamp/torque the bolts and squeeze the parts together you form a low resistant bond path. The surface make direct contact metal to metal contact as the grease flows outward during the squeezing process. The grease provides a long term seal and maintains the low resistant path preventing moisture and contaminants to cause surface corrosion which would start increasing electrical resistant which is bad. So the dielectric is the correct material. You are not using the grease as a conductor only the direct metal to metal contact.

 

[psneeld]

From an expert n the field about corrosion protection...


"The best material to prevent corrosion in a busbar application is a conductive grease, something like Parker Pro-shield. On a busbar there is no potential problem with corrosion products creating electrical leaks or shorts between the terminals.

Dielectric or insulating grease should be reserved for pin or blade type plugs/sockets that are removable. Those type connectors usually have blades or pins that are close together and where corrosion products might cause electrical leakage or shorting between conductors."