SACRIFICIAL ANODE as GROUNDING connection - A good idea? | Ask The Expert with NIGEL CALDER
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- Опубликовано: 25 июл 2024
- Nigel and Jan clarify the difference between a grounding system and sacrificial anodes and explain why you commonly still need both.
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If you have a question for Nigel and Jan, post it in the comments and with a bit of luck we will discuss it in one of our next videos.
If I would put magnesium and zink anodes on the car, does the car have to be grounded?
Thank you so much. I have another question regarding to aluminium hull, particularly about lightning protection. Thank you again.
I have checked for voltage on my engine block and it’s reading .891 DC volts. What could be causing this voltage? The block is bonded to zinc plate.
Great views, great help will need to visit your web site ...
Thank you
I have read everything I can find about sailboat electrical grounding - and still find myself disagreeing with the conventional wisdom illustrated in the diagram at 1:04 - whereby all systems share a common ground connection.
On my boat I am adopting the following design, which I believe is sound.
[A] When lightning strikes I do not want that electrical charge getting into the AC or DC systems (zapping the LFP BMS or destroying other electronics). Thus I have my mast grounded to the lead keel (to dissipate to the water body); and the shrouds connected to air terminals on each side of the hull (to dissipate to the water surface). No connection to a common ground bus.
[B] When there is an AC fault I do not want AC current going to the water (electrocution of swimmer!) or zapping the negative side of the DC system. Thus I rely on a common AC ground going back to both AC sources - inverter and shore power (via galvanic isolator). No connection to a common ground bus. I am still looking for a way to test the integrity of the AC ground on a marina pedestal, before connecting the boat...
[C] What if there is a DC fault with the inverter? Install an inverter with a plastic case. Rely on the fuse on the POS battery terminal and a breaker on the positive supply cable. No separate ground connection to the DC bus.
[D] I have everything I want protected from galvanic corrosion (DC negative system, the engine, fuel tank, prop strut) electrically connected to the prop shaft with its pair of zinc anodes. I separately protect the steering system (SS rudder shaft, aluminium drive wheel, SS cables, aluminium pedestal) with another pair of zinc anodes.
[E] Through-hulls (bronze) are isolated. I assume that the copper powder in the anti-foulfing paint is not proving an electrical path. To mitigate that risk the bronze through-hulls are painted with epoxy barrier that extends past the antifouling paint (so the paint has no electrical path to the bronze).
During your reading, have you come across the ABYC and ISO standards? Those are based on the experience and thoughts of hundreds of experts over multiple decades. There are very good reasons, why you should have a common ground on a boat. We explain them in a lot of details in our Advanced Marine Electrics course in the modules on Grounding, AC, and Lighting Protection.
- Jan
The AC is grounded to the water because of shore power the source of which is itself referenced to some nearby dirt. If your ground fails then a secondary path is achieved through the water which is what electrocutes swimmers. The engine is typically used as a common ground point for AC and it is also typically a DC ground for at least your starting battery. If you do not ever connect to shore power or use an isolation transformer when you do then grounding AC to the water provides no additional protection from AC faults because the path back no longer exists. DC power is always relative to the DC negative (ground) and it serves no purpose whatsoever to reference it to the water but it is difficult to avoid unless you have no engine.
With your setup add a ELCI (GFCI for boats) on the shore power side and call lit a day. The galvanic isolator is one way protecting your boat from incoming current but will not protect swimmers. The ELCI does that when connected to shore power. Consider lightning protection separately. There are many factors there and I don't think there is any silver bullet.