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Post by Boaty on Sept 7, 2019 12:56:19 GMT
Looking at the 240 volt supply on my narrowboat the wiring, starting at the incoming power, is as below: 1) Plug for incoming lead from power source 2) Consumer unit 3) Plugs internal to boat 4) Final plug which earths to the hull.
Thus the earth is at at the end of the run. Is this ok and if I were to fit a galvanic isolator where would be the best place? The easiest place is beyond the final plug in the run. Alternatively I could just go for a plug and go isolator.
Thanks
Colin
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Post by Gone on Sept 7, 2019 13:07:19 GMT
Looking at the 240 volt supply on my narrowboat the wiring, starting at the incoming power, is as below: 1) Plug for incoming lead from power source 2) Consumer unit 3) Plugs internal to boat 4) Final plug which earths to the hull. Thus the earth is at at the end of the run. Is this ok and if I were to fit a galvanic isolator where would be the best place? The easiest place is beyond the final plug in the run. Alternatively I could just go for a plug and go isolator. Thanks Colin The galvanic isolator (gi) goes before the consumer unit (cu). The gi works by putting a few diodes in the earth cable, so the boat Earth is connected to the shore earth via the diodes. You can get permanently wired units, or ones that plug-in. ideally you should get one that complies with ABYC spec, though they do cost more than ones that don’t - that is because it will survive a worst case boat fault.
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Post by Telemachus on Sept 7, 2019 14:09:06 GMT
Looking at the 240 volt supply on my narrowboat the wiring, starting at the incoming power, is as below: 1) Plug for incoming lead from power source 2) Consumer unit 3) Plugs internal to boat 4) Final plug which earths to the hull. Thus the earth is at at the end of the run. Is this ok and if I were to fit a galvanic isolator where would be the best place? The easiest place is beyond the final plug in the run. Alternatively I could just go for a plug and go isolator. Thanks Colin What you are proposing, with the GI after the last plug, would work. However it is not normal practice and risks some future work or even plugging something with an earthed metal case touching the hull, bridging the GI rendering it useless. Normal practice has the GI in the earth wire between shore socket and CU. The hull bonding wire should go from CU earth to hull.
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Post by Boaty on Sept 7, 2019 14:17:08 GMT
Thanks. Yes the position of the isolator between shore socket and cu is how I understood it. I guess my question therefore is - does the fact that the earth to hull is at the end off the run make any difference or do I need to change it, which is not as straight forward as it seems?
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Post by Gone on Sept 7, 2019 14:43:44 GMT
Thanks. Yes the position of the isolator between shore socket and cu is how I understood it. I guess my question therefore is - does the fact that the earth to hull is at the end off the run make any difference or do I need to change it, which is not as straight forward as it seems? From an effectiveness viewpoint, it doesn’t matter where the earth point starts from, but it should end up on the hull AND close to the dc negative earth point. Added - having AC & DC hull bonding wires being on separate studs but close together is a ‘new build’ requirement, but from memory is not a bss requirement. I might look up the bss private boat checklist later. Now it is conventional to bond the earth bus bar in the cu to the hull. There is good reason for this, and that is anyone working on the system would expect to find it there, putting it where it is not easily seen makes future working more difficult - but not for you, as you would know. There is also a risk that a future owner may just assume the earth bond is missing and add one, this then gives two earth points with a risk of galvanic corrosion. So would I do it conventionally, but if difficult you could put a diagram inside the CU showing the earth bonding arrangement.
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