Hull Earth & Negative Bonding Questions

[ditchcrawler]

1 hour ago, Morris said:

Quick update as promised.

 

 

 

Fixed earth and neutral hull bonding studs, got combi and GI wired up, got an electrician in to check everything over and... with 230V going through it the combi has a Christmassy but entirely useless flashing coloured lights function. Hmm. Should have checked this before buying the boat.  Ah well. 

So now the 230V side of things is connected up sans combi and I'm looking for a battery charger.  Victron Ip22 30A single output seems to fit the bill.  Anyone any thoughts on these?

What do you plan to power the charger with, are you going to be on a land line 24/7, in which case you don't need a very big charger at all as it only has to replace the 12 volt loads, even with a 12 volt fridge that would be maybe 50Ah per 24 hours.

[GUMPY]

I only ever use one bolt, however the 12v is on one side of the crossmember and the 230v on the other so unless a large chunk of steel detaches from the crossmember it will be ok.

[Morris]

15 minutes ago, ditchcrawler said:

What do you plan to power the charger with, are you going to be on a land line 24/7, in which case you don't need a very big charger at all as it only has to replace the 12 volt loads, even with a 12 volt fridge that would be maybe 50Ah per 24 hours.

 

Well we are currently in a marina with shore power 24/7 but we would like to get out and about in the future.  It is all very new at the moment so still working the basics out.  My thinking was that a 30A charger would offer quicker charging if we had a brief access to shore power. I'm sure a 5 amp charger would meet our needs atm, just trying to cover possible future eventualities. We don't plan on running a fridge on the 12V system, in fact recently we haven't been using the batteries at all other than for a spark for the cooker! 

[Tony Brooks]

3 minutes ago, Morris said:

My thinking was that a 30A charger would offer quicker charging if we had a brief access to shore power.

 

I would like to see your reasoning for that conclusion. Yes, assuming a well discharged battery, it will start to charge at about six times the rate of a a 5 amp charger BUT within half an hour that will be dropping and a hour later it will be even lower. Typically it will take well over 8 hours to fully recharge the domestic bank whatever power charger you employ, so with a shoreline overnight. I suppose I am taking issue with "brief access" part of your post. For that you need lithium batteries because they don't start reducing the charge soon after starting as lead acids do. I suspect the time difference to fully charged between a 15 amp and 30 amp charger is likely to be around an hour or two.

[nicknorman]

2 hours ago, Tony Brooks said:

 

Because if it is a single stud and for some reason it becomes detached from the hull while keeping the 12 & 240V earths connected a 240V fault to the earth wire would put 240V on the 12V DC negative and thus the hull.  I would agree with anyone who says that is not very likely but for the sake of another stud/nut & bolt why risk it.

I don’t think it’s anything to do with the hull. After all, in your scenario the mains earth wire was previously connected direct to the hull, now with a broken stud it is connected to the hull via the negative dc system. What is the difference?

 

IMO it is to do with the risk of getting mains voltages on the 12v system. Lots of bits of 12v equipment aren’t insulated for high voltage (or at all) and so could give a shock. Although as you say, it is fairly theoretical! But it is also written into the ISO standard and so if the worst should happen it wouldn’t look good that the standard had been ignored.

[Morris]

7 minutes ago, Tony Brooks said:

 

I would like to see your reasoning for that conclusion. Yes, assuming a well discharged battery, it will start to charge at about six times the rate of a a 5 amp charger BUT within half an hour that will be dropping and a hour later it will be even lower. Typically it will take well over 8 hours to fully recharge the domestic bank whatever power charger you employ, so with a shoreline overnight. I suppose I am taking issue with "brief access" part of your post. For that you need lithium batteries because they don't start reducing the charge soon after starting as lead acids do. I suspect the time difference to fully charged between a 15 amp and 30 amp charger is likely to be around an hour or two.

 

By brief I was meaning maybe a night or two in a marina if we had been unable to cruise for long because of weather etc.  Maybe it doesn't make much difference for our needs but is there any disadvantage in having the bigger charger when it is only £30 difference between the 15 and 30A models?  30A is still only 13.6% of our battery bank capacity so surely wont be too hard on the batteries.  

[Alan de Enfield]

45 minutes ago, nicknorman said:

I don’t think it’s anything to do with the hull. After all, in your scenario the mains earth wire was previously connected direct to the hull, now with a broken stud it is connected to the hull via the negative dc system. What is the difference?

 

IMO it is to do with the risk of getting mains voltages on the 12v system. Lots of bits of 12v equipment aren’t insulated for high voltage (or at all) and so could give a shock. Although as you say, it is fairly theoretical! But it is also written into the ISO standard and so if the worst should happen it wouldn’t look good that the standard had been ignored.

 

 

The iso Standard :

 

 

 

Appears to say that both AC and DC  should be on the same stud and as close as possble to the battery 

 

4 General requirements

4.1 The protective conductor insulation shall be green or green with a yellow stripe. Neither colour shall be used for current-carrying conductors. NOTE The equipotential bonding conductor of the d.c. electrical system (see ISO 10133) also uses green, or green with a yellow stripe, insulation and is connected to various exposed conductive parts of direct-current electrical devices, other extraneous conductive parts and the d.c. negative ground/earth.

4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as practicable to the battery (d.c.) negative terminal. NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground (protective conductor).

4.3 For craft with fully insulated d.c. systems (see ISO 10133), the a.c. protective conductor shall be connected to the hull of a metallic hull craft, the craft external ground (earth) or the craft lightning-protection ground plate, if fitted.

4.4 Metallic craft hulls shall not be used as conductors.

4.5 The protective conductor shall be connected to metallic hulls at a location above any anticipated water accumulation

Edited December 30, 2022 by Alan de Enfield