Sterling charger case earth

[Malabarista]

Hello again everybody.
After what feels like a hundred year project i have finally taken the battery bay from temporary status to fully operational. Amazingly it all seems to work. I am however stuck in analysis paralysis over one cable. It’s the case earth from the Sterling battery charger. I have it on a 35mm cable running to the common DC earth ( taken from the engine block). It makes me a little nervous as it’s the only 240VAC/12VDC interface for accidentally connecting both through earth leakage. I know ( or I think i do) that it needs to be able to handle a dc fault with high amps. Hence the 35mm cable. It also needs to be able to trip at the consumer unit on the AC circuit and so needs an earth to the “vehicle chassis”. My questions are;
Can I connect it to the anode which is only serving the ‘P’ bracket at the moment? This would mean a run of about 2m and no connection (inside the boat) to the DC circuit.
Should I just leave it where it is ( a run of about 500mm) and find something else to worry about?
I have seen a couple of installations where it is not connected at all to anything and their systems work ok.
Could anyone please help me with my indecisión?
Many thanks

 

[IanCC]

I have the same problem.

It is probably worth a call to sterling power.

 

[PaulRainbow]

Hmmm, this sounds like a mess, sorry.

First, let's be clear about "Earth" and DC negative. There is no such thing as DC "Earth".

Shore power. All circuits Earths go to a common busbar, in the consumer unit or out, doesn't matter. Incoming sore power Earth goes to a galvanic isolator. From the galvanic isolator a cable goes to the common busbar. Another cable goes from the busbar to "the water". In the case of this particular boat, that can be the anode. No other other Earth wires go to the water.

The sterling charger is wired the same as any other appliance, to the consumer unit, via a switched spur, plug and socket, MCB in the consumer unit, etc. The "normal" Earth and the case Earth both go to the common busbar. DO NOT connect separately to the water. Ignore the Sterling reference to the 12V negative being an "Earth" that's just bollox.

DC connections. Connect the positive outputs to the batteries. These usually bypass the main isolator switches, otherwise the batteries don't get charged when you leave gthe boat and turn the isolators off. Fuse at the battery end, the charger has internal fuses. The negative connection can go straight to the batteries or it can go to the negative busbar, providing the cable to the busbar is suitable rated. If a battery monitor is fitted the negative cable has to go after the shunt (load side).

Important. The heavy negative cable that goes to the engine if for the engine, starter, alternator, etc (unless it's isolated return). But whatever, it does not and must not make the engine part of a circuit. If you have a negative busbar you connect the batteries to that busbar and take all loads from there, the engine negative can come from that busbar or directly from the batteries if there is no battery monitor. If there is a battery monitor take the engine negative from the busbar, with a single cable from the domestic bank to the shunt, then the shunt to the busbar.

 

[nigel1]

Is it OK to connect the case earthing wire to the earth wire connection on the AC input side of the sterling charger?

 

[PaulRainbow]

Is it OK to connect the case earthing wire to the earth wire connection on the AC input side of the sterling charger?

Hard to see why not and even harder to see why it's not done from the factory.

 

[Malabarista]

Thanks Paul for your very detailed and informative reply. I was obviously misreading the Sterling manual. I have the GI going to the consumer box. I have the cables from the charger going to the consumer box but no cable from the box going to the water. That i will fix tomorrow. The CASE earth to dc neg was giving me the jitters and it was correct to do so. The negative ( not earth my bad) busbar goes to the neg terminal on the battery ( via the shunt) and the thick engine neg comes to that busbar ( not through the shunt). I had been reading about the possibility of a dc fault occurring within a ( not sterling) charger and the smaller gauge 240v ac earth cable being asked to carry a dc current which it can’t. So i will just jump the case earth round the corner back into the earth terminal on the sterling. Thanks for being around to ask.
Dave

 

[IanCC]

Interesting that Calder says ABYC requires battery charger case be connected to both AC and DC grounding systems.
Also interesting he goes on at length as to why the connection between the AC and DC grounding circuits should never be cut.

I must emphasise i am a novice and have no opinion of my own.

 

[IanCC]

.... and then somewhere else says European iso standards permit ac to dc grounding connection be omitted in the presence of a whole-boat RCD.

 

[VicS]

.... and then somewhere else says European iso standards permit ac to dc grounding connection be omitted in the presence of a whole-boat RCD.

This was a requirement of now very obsolete editions of the iso standard

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

This was dropped from the 3rd edition way back in 2012.
Unfortunately only the 2nd (2000) edition can be found online

 

[Malabarista]

.... and then somewhere else says European iso standards permit ac to dc grounding connection be omitted in the presence of a whole-boat RCD.

I know it’s so confusing. There seem to be so many differing opinions. I do try and get my head around WHY peoples viewpoints differ around bonding and grounding etc but it hurts my head ?

 

[VicS]

I know it’s so confusing. There seem to be so many differing opinions. I do try and get my head around WHY peoples viewpoints differ around bonding and grounding etc but it hurts my head ?

See My post #9

Then buy the current edition of the standard ( 5th edition 2020) and all should be much clearer

 

[PaulRainbow]

There have been different "standards" over the years. The One Vic mentioned was particularly poor and i think it stemmed from some poor wording and an assumption that the DC negative always had continuity to the water, which is incorrect.

Either way, post #3 is correct (even if i do say so myself). It is current and complies with the very latest standards (i do own a copy of the aforementioned 2020 ISO).

 

[IanCC]

Thanks for reply. Could you tell me the ISO name and number please ? That would be great. Thank you.

 

[PaulRainbow]

Thanks for reply. Could you tell me the ISO name and number please ? That would be great. Thank you.

It is ISO 13297

ISO 13297:2020

 

[VicS]

Thanks for reply. Could you tell me the ISO name and number please ? That would be great. Thank you.

I often wonder if these standards are available in reference libraries.
My local library reopens next week after many months Covid closure and a further closure for refurbishment. Perhaps I'll pop in and ask if they know.

 

[IanCC]

I often wonder if these standards are available in reference libraries.
My local library reopens next week after many months Covid closure and a further closure for refurbishment. Perhaps I'll pop in and ask if they know.

I have got others via inter library loans. Usually a charge £6ish and a goodish wait.

 

[ean_p]

I often wonder if these standards are available in reference libraries.
My local library reopens next week after many months Covid closure and a further closure for refurbishment. Perhaps I'll pop in and ask if they know.

One of the east European countries used to publish standards ( in several languages) as a policy, Hungry or Bulgaria or some such! Maybe worth a search!

 

[VicS]

One of the east European countries used to publish standards ( in several languages) as a policy, Hungry or Bulgaria or some such! Maybe worth a search!

Yes it was Bulgaria


I had a link to the 2012 edition of Iso 13297 and a link to iso 10133 the standard for extra low voltage DC installations but both stopped working after a short time . I guess International copyright law carries more weight than Bulgarian government edicts. Both would be out of date now anyway.

 

[Alex_Blackwood]

Hard to see why not and even harder to see why it's not done from the factory.

Question. What is the construction of the charger case? is it metal or plastic? I would have thought that any earth connection for the case would have been made at the incoming 230v ac connection block. If the case is metal. If plastic the unit probably does not have any earth connected to the case, may even be double insulated. The ultimate answer is: If unsure consult a qualified electrician.

 

[PaulRainbow]

Question. What is the construction of the charger case? is it metal or plastic? I would have thought that any earth connection for the case would have been made at the incoming 230v ac connection block. If the case is metal. If plastic the unit probably does not have any earth connected to the case, may even be double insulated.

I thought i covered this in post #3 Alex. It isn't double insulated or it wouldn't have an Earth (or two). It does have an Earth connection to the case, that's why i said to connect it to the common Earth.

The charger consists of a metal chassis with a plastic cover. The incoming shore power terminal block includes an Earth and there is a separate Earth for the metal chassis. Why Sterling didn't bond the two is a mystery, but nonetheless, both should be Earthed as i described in post #3.

The ultimate answer is: If unsure consult a qualified electrician.

I'll bear that in mind

FYI