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Hull Earth Bond


clbrof

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I intend on fitting 240 electrics

 

Socket - GI - RCD/MCB - Sockets

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Hull earth bond

 

What size does the hull earth cable have to be? and can it be to a wall of the steel nb ? does it matter where it is placed?

 

As i understand from searching the forum it needs to be bolted to the hull with a 8mm bolt.

 

Thanks

 

Colin

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This is just a guess, but I'd assume the cable for the mains earth bond should be no thinner then the earth cable on the rest of the AC system and the earth cable to the mains bollard. So probably 2.5mm2.

 

I think it should be placed somewhere near the DC bond to the hull. Quite a few boats seem to have earth studs through the inside overhang on the uxter plate in the engine room.

Edited by blackrose
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I intend on fitting 240 electrics

 

Socket - GI - RCD/MCB - Sockets

|

Hull earth bond

 

What size does the hull earth cable have to be? and can it be to a wall of the steel nb ? does it matter where it is placed?

 

As i understand from searching the forum it needs to be bolted to the hull with a 8mm bolt.

 

Thanks

 

Colin

The hull earth bond should be adjacent to (or shared with) the point at which the 12 V DC negative is bonded to the hull. If there isn't an obvious DC negative bonding point I would add one.

 

Any clean shiny bit of steel which is part of the hull will do- engine bearers are popular places to drill the hole ( because it's usually handy for the DC bond as well). The Earth Point ought to have a label which identifies what it is. (Buy a pipe earth clip from a DIY shed and nick the label). It ought to be where it cannot easily get damaged/trodden on.

 

The bonding cable needs to be big enough to handle the biggest fault current which can occur until the supply breaker/fuse goes. That can be calculated, if you know something the supply. Practically 2.5mm2 or 6mm2 green and yellow sheathed cable are readily available and both can handle more than 27A . I would use 6mm2 since it is more mechanically robust and the terminals available are more likely to be able to handle a decent sized bolt.

 

M8 will be fine, or anything about that size (5/16). Do fit a locking nut lest it come undone with vibration, and washers on the bolt head and between the termination and the nut to improve the contact.

 

N

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My hull earth bond for the AC system is actually hidden behind the shore power inlet. Because it is hard to get at, when I recently fitted an inverter charger, I connected its earth bolt to the earth bar in the consumer unit. I am assuming that this is OK, as the earth bar of the consumer unit has an earth cable connected to the hull earth bond referred to above, so any fault will find its way to the hull.

 

In reality, given the all of the hull is connected to all of the hull, does it actually matter where the hull earth bond is, and could you have several?

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My hull earth bond for the AC system is actually hidden behind the shore power inlet. Because it is hard to get at, when I recently fitted an inverter charger, I connected its earth bolt to the earth bar in the consumer unit. I am assuming that this is OK, as the earth bar of the consumer unit has an earth cable connected to the hull earth bond referred to above, so any fault will find its way to the hull.

 

In reality, given the all of the hull is connected to all of the hull, does it actually matter where the hull earth bond is, and could you have several?

 

Connecting the inverter earth to the consumer unit earth bar is fine. I assume you do have a neutral-earth bond?

 

 

It doesn't really matter where the AC bond is, but the reason that the DC bond and the earth bond are supposed to be close together is a corrosion prevention thing.

 

 

Multiple earth bonds is not good practice:- it is certain that you don't know where the fault current is going in the event of a fault, it sets up earth loops which any electronics around may not like, and it is hard to be sure that they have all been disconnected should this ever be needed.

 

N

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The hull earth bond should be adjacent to (or shared with) the point at which the 12 V DC negative is bonded to the hull. If there isn't an obvious DC negative bonding point I would add one.

 

Any clean shiny bit of steel which is part of the hull will do- engine bearers are popular places to drill the hole ( because it's usually handy for the DC bond as well). The Earth Point ought to have a label which identifies what it is. (Buy a pipe earth clip from a DIY shed and nick the label). It ought to be where it cannot easily get damaged/trodden on.

 

The bonding cable needs to be big enough to handle the biggest fault current which can occur until the supply breaker/fuse goes. That can be calculated, if you know something the supply. Practically 2.5mm2 or 6mm2 green and yellow sheathed cable are readily available and both can handle more than 27A . I would use 6mm2 since it is more mechanically robust and the terminals available are more likely to be able to handle a decent sized bolt.

 

M8 will be fine, or anything about that size (5/16). Do fit a locking nut lest it come undone with vibration, and washers on the bolt head and between the termination and the nut to improve the contact.

 

N

What he said, except it should ideally be on a separate stud to the DC one but within 3 inches IIRC. A Rolls Royce job is to weld a stainless steel bolt/stud to the steel shell and earth bond to same.

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I assume you do have a neutral-earth bond?

The boat had the AC hull bond in situ when I bought it at 10 years old in 2011. I added a Sterling inverter charger which has a bolt near the connections that go to the battery which is marked with the earth symbol - this I connected to the earth bar in the consumer unit. There are also earth connections where the shore power comes into the inverter, and where the AC power goes from the inverter to the consumer unit.

 

How would I know if I have a neutral-earth bond?

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I notice that amongst the replies to the OP's initial question, that no mention of a galvanic isolator or isolation transformer has been made. Surely this is relevant when creating an earth bond to the vessel?

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Hi Doorman, thanks I have ordered a Galvanic Isolator to go after my offshore socket

 

Socket - GI - RCD/MCB - Sockets

|

Hull earth bond

Thank you.

 

Do you know of a Specsavers outlet in the South Cheshire area?

 

Joking apart, when we were buying our boat, I asked Gibbo (who no longer posts on here) for advice about galvanic isolation and he kindly pointed me in the direction of Isolator Transformers. Far more expensive than a basic GI but far more effective too. My rationale was that I'd sooner pay more at the outset on such equipment than suffer the costly effects of poor isolation on the hull at a later date.

 

Well worth considering!

Edited by Doorman
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:D Glad it's not just me.

 

Lol,

 

I think it's an age thing Catweasel. That's my excuse for everything nowadays and it allows me to get away with murder. Even Chris Pink leaves me alone now that he realises I'm a daft old codger! :-)

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Hi Doorman, thanks I have ordered a Galvanic Isolator to go after my offshore socket

 

Socket - GI - RCD/MCB - Sockets

|

Hull earth bond

 

Hi, sorry for sticking my nose in where it is probably not wanted but I believe this position is incorrect for the GI, try this:-

 

Shoreline Socket - RCD/MCB - Sockets

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GI

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Hull earth bond

Hope this helps,

Edited by NoFixedAbode
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Hi, sorry for sticking my nose in where it is probably not wanted but I believe this position is incorrect for the GI, try this:-

Shoreline Socket - RCD/MCB - Sockets

|

GI

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Hull earth bond

Hope this helps,

Thats so wrong...

Whilst in theory it may be OK, in practice its very easy to have a fault that will bypass the GI and you will never notice until the hull disolves.

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The hull earth bond should be adjacent to (or shared with) the point at which the 12 V DC negative is bonded to the hull.

 

Close to is good.

 

Shared with is NOT!

 

If you have a single connection and it breaks, then any earth fault on the 240v side will place 240v on your 12v negative, just waiting for you to remake the connection to the hull via your body.

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Thats so wrong...

Whilst in theory it may be OK, in practice its very easy to have a fault that will bypass the GI and you will never notice until the hull disolves.

Hi,

 

Obviously we dissagree but what you have just said is that it is ok to have multiple random earth points all over the hull, my suggestion means that if your wiring is carefull the hull is protected whilst there is no illegal device between dodgy (live to earth short) appliance and the the N/E bond at the substation.

 

Whilst I am not an electrician and make no claims for electrical expertise this seems much safer than deliberately interupting the earth integrity of the supply.

 

I notice from your signature that you do claim electrical expetise so I have made my point and shall back out of this debate before sombody accuses me of endangering peoples lives.

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Close to is good.

 

Shared with is NOT!

 

If you have a single connection and it breaks, then any earth fault on the 240v side will place 240v on your 12v negative, just waiting for you to remake the connection to the hull via your body.

Hopefully, prior to this disaster, the RCD will have tripped thus saving your life!

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Close to is good.

 

Shared with is NOT!

 

If you have a single connection and it breaks, then any earth fault on the 240v side will place 240v on your 12v negative, just waiting for you to remake the connection to the hull via your body.

 

at which point an RCD (either boat or shore) trips doesn't it ?

Hi,

 

Obviously we dissagree but what you have just said is that it is ok to have multiple random earth points all over the hull, my suggestion means that if your wiring is carefull the hull is protected whilst there is no illegal device between dodgy (live to earth short) appliance and the the N/E bond at the substation.

 

Whilst I am not an electrician and make no claims for electrical expertise this seems much safer than deliberately interupting the earth integrity of the supply.

 

I notice from your signature that you do claim electrical expetise so I have made my point and shall back out of this debate before sombody accuses me of endangering peoples lives.

 

As black adder used to say opinion is divided ... you say do it like you showed everyone else says do it as the OP's drawing.

 

Gibbo used to argue that a GI was a 'switching device' and therfore 'illegal' to insert into the earth, which I think is what you are suggesting too.

 

The overwhelming practice is that this is not the case and when pressed even gibbo could only quote that a potential future edition of regulations might clarify that a GI would have to be tested to certain limits.

 

Obviously an Isolation transformwr is unambiguous in this respect but some argue introduces other issues...

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Hi,

 

Obviously we dissagree but what you have just said is that it is ok to have multiple random earth points all over the hull, my suggestion means that if your wiring is carefull the hull is protected whilst there is no illegal device between dodgy (live to earth short) appliance and the the N/E bond at the substation.

 

Whilst I am not an electrician and make no claims for electrical expertise this seems much safer than deliberately interupting the earth integrity of the supply.

 

I notice from your signature that you do claim electrical expertise so I have made my point and shall back out of this debate before somebody accuses me of endangering peoples lives.

I did not say that multiple earths are OK I said it can and does happen.

I agree that interupting the mains earth is not the best or safest policy which is why I would recommend using an isolation transformer at the supply.

I also restrict my postings to subjects that are within my field of expertise, might I suggest you do the same.

Edited by Loddon
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