Battery Isolator switch/es?

[Mrs Woman]

Although not marine electricians, we were surprised to find that our recently purchased old narrowboat had its single isolator on the neutral/return cable, rather than positive (which, with a cranking battery and leisure pair would require two switches or a combination switch).

 

Neither a boatyard proprietor nor the well-regarded surveyor who issued our BSS certificate seemed to find this surprising or worrying, even though, on a DC circuit, damage to wiring or equipment anywhere round the boat could ground through the hull when the isolator was closed, causing a potentially serious dead short that couldn’t quickly be cut off.

 

I can see no specific advice against this arrangement in the BSS guide (possibly because it was such an unwise/unlikely eventuality?), although there is reference to separate isolation of each battery bank and an illustration of a battery box with two removable keys ...there are two isolator brackets on our boat, suggesting that this neutral isolation was not a feature of the boat when built for hire, half a century ago.

 

Any thoughts on the safety and legality implications of our wiring?

[Machpoint005]

Mine's the same - so probably not so very unusual (1995 hull)

[Guest]

I have seen several boats wired thus. Not brilliant IMHO, for reasons that you already have stated. That said it appears to have been wired that way for a number of years.

Edit

On thinking about it it is possible to use an isolator this way, because it can be used to break the neg to the hull thus removing any danger of a short. It will depend on how the neg from the engine is connected etc though. I would much sooner isolate the positive immediately after the batteries personally, but of course others may think differently.

Edited August 27, 2008 by Guest

[heckmotor]

Mine's the same - so probably not so very unusual (1995 hull)

 

Yes, Ian, I'm beginning to think it's probably quite common ...but surely not very satisfactory? The whole point of easy-access isolation, as close as possible to the batteries, is to be able to break all circuits instantly in the event of an emergency, even when unfamiliar with the boat ...and a convenient consequence of positive isolation is the reduction of piggy-back terminals on the battery posts.

 

Another IAN

[Chris Pink]

Any thoughts on the safety and legality implications of our wiring?

 

As long as it is the first thing 'upstream' of the batteries, and all battery negatives are connected together, it is fine and a very good way of isolating both banks with one switch. ie Problem - switch off electric - done.

 

If there was an engine negative to the battery independent of this then it is neither safe nor BSS compliant but this would be unusual.

 

The rationale may depend on what arrangement you have for your split charging.

Edited August 27, 2008 by Chris Pink

[Guest]

http://www.smartgauge.co.uk/whereiso.html

[heckmotor]

http://www.smartgauge.co.uk/whereiso.html

 

 

Excellent link, Catweasel! Not sure Chris Pink has thought through the concept of 'upstream' of the batteries on the neutral side - we're talking DIRECT current, after all, so a neutral isolator next to the battery box is about as downstream as you can get, surely (IMHO!)?

 

IAN

[Eeyore]

Neither a boatyard proprietor nor the well-regarded surveyor who issued our BSS certificate seemed to find this surprising or worrying, even though, on a DC circuit, damage to wiring or equipment anywhere round the boat could ground through the hull when the isolator was closed, causing a potentially serious dead short that couldn’t quickly be cut off.

 

Any thoughts on the safety and legality implications of our wiring?

Again not uncommon, my 1996 built NB has the same arrangement.

The important thing is that the only thing connected to the battery negative is the switch.

Opening the switch (turning it off) will then disconnect battery negative from both the hull and the electrical circuits.

Obviously a fault can only exist if it "can see" both sides of the battery; so in this case a switch in the negative has the same effect as one in the positive from a users point of view.

The BMEA code of practice also only shows switches in the positive cabling; lets wait for the technical boys to explain the reason for that.

 

Oh look someones already said it whilst I was still typing!

Edited August 27, 2008 by Eeyore

[Guest]

Probably in days gone by when requirements were much simpler on boats, it was OK to wire the isolator in the neg side. Certainly one of my previous boats had just one leisure battery (and that was knackered) and just simple 12V lighting along with a fag lighter socket. I daresay it would have been acceptable in this instance (although I still put the isolator in the positive; mostly out of instinct being as I was an electrician anyway) . Today though as Gibbo states on his Smartgauge site, we have all the inverters and suchlike, biolers and alarms ec that bypass isolators, so to put isolators in the negative side can actually complicate the issue. It wouldn't do for me TBH.

[Chris Pink]

http://www.smartgauge.co.uk/whereiso.html

 

oh dear, disgreeing with Gibbo again.

 

i do agree with this

Separate isolator switches allows each battery bank to be treated (and therefore worked on) independantly. This is a great bonus in many circumstances.

but would take issue with an 'isolator' that left either the central heating or an inverter charger still connected to the batteries.

 

As far as i am concerned, my interpretation of BSS is that it is only essential systems that can be independent of the battery isolater - bilge pump for instance.

 

Corrosion aside there is as much potential for fault with the -ve's connected throughout the boat as the postive's in Gibbo's scenario the naming is simply a convention.

 

So perhaps the answer is 2-pole isolators - 1 per bank.

[Guest]

oh dear, disgreeing with Gibbo again.

 

i do agree with this but would take issue with an 'isolator' that left either the central heating or an inverter charger still connected to the batteries.

 

As far as i am concerned, my interpretation of BSS is that it is only essential systems that can be independent of the battery isolater - bilge pump for instance.

 

Corrosion aside there is as much potential for fault with the -ve's connected throughout the boat as the postive's in Gibbo's scenario the naming is simply a convention.

 

So perhaps the answer is 2-pole isolators - 1 per bank.

I used to take issue too about connecting things such as inverters directly to batteries. However it clearly states in the boat safety that circuits such as chargers, inverters, alarms and so on can bypass the isolator providing they are fitted with inline fuses. I carefully checked this out when I found a new boat where the inverter was connected directly. My inverter is connected through an isolator and will remain thus. I suspect inverters are allowed to bypass because of combination inverter/chargers, but there may be other reasons. Alarms, boilers and bilge pumps etc though don't really leave you a choice. I can't speak for any other standards as I have only dealt with Boat Safety Scheme.

 

Quote Boat Safety:

 

Identify any electrical circuits bypassing the battery isolator.

Check that any electrical circuits bypassing the battery isolator supply

the following equipment:

automatic bilge pumps;

security alarms (including marine radios);

fire pumps;

electronic navigation equipment with memories;

any other equipment where the manufacturer’s instructions indicate

or specifically require direct connection to a battery, such as

diesel-fired central heating boilers;

battery charger outputs;

inverters or combination inverter/chargers.

 

And I thought my English was crap!

Edited August 27, 2008 by Guest

[Mrs Woman]

Thanks to all for prompt responses and particularly for the smartgauge link from Catweasel! K

[heckmotor]

Corrosion aside there is as much potential for fault with the -ve's connected throughout the boat as the postive's in Gibbo's scenario the naming is simply a convention.

 

So perhaps the answer is 2-pole isolators - 1 per bank.

 

Sorry to be picky again, Chris, and labouring the point, but these DC circuits are a 'one-way street' and the naming of +ive and -ive is anything but just a convention ...hence, no need for 2-pole isolators, surely?

 

BTW, one thing that occurred to me is that our Bukh engine's cut-off is a powered solenoid, and there might be a case, on safety grounds, for bypassing the isolator to that? ...if someone's overboard, you want the engine off pronto, and if the isolator's been thrown, I'd have to raise the whole deck to decompress the engine. Suppose I should consider a cable decompressor stop, really, shouldn't I!

 

IAN

[Timleech]

Thanks to all for prompt responses and particularly for the smartgauge link from Catweasel! K

 

It used to be quite common, as a way of using one switch to isolate more than one battery or battery bank.

I don't really understand your concerns over shorting, an isolator will do the job of isolation just as effectively whichever end of the battery it's connected to.

There are other issues, as has been pointed out, over corrosion and with high-tech systems, which noone knew about at the time that many of these switches were fitted.

 

Tim

[RobinJ]

I used to take issue too about connecting things such as inverters directly to batteries. However it clearly states in the boat safety that circuits such as chargers, inverters, alarms and so on can bypass the isolator providing they are fitted with inline fuses.

In a situation where there is only a negative isolator, the best policy is obviously to put the fuses in the negative, otherwise there is an unprotected negative connection direct to the battery - I feel a short coming!

[heckmotor]

...an isolator will do the job of isolation just as effectively whichever end of the battery it's connected to.

 

Tim

 

No, no, no it won't, Tim - that's the whole point! If you isolate the positive and then short out anything at all against the hull, due to physical damage, or a fire, or anything, then no problem because the whole boat's 'dead'. Isolate the neutral 'return' and do the same thing and you've got an open circuit, because the boat's always potentially 'live' - re-read the Smartgauge link ...it's definitive and unequivocal! It really worries me that this area seems to be so misunderstood and, indeed, that negative/neutral isolation hasn't been outlawed.

 

IAN

[Gibbo]

....... but would take issue with an 'isolator' that left either the central heating or an inverter charger still connected to the batteries.

 

You need to read the webpage *properly*. It makes no mention of leaving the central heating system or inverters connected. It *does* mention leaving the control systems such as combined battery monitor/inverter remotes connected and central heating time switches which *do* need to remain connected.

 

That's in addition to the problem of stray current corrosion.

 

The webpage is indeed quite correct.

 

I lost count of the number of Freedom 25 combi and Link 2000 battery monitors (combined RRP of nearly £3000 at the time) or MasterVolt Dakars and Masterlink control panels (combined £2500 at the time) completely blown to pieces because someone had put the isolator in the negative.

 

Anyone who puts an isolator switch in the negative on a typical modern boat doesn't understand electricity or electrical systems and is living in the past.

 

Gibbo

[Chris Pink]

Sorry to be picky again, Chris, and labouring the point, but these DC circuits are a 'one-way street' and the naming of +ive and -ive is anything but just a convention ...hence, no need for 2-pole isolators, surely?

 

Explain yourself? How do the little electrons know which way we decided they should be labelled? - especially as electrons flow counter-intuitively as no-one knew about them when batteries were first labelled.

 

And i take serious issue with the boat safety quote above, especially as there have been a number of reported fires with inverters recently all of which i assume to have been fused. I repeat - the only piece of equipment that should bypass the isolator on an inland waterway boat is the bilge pump, and it should have its own wiring and fuse and isolator with no possible connection to the main system.

 

And if it is becoming common to fit equipment that has a memory it should run off an internal battery like a computer does.

 

On safety grounds it should be possible to throw an isolator and have the whole boat shut down when you leave it.

 

I do think solenoid engine stop mechanisms are another safety issue as a lot of the (car-type) multiway connector used in modern engine wiring looms are just not up to life in an engine room. I recently had to cut through a 4mm steel bulkhead to repair one and it took me 2 hours to get to the boat where the distressed owner was unable to switch off her engine because the manual did not explain how to use the stop lever manually.

 

o dear what a Tuesday, disagreeing with BSS and Gibbo on the same day.

 

I lost count of the number of Freedom 25 combi and Link 2000 battery monitors (combined RRP of nearly £3000 at the time) or MasterVolt Dakars and Masterlink control panels (combined £2500 at the time) completely blown to pieces because someone had put the isolator in the negative.

 

Anyone who puts an isolator switch in the negative on a typical modern boat doesn't understand electricity or electrical systems and is living in the past.

 

Gibbo

 

Well then the only answer to this is to use a double-pole isolator, an 'isolator' that leaves anything connected is by definition not an isolator.

 

And if you can afford £2K+ for a piece of electrical kit then why not spend another £100 to buy the proper switch rather than what (with respect) i would call a bodge.

Edited August 27, 2008 by Chris Pink

[Gibbo]

Well then the only answer to this is to use a double-pole isolator, an 'isolator' that leaves anything connected is by definition not an isolator.

 

That doesn't cure the problem. In order for a battery monitor to work it has to be PERMANENTLY connected to the batteries otherwise it cannot know what happened to the batteries during the period it wasn't connected and therefore cannot know the state of charge therefore it cannot do its job if it keeps being disconnected from the batteries. So a battery monitor HAS to be permanently connected to the batteries.

 

If that battery monitor is also the remote for the inverter (such as a Heart Interface Link 2000 or Mastervolt Masterlink) then it has to have a ground connection between the two. If the inverter negative is disconnected from the batteries the inverter will try to draw its negative current through the remote panel. BANG. There is nothing that can be done about this.

 

And if you can afford £2K+ for a piece of electrical kit then why not spend another £100 to buy the proper piece of kit rather than what (with respect) i would call a bodge.

 

And (with respect) I would suggest anyone who thinks it is a bodge doesn't understand enough about how inverters and battery monitors work.

 

Another £100 would not cure the problem. Another £1000 wouldn't cure the problem. Another £10,000 wouldn't cure the problem.

 

But putting the isolator switch where the BMEA and ABYC say it should be DOES cure the problem.

 

Gibbo

[Guest]

I undertsand we should now have a permanent (i.e. not through an isolator) earth bond tied to the hull from our negative post on the domestic battery bank? If we isolate the negative side of the circuits from the batteries batteries via an isolator, surely that will still leave the hull at neutral potential? If anything at positive potential then comes in contact with the hull what will happen? Surely the only place for the isolator on a boat wired today is in the positive sde?

[heckmotor]

Explain yourself? How do the little electrons know which way we decided they should be labelled? - especially as electrons flow counter-intuitively as no-one knew about them when batteries were first labelled.

 

Certainly, Chris!

 

An analogy (for anyone who's not too sure of the difference between AC and DC!): Imagine those demonstrations of stationary engines that you see at steam fairs, where water is piped from a cistern to a pump that returns the water back to the top of the cistern (stick with this - it is relevant ...just!). If you close a tap on the cistern outlet, you can drill a hole in the plumbing or smash the pump and the tap will prevent any further loss from the cistern (think of the water as direct current). If you move your tap (or isolator) to the end of the hose that returns water to the cistern, any breach of the plumbing or pump (a short?) will cause unstoppable loss of all the water (or current, until the battery's flat). Yes, the water's acting like DC current, d'you see?

 

On safety grounds it should be possible to throw an isolator and have the whole boat shut down when you leave it.

 

Of course it should but, if it's a negative/return isolator, the boat's only shut down until water ingress, heat, physical damage, or some other event, leads to an unintended grounding to the hull anywhere inside the boat - you can complete the circuit anywhere, without going anywhere near the isolator.

 

I know! ...I am probably labouring this, but I'm not sure the penny's dropped yet! ...or is it just me?

 

LoL IAN

[Gibbo]

Surely the only place for the isolator on a boat wired today is in the positive sde?

 

Absolute, totally, completely and utterly.

 

There simply is no question about it or room for debate.

 

Gibbo

[Guest]

Certainly, Chris!

 

An analogy (for anyone who's not too sure of the difference between AC and DC!): Imagine those demonstrations of stationary engines that you see at steam fairs, where water is piped from a cistern to a pump that returns the water back to the top of the cistern (stick with this - it is relevant ...just!). If you close a tap on the cistern outlet, you can drill a hole in the plumbing or smash the pump and the tap will prevent any further loss from the cistern (think of the water as direct current). If you move your tap (or isolator) to the end of the hose that returns water to the cistern, any breach of the plumbing or pump (a short?) will cause unstoppable loss of all the water (or current, until the battery's flat). Yes, the water's acting like DC current, d'you see?

 

 

 

Of course it should but, if it's a negative/return isolator, the boat's only shut down until water ingress, heat, physical damage, or some other event, leads to an unintended grounding to the hull anywhere inside the boat - you can complete the circuit anywhere, without going anywhere near the isolator.

 

I know! ...I am probably labouring this, but I'm not sure the penny's dropped yet! ...or is it just me?

 

LoL IAN

Like the earth bonding wire from the neutral post to the shell?

[heckmotor]

Absolute, totally, completely and utterly.

 

There simply is no question about it or room for debate.

 

Gibbo

 

 

Hear! Hear! Pay attention, everyone! (Thanks, Gibbo!) IAN

 

Like the earth bonding wire from the neutral post to the shell?

 

Bl***y right! IAN

[Timleech]

No, no, no it won't, Tim - that's the whole point! If you isolate the positive and then short out anything at all against the hull, due to physical damage, or a fire, or anything, then no problem because the whole boat's 'dead'. Isolate the neutral 'return' and do the same thing and you've got an open circuit, because the boat's always potentially 'live' - re-read the Smartgauge link ...it's definitive and unequivocal! It really worries me that this area seems to be so misunderstood and, indeed, that negative/neutral isolation hasn't been outlawed.

 

IAN

 

IF there is nothing else connected to the battery negative, then the battery is isolated. That is how these sytems with the isolator in the -ve would have been set up.

If you start adding permanent bonds between -ve and the hull, the whole picture is different and the isolator ceases to be an isolator.

 

Tim