Use of Isolating switch on engine

[arn.george]

Should an isolation switch be incorporated inbetween the battery and the engine - my preference would be to do so for safety and security - however I have heard that a failure on the switch can result in a spike to the engine management system and thus a big bill. Would a diode or rectifier solve this potential problem?

[Swifty]

Allways a good idea to fit a switch. Go for a good quality unit and not a cheap one. As regards spikes... check what the engine manufacturer recommends.

[mark-f]

I am just picking up a new merc optimax and asked for an isolating switch be fitted and was told they would fit it but if there was a faut in the charging cct or electronics they thought there would be trouble with the warentee if one was fitted as even having it isolated and switching it on whilst the engine was running could cause a spike that could either damage the engine or the electronics on the boat. :-(

Mark

[Searider]

Originally Posted by mark-f

I am just picking up a new merc optimax and asked for an isolating switch be fitted and was told they would fit it but if there was a faut in the charging cct or electronics they thought there would be trouble with the warentee if one was fitted as even having it isolated and switching it on whilst the engine was running could cause a spike that could either damage the engine or the electronics on the boat. :-(

Mark

I annoys me when so called professionals (outboard dealers / riggers / boat sales) completely miss the point and show themselves to be ignorant.

All boats should have an isolation switch between the battery and the engine / services.
The switch should not be switched off when the engine is running - this will damage the alternator and possibly other engine electronics.
The switch cannot be switched on with the engine running as it would not have been possible to start the engine with it in the off position.

The only thing that should not be switched should be the bilge pump.

Presumably your boat will be/is CE Marked? Part of this requires that the electrical system is safe and the most common way of proving this is for the system to comply with the relevent ISO standard. This requires an isolation switch.

Perhaps you would be better off buying your engine from someone who knows what they are doing.

Rant over.

[jwalker]

Originally Posted by Searider

...The only thing that should not be switched should be the bilge pump...

And the device which gives the thieves 20kv.

[quinquarimarine]

Originally Posted by Searider

I annoys me when so called professionals (outboard dealers / riggers / boat sales) completely miss the point and show themselves to be ignorant.

All boats should have an isolation switch between the battery and the engine / services.
The switch should not be switched off when the engine is running - this will damage the alternator and possibly other engine electronics.
The switch cannot be switched on with the engine running as it would not have been possible to start the engine with it in the off position.

The only thing that should not be switched should be the bilge pump.

Presumably your boat will be/is CE Marked? Part of this requires that the electrical system is safe and the most common way of proving this is for the system to comply with the relevent ISO standard. This requires an isolation switch.

Perhaps you would be better off buying your engine from someone who knows what they are doing.

Rant over.

Duncan

110% percent agree and well put forward.

What I see in many cases is that the boat fitter finds it difficult to find a proper cum easy position for the isolation switch and his margin on it dicatates that it is easier to get out of it. Without it is a potential timebomb and obvious breach of RCD and/or commercial applications.

Suggest the fitter is reported to the local trading standards/public protection who agent the RCD.

If I remember right, and it is a bit late, but all is in ISO 1033 (low voltage marine wires etc). Apart from no isolation switches common faults are not taking into account voltage drops on the main runs and also fuse protection runs to be limited to 200mm.

Cheers

John
www.quinquari.co.uk

[jwalker]

Whilst not disagreeing and my boat has a switch etc. I do wonder why there is such importance placed upon it. Motor vehicles have essentially similar, and often more complex, electrical systems and one would be hard pushed to find a battery isolator fitted to any vehicle, except competition ones where the facility to disconnect the system externally is important. Surely an electrical failure is more likely while the boat is being used and bouncing and crashing through waves than it is when it's moored or on its trailer. Or am I missing something like a requirement to have access to the main switch at all times?

[jwalker]

Originally Posted by quinquarimarine

... and also fuse protection runs to be limited to 200mm.

John, do you mean the max distance to the main fuse/breaker must not be more than 200mm?

[Daniel]

Any unprotected run i beleive... so that's normally battery to fuse box. Technically to CE mark a boat it shoudl comply a boat it shoudl comply with "all relevent standards" but i woudl say few boat manufacturers follow this one.

[Scary Des]

Originally Posted by Searider

......The switch should not be switched off when the engine is running - this will damage the alternator and possibly other engine electronics......

This is where the ‘removable key’ type switches fall down because they are easily turned off by things banging against them, the 3 position (off, Batt1, Both) Plastimo switch seems to offer better general function with the only disadvantage being some loss in security.

Originally Posted by Jwalker

I do wonder why there is such importance placed upon it. Motor vehicles have essentially similar, and often more complex, electrical systems and one would be hard pushed to find a battery isolator fitted to any vehicle, except competition ones.......

I think this due to the level of development and testing that goes into an automotive loom, by comparison a marine loom is a joke (unless you have a P22 ). And when I say marine loom generally speaking, other than the engine specific parts, it is hand made on each boat and is therefore very variable.
By fitting an isolator switch you have a quick way of make the whole system safe (in theory) without the need for lots of testing.

Des (at full spout)

[gavin]

Whereas as an isolator switch is good practice and important, switchs also help to reduce dramatically electrolliss, no matter how good your gear, your insulation etc, in damp wet conditions, there absolutly will be electrical leaks and stray current leaks to earth.People find this hard to accept, if you have a cut on a finger or wart, and I have felt this often, you can recieve minute shocks from the 12 v side of things, just as you would if you put a 9v battery across your tounge!!
And I dont mean from equipment, but things like steel steering rams, or metal on the boat, our last radio, Icom 401 , had a connection to the steel bracket on the handpiece so when it touched the negative on the rib, it reverted to ch 16, we disconnected the wire in the handpiece, and mounted it on fiberglass.A couple of inches maybe 5 or 6 away was a large metal earth on the boat, in soaking conditions, the current would track to this and the radio would factory go to 16.Just dampness caused this.
But having the switch off apart from helping to stop batterys going flat, theft etc dramatically reduces factors which can contribute to electrolis.If you have a batt switch and have bypassed this to connect the bilge pump, you may as well not have bothered fitting a batt isolator, as again in damp conditions you will have tracking from the pump, driving electrolisis and could still turn up to a flat battery

[quinquarimarine]

Originally Posted by jwalker

John, do you mean the max distance to the main fuse/breaker must not be more than 200mm?

JW

Daniel is correct in that it is any unprotected run, however the main from the battery to distribution board can be accepted but in this case double insulation should be provided. This can be achieved by conduit,spirwrap etc with self extingushing properties.

CE alows for the main to distribution to be non fused. In many cases a permanent live is also required for the autobilge.

If you have busbars to which your switched main runs to then the max distance from there on feeds to your switch panel/fuses needs to be 200mm or less.

Some deviation from the rules may be posssible provided that it is noted in the build file and if necessary on the vsl PLUS you can make a clear justification by tests etc.

Cheers

John
www.quinquari.co.uk