Electric cables via engine bay accepted by BSS?

[ditchcrawler]

6 hours ago, Flyboy said:

It looks to me that the op has ordinary domestic twin/3 core PVC  sheathed flex. This would be totally unsuitable in an engine compartment as it will become very soft in this hot environment.  Proper high temperature vehicle/marine cable should be used and protected by spiral wrap ducting or similar.

If you engine bay runs that hot what is the life of your alternators

[Flyboy]

22 hours ago, ditchcrawler said:

If you engine bay runs that hot what is the life of your alternators

Alternators are designed to run in an engine environment (ie hot).   Ordinary houseold wiring isn't apart from high temp cable for boilers & immersion heaters. It's also not oil resistant.

[ditchcrawler]

1 hour ago, Flyboy said:

Alternators are designed to run in an engine environment (ie hot).   Ordinary houseold wiring isn't apart from high temp cable for boilers & immersion heaters. It's also not oil resistant.

I would disagree, most are designed to run under car bonnets where there is ample air flow.

[Flyboy]

1 hour ago, ditchcrawler said:

I would disagree, most are designed to run under car bonnets where there is ample air flow.

Next time you thrash your car down a motorway, after you exit stop. lift up the bonnet and grab hold of the anternator. I think you will very surprised how hot it is. There is an awful lot of very hot air from the radiator which the alternator is sucking in.

[Batainte]

Thanks everyone for the wealth of advice.

All has been taken on board and by the looks of it the whole interior will require a rewire (oh never ending joys of boat refit and amendments).

Any pointers where youd be getting your cables from to fit for this? Bought the above mentioned 0.75mm wire loom at "Yess Electrics", after having explained to the sales staff that this would be used on a 12v boat project... although now it seems that perhaps their knowledge is limited to domestic electrics. And this being rather specific requirement (voltage drops, engine bay heat resistence, etc..) would prefer to use more specified supplier.

[MtB]

14 minutes ago, Batainte said:

Thanks everyone for the wealth of advice.

All has been taken on board and by the looks of it the whole interior will require a rewire (oh never ending joys of boat refit and amendments).

Any pointers where youd be getting your cables from to fit for this? Bought the above mentioned 0.75mm wire loom at "Yess Electrics", after having explained to the sales staff that this would be used on a 12v boat project... although now it seems that perhaps their knowledge is limited to domestic electrics. And this being rather specific requirement (voltage drops, engine bay heat resistence, etc..) would prefer to use more specified supplier.

 

The trouble with trade counter sales staff I've learned over the decades, is that they are usually unqualified bods who pick up smatterings of knowledge here and there simply by knowing and chatting and with the regular customers some of whom ARE qualified, and seeing the stuff they buy for various tasks.

 

I'd say trusting advice from the sales counter staff is highly risky because it often sounds highly credible because the staff themselves believe what they are telling you and are giving it to you in good faith, but it is a bit like getting your medical advice from the doctor's receptionist rather than the GP. 

 

 

 

 

[Balliol]

31 minutes ago, Batainte said:

Thanks everyone for the wealth of advice.

All has been taken on board and by the looks of it the whole interior will require a rewire (oh never ending joys of boat refit and amendments).

Any pointers where youd be getting your cables from to fit for this? Bought the above mentioned 0.75mm wire loom at "Yess Electrics", after having explained to the sales staff that this would be used on a 12v boat project... although now it seems that perhaps their knowledge is limited to domestic electrics. And this being rather specific requirement (voltage drops, engine bay heat resistence, etc..) would prefer to use more specified supplier.

We used to use 44/0.30  (3 sq.mm 27.5 amp) multi-strand single core cable for all domestic wiring circuits in our narrow boats and barges (lighting, fridge, water pumps etc).

 

Here are links to one company found at random:

https://www.electricalcarservices.com/tinned-multi-strand-single-core-29a-2.5mm²-cm2.5/p-168-259-486-4142

https://www.electricalcarservices.com/tinned-multi-strand-single-core-39a-4.0mm²-cm4/p-168-259-486-4143

 

The first cable should be fine for a shorter boat up to say 50'. The second for >50. 

 

 

 

[Alan de Enfield]

14 minutes ago, Balliol said:

We used to use 44/0.30  (3 sq.mm 27.5 amp) multi-strand single core cable for all domestic wiring circuits in our narrow boats and barges (lighting, fridge, water pumps etc)

If that is a recommendation, unfortunately it is not valid and could cause huge problems with volt drop.

 

The current draw and distance from the batteries / busbars needs to be measured for EVERY appliance.

 

Just as an example the fridge manufacturers state that you should allow 1mm2 for each metre distance from the batteries. I had to use 10mm2 on mine. I tried it with 4mm2 and the fridge would not run correctly.

 

Remember that electricity is in a circuit and goes from the battery, to the appliance and back to the battery so you should take into account 'doubling' the distance.

 

Current rating is rarely relevant when wiring up a boat - VOLT DROP is the deciding criteria.

 

 

Screen Shot from my fridge manual, you can see for example that at 12v they recommend 14mm2 cable for a distance of 10 metres.

 

 

 

 

 

[Balliol]

If that is a recommendation, unfortunately it is not valid and could cause huge problems with volt drop.

 

Not in my experience. 

[TheBiscuits]

2 hours ago, Batainte said:

All has been taken on board and by the looks of it the whole interior will require a rewire (oh never ending joys of boat refit and amendments).

 

The real problems with boat wiring as you have found out is that what would usually be the correct answer for a house or a car is usually the wrong answer for a boat.

 

Alan's example of the fridge wiring is a case in point.  On my 1970's cruiser, the 12v fridge was about 1m away from the batteries, so 2m total run of cable and the size is largely irrelevant - that leftover bit I have in my wiring box will do.

 

On my narrowboat the 12v fridge is 7m away from the batteries, so 15m total run of cable, and if I undersize it I will have a fridge that won't work sometimes and will burn itself out faster - and they are about £600 to replace!

 

As boats get older, it gets worse too.  Different owners add or change bits, some doing a good job but not bothering to fix older bodges and others adding their own bodges.  The typical wiring on an older boat looks like a bag of snakes.

 

[David Mack]

2 hours ago, Balliol said:

 

Here are links to one company found at random:

https://www.electricalcarservices.com/tinned-multi-strand-single-core-29a-2.5mm²-cm2.5/p-168-259-486-4142

https://www.electricalcarservices.com/tinned-multi-strand-single-core-39a-4.0mm²-cm4/p-168-259-486-4143

 

Another supplier

https://www.vehiclewiringproducts.co.uk

[WotEver]

11 hours ago, Balliol said:

If that is a recommendation, unfortunately it is not valid and could cause huge problems with volt drop.

 

Not in my experience. 

Well, let’s look at that experience.
 

If you were powering a fridge with that cable size more than a metre or so from the batteries it simply wouldn’t work. If you were powering a water pump on a long boat with that size cable you’d have over 10% voltage drop so whilst the pump would probably work it wouldn’t work very well, and would burn out the contacts on the pressure switch faster due to the higher current. If you were powering a tunnel lamp with that size cable it would be quite dim. A 12V TV would struggle.  The list goes on. 
 

So no, you can’t simply say that you’d wire all circuits with 2.5mm², as it would be quite unsuitable for some consumers. You need to calculate the voltage drop for each circuit and cable it appropriately. 

[Chewbacka]

12 hours ago, Balliol said:

If that is a recommendation, unfortunately it is not valid and could cause huge problems with volt drop.

 

Not in my experience. 

One of the problems will be that if for a given circuit when all appliances on that circuit are switched on and taking full load, each and every appliance on that circuit must NOT have a volt drop of more than 10% of the nominal supply voltage.  If it does, then the vessel does not comply with the iso standard and therefore should not be CE marked.

[Keith M]

Do not forget there is also a 3 % volt drop rule for essential items of equipment such as bilge pumps etc.

This is a requirement of ISO 13297 which now also covers 10133 from January this year.

[WotEver]

1 minute ago, Keith M said:

Do not forget there is also a 3 % volt drop rule for essential items of equipment such as bilge pumps...

 

1 hour ago, WotEver said:

If you were powering a water pump on a long boat with that size cable you’d have over 10% voltage drop so whilst the pump would probably work it wouldn’t work very well, and would burn out the contacts on the pressure switch faster due to the higher current.

And that is why the 3% rule exists. 

[Alan de Enfield]

[Balliol]

30 minutes ago, Keith M said:

Do not forget there is also a 3 % volt drop rule for essential items of equipment such as bilge pumps etc.

This is a requirement of ISO 13297 which now also covers 10133 from January this year.

OK, so do the calculation for an Engel under counter fridge (about 3.3 amps) at 8 metres run from distribution board, 2.5 ring. Please show working.

[Tracy D'arth]

12 minutes ago, Balliol said:

OK, so do the calculation for an Engel under counter fridge (about 3.3 amps) at 8 metres run from distribution board, 2.5 ring. Please show working.

Ah, but.  A fridge takes a considerable amount more current to start the motor, you cannot work it out on the running current. Distribution board ring circuit? On a boat? @12v?

TD'

[Alan de Enfield]

27 minutes ago, Balliol said:

OK, so do the calculation for an Engel under counter fridge (about 3.3 amps) at 8 metres run from distribution board, 2.5 ring. Please show working.

Trying to put it simply :

 

That is probably the average (over a period) and will not take into account that the running current is maybe 3x higher, then it switches off for 15 minutes, then it starts again etc)

Our fridge is around 30Ah per day but as it is only running for approximately 1/3rd of the time. 

 

Therefore if you did not understand you could say that it is 90Ah per day if running continuously, so, equivalent to 90/24 which is 3.75 amps

 

You would appear to not understand - we need the peak (start up / running) current or watts.

 

If we, at this stage, take 10 amps as the actual running current then the volt drop over 8 metes is 9.2% (or 1.1v) taking your nominal 12.5v down to 11.4v

Edited April 9, 2020 by Alan de Enfield

[WotEver]

32 minutes ago, Balliol said:

OK, so do the calculation for an Engel under counter fridge (about 3.3 amps) at 8 metres run from distribution board, 2.5 ring. Please show working.

We would need to know the start-up current, but it’s generally simpler to take the manufacturer’s advice than to guess at the equipment’s tolerance to voltage droop. I don’t know what Engel specify but Shoreline’s advice for a fridge 8m from the Dis Board would be minimum 8mm². 

[Keith M]

35 minutes ago, Balliol said:

OK, so do the calculation for an Engel under counter fridge (about 3.3 amps) at 8 metres run from distribution board, 2.5 ring. Please show working.

This is a simply question to answer use 10 mm cable from the Batteries directly to the Fridge using the correct protection 

[WotEver]

I just looked at a couple of Engel user manuals for the smaller portable fridges and they all state “IMPORTANT:
WIRING
Never use wiring less than AWG #12 between the battery and refrigerator.” AWG 12 is 4mm² and these instruction presuppose that the fridge will be close to the power source. So I’d guess that it’ll be much the same as Shoreline - 1mm per metre distance from the source. 

[Chewbacka]

6 hours ago, Keith M said:

Do not forget there is also a 3 % volt drop rule for essential items of equipment such as bilge pumps etc.

This is a requirement of ISO 13297 which now also covers 10133 from January this year.

I think the 3% requirement was added since I fitted out our boat, so I am behind - again?

[Keith M]

8 hours ago, Chewbacka said:

I think the 3% requirement was added since I fitted out our boat, so I am behind - again?

The 3 and 10 % rule  was added to the ISO in 2013.

Most installer are not aware of this within the ISO.

[Alan de Enfield]

4 minutes ago, Keith M said:

The 3 and 10 % rule  was added to the ISO in 2013.

Most installer are not aware of this within the ISO.

 

Looking at a number of boats, I'd suggest that few NB builders are even aware of ISO 13297