[[email protected]]

I've been doing a major re-wire of the boat we recently bought in
Belgium, it's going pretty well and much of the horror is now tidied
up (it had suffered from the typical car wiring types of bodges, wires
draped around the place, lots of ends poked into one terminal, etc.,
etc.)

I have installed a couple of consumer units to provide switching and
protection for individual circuits but there are still two 'master'
fuses between the batteries (separate leisure and starter batteries)
and the consumer units feeding all the circuits.

The existing fuses are 'bottle' fuses and I'm wondering whether to
retain them or to replace them. I certainly want easy to replace
fuses (i.e. not needing a screwdriver or spanner) as one doesn't want
to have to find tools in an emergency. I need something in the region
of 60 to 100 amps though. Currently one fuse is 63 amps and the other
is 35 amps. If I stay with the bottle fuses I want to make both 63
amps which means I need to change one of the fuse holders and getting
a replacement fuseholder may be a problem although it looks as if
Farnell have a possible DIN rail mounting holder, I'm not sure how
easy this will be to fit.

So, are there any reasonably economical alternatives with 'replace by
hand' fuses with ratings in the 60 to 100 amps region? They want to
be reliable as well though don't need to be capable of use at high
voltages, this is a 12 volt system.

Then, in addition, I want to protect the 'heavy' stuff. The starter
battery also feeds the starter motor (surprise!) and the bow
propellor. Currently (no pun intended) these are wired direct to the
battery and I'm thinking some sort of protection for this wiring would
be a good thing too. The connection to the bow propellor in
particular is long and circuitous and a fault could easily start a
nasty fire in an inaccessible place. The wires from the batteries to
the existing bottle fuses are also unprotected (only a couple of feet
or so, but still a fault is possible).

I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. Are there any practical alternatives
to the 'mega fuse'?

--
Chris Green

[harry]

On 14 Sep, 11:43, wrote:
I've been doing a major re-wire of the boat we recently bought in
Belgium, it's going pretty well and much of the horror is now tidied
up (it had suffered from the typical car wiring types of bodges, wires
draped around the place, lots of ends poked into one terminal, etc.,
etc.)

I have installed a couple of consumer units to provide switching and
protection for individual circuits but there are still two 'master'
fuses between the batteries (separate leisure and starter batteries)
and the consumer units feeding all the circuits.

The existing fuses are 'bottle' fuses and I'm wondering whether to
retain them or to replace them. *I certainly want easy to replace
fuses (i.e. not needing a screwdriver or spanner) as one doesn't want
to have to find tools in an emergency. *I need something in the region
of 60 to 100 amps though. *Currently one fuse is 63 amps and the other
is 35 amps. *If I stay with the bottle fuses I want to make both 63
amps which means I need to change one of the fuse holders and getting
a replacement fuseholder may be a problem although it looks as if
Farnell have a possible DIN rail mounting holder, I'm not sure how
easy this will be to fit.

So, are there any reasonably economical alternatives with 'replace by
hand' fuses with ratings in the 60 to 100 amps region? *They want to
be reliable as well though don't need to be capable of use at high
voltages, this is a 12 volt system.

Then, in addition, I want to protect the 'heavy' stuff. *The starter
battery also feeds the starter motor (surprise!) and the bow
propellor. *Currently (no pun intended) these are wired direct to the
battery and I'm thinking some sort of protection for this wiring would
be a good thing too. *The connection to the bow propellor in
particular is long and circuitous and a fault could easily start a
nasty fire in an inaccessible place. *The wires from the batteries to
the existing bottle fuses are also unprotected (only a couple of feet
or so, but still a fault is possible).

I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. *It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. *Are there any practical alternatives
to the 'mega fuse'?

--
Chris Green

Most fuses and switches intended for AC mains are not suitable for DC
even thought it's a lower voltage.
That's why a lot of automotive stuff gets used on boats.

[tony sayer]

I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. *It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. *Are there any practical alternatives
to the 'mega fuse'?

--
Chris Green

Most fuses and switches intended for AC mains are not suitable for DC
even thought it's a lower voltage.
That's why a lot of automotive stuff gets used on boats.

Concur with that, we used some mains fuses on DC 24 volt supplies they
blew at a lot more then what they were supposed to. Automotive sounds
far more appropriate..

Suppose on of those car hi-fi places might have something suitable
unless anyone else knows different?..
--
Tony Sayer

[Jules Richardson]

On Tue, 14 Sep 2010 11:43:43 +0100, tinnews wrote:
Then, in addition, I want to protect the 'heavy' stuff. The starter
battery also feeds the starter motor (surprise!) and the bow propellor.
Currently (no pun intended) these are wired direct to the battery and
I'm thinking some sort of protection for this wiring would be a good
thing too. The connection to the bow propellor in particular is long
and circuitous and a fault could easily start a nasty fire in an
inaccessible place. The wires from the batteries to the existing bottle
fuses are also unprotected (only a couple of feet or so, but still a
fault is possible).

Not just a fuse, but fit a physical kill-switch too. I remember last year
when the starter solenoid on the tractor jammed closed - cue starter
motor turning the engine over continuously even with the ignition off; by
the time I'd run to the workshop for a suitable spanner to disconnect the
terminals, there was smoke billowing from the starter. Left a bit longer,
I probably would have had a fire...

If there had been a fuse in the circuit it probably would have gone
eventually, but a simple physical switch would have been nice.

I'm thinking that the easiest approach for this is a fuse in the ground
wire to the batteries

I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

cheers

Jules

[Man at B&Q]

On Sep 14, 1:18*pm, harry wrote:
On 14 Sep, 11:43, wrote:



I've been doing a major re-wire of the boat we recently bought in
Belgium, it's going pretty well and much of the horror is now tidied
up (it had suffered from the typical car wiring types of bodges, wires
draped around the place, lots of ends poked into one terminal, etc.,
etc.)

I have installed a couple of consumer units to provide switching and
protection for individual circuits but there are still two 'master'
fuses between the batteries (separate leisure and starter batteries)
and the consumer units feeding all the circuits.

The existing fuses are 'bottle' fuses and I'm wondering whether to
retain them or to replace them. *I certainly want easy to replace
fuses (i.e. not needing a screwdriver or spanner) as one doesn't want
to have to find tools in an emergency. *I need something in the region
of 60 to 100 amps though. *Currently one fuse is 63 amps and the other
is 35 amps. *If I stay with the bottle fuses I want to make both 63
amps which means I need to change one of the fuse holders and getting
a replacement fuseholder may be a problem although it looks as if
Farnell have a possible DIN rail mounting holder, I'm not sure how
easy this will be to fit.

So, are there any reasonably economical alternatives with 'replace by
hand' fuses with ratings in the 60 to 100 amps region? *They want to
be reliable as well though don't need to be capable of use at high
voltages, this is a 12 volt system.

Then, in addition, I want to protect the 'heavy' stuff. *The starter
battery also feeds the starter motor (surprise!) and the bow
propellor. *Currently (no pun intended) these are wired direct to the
battery and I'm thinking some sort of protection for this wiring would
be a good thing too. *The connection to the bow propellor in
particular is long and circuitous and a fault could easily start a
nasty fire in an inaccessible place. *The wires from the batteries to
the existing bottle fuses are also unprotected (only a couple of feet
or so, but still a fault is possible).

I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. *It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. *Are there any practical alternatives
to the 'mega fuse'?

--
Chris Green

Most fuses and switches intended for AC mains are not suitable for DC
even thought it's a lower voltage.
That's why a lot of automotive stuff gets used on boats.

Not so much unsuitability for DC, just that the rating will be a lot
lower when used for DC.

Arcs when breaking the circuit will self extinguish with AC when the
current falls to zero each half cycle. When switching DC the arc is
sustained until mechanically broken by the contact separation.

MBQ

[[email protected]]

Jules Richardson wrote:
On Tue, 14 Sep 2010 11:43:43 +0100, tinnews wrote:
Then, in addition, I want to protect the 'heavy' stuff. The starter
battery also feeds the starter motor (surprise!) and the bow propellor.
Currently (no pun intended) these are wired direct to the battery and
I'm thinking some sort of protection for this wiring would be a good
thing too. The connection to the bow propellor in particular is long
and circuitous and a fault could easily start a nasty fire in an
inaccessible place. The wires from the batteries to the existing bottle
fuses are also unprotected (only a couple of feet or so, but still a
fault is possible).

Not just a fuse, but fit a physical kill-switch too. I remember last year
when the starter solenoid on the tractor jammed closed - cue starter
motor turning the engine over continuously even with the ignition off; by
the time I'd run to the workshop for a suitable spanner to disconnect the
terminals, there was smoke billowing from the starter. Left a bit longer,
I probably would have had a fire...

If there had been a fuse in the circuit it probably would have gone
eventually, but a simple physical switch would have been nice.

There are battery isolation switches which are fairly accessible so
that's covered at least.


I'm thinking that the easiest approach for this is a fuse in the ground
wire to the batteries

I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking
of when you say "accidental ground path back to the battery". Surely
I'm protecting against just that, the chance of one of those big,
heavy wires shorting to the hull/superstructure - which can't happen
on a wooden/plastic boat.

--
Chris Green

[John]

wrote in message ...
Jules Richardson wrote:
On Tue, 14 Sep 2010 11:43:43 +0100, tinnews wrote:
Then, in addition, I want to protect the 'heavy' stuff. The starter
battery also feeds the starter motor (surprise!) and the bow propellor.
Currently (no pun intended) these are wired direct to the battery and
I'm thinking some sort of protection for this wiring would be a good
thing too. The connection to the bow propellor in particular is long
and circuitous and a fault could easily start a nasty fire in an
inaccessible place. The wires from the batteries to the existing
bottle
fuses are also unprotected (only a couple of feet or so, but still a
fault is possible).

Not just a fuse, but fit a physical kill-switch too. I remember last year
when the starter solenoid on the tractor jammed closed - cue starter
motor turning the engine over continuously even with the ignition off; by
the time I'd run to the workshop for a suitable spanner to disconnect the
terminals, there was smoke billowing from the starter. Left a bit longer,
I probably would have had a fire...

If there had been a fuse in the circuit it probably would have gone
eventually, but a simple physical switch would have been nice.

There are battery isolation switches which are fairly accessible so
that's covered at least.


I'm thinking that the easiest approach for this is a fuse in the ground
wire to the batteries

I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking
of when you say "accidental ground path back to the battery". Surely
I'm protecting against just that, the chance of one of those big,
heavy wires shorting to the hull/superstructure - which can't happen
on a wooden/plastic boat.

--
Chris Green



Would it make sense to have a separate battery for the bow thruster -
located near the thruster. You must be getting quite a voltage drop at the
moment. A local battery could be charged with thinner cable than the cable
that is needed to transmit the motor power. It would also make the starter
battery totally dedicated to engine starting.

[The Natural Philosopher[_2_]]

tony sayer wrote:
I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. Are there any practical alternatives
to the 'mega fuse'?

--
Chris Green
Most fuses and switches intended for AC mains are not suitable for DC
even thought it's a lower voltage.
That's why a lot of automotive stuff gets used on boats.

Concur with that, we used some mains fuses on DC 24 volt supplies they
blew at a lot more then what they were supposed to. Automotive sounds
far more appropriate..

Suppose on of those car hi-fi places might have something suitable
unless anyone else knows different?..

I looked it up. 50A is the biggest blade type fuse.

I started looking at DC motor contactors/trips for low voltage, but got
side tracked.

I am not sure that a fuse in a starter motor is something you want
anyway. Those things can surge to several hundred amps.

There is a reason why they are connected directly to batteries via a
heavy duty solenoid operated contactor.


I would be more inclined to wire them up directly, and have a simple car
blade style fuse panel (any scrappie will have dozens) and make sure the
(upstream) wiring to it is of the highest quality,

[Dave Osborne[_2_]]

tony sayer wrote:

Most fuses and switches intended for AC mains are not suitable for DC
even thought it's a lower voltage.
That's why a lot of automotive stuff gets used on boats.

Concur with that, we used some mains fuses on DC 24 volt supplies they
blew at a lot more then what they were supposed to. Automotive sounds
far more appropriate..

Suppose on of those car hi-fi places might have something suitable
unless anyone else knows different?..

Not so. Fuses "blow" because the current flowing in them causes the fuse
wire[1] to heat up - eventually to the point where the fuse wire ruptures.

The AC current rating of the fuse is defined as "symmetrical RMS
current" which is mathematically equivalent to a direct current of the
same magnitude. The fuse has no idea (and doesn't care) whether the
current flowing is a.c. or d.c. until the point where it ruptures due to
overheating. At the point it ruptures, if the current flowing is A.C.,
then the arc is quenched immediately. If the current flowing is D.C.
then the arcing time will be longer. Therefore, the rated breaking
capacity of a fuse is lower for D.C. than for A.C., but the current/time
characteristic curves are the same.

The voltage rating and the rated breaking capacity of a fuse are defined
in accordance with national and/or international standards which require
the rated breaking current to be broken without the fuse cracking,
falling to bits or indeed exploding.

The effect you may be experiencing (i.e. A.C. fuses blow more often on
D.C.) is probably due to the fact that with the D.C. voltage being lower
and therefore the load resistance being lower, the opportunity for a
significant overload is somewhat enhanced cf mains-voltage a.c.

see he http://www.lawsonfuses.eu/lowvoltage.pdf

Note that some fuses have a D.C. rating and some don't. The ones that
don't have a D.C. rating are just as suitable for D.C. as the ones that
do have a rating, but the manufacturer does not test all product lines
on D.C. and therefore does not publish a D.C. Voltage/breaking capacity
for all lines.

Note further that for fuses that *are* rated for D.C. use, the
manufacturer does not publish separate time/current characteristic
curves for D.C. and neither do they publish any correction factors for
D.C. use.

Ergo, direct current and "symmetrical RMS alternating current have the
same effect on the fuse wire and have identical tripping characteristics.


[1] Fuse wire or equivalent "fusible link".

[Dave Osborne[_2_]]

js.b1 wrote:
PAL type automotive fuses go 100A (if not more).

Some french cars use a flat fuse for 100-150-200A as I recall, right
at the battery terminals in a busbar arrangement. The objective I
assume is to disconnect a starter cable short fault in event of an
accident - high pressure (petrol) and very high pressure (diesel) fuel
lines are usually extremely close to such cables on most cars.

Incidentally, check if there are any requirements of your boat
insurance - by that I mean fusing or emergency disconnect. Nylon
flexible conduit is good for protecting cables, which for marine
should be of the tinned fine variety.

I presume you mean the cables should be tinned fine? I read this as
"Nylon flexible conduit [...] should be of the tinned fine variety" ;-)

[David Hansen]

On Tue, 14 Sep 2010 16:23:00 +0100 someone who may be Dave Osborne
wrote this:-

The fuse has no idea (and doesn't care) whether the
current flowing is a.c. or d.c. until the point where it ruptures due to
overheating. At the point it ruptures, if the current flowing is A.C.,
then the arc is quenched immediately. If the current flowing is D.C.
then the arcing time will be longer. Therefore, the rated breaking
capacity of a fuse is lower for D.C. than for A.C., but the current/time
characteristic curves are the same.

Within the limits of the discussion I agree, with the minor niggle
that the arc will only be quenched "immediately" on AC if the
current is less than the breaking capacity of the fuse. If it is
more then the fuse cracking, falling to bits or exploding is
possible. The damage if this happens has to be seen to be believed.

see he http://www.lawsonfuses.eu/lowvoltage.pdf

The difference between AC and DC is dramatic. That reference says

"Breaking Capacity

"The standardized values of Breaking Capacity for fuse-links to
BS88 are 80kA for voltages of 415V a.c., and above, and 40kA for
d.c., applications. The 240V a.c., designs have a breaking capacity
of 16kA minimum."

Fuses are good devices, other types of AC equipment may not be
suitable for use on DC at all.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

[Dave Osborne[_2_]]

David Hansen wrote:
On Tue, 14 Sep 2010 16:23:00 +0100 someone who may be Dave Osborne
wrote this:-

The fuse has no idea (and doesn't care) whether the
current flowing is a.c. or d.c. until the point where it ruptures due to
overheating. At the point it ruptures, if the current flowing is A.C.,
then the arc is quenched immediately. If the current flowing is D.C.
then the arcing time will be longer. Therefore, the rated breaking
capacity of a fuse is lower for D.C. than for A.C., but the current/time
characteristic curves are the same.

Within the limits of the discussion I agree, with the minor niggle
that the arc will only be quenched "immediately" on AC if the
current is less than the breaking capacity of the fuse. If it is
more then the fuse cracking, falling to bits or exploding is
possible. The damage if this happens has to be seen to be believed.

But that (the physical destruction of the fuse) demonstrates either a
flawed design or a catastrophic event, does it not?

The prospective short circuit current should in all cases be less than
the breaking capacity of the protective device for all foreseeable,
manageable risks.

For the vast majority of domestic installations, the prospective short
circuit current is an order of magnitude less than the breaking capacity
of the fuse. E.g. The breaking capacity of a BS1361 fuse in a house
service cut-out is rated at 33kA and (I would say) the prospective short
circuit current in the vast majority of dwellings is less than 3.3kA, so
in fact there is a (worst-case) safety factor of 10 on the main supply fuse.


see he http://www.lawsonfuses.eu/lowvoltage.pdf

The difference between AC and DC is dramatic. That reference says

"Breaking Capacity

"The standardized values of Breaking Capacity for fuse-links to
BS88 are 80kA for voltages of 415V a.c., and above, and 40kA for
d.c., applications. The 240V a.c., designs have a breaking capacity
of 16kA minimum."

It's not that dramatic if it merely reduces your worst-case safety
factor from 10 to 5.

Cheers,
DaveyOz

[Tabby]

On Sep 14, 11:43*am, wrote:
I've been doing a major re-wire of the boat we recently bought in
Belgium, it's going pretty well and much of the horror is now tidied
up (it had suffered from the typical car wiring types of bodges, wires
draped around the place, lots of ends poked into one terminal, etc.,
etc.)

I have installed a couple of consumer units to provide switching and
protection for individual circuits but there are still two 'master'
fuses between the batteries (separate leisure and starter batteries)
and the consumer units feeding all the circuits.

The existing fuses are 'bottle' fuses and I'm wondering whether to
retain them or to replace them. *I certainly want easy to replace
fuses (i.e. not needing a screwdriver or spanner) as one doesn't want
to have to find tools in an emergency. *I need something in the region
of 60 to 100 amps though. *Currently one fuse is 63 amps and the other
is 35 amps. *If I stay with the bottle fuses I want to make both 63
amps which means I need to change one of the fuse holders and getting
a replacement fuseholder may be a problem although it looks as if
Farnell have a possible DIN rail mounting holder, I'm not sure how
easy this will be to fit.

So, are there any reasonably economical alternatives with 'replace by
hand' fuses with ratings in the 60 to 100 amps region? *They want to
be reliable as well though don't need to be capable of use at high
voltages, this is a 12 volt system.

Then, in addition, I want to protect the 'heavy' stuff. *The starter
battery also feeds the starter motor (surprise!) and the bow
propellor. *Currently (no pun intended) these are wired direct to the
battery and I'm thinking some sort of protection for this wiring would
be a good thing too. *The connection to the bow propellor in
particular is long and circuitous and a fault could easily start a
nasty fire in an inaccessible place. *The wires from the batteries to
the existing bottle fuses are also unprotected (only a couple of feet
or so, but still a fault is possible).

I'm thinking that the easiest approach for this is a fuse in the
ground wire to the batteries, it's where the battery isolation
switches are already wired so adding a fuse here would be reasonably
accessible. *It looks to me as if a couple of Littelfuse 'mega fuse'
links would do here, they have screw connections but at around 500
amps I guess that's inevitable. *Are there any practical alternatives
to the 'mega fuse'?

Fuse wire sounds ideal, but replace the 2 screws fixing it with thumb
screws, wingnuts etc, so no tool needed. Its pretty much impossible to
beat wire fuses for reliability & economy. Attach spare fuse wire to
the holder.


NT

[Dave Plowman (News)]

In article ,
wrote:
So, are there any reasonably economical alternatives with 'replace by
hand' fuses with ratings in the 60 to 100 amps region? They want to
be reliable as well though don't need to be capable of use at high
voltages, this is a 12 volt system.

Maxi-blade? The same as ordinary car ones but larger. Half way down the
page.

http://www.vehicle-wiring-products.e...uses/fuses.php

--
*I wish the buck stopped here. I could use a few.

Dave Plowman London SW
To e-mail, change noise into sound.

[David Hansen]

On Tue, 14 Sep 2010 19:29:25 +0100 someone who may be Dave Osborne
wrote this:-

But that (the physical destruction of the fuse) demonstrates either a
flawed design or a catastrophic event, does it not?

A flawed design of the installation, yes. As I said it was a minor
niggle.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

[Jules Richardson]

On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

[The Natural Philosopher[_2_]]

Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

This may be of interest.

http://www.electricalcarservices.com...es-p-1383.html

If you want a safety cutoff that will handle hundreds of amps.

[The Natural Philosopher[_2_]]

Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

Oh here is a 70A rated trip...

http://www.greenpower.co.uk/shop/electrical.php

[[email protected]]

David Hansen wrote:
On Tue, 14 Sep 2010 19:29:25 +0100 someone who may be Dave Osborne
wrote this:-

But that (the physical destruction of the fuse) demonstrates either a
flawed design or a catastrophic event, does it not?

A flawed design of the installation, yes. As I said it was a minor
niggle.

It's still a whole lot better than setting fire to the wiring. I
suppose the exploding fuse might start a fire but 10 metres (in my
case) of smouldering insulation sounds decidedly worse than some bits
of exploded fuse sprayed around the engine compartment.

In reality I doubt if I have any really serious worries as regards
rupture capacity with fuses on a 12 volt system driven by just one
(admittedly big, 1050 amp CCA) battery.

Actually, looking at the Littelfuse data, the 'interrupt capacity' of
the Mega Fuse range is only 2000 Amps at 32 volts so it's possibly
marginal for my application. Although what happens if you exceed the
interrupt capacity is anybody's guess.

--
Chris Green

[[email protected]]

John wrote:

Would it make sense to have a separate battery for the bow thruster -
located near the thruster. You must be getting quite a voltage drop at the
moment. A local battery could be charged with thinner cable than the cable
that is needed to transmit the motor power. It would also make the starter
battery totally dedicated to engine starting.

Some boats are equipped that way but I think we'll stay as we are,
it's not *that* big a boat and it doesn't make sense to add yet
another battery.

--
Chris Green

[[email protected]]

Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

OK, I think I see where you're coming from. However, as you say, I'm
aiming to put a fuse close to the battery in the -ve lead and as far
as I can see that protects against more failures than putting it
anywhere else.

--
Chris Green

[David Hansen]

On Wed, 15 Sep 2010 15:26:58 +0100 someone who may be
wrote this:-

Actually, looking at the Littelfuse data, the 'interrupt capacity' of
the Mega Fuse range is only 2000 Amps at 32 volts so it's possibly
marginal for my application. Although what happens if you exceed the
interrupt capacity is anybody's guess.

What happens in those circumstances is not a guess. If there is a
fault the fuse will not reliably break the current. You might be
lucky and it will manage to break the current without damage. You
might be unlucky and it manages to break the current, though with
damage ranging from overheating to destruction of the fuse and
things around it. You might be more unlucky and the fuse fails to
break the current at all, meaning damage to the rest of the
installation.

Fuses are better than circuit breakers when abused. A fuse might
break the current eventually, a circuit breaker with the contacts
welded together will probably not break the current.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000...#pt3-pb3-l1g54

[[email protected]]

The Natural Philosopher wrote:
Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

This may be of interest.

http://www.electricalcarservices.com...es-p-1383.html

If you want a safety cutoff that will handle hundreds of amps.

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green

[harry]

On 15 Sep, 18:18, wrote:
The Natural Philosopher wrote:



Jules Richardson wrote:
On Tue, 14 Sep 2010 15:12:50 +0100, tinnews wrote:
I take it it's a wood / fibreglass hull then, with no chance of an
accidental ground path back to the battery?

No, it's steel hull. *What sort of accident/problem are you thinking of
when you say "accidental ground path back to the battery". *Surely I'm
protecting against just that, the chance of one of those big, heavy
wires shorting to the hull/superstructure - which can't happen on a
wooden/plastic boat.

Mostly misreading on my part, I think :-)

I just think of a metal hull as a nice chunky ground (similar to the
chassis in a car), and of motors etc. as having their metal cases
connected to ground too. Say the mounts for two of those motors wear or
are installed incorrectly, you may end up with the two motor cases linked
via the hull - something that could go unnoticed for a long time. A
positive-side fuse would protect Motor 1, but a ground-side wouldn't
because the motor would still have a ground path back to the battery via
the hull and Motor 2.

It takes a couple of faults for it to happen, but I've seen that kind of
thing done due to botched installations, manufacturing faults, or age-
related wear. As for why it's relevant in your case? It's probably
not ;-) I only realised later that you were talking about having a ground
disconnect very close to the battery - and so long as there's no way that
the -ve terminal of the battery could find a path to the hull, it's a non-
issue...

cheers

Jules

This may be of interest.

http://www.electricalcarservices.com...tery-isolator-...

If you want a safety cutoff that will handle hundreds of amps.

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! *I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green- Hide quoted text -

- Show quoted text -

A switch and an isolator are not the same thing. Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.

[[email protected]]

harry wrote:

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! Â*I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green- Hide quoted text -

- Show quoted text -

A switch and an isolator are not the same thing. Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.

True, I was just meaning that it isn't an overload protection device.

It's not actually clear whether the device in question is intended to
*switch* the current or not. Given that it's a solid state device it
might actually be able to switch while on load without much distress.

--
Chris Green

[The Natural Philosopher[_2_]]

wrote:
harry wrote:
That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green- Hide quoted text -

- Show quoted text -
A switch and an isolator are not the same thing. Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.

True, I was just meaning that it isn't an overload protection device.

It's not actually clear whether the device in question is intended to
*switch* the current or not. Given that it's a solid state device it
might actually be able to switch while on load without much distress.

Yes. The race car rules say you have to have a master wotsit that will
isolate the battery whatever load is being drawn. In a crash the
marshalls MUST be able to render the car safe in every sense electrically.

Those solid state isolators WILL switch full current.

[harry]

On 16 Sep, 14:37, wrote:
harry wrote:

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! *I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.

--
Chris Green- Hide quoted text -

- Show quoted text -

A switch and an isolator are not the same thing. *Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.

True, I was just meaning that it isn't an overload protection device.

It's not actually clear whether the device in question is intended to
*switch* the current or not. *Given that it's a solid state device it
might actually be able to switch while on load without much distress.

--
Chris Green- Hide quoted text -

- Show quoted text -

A solid state device is not an isolator. The circuit has to be
phyisically broken in both poles to be considered to be isolated.

[Dave Osborne[_2_]]

harry wrote:
On 16 Sep, 14:37, wrote:
harry wrote:

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.
--
Chris Green- Hide quoted text -
- Show quoted text -
A switch and an isolator are not the same thing. Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.
True, I was just meaning that it isn't an overload protection device.

It's not actually clear whether the device in question is intended to
*switch* the current or not. Given that it's a solid state device it
might actually be able to switch while on load without much distress.

--
Chris Green- Hide quoted text -

- Show quoted text -

A solid state device is not an isolator. The circuit has to be
phyisically broken in both poles to be considered to be isolated.


Well, that's not strictly true Harry. Whilst a solid-state device cannot
offer an isolation function (because it can't achieve the prescribed
"separation distance" of contacts and because the wiring regs simply
don't allow it), the isolation function does not *by definition*
require the neutral to be disconnected.

Section 537 of the wiring regs applies. You need to read the whole
section, but here's three short extracts:-

=====

"537.1.4

[...]

A main switch intended for operation by ordinary persons, e.g. of a
household or similar installation, shall interrupt both live conductors
of a single phase supply."

So, in a domestic environment, the main switch (in the consumer unit)
must be two pole.

However,

=====

"537.2.1.1

Every circuit shall be capable of being isolated from each of the
supply's live conductors. In a TN-S or TN-C-S system, it is not
necessary to isolate or switch the neutral conductor where it is
regarded as being connected to earth by a suitably low impedance."

Thus, by inference, the requirements for TT systems are different in
that, as the neutral is not "regarded as being connected to earth by a
suitably low impedance", isolation of the neutral *is* required.

=====

"537.2.2.1

A device for isolation shall isolate all live supply conductors from the
circuit concerned [...].

[...]

Semiconductor devices shall not be used as isolating devices."

[harry]

On 17 Sep, 11:23, Dave Osborne wrote:
harry wrote:
On 16 Sep, 14:37, wrote:
harry wrote:

That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! *I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.
--
Chris Green- Hide quoted text -
- Show quoted text -
A switch and an isolator are not the same thing. *Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.
True, I was just meaning that it isn't an overload protection device.

It's not actually clear whether the device in question is intended to
*switch* the current or not. *Given that it's a solid state device it
might actually be able to switch while on load without much distress.

--
Chris Green- Hide quoted text -

- Show quoted text -

A solid state device is not an isolator. *The circuit has to be
phyisically broken in both poles to be considered to be isolated.

Well, that's not strictly true Harry. Whilst a solid-state device cannot
offer an isolation function (because it can't achieve the prescribed
"separation distance" of contacts and because the wiring regs simply
don't allow it), *the isolation function does not *by definition*
require the neutral to be disconnected.

Section 537 of the wiring regs applies. You need to read the whole
section, but here's three short extracts:-

=====

"537.1.4

[...]

A main switch intended for operation by ordinary persons, e.g. of a
household or similar installation, shall interrupt both live conductors
of a single phase supply."

So, in a domestic environment, the main switch (in the consumer unit)
must be two pole.

However,

=====

"537.2.1.1

Every circuit shall be capable of being isolated from each of the
supply's live conductors. In a TN-S or TN-C-S system, it is not
necessary to isolate or switch the neutral conductor where it is
regarded as being connected to earth by a suitably low impedance."

Thus, by inference, the requirements for TT systems are different in
that, as the neutral is not "regarded as being connected to earth by a
suitably low impedance", isolation of the neutral *is* required.

=====

"537.2.2.1

A device for isolation shall isolate all live supply conductors from the
circuit concerned [...].

[...]

Semiconductor devices shall not be used as isolating devices."- Hide quoted text -

- Show quoted text -

Well, every isolator I have seen has broken phase and neutral
conductors.

[Dave Osborne[_2_]]

harry wrote:
On 17 Sep, 11:23, Dave Osborne wrote:
harry wrote:
On 16 Sep, 14:37, wrote:
harry wrote:
That's just a switch, it's not difficult to buy battery isolation
switches to do the same and they don't cost more than £200 like the
one above! I can see good reasons for using something like the one
above in motorsport and similar applications but it really isn't that
necessary on a boat as long as you have a readily accessible
mechanical switch.
--
Chris Green- Hide quoted text -
- Show quoted text -
A switch and an isolator are not the same thing. Isolators are meant
to be opened under no-load conditions.
They won't last long used as switches which will interrupt their rated
current.
True, I was just meaning that it isn't an overload protection device.
It's not actually clear whether the device in question is intended to
*switch* the current or not. Given that it's a solid state device it
might actually be able to switch while on load without much distress.
--
Chris Green- Hide quoted text -
- Show quoted text -
A solid state device is not an isolator. The circuit has to be
phyisically broken in both poles to be considered to be isolated.
Well, that's not strictly true Harry. Whilst a solid-state device cannot
offer an isolation function (because it can't achieve the prescribed
"separation distance" of contacts and because the wiring regs simply
don't allow it), the isolation function does not *by definition*
require the neutral to be disconnected.

Section 537 of the wiring regs applies. You need to read the whole
section, but here's three short extracts:-

=====

"537.1.4

[...]

A main switch intended for operation by ordinary persons, e.g. of a
household or similar installation, shall interrupt both live conductors
of a single phase supply."

So, in a domestic environment, the main switch (in the consumer unit)
must be two pole.

However,

=====

"537.2.1.1

Every circuit shall be capable of being isolated from each of the
supply's live conductors. In a TN-S or TN-C-S system, it is not
necessary to isolate or switch the neutral conductor where it is
regarded as being connected to earth by a suitably low impedance."

Thus, by inference, the requirements for TT systems are different in
that, as the neutral is not "regarded as being connected to earth by a
suitably low impedance", isolation of the neutral *is* required.

=====

"537.2.2.1

A device for isolation shall isolate all live supply conductors from the
circuit concerned [...].

[...]

Semiconductor devices shall not be used as isolating devices."- Hide quoted text -

- Show quoted text -

Well, every isolator I have seen has broken phase and neutral
conductors.

There is a good precis on page 14 (6/12) he

http://www.gil-lec.co.uk/custom/uplo...s_Switches.pdf