Bow Thruster Circuit Breaker Question

[Baggy]

I have an in line Bow Thruster fuse at 125 amps from BT battery to BT
which has now blown twice
This was probably due to over use of running my new BT,( as a test ) and battery going flat, low volts high amps

The BT on start up will probably draw over 300 amps

Would it be ok to fit a circuit breaker instead ?

if so, Should I go for a 150 or 200 amp circuit breaker ?

 

[LittleSister]

What does the manufacturer say in its installation instructions?

My bow thruster has a nominal current draw of 315A, and the manufacturer recommends an ANL 250 fuse. It also says 'This fuse should be of a adequate quality which normally means that it is physically large as these have less voltage drop than the simple / small ones. It should be of the slow type and sized to take the amperage draw for at least 5 minutes.'

 

[adamlang]

I think an important factor will be the wiring size you're using and what it can cope with. The breaker/fuse needs to be sized to the wire.

The page from bluesea, including the wire size table might help:
Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems

 

[Baggy]

Hi LittleSister

I have a Max Power CT45 at 3.2 Kw power, rated at 250 amps at 11 volts
I have a 70mm2 cable, 2 mtrs) from BT batt to BT, this should be more than adequate

The BT batt is connected to the Starter batt, with the engine running, I can see 14.4 volts at the BT
then down to over 10 volt when runnng.



Is their any reason not to used a 150 /200 circuit breaker, or as you say or up rate the fuse ?
I think I will have to give Max Power a call

 

[pvb]

What does the manufacturer say in its installation instructions?

My bow thruster has a nominal current draw of 315A, and the manufacturer recommends an ANL 250 fuse. It also says 'This fuse should be of a adequate quality which normally means that it is physically large as these have less voltage drop than the simple / small ones. It should be of the slow type and sized to take the amperage draw for at least 5 minutes.'

ANL fuses are often specified for thrusters as they have a decent slow-blow profile. MaxPower recommend a 175A ANL fuse for the CT45 thruster.

This graph from the BlueSea website shows the slow-blow characteristic of ANL fuses.

 

[PaulRainbow]

I think an important factor will be the wiring size you're using and what it can cope with. The breaker/fuse needs to be sized to the wire.

The page from bluesea, including the wire size table might help:
Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems

In the case of a bow thruster, the fuse/breaker is there to protect the cables and the thruster motor, so fusing 70mm cable to suit the cable would not be protecting the thruster, as the cable has a rating close to 500a.

 

[rogerthebodger]

In the case of a bow thruster, the fuse/breaker is there to protect the cables and the thruster motor, so fusing 70mm cable to suit the cable would not be protecting the thruster, as the cable has a rating close to 500a.

Paul

Do you mean 70mm dia cable or 70mm squared area cable is rated at 500 Amps

 

[RichardS]

Paul

Do you mean 70mm dia cable or 70mm squared area cable is rated at 500 Amps

How could he mean 70mm diameter cable? That's not cable .... it's scaffolding pipe.

Richard

 

[rogerthebodger]

How could he mean 70mm diameter cable? That's not cable .... it's scaffolding pipe.

Richard

I'm trying to be diplomatic.

I have 38mm x 24mm 2 12mm thick aluminium buss bars feeding my 600 Amp Bow thruster. this being 912 sq mm area.

My current capacity tables specifies 147 to 180 Amps for a 70 sq mm copper cable Aluminium a little less.

The top bar is the positive (later covered in red tape) and the bottom is the negative.

The 600 Amp fuse if next to the battery feed to the isolation switch.

 

[PaulRainbow]

Paul

Do you mean 70mm dia cable or 70mm squared area cable is rated at 500 Amps

In post #4, the OP stated "I have a 70mm2 cable, "

In post #6, i stated "fusing 70mm cable to suit the cable would not be protecting the thruster, as the cable has a rating close to 500a. "

How could i possibly be talking about 70mm dia cable ?

My current capacity tables specifies 147 to 180 Amps for a 70 sq mm copper cable Aluminium a little less.

No idea what sort of 70mm2 cable you have over there that only has a current carrying capacity of 147 to 180 amps. When i use 70mm cable i use this stuff:

OceanFlex Marine Tinned Battery Cable - 70mm - 2/0 AWG - 485 amps - PER METRE

Rated at 485 amps (close to 500a, as i said in post #6)

 

[rogerthebodger]

In post #4, the OP stated "I have a 70mm2 cable, "

In post #6, i stated "fusing 70mm cable to suit the cable would not be protecting the thruster, as the cable has a rating close to 500a. "

How could i possibly be talking about 70mm dia cable ?



No idea what sort of 70mm2 cable you have over there that only has a current carrying capacity of 147 to 180 amps. When i use 70mm cable i use this stuff:

OceanFlex Marine Tinned Battery Cable - 70mm - 2/0 AWG - 485 amps - PER METRE

Rated at 485 amps (close to 500a, as i said in post #6)

I use welding cable where 70mm2 is rated at 350 on a 100% duty cycle in open air (not enclosed)

If I wished to use tinned I would have to import it direct at a large expense as it has duty to protect the local industry.

The other issue is what volt drop would 40mm2 at 500 Amp would you get.

This is an chart from the UK that indicated the current capacity under various applications.



IEE Current Ratings Regulations Table 4E1A

 

[pvb]

This is an chart from the UK that indicated the current capacity under various applications.



IEE Current Ratings Regulations Table 4E1A

You'll have noticed that the chart is for single-core cable...

 

[rogerthebodger]

You'll have noticed that the chart is for single-core cable...

Yes single cables in different configurations of 2, 3 or 4 cables

The first column shows 2 singles cables there and back. I know it's not always installed like that but on long runs to say a bow thruster or windlass its quite likely to be run that way.

There are many different current carrying capacities. There can depend on the material of insulation. If the cable is in open are or enclosed in trunking or conduit and duty cycle. the conductor material (resistance)

This is all based on the heat generated as the current flow and the ambient temperature and ability for that heat to disperse.

Duty cycle is often ignored until you used a power too long and it burns out. Mush to my frustration even the top power tool manufactures don't quote duty cycle which can be as low as 10 -15 %.

I would not run 500 Amps down a 70mm2 cable I may be just too conservative but I prefer to be safe than sorry

 

[pvb]

Here's a typical battery cable specification...

70mm2 (#00 AWG) Battery Starter Cable (Red or Black)

The duty cycle of a bow thruster is so small that, even if you don't believe the cable's rating, there'd be no problems!

 

[rogerthebodger]

No, single-core cable, ie just one rod of copper, not the multi-core flexible cable which we usually use on boats.

May be but its the area of the conductor that is important for current carrying capacity.

A stranded cable of the same as a solid core will be a little bigger in diameter but its area that matters.

I would view single core cable different to a solid core cable or a stranded cable.

The cable that PR posted is to me single core stranded cable as opposed to single core solid cable or multi core stranded cable or multi core solid cable

My interpretation of a multi core cable having a number of current carrying cables like 2 core or 3 core mains cable could be solid core or stranded cable. Stranded cable also has variations in the number and size of the strands.

When I wired my boat I used welding able for the very big cables and what we call panel cable which has much finer strands than mains stranded cable. sizes I use is 1.5, 2.5 and 4mm2 panel cable and 10, 50, 70mm2

Again its a matter of interpretation and works used for different meanings to different people .

This is where things get mixed up as different use different terms for the same thing.

 

[TernVI]

Single core cable does not normally mean the same as single strand, AKA solid core.
e.g.
4520001 | Lapp H07V-K Green/Yellow Single Core Control Cable, 1.5 mm² CSA 750 V, 100m | RS Components
Of course lots of solid core cables are single core, but not all, e.g. bellwire.
Some would say single core cable is a contradiction in terms, one core is a wire, two or more cores make a cable. But in reality street, people use cable and wire interchangeably,

 

[PaulRainbow]

Let's have another look.

It was suggested that the Op fuse the circuit based on the cable rating, which is 485a. I said:

In the case of a bow thruster, the fuse/breaker is there to protect the cables and the thruster motor, so fusing 70mm cable to suit the cable would not be protecting the thruster, as the cable has a rating close to 500a.

In other words, fitting a 485a fuse in the bow thruster circuit, to protect the wiring, does not offer any overload protection for the the bow thruster motor. Bow thrusters, like windlesses and electric winches must have overload protection, or anything jamming can cause damage to the motor.

The OP has told us he has 2 meters of 70mm cable, rated at 485a continuous, his bow thruster draws 300a max, with a 3 minute duty cycle.

There aren't any interpretations there, those are all facts. I fail to see where this is going ?????

 

[rogerthebodger]

Here's a typical battery cable specification...

70mm2 (#00 AWG) Battery Starter Cable (Red or Black)

The duty cycle of a bow thruster is so small that, even if you don't believe the cable's rating, there'd be no problems!

Well your link says it can carry 485 Amp continuous so can accept that but I does not stated and temperature or installation conditions

 

[PaulRainbow]

I have an in line Bow Thruster fuse at 125 amps from BT battery to BT
which has now blown twice
This was probably due to over use of running my new BT,( as a test ) and battery going flat, low volts high amps

The BT on start up will probably draw over 300 amps

Would it be ok to fit a circuit breaker instead ?

if so, Should I go for a 150 or 200 amp circuit breaker ?

Firstly, a 125a fuse is underrated.

Secondly, there is nothing to prevent you from using a thermal circuit breaker in place of a fuse. Looking at the specifications of your bow thruster it has internal thermal protection, so my comment above regarding motor protection does not apply, you can fit a circuit breaker up to the current rating of the cable.