Explain to me about circuit breakers

[oilybilge]

I'm installing a 500w Lofrans X1 windlass. They recommend fitting a 35 amp circuit breaker.

Can this be right? By my calculations the motor will be pulling around 40 amps under normal use, so wouldn't the CB be tripping the whole time?

Or is there something I'm not understanding here? Cheers!

 

[wonkywinch]

From the manual :

4.3 Circuit breakers. The circuit breakers recommended by Lofrans have an intervention curve and not a simple plate value.

CBs normally protect the cable not the device and don't trip at the rated current, eg domestic MCBs (type B) trip at 3-5x the rated value.

What are the Different Types of MCB Trip Curves?

 

[noelex]

The current rating does sound slightly lower than I would expect, but I would use the manufacturer’s recommended value.

The wattage rating of windlass motors is a very nominal number. Often they will draw significantly more power near their maximum rated pulling capacity, but significant less much of the time.

Most circuit protection is simply designed to protect the wiring in a fault (short circuit) situation. Windlass circuit breakers are one of the few exceptions. These are designed to trip before the windlass motor overheats. The motors are not continually rated. For this reason it is important to use the correct value and trip curve.

 

[VicS]

A couple of videos from John Ward.

One shows what's inside and explains how they work
The other explains the different types but that is covered by the link in #2

Circuit Breakers - What's inside, how do they work

Types of Circuit Breakers, B C D K and Z

 

[Gsailor]

24 minute video ...

I was once told by a child that videos had to be over 10 minutes to be able to be monetised- has it now increased to 24 minutes?

I was told that some years ago- the 10 minute rule I mean - the child would now be an adult !

I do appreciate the link by the forum member however ... I love to learn -I am only grumbling because I just watched a video by La Vagabond - a sailing video couple that was also 24 minutes approx - they used to be 10 minutes maximum.

24 minutes can be a long time for a video - short films on tv can be of similar duration - made with a professional crew - I reserve judgement upon the circuit breaker video because I had to switch off for a while - it may be that the 24 minutes is totally justified... it will certainly be more beneficial than the awful La Vagabond sailing video (that I skipped through a lot, because I was not going to watch 24 minutes of their video I am sorry to say).

 

[Neeves]

24 minute video ...

I was once told by a child that videos had to be over 10 minutes to be able to be monetised- has it now increased to 24 minutes?

I was told that some years ago- the 10 minute rule I mean - the child would now be an adult !

I do appreciate the link by the forum member however ... I love to learn -I am only grumbling because I just watched a video by La Vagabond - a sailing video couple that was also 24 minutes approx - they used to be 10 minutes maximum.

24 minutes can be a long time for a video - short films on tv can be of similar duration - made with a professional crew - I reserve judgement upon the circuit breaker video because I had to switch off for a while - it may be that the 24 minutes is totally justified... it will certainly be more beneficial than the awful La Vagabond sailing video (that I skipped through a lot, because I was not going to watch 24 minutes of their video I am sorry to say).

Similarly

I was once told by an editor (sailing magazines - and no-one whom anyone will know) to write my articles as if for a 12 year old.

Jonathan

 

[Alex_Blackwood]

The current rating does sound slightly lower than I would expect, but I would use the manufacturer’s recommended value.

The wattage rating of windlass motors is a very nominal number. Often they will draw significantly more power near their maximum rated pulling capacity, but significant less much of the time.

Most circuit protection is simply designed to protect the wiring in a fault (short circuit) situation. Windlass circuit breakers are one of the few exceptions. These are designed to trip before the windlass motor overheats. The motors are not continually rated. For this reason it is important to use the correct value and trip curve.

You are of course correct in what you say. However, being a bit, well quite a lot, pedantic. Technically a circuit breaker won't protect against overheating. The thermal/ magnetic or hydraulic/magnetic circuit breakers, commonly used for windlasses, will protect against overcurrent and faults such as short circuits. If a non continuously rated motor, eg 20 minutes FLC is run at say, 75% FLC for an extended time it will not trip the breaker but it will overheat and possibly burn out the motor. At which stage it will probable trip. Too late! Sorry if that is nit picking and possibly a bit confusing but just trying to clarify.

 

[Stemar]

Similarly

I was once told by an editor (sailing magazines - and no-one whom anyone will know) to write my articles as if for a 12 year old.

Jonathan

IIRC, 12 is the average reading age of adults.

 

[LittleSister]

IIRC, 12 is the average reading age of adults.

If the average adult has the reading age of the average 12 year old . . .

one has to wonder what is the reading age of an average 12 year old.

 

[Alex_Blackwood]

If the average adult has the reading age of the average 12 year old . . .

one has to wonder what is the reading age of an average 12 year old.

Essential information for someone who wants to know about circuit breakers

 

[B27]

You are of course correct in what you say. However, being a bit, well quite a lot, pedantic. Technically a circuit breaker won't protect against overheating. The thermal/ magnetic or hydraulic/magnetic circuit breakers, commonly used for windlasses, will protect against overcurrent and faults such as short circuits. If a non continuously rated motor, eg 20 minutes FLC is run at say, 75% FLC for an extended time it will not trip the breaker but it will overheat and possibly burn out the motor. At which stage it will probable trip. Too late! Sorry if that is nit picking and possibly a bit confusing but just trying to clarify.

I don't think that's entirely true.
A carefully sized circuit breaker with the right 'curve' can often be made to trip before a motor suffers damage.

Unlikely to be 'complete protection' but often a useful level of protection from extended overload or stalling.

So I would suggest following the manufacturer's guidance is a good starting point.

 

[PaulRainbow]

I don't think that's entirely true.
A carefully sized circuit breaker with the right 'curve' can often be made to trip before a motor suffers damage.

Unlikely to be 'complete protection' but often a useful level of protection from extended overload or stalling.

So I would suggest following the manufacturer's guidance is a good starting point.

That's all correct, which is why the Quick breaker "appears" to be to low a current.

 

[noelex]

I agree it is not perfect protection, but the principle of selecting the value and trip curve of the breaker to prevent the windlass overheating is sound.

An example may make the reasoning clearer. Below is a graph of current vs pull for my windlass. This windlass is nominally rated at 2000w at 24v and the manufacturer recomends a 135A breaker. I have also posted a typical breaker trip curve below.

At full load the graph below shows that my windlass will draw 450A (over 9kW ). The trip curve of the breaker shows it will withstand this current for around 6 seconds. At around 270A the windlass will pull about 2/3 of its maximum load and the breaker will trip in about 20 seconds.

At 135A my windlass will pull about 1/4 of its rated load and at this current the breaker will never trip.

If Maxwell have done their sums and practical tests correctly, my windlass is continually rated at 1/4 the maximum load. It can pull at 2/3 the maximum load for around 20 seconds and the full maximum rated load for around 6 seconds before overheating. If this was not the case, Maxwell would have recommended a smaller breaker. This would reduce the run times before the breaker trips. If the motor was more resistant to overheating, Maxwell would have recommend a larger breaker and this would increase the run times at the various loads.

So a breaker can be selected with a value and a trip curve that will protect the windlass from overheating over a wide range of loads. While this is not a perfect system, it works well in practice with few reports of motor damage from overheating, but you need to follow the manufacturer’s guidelines for this system to work.

 

[oilybilge]

Wow ... complicated. Thanks, guys! I knew I could rely on you.

One of the reasons I was asking is that the CB recommended by Lofrans costs £118.

OTOH if it's protecting the motor as well as the wiring then I'm thinking it's just a case of 'suck it up'. I wouldn't feel confident about choosing an alternative, no matter how many graphs I stare at.

Cheers!

 

[PaulRainbow]

Wow ... complicated. Thanks, guys! I knew I could rely on you.

One of the reasons I was asking is that the CB recommended by Lofrans costs £118.

OTOH if it's protecting the motor as well as the wiring then I'm thinking it's just a case of 'suck it up'. I wouldn't feel confident about choosing an alternative, no matter how many graphs I stare at.

Cheers!

Cheaper if you do a Google search for the part number lofrans 187331