When is a 30A fuse not a 30A fuse?

[Martin_J]

Just installing a new Wind generator and associated HRDi controller.

Requirement is for 4mm sq cables (as short as possible) from controller to battery and inline fuse to each battery as well.

I thought, easy.. Cable should be good for 39A.. Fuse at 30A, perfect so I went to Furneaux Riddall bought a couple of Midi fuse holders and some 30A Midi fuses to go with the nice 4mm sq tinned cable.
Midi Fuses at Furneaux Riddall

But.. I just read that these 30A fuses are Continuous Rating 30A, blow at 60A.

What's this all about? :ambivalence:

Does this mean that they will take for example 45A for a certain amount of time.. then what!

Were these a bad buy?

 

[VicS]

Just installing a new Wind generator and associated HRDi controller.

Requirement is for 4mm sq cables (as short as possible) from controller to battery and inline fuse to each battery as well.

I thought, easy.. Cable should be good for 39A.. Fuse at 30A, perfect so I went to Furneaux Riddall bought a couple of Midi fuse holders and some 30A Midi fuses to go with the nice 4mm sq tinned cable.
Midi Fuses at Furneaux Riddall

But.. I just read that these 30A fuses are Continuous Rating 30A, blow at 60A.

What's this all about? :ambivalence:

Does this mean that they will take for example 45A for a certain amount of time.. then what!

Were these a bad buy?

Fuses will withstand the rated current contiuously. They only blow when overloaded The bigger the overload the faster they blow... there are fast and slow blow fuses to take into account too.

Your fuses should only be rated at the max current output expected from the wind gen, or only slightly more. You are, I think, making the mistake of rating the fuse to the ( oversize) cable.

 

[rogerthebodger]

Just installing a new Wind generator and associated HRDi controller.

Requirement is for 4mm sq cables (as short as possible) from controller to battery and inline fuse to each battery as well.

I thought, easy.. Cable should be good for 39A.. Fuse at 30A, perfect so I went to Furneaux Riddall bought a couple of Midi fuse holders and some 30A Midi fuses to go with the nice 4mm sq tinned cable.
Midi Fuses at Furneaux Riddall

But.. I just read that these 30A fuses are Continuous Rating 30A, blow at 60A.

What's this all about? :ambivalence:

Does this mean that they will take for example 45A for a certain amount of time.. then what!

Were these a bad buy?

Yes you will find with fuses there is a time/overload graph which can vary depending it it's fast blow or slow blow.

 

[Martin_J]

Your fuses should only be rated at the max current output expected from the wind gen, or only slightly more. You are, I think, making the mistake of rating the fuse to the ( oversize) cable.

VicS
Thanks I was also looking at the US website where the 914i is sold as a kit with a 30A inline fuse.

Since the HRDi will also take 160W solar input, on a windy day then a 30A fuse still looks suitable.

I just didn't realise or expect that some fuses are sold as 'Continuous Rating' and seems like I expected (wrongly) that a 30A fuse would protect something utilising a 39A capable cable.

The other 'inline' fuses sold at Furneaux Riddall didn't appear to be capable of taking the 4.0mm sq wires.

 

[VicS]

Fuses will withstand the rated current contiuously. They only blow when overloaded The bigger the overload the faster they blow... there are fast and slow blow fuses to take into account too.

Your fuses should only be rated at the max current output expected from the wind gen, or only slightly more. You are, I think, making the mistake of rating the fuse to the ( oversize) cable.

No mention of fuses in the HRDi installation instructions :mad-new:

But yes you have to add the solar output in as well (You did not mention solar) So should have said the max output from the system

 

[Martin_J]

Fig 2 in the HRDi Manual suggests you use the fuse supplied with the wind charger!

Marlec - HRDi-Manual.pdf

... but I didn't get any fuses with my 914i.....!

Looks like I could be looking for a 20A fuse then with a holder that accepts 4mm wire...

 

[pvb]

Fig 2 in the HRDi Manual suggests you use the fuse supplied with the wind charger!

Marlec - HRDi-Manual.pdf

... but I didn't get any fuses with my 914i.....!

Looks like I could be looking for a 20A fuse then with a holder that accepts 4mm wire...

The manual suggests putting an inline fuse close to the battery. This is a sensible precaution, designed to safeguard the wiring in the event of a short-circuit (which would otherwise potentially cause a fire). Your 30A MidiFuse will be fine for this purpose; the 4 sq mm wire will be suitably protected. The fuse rating really has nothing to do with the output of the wind generator.

 

[Martin_J]

Pvb... yes, I was tending towards installing what I have. The wire run between the controller and the batteries will be about 1 metre in a protected conduit. Those Midi fuses and holders just look nice and secure.

 

[jdc]

The function of fuses is to protect wiring getting so hot that it, or whatever it's touching, catches fire. It has nothing whatever to do with the piece of equipment which, if it has protection at all, will have that protection built into it.

In the case of battery charging you should realise that much the largest source of power is the battery, not the charger. Thus a wire attached to a battery needs fusing upstream, ie close to the battery.

As for the length of time it takes to heat up, you should compare it to the wire. A 4mm^2 wire will have a much longer time-constant than a fuse, so it's just fine that you install a 30A continuous rating fuse: there will be no current - time history where the wire will get dangerously hot before the fuse blows.

 

[coopec]

Martin

I used to wonder why you needed fast acting fuses and slow acting fuses but articles like this explained the reason.

Slow Blow vs Fast Acting Fuse
http://electronics.stackexchange.com/questions/25055/slow-blow-vs-fast-acting-fuse

Clive

 

[nigelmercier]

The function of fuses is to protect wiring getting so hot that it, or whatever it's touching, catches fire. It has nothing whatever to do with the piece of equipment which, if it has protection at all, will have that protection built into it...

BONG!

Next please.

 

[Len Ingalls]

The function of fuses is to protect wiring getting so hot that it, or whatever it's touching, catches fire. It has nothing whatever to do with the piece of equipment which, if it has protection at all, will have that protection built into it.

In the case of battery charging you should realise that much the largest source of power is the battery, not the charger. Thus a wire attached to a battery needs fusing upstream, ie close to the battery.

As for the length of time it takes to heat up, you should compare it to the wire. A 4mm^2 wire will have a much longer time-constant than a fuse, so it's just fine that you install a 30A continuous rating fuse: there will be no current - time history where the wire will get dangerously hot before the fuse blows.

Correct!

 

[nigelmercier]

Correct!

The first paragraph certainly isn't!

 

[jdc]

The first paragraph certainly isn't!

Perhaps you'd explain why? Or maybe it needs reading twice (it would be clearer if I'd put in the assumed 'from')? By the way, if I'm very wrong, God help us all - circuit breakers to my design have been made in tens of millions.

 

[pvb]

By the way, if I'm very wrong, God help us all - circuit breakers to my design have been made in tens of millions.

You can sleep easy, you're not wrong!

 

[JumbleDuck]

The function of fuses is to protect wiring getting so hot that it, or whatever it's touching, catches fire.

That is one function of a fuse, yes. It is also there to deal with unexpected current draws at the equipment, which is why we fit fuses to mains plugs based on the load and not the wire size. The supply to my radio will happily stand 20A, but if the radio starts drawing 20A I want it disconnected.

 

[DickieT]

That is one function of a fuse, yes. It is also there to deal with unexpected current draws at the equipment, which is why we fit fuses to mains plugs based on the load and not the wire size. The supply to my radio will happily stand 20A, but if the radio starts drawing 20A I want it disconnected.

Exactly ! In the small boat situation we are talking about here, the fuse is there for overload protection of the cable AND the device it is supplying. A GPS receiver may draw less than an amp but the cable will almost certainly be rated far higher than that, so I would probably choose a fuse about 2A. This gives protection to both the load and the cable. Not all equipment has built in adequate fusing, I have seen a couple of GPS receivers a melted mess inside, the owner having fitted a "large" fuse chosen on cable size. Also any inboard equipment fuses offer no protection to the often rather dodgy termination attempt someone may have made to the plug bringing power into the device. Installation instructions give guidance as to suitable fuse size, they do not say bung a fuse in selected for the cable you are using.

 

[Len Ingalls]

1. When fusing a distribution wire-from a distribution panel or other source of current-you MAY fuse to that wire's rated capacity.
ie: size of wire is 14ga-fuse 15A
Reason: That wire may have several loads,now or in future, & you are only interested in protecting that wire from melting until it gets to it's load(s).
You MAY under fuse that wire if you wish,but there is no benefit,& there is potential of "nuisance blows" in future,as more loads are connected.

2. Each load on that wire should be individually fused for that load's rated max draw + 10%-15% or according to mfgr's label.
Most decent equipment includes a fuse built in, or inline, close to the equipment.
This is where it can get tricky. If the equipment came with a meter of 10A rated wire & it's fuse is at or within that equipment,then you have a meter of improperly fused wire between the join to the 15A feed & the fuse at the equipment.
Proper practice states that you should install an inline(or other) 10A fuse at the join to protect that meter of wire.(or cut eqpt wire shorter?)

3. In the case of a charge source (solar panel,wind chgr,generator,bat. charger,etc.) connected to a battery source (of 1000's A),you MAY still fuse to the ampacity of the wire between battery & charge source,but it would be prudent to install another smaller fuse at the charging source to protect the charging source from battery "backfeed" in the event that charging source shorted internally. In this case,it probably would make more sense to fuse the wire at the battery end with this smaller fuse.

4. Note however that any charging source is just like a (small) battery.It is a source of current & should be fused at it's output. A charging source can melt wires also.

https://www.bluesea.com/articles/1441

5. The same rules apply if you are using breakers instead of fuses. Slow blow fuses are fine for fusing wire. Fast blow fuses MAY be preferable for fusing at the equipment.

6. The same provisions apply to AC also.

 

[DickieT]

1. When fusing a distribution wire-from a distribution panel or other source of current-you MAY fuse to that wire's rated capacity.
ie: size of wire is 14ga-fuse 15A
Reason: That wire may have several loads,now or in future, & you are only interested in protecting that wire from melting until it gets to it's load(s).
You MAY under fuse that wire if you wish,but there is no benefit,& there is potential of "nuisance blows" in future,as more loads are connected.

2. Each load on that wire should be individually fused for that load's rated max draw + 10%-15% or according to mfgr's label.
Most decent equipment includes a fuse built in, or inline, close to the equipment.
This is where it can get tricky. If the equipment came with a meter of 10A rated wire & it's fuse is at or within that equipment,then you have a meter of improperly fused wire between the join to the 15A feed & the fuse at the equipment.
Proper practice states that you should install an inline(or other) 10A fuse at the join to protect that meter of wire.(or cut eqpt wire shorter?)

3. In the case of a charge source (solar panel,wind chgr,generator,bat. charger,etc.) connected to a battery source (of 1000's A),you MAY still fuse to the ampacity of the wire between battery & charge source,but it would be prudent to install another smaller fuse at the charging source to protect the charging source from battery "backfeed" in the event that charging source shorted internally. In this case,it probably would make more sense to fuse the wire at the battery end with this smaller fuse.

4. Note however that any charging source is just like a (small) battery.It is a source of current & should be fused at it's output. A charging source can melt wires also.

https://www.bluesea.com/articles/1441

5. The same rules apply if you are using breakers instead of fuses. Slow blow fuses are fine for fusing wire. Fast blow fuses MAY be preferable for fusing at the equipment.

6. The same provisions apply to AC also.

Yes Len, totally agree with that. Fuse from distribution board chosen to suit cable size, then subsequent fuses (which I would always fit) chosen primarily for the individual or group of equipment they are feeding. Same as house wiring (MCB's in consumer unit) or cars, big fuse(s) at battery terminals, smaller fuses down the line feeding individual loads.

 

[TQA]

Errr you have a wind generator with an output of 30+ amps ? On a boat?

This I gotta see.