Fuse position

[Cloven]

On separate thread on solar panels, VicS stated:

"Don't forget appropriate fuses as close as possible to the battery in all wiring"

Please could someone explain why. I don't doubt Vic, just interested why.

 

[lw395]

The fuse protects the wiring from catching fire due to something shorting the wiring.
The battery has the current capability to do damage, the solar panel does not, so you need a fuse close to the battery to potect the maximum amount of the wiring.
The wiring needs to be thick enough to carry anything the panel can produce.

 

[sarabande]

both +ve and -ve wires fused, or one only, if so which is best practice, please ?

 

[Cloven]

The fuse protects the wiring from catching fire due to something shorting the wiring.
The battery has the current capability to do damage, the solar panel does not, so you need a fuse close to the battery to potect the maximum amount of the wiring.
The wiring needs to be thick enough to carry anything the panel can produce.

Does this apply to anything connected from the battery - ie VHF, Plotter etc?

 

[rob2]

Does this apply to anything connected from the battery - ie VHF, Plotter etc?

Yes, although it is not uncommon to find circuits fused at the switch panel rather than a single fuse on the feed to the panel (close to the battery). Ideally one should have both - a large fuse next to the battery protecting the whole wiring system and then individual fuses for each circuit taken from the switch panel.

Rob.

 

[prv]

Does this apply to anything connected from the battery - ie VHF, Plotter etc?

Yes.

Any wire running straight from the battery is potentially dangerous, as a short-circuit in it will cause a spray of sparks and/or melt the wire. A decent-sized battery will melt a spanner across the terminals, let alone a puny bit of wire. Once the wire has passed an appropriate-sized fuse it is rendered safe, because in the event of a short the fuse will blow instead of the wire melting.

I have a 150amp Megafuse four inches from my service battery terminal, to cover shorts in the heavy wiring to the panel. The panel has an appropriate fuse on each circuit to protect the smaller wiring running out from there (which could melt without blowing the Megafuse).

Pete

 

[Cloven]

rob2 & prv, many thanks for the prompt and clear replies

Dave

 

[lw395]

both +ve and -ve wires fused, or one only, if so which is best practice, please ?

In a car, with a metal body connected to _ve, you fuse the +ve, so if the fuse blows, that circuit is at body potetial, so the short draws no current.
In a boat, there is no 'body' and the engine may or may not be negative, but the principle is still good. IMHO, you should fuse all of the positives, or all of the negatives, otherwise there is some chance of two unfused bits touching.
Blown fuses in the negatives can cause the return current to flow via data lines in some things, which is not a good idea.
Keeping the negative continuous and un fused is a good system, but not the only way. It'sd what most equipment makers have in mid though, as anyone who's installed a stereo in a +ve earth Morris Minor will explain!

 

[David2452]

All a bit over simplistic, an over current device is there to protect a circuit which includes the conductor but is not limited to the conductor of course and should reflect the downstream circuit. So whilst a fuse protecting say a conductor from the battery to a distribution point or power post may be appropriate to protect that conductor, there needs to be protection from that point to the almost certainly lower capacity circuit downstream of that, this can mean that between the battery and a load (plotter, bulb, motor etc.) there can be a number of gradually reducing value over current devices., each reflecting the lower value required downstream. For initial connection to batteries I prefer to use an MRBF as they protect every mm of the connected conductor unlike mega or midis which do not.

 

[Rigger Mortice]

MRBF?

 

[rogerthebodger]

MRBF?

http://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

Google is your friend

 

[Rigger Mortice]

http://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

Google is your friend

Cheers. I suppose I should have tried Mr Google!

 

[VicS]

For initial connection to batteries I prefer to use an MRBF

But the original question was about a garden shed

 

[David2452]

MRBF?

Marine Rated Battery Fuse,

 

[David2452]

But the original question was about a garden shed

Didn't look at that, only this thread, I assumed it was boat related, this being a boat forum rather than a gardening one

 

[Cloven]

But the original question was about a garden shed

Yes, this thread was prompted by the one in "the lounge" which referred to a garden shed solar panel but as the OP of this thread, I was referring to boats, hence this forum

 

[David2452]

Yes, this thread was prompted by the one in "the lounge" which referred to a garden shed solar panel but as the OP of this thread, I was referring to boats, hence this forum

Ah, I see, perhaps a link to the origonal thread would have helped, mind you, my comment on protecting every inch of the conductor still stands.

 

[prv]

http://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

That's an interesting device; wasn't aware of such things.

I'm quite relaxed about the few inches of unfused cable inside my battery locker, though

Pete

 

[JumbleDuck]

That's an interesting device; wasn't aware of such things.

I'm about to experiment with a couple of 250A circuit breakers like this

right beside the house and start batteries. If they prove over-sensitive to engine starting demands (the starter should draw 80A but may well take a lot more as it starts) I'll use fuses instead.

 

[rogerthebodger]

Do you have a web site link