installing new electrics

[Rigger]

Is it always necessary when installing new equipment (GPS,VHF etc) that has its own on /off switch,to wire to a seperate switch in the main switch panel? If the new unit can be protected by its own in-line fuse is that not adequate,thus reducing the amount of wiring in the vicinity of the main panel?

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[oldsaltoz]

G'day Jim,

As long as the main panel fuse is large enough to cope with the new device as well the one being added there is no reason why it can not be wired to an existing switch.

But avoid things like adding radio and sounder on the same supply, you may get some interference from the sounder over the radio, also avoid connecting items that draw very little to large capacity fuses etc.

Most of the older boats around run on 6 fuses at the main panel and have in line fuses hidden all over the place, so it's a good idea to keep the in-line fuse, in or close to the main panel.

Also, have a thing about what you will lose when one main fuse blows, and, possible cable damage; you don't want to loose your radio, GPS and sounder all at once, so spread what you consider essential items over different main fuses.

Some devices demand high current and may effect other equipment on the same fuse due to drops in voltage, some cause interference to others. Cabin lights should be spread over 2 fuses on the main panel so you are not left in total darkness fumbling for that torch to fix the find the spare fuse.

Hope this helps.



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[ParaHandy]

g'day .. you've said it all .......... but do carefully mark what comes off each switch otherwise you'll get woken up at 4am by crew asking which switch operates radar. simple things that get you?

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[Capt_Marlinspike]

In line fuses are in every way bad news. You can never find them when you need to (the fuses always go at night, in a storm etc), they are usually wrongly rated and the holders corode before your eyes.
Best to use breakers in a panel.
Remeber that the purpose of fuses / breakers is to protect the cabling not the equipment.
Ensure that the fuse /breaker rating is right for the cable used.

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[Omatako]

>>As long as the main panel fuse is large enough to cope with the new device as well the one being added<<

Surely if the fuse is large enough to cope with both devices, it is too large to protect each one individually?

I would advocate a suitable fuse (even better, circuit breaker) for each device. And I agree with other post regarding inline fuses. Troublesome things that play the best game of hide-and-seek you ever saw.

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[oldsaltoz]

G'day Omatako,

All fuses should be rated for the equipment connected, fuses protect cables first, and prevent fires on board, if you connect a second device the fuse rating may have to be reviewed/replaced, but, connecting two devices to one fuse is not a problem. If it were your home would have burnt down some time ago.....

Avagoodweekend

<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[gjeffery]

I have never been convinced by the argument that the breakers/fuses are to protect the wiring and should be rated on that basis. I would not, for instance, fuse a 12W soldering iron at 13A!

The purpose of fuses is to prevent dangerous overcurrents, and fusing at a current that far exceeds the design current for the equipment does not seem sensible. Also, bear in mind the time/current characteristics of wire fuses, which may permit transient currents of several times the fuse rating.

There is a strong argument that the VHF should be wired independently of the main breakers. Some wire it directly to the battery, via an inline fuse. Mine is wired back to the battery switch.

I also dislike fuses that are buried, and where I have installed cartridge fuses to protect instruments, these are Quick Blow types, and located in Vero Boxes, with spare fuses.

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[MainlySteam]

The fuse/breaker is definitely there to protect the circuit and only the circuit, not the equipment connected to it. There is no reason why one cannot overprotect the circuit eg fit a 5 amp breaker to a 30 amp capable circuit, but that does not seem to have much sense. Following Oldsaltoz's line of thought one would not rush out to install 0.05 amp fuse or breaker (assuming such an animal existed) on your house electrical board because you were going to use a 12 w soldering iron on the 230 v circuit.

If the equipment, or some part of it needs protecting by a fuse you will find that it will be and that fuse(s) will be built into the equipment itself (ssb radio, or whatever) and you may not even be aware of it (they do not often fail). Again, in the home situation your TV does not get excited becasue there is a 15 amp fuse protecting the circuit it is on. However, it may get excited if there is some internal failure in the set which could lead to a dangerous situation, in which case you will find the set is internally fused.

John

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[gjeffery]

UK, domestic ring mains typically are tripped at 30A, with items also individually fused at the plug. Plugs are rated at 13A, and were almost invariably supplied with 13A fuses, but this is no longer so. There is emphasis on fusing to protect the appliance/user. A soldering iron, for instance, would be fused at 1 Amp.

I agree that electronic equipment (but certainly not all electrical equipment) is normally internally protected, but the manufacturers sensibly fit fuses to moulded plugs, that are below the 13A level needed to protect the wiring behind the socket. The computer that I have just investigated is fused typically at 5A at the plug.

Is there any benefit in fusing only to protect the supply circuit, to trade against the opportunity to limit the fault current at the connected equipment, cable, switch, and so on?



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[MainlySteam]

<<<There is emphasis on fusing to protect the appliance/user>>>

But, as you say, that protection is at the appliance, not at the circuit's source. The 30 amp (or whatever rating) fuse/breaker at the board is to protect the circuit and nothing else, anything in the appliance (including its line cord) is to protect, if required, the appliance.

That is how it should be on a boat also, and is always professionally done so. Furthermore, if it was not done that way one could only have one appliance on a breaker - for example, each cabin light on board would have to have its own dedicated breaker.

John

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