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Switches And Fuses Double Check


AskJacob

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Guys,

 

Last night was under the bonnet of my cab, decided it was time to replace the skanky old power cord. Also figured it was time to check out the mains wiring in general

 

Here is what I found:

 

- A small metal box, with fuse and power switch

- The Earth was connected to AN INSULATED TERMINAL (so the metal box was not earthed!)

- The Power Switch was only a single pole (not great) but was in the Active Line (good)

- The Fuse was in the Neutral line. I assume this is a BAD THING as it has the potential of the machine being live even with a blown fuse.

 

Fixes/Changes I made:

 

- Switch and fuse are now in active line

- Earth terminated properly to metal. Now I have a solid basis to earth the rest of the metalwork in the cab

- New powercord (just buy a good extension lead and cut off the socket end)

- Added a small powerboard to the switched side of the power circuit (in case I ever want to put in a fan, mame or whatever in the future) - this is a reversible change!

 

What I still need to do:

 

- Check fuse rating (I am not powering it up at the moment) - whats usual for a standard cab - 120v chassis, peter chou PSU I am guessing a 1.5 - 2A fuse should be OK

- Probably add a line filter

 

----

 

It's been said before, I'll say it again - always check your new cab before plugging it in!

 

Cheers

Jacob

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Just for the record mate.

 

I've found that it's cheaper when replacing a power lead on any appliance to buy a cheapie extension lead from bunnings with a molded plug, rather than go for the cable and a DIY plug. (That usually fall to bits anyway..)

 

Just cut off the female end of the extension lead and strip the wires down.

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I think you'll want a fuse rated a bit higher than 1.5-2A. Also I recommend you exchange that switch for a double pole.

 

Yeah, I'll stop being lazy with the switch and replace it.

 

Hmm lets say 600 watts or so? 3 Amp then? Or 5 for inrush?

 

Guys,

 

- New powercord (just buy a good extension lead and cut off the socket end)

 

Got ya there BigGeorge - its a good tip, I've been doing it for ages!

 

Cheers

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:lol2: Whoever wired up your cab is obviously a fucking moron.

Yes it seems silly by today's standards, but it was quite common (and legal I believe) to have the fuse in the neutral line 20 years ago. It's not really all that bad in some ways.

 

The moron part comes into play when someone (the moron) assumes that just because the equipment's switch is off, there is no danger of live parts.

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Yes it seems silly by today's standards, but it was quite common (and legal I believe) to have the fuse in the neutral line 20 years ago. It's not really all that bad in some ways.

 

The moron part comes into play when someone (the moron) assumes that just because the equipment's switch is off, there is no danger of live parts.

 

:) that is true. I may not be that silly, but I can't guarantee anyone else won't be. So I'll consider it my Civic Duty to fix it.

 

I actually think the re-wire job was sort of recent - it certainly wasn't the original wiring in that box...

 

Cheers

Jacob

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:) that is true. I may not be that silly, but I can't guarantee anyone else won't be. So I'll consider it my Civic Duty to fix it.

 

I actually think the re-wire job was sort of recent - it certainly wasn't the original wiring in that box...

 

Yes, quite possible that it was rewired after the rules changed. Maybe they just copied the old wiring! Probably didn't know any better is more likely. :unsure

 

Good on you for fixing it up. When I got my cocktail cab, I'm surprised it didn't go flash - bang. There was loose stuff and bare wires galore! :o

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Yes it seems silly by today's standards, but it was quite common (and legal I believe) to have the fuse in the neutral line 20 years ago. It's not really all that bad in some ways.

 

The moron part comes into play when someone (the moron) assumes that just because the equipment's switch is off, there is no danger of live parts.

Can't understand why itd be common. Common sense tells you to put the fuse on the wire that actually contains the current.

 

However I'm not disagreeing with you, this is far from the first time I've heard of the neutral being fused/switched.

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Can't understand why it'd be common. Common sense tells you to put the fuse on the wire that actually contains the current.

Both active and neutral carry exactly the same current. I'm sure that's not what you meant though. ;)

 

As another example, touching a loose neutral wire can be just as dangerous as touching the active. The current path is from active, through the appliance's circuit and sitting on that loose neutral. You touch it and soon know about it, becoming the return path! :o

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Both active and neutral carry exactly the same current. I'm sure that's not what you meant though. ;)

 

As another example, touching a loose neutral wire can be just as dangerous as touching the active. The current path is from active, through the appliance's circuit and sitting on that loose neutral. You touch it and soon know about it, becoming the return path! :o

How can they have the same current? Some of it gets used by the appliance.

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The current remains constant in a total circuit but the voltage is dropped across the load.

The amount of current is determined by the voltage across the load and the resistance of the load, i.e. I = V/R

Edited by arcadus
too complicated
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:lol2: Now that's funny! I thought you had a (semi) technical background. Must have you confused with another member. :unsure

 

Current isn't consumed in the way (that I suspect) you think. Current flows, and if there's only one "entry point" (active) and one "exit point" (neutral) the current flow in both is the same. (I have simplified this somewhat)

 

If you put a battery and a lamp in series, you can measure the current in either wire and it will be the same. The current doesn't "go" anywhere. Maybe you're thinking of the power that a circuit dissipates?

 

I apologise if you've taken offence me correcting you, but I don't like seeing incorrect information propagated. I'm always open to corrections myself of course as I don't presume to know everything. I do know a fair bit about electricity and electronics in general though. :D

 

EDIT: As Ralph alluded to, check out "Ohms Law". It's a great way to learn about electrical principles.

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I do have a semi technical background and I'm familiar with Ohms Law, I just don't fully understand the concept of current.

 

It's a concept that's pretty central to understanding all the "dark and mystical" things about electricity. I encourage you (and anyone else who's interested) to learn a little more about voltage and current flow. It will really fill those gaps and get you a lot further when trouble shooting your arcade stuff. Again, no offence intended. It's easy to assume others know particular stuff when it's second nature to yourself.

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Current is a measure of the rate of flow of electrons. 1 Amp is equal to 1 Coulomb of charge passing through any point in the circuit per second. In a series circuit the same amount of current will be flowing through all parts of the circuit (ignoring harmonic currents) at any given time.

 

In the case of an arcade machine drawing 4 amps from the supply, 4 amps will be flowing through the active conductor, and through the fuse, through the switch, through the machine (and gets divided between the PCB, monitor, power supply losses etc), through the neutral conductor, through the power lines all the way back to the transformer where 4 amps will flow through the windings back to the start.

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Hmmm... I think that the material in those links is way over the heads of most people here. I really mean that in a nice way! :p

 

Honestly, fiddling about with batteries, lamps and a multimeter will give great insight into basic electricity theory. There's nothing that makes something "click" as when you do hands-on (that sounds sus!) experiments yourself. The number of job applicants I've seen that have EE diplomas but can't wire a simple circuit still astounds me.

 

Myself, I read a bit then combine that with some practical stuff to get a grip on it. I've never been one for just reading the theory as that just doesn't work for me. Hewitson is certainly not on his own when it comes to not knowing about current flow. There's plenty I don't know well (RF for example), but voltage and current are essential elements that you need to base almost everything else on.

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so to clarify something for a newbie to all this... an australian plug has three poles. I presume that one is active (red?), one is common (black?) and one is ground (green?).

 

So I understand about the active and common, but what is the ground? I know everything metal has to be earthed... and I know ground is earthed via a pole into the ground :unsure, but what is it all about then?

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so to clarify something for a newbie to all this... an australian plug has three poles. I presume that one is active (red?), one is common (black?) and one is ground (green?).

 

So I understand about the active and common, but what is the ground? I know everything metal has to be earthed... and I know ground is earthed via a pole into the ground :unsure, but what is it all about then?

 

In a nutshell, in case of a fault or wiring problem, current will flow via the ground(green wire) to the "ground" (earth - as in that post near the powerbox) instead of YOU - which is also a path to the earth... but won't be as good as a nice copper wire. Current likes to follow the easiest path, so should make things safer.

 

Nowadays, GFI's or RCDs can also detect when current is NOT returning as expected along the neutral (so it must be going to ground, either the wire or possibly a person) and trip!

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That is a fairly old wiring standard. It's now Active = brown , neutral = blue and earth is yellow green.

Neutral is connected to earth at various points across the grid including at the power box on the house.

This means any thing you connect the power earth to, is also at neutral potential.

That's why they designate the difference between Active and Neutral and is important to wire power the right way.

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so to clarify something for a newbie to all this... an Australian plug has three poles. I presume that one is active (red?), one is common (black?) and one is ground (green?).

 

The current colour for flexible connections are: brown (active), blue (neutral) and yellow/green (earth). For fixed cabling (in the walls), the colours are red, black and green respectively. There's no conductor called common.

 

So I understand about the active and common, but what is the ground? I know everything metal has to be earthed... and I know ground is earthed via a pole into the ground :unsure, but what is it all about then?

 

Australia uses the MEN (Multiple Earth Neutral) system of power distribution. I have been looking for the last 10 minutes but can't find an easy to understand diagram of how it all work. It's easy, but a picture tells a thousand words. If I find one I'll post back here.

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Australia uses the MEN (Multiple Earth Neutral) system of power distribution. I have been looking for the last 10 minutes but can't find an easy to understand diagram of how it all work. It's easy, but a picture tells a thousand words. If I find one I'll post back here.

 

I still remember how startled I was when I found out that Neutral is bonded to earth at the distribution box in a domestic setup....

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