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In Reply to: RE: Is Ralph Lauren making fuses now? posted by Lew on September 29, 2014 at 19:05:49
I will start by making assumptions;
The electricity coming from the wall enters my gear.
The electricity has a positive and a neutral side (black wire, white wire). I will call the neutral feed 'negative' from here on in.
The positive side goes straight to the gear, the negative side goes through that itsy bitsy teeny tiny little piece of wire inside the fuse. This negative side now goes to the gear.
This is an alternating current.
1)Please explain to me in electrical terms what the difference would be if we put the fuse on the positive (black wire) coming into the gear? as opposed to the negative (white) wire.
2) I know we have fuses to protect our gear. I know lightning strikes might fry our gear without fuses. Please enlighten me as to what other situations would fry my gear if I didn't have fuses?
Follow Ups:
"1)Please explain to me in electrical terms what the difference would be if we put the fuse on the positive (black wire) coming into the gear? as opposed to the negative (white) wire."
I would not consider it good practice to put the fuse on the neutral side, as in your original supposition. If there were a fault condition that blew the fuse, you would now have just the mains live wire and the ground wire connected into the equipment. Depending on the nature of the fault that had caused the fuse to blow, one could now imagine that the entire chassis might be live. (For example, if the fault was that (unfused) live wire had shorted to the chassis, and if that had then caused the connection to the ground return wire to burn out.) It is therefore much safer to put the fuse on the live side, so that if it blows there is no longer any live connection into the equipment.Chris
(By the way, your choice of the labels "positive" and "negative" for the live and the neutral wires is a little unfortunate: Almost anything else would have been better, and less liable to cause confusion! But in fact "live" and "neutral" usually serve reasonably well for the purpose!)
Edits: 09/30/14 09/30/14
At last! A chance to really show my ignorance . . .
But the thing that occurs to me immediately is internal component failure, particularly in the power supply. Short circuits--with their near instantaneous high current flow--can be caused by many things: a blown tube; a bad capacitor; hot leads touching each other. I think even power surges on the incoming AC line.
Lew, can you add and/or subtract from these?
Thank you guys.
Quick question, could a faulty tube cause damage?
For example, as most of us know, you can blow an output tube in an Atma-sphere amp without even being aware it happened, unless or until enough of them have blown so as to reduce the apparent "power" of the amplifier.
My MP-1 pre-amp is powered by the BPT balanced power supply.
This simply means there is +60v coming in on the 'hot' wire, and -60V on the 'neutral' wire. This instead of the +120V/0V scenario.
If there is a short in one of the capacitors, and it blows the fuse on the 'hot' lead, would I still be getting shocked from the -60V from neutral to ground?
One thing about balanced power- equipment is not designed for it. Here is an example:
If you are to meet UL or EU directives (CE mark), the fuse has to be able to blow to protect the user. The tricky area is what if the power switch, which is mounted to the chassis, gets shorted to the chassis and allows it to become 'hot'? The fuse will blow, because it is in series with the chassis. Now the same thing is true of balanced power.
But what if something happens such that the other side of the line shorts to the chassis? What then? There is no fuse for that. As best I can make out, in this situation there will be 60VRMS on the chassis- IOW it will be 'live', as in a balanced situation there is no 'hot' and 'cold'; both side are 'hot'.
As long as everything is working, balanced power offers lower noise if you have bugs in your equipment's grounding scheme. This is because if there is a grounding bug, there will be current in the ground connection. This can cause ground loops and in a really bad situation even damage something. Balanced power offers a solution for this. But ideally, there will be no appreciable current in the ground, because in a properly grounded audio system, the circuit ground floats at chassis potential, but they are not the same circuit- IOW its bad design practice to use the chassis for a ground!
A lot of audio manufacturers have not sorted this out, and it does not matter what field (pro audio, broadcast, high end audio) they are operating in. For this reason you will see some pretty respected names extolling the virtues of balanced power.
If balanced power is employed all the outlets used have to be of the GFCI type. This will prevent shock hazard.
This is potentially dangerous stuff, so I would rather not give you an uninformed opinion. You need facts. Perhaps there is an EE around here who can comment, or Ralph. I can only say that some very qualified persons on other Asylums have questioned the safety aspect of balanced power.
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