Maybe we are having lander differences... Take a look at the pic, a common enough circuit diagram. There have been decades of amps wired up like this with switch first.
r:-
Hi ,
the attachment by richwalters showing an Power input on an very old device from Europe , probably from germany.
And here in germany we had in the past lots of mains topologies with both sides of the socket hot against ground. The most common was a 220V mains, a 3 wire three phase system. The neutral in the supply transformer were grounded only for safety reasons. And the other type were a center tapped 220V single phase system , with 110V against ground. The same like in USA today. And thus were both legs live.
The remains from this age is our plug system, Plug-Typ F (CEE 7/4, Schuko-plug). An bavarian engineer, Albert Buettner invented this plug 1926 and sold the patent later to Siemens AG
An externally hosted image should be here but it was not working when we last tested it.
There was no need in those day to have polarisized plug.
The todays common 220/380V(230/400) mains were rare and only to supply the countrysides especially the Farms. And today like in most other eurpean coutries we have now 230V with on leg on ground potential.
All Equipment from these days will found with 2 fuses and 2 pole switch.
Germans Eletrical Rules (VDE) say fuses first, than the switch.
Due to the our unipolar plugs , I insert alway 2 fuses/2-pole CB and a 2-pole switch in the line input.
Sorry for being slightly off topic.
73
Wolfgang
One more thing.........Always use ceramic fuses, not the cheap clear glass types. Why? When a fuse blows "hard" it will evaporate the filament, coating the inside of the glass ..........recall the "vapor deposit" coating technique? Same thing. Upshot is the fuse will still conduct even after it has "failed".
______________________________________________Rick......................
______________________________________________Rick......................
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Hi,
The kind of fuse which came into question should be chosed by the max. possible short circuit current. This depends on the impedance loop of your mains. The wiring of your home, the feeder line and the secondary of the pole transformer is part of this loop even the lead from the socket to your amp. An underestimated Fuseholder can vaporise in case of a short.
Any cb or fuse must have a braking capacity which fits the max. possible current to interupt a faulty circuit safe without any damage to your home electric installations or your appliance. "Normal" sockets ( here) can provide app. 700-1000A.
These tiny Radio fuses (5x20mm) are capable to interupt 150A safe, special ones are made for 1500A. The US standard fuses 1,25x0,25" are available with different breaking capacities. If your mains is "stiff" the currents can going up to 10kA in residential areas.
Here in Germany and most EU-Countries circuit brakers in domestic installations shall be have a breaking capacity of least 6kA, Buildings with own transformers must have devices that can handle 10kA.
I suggest you get only quality fuseholder , fuses and cb´s from major switchgear makers . Serious manufacturer have datasheets of their products available in paper on request or in the internet.
Thats does mean also to all other mains related parts in your homebrew projects.
Take elektricity always serious! ´
73
Wolfgang
The kind of fuse which came into question should be chosed by the max. possible short circuit current. This depends on the impedance loop of your mains. The wiring of your home, the feeder line and the secondary of the pole transformer is part of this loop even the lead from the socket to your amp. An underestimated Fuseholder can vaporise in case of a short.
Any cb or fuse must have a braking capacity which fits the max. possible current to interupt a faulty circuit safe without any damage to your home electric installations or your appliance. "Normal" sockets ( here) can provide app. 700-1000A.
These tiny Radio fuses (5x20mm) are capable to interupt 150A safe, special ones are made for 1500A. The US standard fuses 1,25x0,25" are available with different breaking capacities. If your mains is "stiff" the currents can going up to 10kA in residential areas.
Here in Germany and most EU-Countries circuit brakers in domestic installations shall be have a breaking capacity of least 6kA, Buildings with own transformers must have devices that can handle 10kA.
I suggest you get only quality fuseholder , fuses and cb´s from major switchgear makers . Serious manufacturer have datasheets of their products available in paper on request or in the internet.
Thats does mean also to all other mains related parts in your homebrew projects.
Take elektricity always serious! ´
73
Wolfgang
This is not rocket science.
One not uncommon cause of a blown mains fuse is a mains switch with insulation (to chassis)breakdown.
Absolutely always have the fuse as the first thing in the chain, BEFORE the switch.
The wire used for the mains wiring must have a current rating higher than the fuse rating.
At a minimum:
Use active wire (Black in US, brown most other places) from Mains Scocket to Fuse to Switch to transformer primary with the other end of the primary wired back to Mains Socket neutral ( White in US and Blue most other places).
This will protect you and your amp against the majority of failure modes.
If your mains switch is a changeover contact switch then make sure you wire the feed from the fuse to the Normally Open Contact and wire the Common Contact to the transformer, This make sure that there is not a HOT Normally Closed contact on the switch when it is turned OFF. This may save you a nasty surprise when working on your amp if you forget to unplug it. To give yourself a "zap" you then have to make 2 mistakes (forget to turn it OFF as well) not just one.
In any protection scheme you always aim to create a situation where a single fault/mistake will not cause damage/hazard.
I did my electronics apprenticeship in a major hospital. Different standards applied to medical equipment, we always fused both active and neutral and used a double pole switch to switch both active and neutral. I generally do this in my DIY Tube Amps but it is not required by law. It gives maximum protection even if the wall socket has active and neutral wires reversed.
Most of this is common sense. Just think "What will give me and my gear the maximum protection?" That will often be incompatible with "what is the cheapest/easiest way of doing this?"
Cheers,
Ian
One not uncommon cause of a blown mains fuse is a mains switch with insulation (to chassis)breakdown.
Absolutely always have the fuse as the first thing in the chain, BEFORE the switch.
The wire used for the mains wiring must have a current rating higher than the fuse rating.
At a minimum:
Use active wire (Black in US, brown most other places) from Mains Scocket to Fuse to Switch to transformer primary with the other end of the primary wired back to Mains Socket neutral ( White in US and Blue most other places).
This will protect you and your amp against the majority of failure modes.
If your mains switch is a changeover contact switch then make sure you wire the feed from the fuse to the Normally Open Contact and wire the Common Contact to the transformer, This make sure that there is not a HOT Normally Closed contact on the switch when it is turned OFF. This may save you a nasty surprise when working on your amp if you forget to unplug it. To give yourself a "zap" you then have to make 2 mistakes (forget to turn it OFF as well) not just one.
In any protection scheme you always aim to create a situation where a single fault/mistake will not cause damage/hazard.
I did my electronics apprenticeship in a major hospital. Different standards applied to medical equipment, we always fused both active and neutral and used a double pole switch to switch both active and neutral. I generally do this in my DIY Tube Amps but it is not required by law. It gives maximum protection even if the wall socket has active and neutral wires reversed.
Most of this is common sense. Just think "What will give me and my gear the maximum protection?" That will often be incompatible with "what is the cheapest/easiest way of doing this?"
Cheers,
Ian
I've got a identical pair of Coffee maker SPDT switches.....so happens , one is black & the other is white...Hmmmmmmmm?? IEC socket to dual switches, to dual fuse-holders , One Hot the other neutral...color coded. Rated 6.5A, 250VAC.
_______________________________________________________Rick............
_______________________________________________________Rick............
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