Just finishing up some wiring on the amplifier and I always run into this question before I wire it up.
What's the usual (meaning safe) way to wire up the mains to the amplifier?
I'm using a 3 prong USA 120V grounded AC outlet cord, White = Neutral, Black = Hot, Green = Ground (just tied to chassis).
Scenario 1:
White tied directly the transformer, and Black directly to fuse, then fuse to switch, then switch to transformer?
Scenario 2:
I have seen some schematics where the fuse is in one of the legs of the transformer (not switched) and the other is a switch.
Or does it make much difference? Scenario 1 is what I have been doing, but figured I would double check...
Thanks
Sandy Ganz
What's the usual (meaning safe) way to wire up the mains to the amplifier?
I'm using a 3 prong USA 120V grounded AC outlet cord, White = Neutral, Black = Hot, Green = Ground (just tied to chassis).
Scenario 1:
White tied directly the transformer, and Black directly to fuse, then fuse to switch, then switch to transformer?
Scenario 2:
I have seen some schematics where the fuse is in one of the legs of the transformer (not switched) and the other is a switch.
Or does it make much difference? Scenario 1 is what I have been doing, but figured I would double check...
Thanks
Sandy Ganz
Scenario 1 for sure, and especially so if you're including MOVs. These have a nasty tendency to stay on once switched on. You definitely want the fuse to pop before the MOV does. You also want the fuse ahead of the switch in case the switch fails to disconnect if something goes wrong.
Current safety standards are specific: Hot wire goes to rear terminal of chassis mounted fuseholder, side terminal to switch, switch to transformer. Switching both sides of line is allowed, but a single-pole switch must be in hot wire. Safety ground wire must be connected to chassis directly using a lockwasher, on its own screw (not a a screw that mounts something else).
I thought regardless of design, mains cable first goes to the switch, then the fuse holder centre pin (deepest). That fuse contact is connected to the switch. This avoids the possibility of shock on older fuse holders should the fuse not having blown, make contact with the upper metal shoulder of the fuse holder, that is if incorrectly wired. Also the earth wire should be longest within the chassis under, the reason is user safety as this should remain on the chassis is someone inadvertently trips and rips the live and neutral wires out.
Am I correct or not ?
richy
Am I correct or not ?
richy
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Many years ago this what I found in Holland, in fact both were live, ie each phase to ground is 110V. It's imperative the d.p.d.t switch comes first.
r.-
The fuse must be the first thing connected to the hot side.
Essentially all DIY amps are class I. Tom Bavis explained the proper way to do it.
It is poor practice to have un-fused power going anywhere through your amp. Seems to me something you touch like a switch should fused and grounded. (If metal).
Could somebody miss wire a fuse holder and have the shoulder hot? Yes. So what, wire it properly, triple check your work. This is hardly a valid reason to compromise other safety.
If you are using 3-phase power, then yes you have 2 hot lines and would want to switch and fuse them both.
As Fpitas said, you could fuse both sides if needed.
For the love of Bob unplug the thing if you have a problem, what kind of person is changing fuses on live amps?
Essentially all DIY amps are class I. Tom Bavis explained the proper way to do it.
It is poor practice to have un-fused power going anywhere through your amp. Seems to me something you touch like a switch should fused and grounded. (If metal).
Could somebody miss wire a fuse holder and have the shoulder hot? Yes. So what, wire it properly, triple check your work. This is hardly a valid reason to compromise other safety.
If you are using 3-phase power, then yes you have 2 hot lines and would want to switch and fuse them both.
As Fpitas said, you could fuse both sides if needed.
For the love of Bob unplug the thing if you have a problem, what kind of person is changing fuses on live amps?
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.
In instances where you have power where there is no clear neutral it is safest to place fuses in both sides of the mains, and then proceed to the dpst switch. Switches can short to chassis (I have first hand experience of this unfortunately) and shorts between contacts may also occur if there is a mechanical failure internally. I'd want a local fuse that could open before serious mischief occurs in the event that the distant circuit breaker does not open immediately.
On fuse holders mains should always go to the rear contact that way there is no shock hazard in the event the user goes to replace a fuse with mains still connected. (I wouldn't with mains connected, and would not replace the fuse without looking for failures first.)
Just because there is historical precedent for an approach that could be dangerous under some predictable circumstances (component failure) does not justify its continued use in the light of newer knowledge.
Electrical codes here and in Canada are harmonized, as they are in the EU, requirements are generally similar, but not always identical.
On fuse holders mains should always go to the rear contact that way there is no shock hazard in the event the user goes to replace a fuse with mains still connected. (I wouldn't with mains connected, and would not replace the fuse without looking for failures first.)
Just because there is historical precedent for an approach that could be dangerous under some predictable circumstances (component failure) does not justify its continued use in the light of newer knowledge.
Electrical codes here and in Canada are harmonized, as they are in the EU, requirements are generally similar, but not always identical.
Yes, I think the 'Scenario 1' is the way to go seems the most safe and logical. If this were a 220 vac amp possibly a DPDT switch but still seems overkill and fuse before the switch especially in that case. I have a few 220VAC Ham amplifiers that none use DPDT switches.
Also I don't think it's a huge issue to worry about bad home wiring, things like that tend to fix themselves in 'short' order
Sandy
Yes, I think the 'Scenario 1' is the way to go seems the most safe and logical. If this were a 220 vac amp possibly a DPDT switch but still seems overkill and fuse before the switch especially in that case. I have a few 220VAC Ham amplifiers that none use DPDT switches.
Also I don't think it's a huge issue to worry about bad home wiring, things like that tend to fix themselves in 'short' order
Sandy
I'd certainly want fuses in both sides of mains in a 230V powered ham radio linear amp and a DPST power switch. Both sides are hot to ground with single phase 230V here, in Canada and Mexico..
Primary to core shorts do happen in power transformers, and I've had that experience first hand as well.
Yes bad house wiring tends to be resolved quite quickly either by electrocution of the unwitting homeowner or family member or by the house burning to the ground.
You know what I am going to say next, seen that too, unfortunately a house right down the street burned to the ground recently due to faulty ancient electrical wiring and overloading. (And another a few blocks away last week..) And I live in a neighborhood where 'fixer-uppers' go for north of $300K..My wife's ex-boyfriend fancied himself an electrician, wired neutral and ground together on a number of AC receptacles, the only problem with that besides being stupid - and dangerous if neutral goes open is that the house was still on 18 - 20ga knob and tube wiring at the time, and the IR drop across neutral was significant. Kept wondering why I got shocked by my grounded soldering iron upstairs..
House has long since been professionally rewired.
Kevinkr -
It's interesting to see how some commecial made equipment is done. On the Drake L7 amp it's a SPST, single fuse, on the Henry 2k4 it's a DPDT and 2 Fuses. Clearly the Henry was made more to spec for 220 wiring it seems.
And yes, I had a house that with some odd 'Edison' wiring topology or what ever ya' call it. I had been replacing wall sockets and for some reason though it OK to work hot... Well I lifted a neutral off one of the sockets and listened as my computer UPS went off and started smelling smoke. Burnt up 2 surge protectors and the UPS's internal MOV. Computers were OK so I had that going...
Sandy
It's interesting to see how some commecial made equipment is done. On the Drake L7 amp it's a SPST, single fuse, on the Henry 2k4 it's a DPDT and 2 Fuses. Clearly the Henry was made more to spec for 220 wiring it seems.
And yes, I had a house that with some odd 'Edison' wiring topology or what ever ya' call it. I had been replacing wall sockets and for some reason though it OK to work hot... Well I lifted a neutral off one of the sockets and listened as my computer UPS went off and started smelling smoke. Burnt up 2 surge protectors and the UPS's internal MOV. Computers were OK so I had that going...
Sandy
Lets put these problems in another light: I'm going to be more awkward off conventional so that others can see.
I use switchmode power in many of my amps with a classic XY capacitive common mode input filter with the common method of the mandatory ground used as a capacitive divider between the mains phases and the chassis connected to the yell/grn. .... If one assumes with one fuse in the AC chassis input wiring and it pops, and with a loose earth wire or defective one, (it's happened to me) it can end up with the chassis exposed live i.e via a 1nF cap to 230VAC, if that is using an isolated signal input transformer (as I do). The value of the Y cap is safety certified, but neverless one will get a "mA tickle" from the chassis, and may not trip an earth leakage switch. The dpdt switch with a non conducting knob is absolutely essential on the chassis mains input !! as is the standard IEC chassis socket, so the plug can be quickly withdrawn.
We are all on the right regarding issues of user safety; issues have come a long way and drastically improved since my early days when the AC/DC radiogram chassis was directly connected to the two pin mains, no matter which way round. A lethal combination.
r:-
I use switchmode power in many of my amps with a classic XY capacitive common mode input filter with the common method of the mandatory ground used as a capacitive divider between the mains phases and the chassis connected to the yell/grn. .... If one assumes with one fuse in the AC chassis input wiring and it pops, and with a loose earth wire or defective one, (it's happened to me) it can end up with the chassis exposed live i.e via a 1nF cap to 230VAC, if that is using an isolated signal input transformer (as I do). The value of the Y cap is safety certified, but neverless one will get a "mA tickle" from the chassis, and may not trip an earth leakage switch. The dpdt switch with a non conducting knob is absolutely essential on the chassis mains input !! as is the standard IEC chassis socket, so the plug can be quickly withdrawn.
We are all on the right regarding issues of user safety; issues have come a long way and drastically improved since my early days when the AC/DC radiogram chassis was directly connected to the two pin mains, no matter which way round. A lethal combination.
r:-
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A lot of amps are wired unpolarized, Which means there is no bigger neutral blade or ground on the plug.
I have actually read some amplifier manuals that said to reverse the plug as it may sound better that way.
Now I really don't buy into that myself but historically it has been done this way.
Personally I put a fuse directly on the primary wire before the switch and on my hot wire.
But what's just as important, (well if you like your outputs anyway) Is that you put a fuse on the primary of the B+
I have actually read some amplifier manuals that said to reverse the plug as it may sound better that way.
Now I really don't buy into that myself but historically it has been done this way.
Personally I put a fuse directly on the primary wire before the switch and on my hot wire.
But what's just as important, (well if you like your outputs anyway) Is that you put a fuse on the primary of the B+
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