AC Mains switch testing, acceptable tolerance

[ViperDoc]

I just decently cooked the mains switch when desoldering to correct the fuse placement on my PR2 build. It tests fine open and closed, but when plugged into the wall, the switch passes very low current, like 0, then 20 mA, then 0, the 170 mA, all momentarily. This may be rhetorical, but would you tolerate NO current passing when closed? Does this constitute arcing inside the switch? Also, now when I play the amp, it sounds like a buzzsaw when digging in.

[xtian]

I don't know, but that sounds super flaky, like a croissant. Yummy, but probably bad in a guitar amp.

[ViperDoc]

LOL. You're fast.

[ViperDoc]

I had the fuse on the neutral AC wire, like the original circuit. I rewired the hot AC wire directly into the fuse and then into the switch, then into the hot primary. Nothing is on the neutral now, just straight into the PT primary.

[sluckey]

It's digital, ie, it's either on or off. In betweens are not acceptable. The only acceptable tolerance for ANY switch is open equals infinite resistance/zero current. Closed equals zero resistance/whatever current the load demands. I would throw that switch away before you get hurt.

[pdf64]

I had the fuse on the neutral AC wire, like the original circuit...

I don’t think that’s correct.
The original design was for a 2 pin unpolarised mains connection.
Either wire might be live or neutral, every time it was plugged in, it was a coin flip which would be which. Hence the ground switch, ie to be set such that the amp’s operation would be quietest (and a lot less tingly) when the chassis was ac connected to neutral, rather than live.

As most regions now have polarised mains connectors, equipment designers (which includes DIY builders) are obliged to ensure that the fuse and switch are on the live side of things.
To accommodate for outlet miswires, double pole mains switches are good practice, may be mandated in some regions.

[ViperDoc]

That’s an interesting point, you’re right. The AA1164 schematic has the switch on one primary wire and the fuse on the other, giving you a 50% chance of having the fuse on the hot wire depending on how you plug the amp in, right?



I deleted the ground switch in both my PR builds because I just don’t see the point. No AC receptacle either. So I switched it to POWER CORD AC HOT—>FUSE—>SPST MAINS SWITCH—>PT primary and let the neutral straight into the PT with a dedicated AC ground point.

[ChopSauce]

Sounds much better but a DPxT switch is mandatory with non detachable power cords here, in France and most likely in Europe too.

Might sound like overkill but I did had a power cord factory built with mixed (live, neutral) wires inside, meaning that even if both your wall socket and your amp are correctly wired, you're still not safe.

[Phil_S]

What you see for the mains wiring on that Fender schematic would never be allowed today anywhere in the world. I believe it was ill conceived, but was, at one time, the accepted standard. In the US and probably Canada, at one time our wall sockets were not polarized and it was Russian roulette every time you plugged in anything but a lamp.

[R.G.]

Dead right Phil and pdf64. Two wire, unpolarized AC connections do not match modern electrical safety standards. Anyone rewiring the AC inlet circuitry on an amp ought to wire it much like ViperDoc says: AC hot => fuse => hot side of switch => [anything using AC]. It's not required in all places, but really ought to be, to run the neutral wire to a DPxT switch to disconnect both sides.

In today's highly lawsuit crazy society in the US at least, I think it would be crazy to build and sell an amp wired the old way. The buyer's surviving family members after the electrocution or fire have ready-made grounds to sue. That's whether or not the amp itself had anything to do with the event. Worse, that never goes away, even after decades and the amp being sold, given, or loaned to someone else.

I've wondered at why the older way used to be one AC wire to switch, the opposite side to the fuse. All I could come up with was that in a two-wire, ungrounded world, it was as good as any other way, and that it had the advantage that there was a convenient component lug for each side (ie. fuse for one side, switch for the other) handy near where the line cord entered the chassis. That way it was handier to wire. It's a theory.

[ViperDoc]

If that is the current standard, I’ll be sure to make that part of my future builds.

[Delidroid]

Hello.
In the UK all mains to earth parts have to be tested to withstand double the mains voltage.
We use a simple instrument, a Megger which puts 500V across live and earth and resistance must be over 500K ohm.

Nowadays “elf n safety” the great Industry in it’s own right insists every appliance in the workplace be annually tested and labelled.
So to answer your question you need to test your switch with a high voltage source. A wimpy meter with a 9v battery may show infinity across the switch.

[SoulFetish]

Dead right Phil and pdf64. Two wire, unpolarized AC connections do not match modern electrical safety standards. Anyone rewiring the AC inlet circuitry on an amp ought to wire it much like ViperDoc says: AC hot => fuse => hot side of switch => [anything using AC]. It's not required in all places, but really ought to be, to run the neutral wire to a DPxT switch to disconnect both sides.

UL required all currently manufactured, mains powered class I equipment be switched with a DP*T switch (for all equipment with a permanent mains chord attached). They switched over to IEC 62368-1 standard Dec 20,2020, which I can't afford to purchase right now, so I'm not sure about any changes (if any) were made to that standard.
One of the frustrating things when trying to update the mains wiring on vintage Fenders to bring them up to modern standards, is finding a suitable replacement DPST power switch with a short bat to replace the original Carling SPST. Does anyone have any some recommendations?

For all custom and personal builds, I install Schurter fused IEC inlet which meet all major electrical appliance standards.
Schurter IEC=>Schurter Voltage Selector=>NKK SP*T Switch (or DPDT if I get a really good price on them)

[ViperDoc]

Try the Carling 2BL62 switches:

https://www.mouser.com/datasheet/2/65/1 ... 670504.pdf