switches and voltage ratings

[Randall]

What do the voltage ratings on switches actually mean? How is it we can use a SPST switch rated at 250v for a standby switch when it is seeing 425v? Same for pentode/triode switches that switch the screen from B+2 to B+, sometimes I see mini DPDT switches employed.

[Justin Thomas]

The standard answer around these parts is because we're working with such low currents on those standby switches that arcing isn't really a big problem. Now if we were running them at their rated current, we might get some serious issues...

Justin

[Enzo]

yeah^^^^

A switch rated for 10 or 15 AMPS at 250v is not going to be stressed by 100ma. even at 450v.

[Randall]

The carling switches I have are rated 6A at 125v and 3A at 250v. Is it correct to follow with 1.5A at 500v?

[The Dude]

If the switch isn't rated for 500v, it isn't. The voltage rating of the switch is the rating at which the voltage may jump the contacts. That said, I agree with the above. HT current is low enough that it isn't normally of any concern. Fender and most others have been using standby switches with "underrated" voltage for years.

[Enzo]

No, you cannot extrapolate specs on parts.

I would imagine those are AC voltages anyway. 125vAC peaks at a bit over 170v. Also, 60Hz AC that the switch is rated for crosses zero 120 times a second, so unlike DC, an arc may tend to extinguish itself.

Just consider that the exact same spec parts have been used on Fender amps for the last, what, 70 years.

[Chuck H]

Fender and most others have been using standby switches with "underrated" voltage for years.

And they've been making an audible pop when switched for years too

[The Dude]

And they've been making an audible pop when switched for years too

That's how you know it's working.

[Justin Thomas]

In my limited experience, when the Pop stops, so does the movement of the part that's supposed to move... but usually when that happens they're either pushing 40-50 years old, or they're new. Make of that what you will.

Justin

[bob p]

those rating on the switches are AC voltage ratings. totally not applicable to use in a DC circuit.

we push the envelope using them in guitar amps.

[Enzo]

I had an audible pop. Every weekend, "That lawn isn't going to mow itself, you know."

[J M Fahey]

Plus another important factor: those switches are expected to switch, specially *OFF* which is the hard job, highly inductive loads such as electric motors, transformers and solenoids.

I think switching 450VDC, resistive load, is way simpler than switching off a bench drill, any power tool, a table saw , a bench grinder, many powered kitchen appliances, etc.

I read a "250VAC" switch rating as "suitable for constant use wiith any of the above mentioned inductive loads, plugged into *mains* up to 250VAC" ... whatever high peaks are generated during operation.

[pdf64]

The Carling 110 series switches traditionally used have a fast action, suitable for ac/dc see http://www.carlingtech.com/sites/def...ls_%26_COS.pdf
I remember Fenders carrying the UL logo, so I guess they must have assessed and approved its use on the HT dc circuit.

All else being equal, dc is more difficult to switch, as an ac arc tends self extinguish.
Heavy duty switches suitable for ac inductive loads have a slow switching action.
Good info here http://www.aeroelectric.com/Referenc...ing_Manual.pdf
From that 'a 120V rated ac switch (ie slow action) is suitable for up to 30Vdc'

The pop from standby switching is due to the voltage spike from the choke when its current flow stops; loads of better ways to implement standby but generally the simplest is to wire it out or just not use it.

[Randall]

"
Just consider that the exact same spec parts have been used on Fender amps for the last, what, 70 years."

Sure. And exactly why I asked the question.

[Chuck H]

Well, a POP! isn't a failure. A bit unnerving maybe. Your call. I order typical on/off switches rated for 220VAC (modern 230-240?) and haven't had a problem. The "fast action" aspect sited by Pete is probably relevant? I don't know if there's a difference in toggles. It could be that toggles are typically "fast" and it's only longer throw switches (like blade switches) that are considered "slow"? Anyway... 220VAC toggles intended for mains power have been working fine for me.