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Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
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Old 29th October 2013, 09:59 PM   #1
bulgin is offline bulgin  South Africa
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Default Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier

Hi Guys

For the past several years, I've had a mini 230VAC on/off toggle switch installed at the rear of my Quad 405 amplifier. The switch stopped working a few days ago, being seized in the "on" position.

Today, I removed the switch and noticed that one of the switch solder tags had quite a bit of melted and burned plastic around it.

Then I looked at the rating on the old switch and saw "250VAC, 3A". Will this relatively low ampere rating for 250VAC be safe to use?

I then had a look in my stock of replacement switches and found a new toggle switch identical to the item I removed. I also found another on/off switch which is a pushbutton 3-pole on/off item with the following stamped on it:

"DS -250
125VAC 6A"

The DS-250 bit confuses. What does this mean?

If I decide to use the pushbutton item, is it correct to assume that this spec (125VAC 6A) will be equivalent to 250VAC, 3A?

Thanks in advance

bulgin

Last edited by bulgin; 29th October 2013 at 10:11 PM.
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Old 30th October 2013, 05:17 AM   #2
Ian Finch is offline Ian Finch  Australia
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It could mean anything at all - a manufacturers reference, like the part number, descriptive coding etc. If you can identify the manufacturer, you may be able to find what it means.

All you are likely to learn about the part is in the "125V 6A" rating. As a DIY retrofit, the switch may be an inexpensive replacement part, such as you can still buy in retail electrical components stores like Radio Shack. 'Not sure what 3-pole means in relation to mains rated switches, though. Ordinarily, I only see SPST, SPDT or DPST, DPDT rated for use at single phase AC mains voltages.

I'd be looking for some approval marks on the case or documentation of any switch I was going to use on the mains power. Logos like UL, CE and all those international electrical authorities who do insurance type approvals, should be evident somewhere. If you don't see any, assume the 125V rating is only a recommendation. Frankly, there are a lot of switches with generous max. voltage ratings that look like mains voltage. Most of them are trash that should only be used intermittently on low voltage.

AFAIK, There is no equivalence between different voltage ratings unless it is also clearly marked for use at 250VAC. Don't presume it will be, because higher voltages may require more generous spacing and insulation qualities. After all, the switch has failed and likely at much lower duty than the rating so whatever the identical switch is rated at, don't risk it.
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Old 30th October 2013, 10:01 AM   #3
Mooly is offline Mooly  United Kingdom
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Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
The problem is caused by switching an inductive load (the mains transformer). Realistically you should be looking at 10 to 15 amp switches to "survive" long term. The actual current drawn by the Quad will be quite low, probably around 100 milliamps at idle and perhaps 1.5 amps at full whack (both channels fully driven, sine wave into 100 watts rms at 8 ohms). Its at switch on and switch off the switch damage (arcing) occurs. Would a snubber placed across the contacts help such as a 0.1 and 10 ohm in series. They would have to be suitably rated parts, Class X or Y for the cap and a 1watt non flammable for the resistor.
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Old 30th October 2013, 10:55 AM   #4
Johno is offline Johno  Australia
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Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
I know I am preaching somewhat, but actually a snubber across the mains switch contacts is dangerous, does not help and is certainly not needed.

Note that a properly rated and constructed mains switch from a reputable manufacturer is designed to break loads of moderate inductive power factor at the rated current for many years (or off-on cycles). For mains duty, the switch mechanism is designed to wipe the contacts against each other and self clean while having sufficient contact separation to quench any spark within the half cycle etc etc.

Also note that the load presented by a transformer primary, at switch off, reflects the secondary load and as a result is largely resistive tending capacitive.

A snubber across the switch simply ensures that there is enough potential, when switched OFF, to electrocute you when you dive inside the box while forgetting to unplug it from the wall. All it takes is 10mA through your 650 ohm body, assuming sweating fingers, to cause fibrillation.

Now I know that many equipment manufacturers (who would be expected to know better) do add the dreaded capacitor but this is simply compensation for low cost switches and ignorance in the design department.
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Old 30th October 2013, 11:22 AM   #5
DF96 is offline DF96  England
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If necessary, a cap or snubber should be wired across the mains transformer primary, not the switch. Then it acts to suppress switch-off arcs, but creates no safety hazard when off and suffers no continuous AC stress when off: long life for the capacitor and the owner!
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Old 30th October 2013, 12:11 PM   #6
Mooly is offline Mooly  United Kingdom
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Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
Quote:
Originally Posted by Johno View Post
I know I am preaching somewhat, but actually a snubber across the mains switch contacts is dangerous, does not help and is certainly not needed.

Note that a properly rated and constructed mains switch from a reputable manufacturer is designed to break loads of moderate inductive power factor at the rated current for many years (or off-on cycles). For mains duty, the switch mechanism is designed to wipe the contacts against each other and self clean while having sufficient contact separation to quench any spark within the half cycle etc etc.

Also note that the load presented by a transformer primary, at switch off, reflects the secondary load and as a result is largely resistive tending capacitive.

A snubber across the switch simply ensures that there is enough potential, when switched OFF, to electrocute you when you dive inside the box while forgetting to unplug it from the wall. All it takes is 10mA through your 650 ohm body, assuming sweating fingers, to cause fibrillation.

Now I know that many equipment manufacturers (who would be expected to know better) do add the dreaded capacitor but this is simply compensation for low cost switches and ignorance in the design department.
Can't say I agree with much of that. Adding a cap or snubber across the switch has been used throughout the industry by numerous manufacturers. Switch failure is extremely rare.

Not sure where your shock hazard potential comes from either. A cap across the switch contacts does allow a small current to pass but that is absorbed by the transformer primary resulting in a small (a very small) voltage permanently appearing across the primary when off. No shock hazard as such.
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Old 30th October 2013, 03:24 PM   #7
bulgin is offline bulgin  South Africa
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Guys, thanks a lot.

I finally went with a pushbutton switch rated at 125VAC 6A. This partuicular switch (as the others I had in stock) was bought from RS. The body of the item is also twice the size as the item which lasted at least 8 years before seizing. Presumably but not verified - its contacts inside could also be twice the size as the old.

On the old item, I also use to hear a very soft 'plop' sound on switch on or off - the new switch is quiet.

I will just keep an eye on things in a few weeks and see if there's been arcing.

Regards all

bulgin
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Old 30th October 2013, 03:29 PM   #8
Mooly is offline Mooly  United Kingdom
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Safe Ampere Rating for 230VAC On/Off Switch for my Quad 405 Amplifier
Is it specified as suitable for your mains voltage though ?
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Old 30th October 2013, 04:01 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

Typically you downrate the current of a 125V switch for 250V.
(Or uprate the current of a 250V switch for 125V.)
I've never seen a 125V mains switch that can't switch 250V.
Some switches are rated the same current for both voltages.

rgds, sreten.
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Old 30th October 2013, 10:11 PM   #10
Ian Finch is offline Ian Finch  Australia
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As we are talking generally about 125V/3A to 6A rated switches, would anyone seriously specify any of these subminiature jobs for mains use? Introduced by C&K many years ago, they're now offered by many suppliers in a range of quality from trash to good but good enough for 230V mains use?

I once used dozens of similar types in DIY mains projects - even sold a few with them fitted. Like the contacts, I have been burned by these and similarly rated 125/250V switches that weren't mains rated and so, illegal to fit to mains appliances. Good job they aren't mains rated either but no one tells DIYs what they should know about mains switches or component safety generally, unless they go looking for proper advice.

'Agreed that switching transients are the killer and the slow switching speed of some rocker and PB types makes this much worse. If you flick some cheapo, switched IEC chassis sockets near the rated current in a darkened room, you'll see what that means.
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Last edited by Ian Finch; 30th October 2013 at 10:13 PM.
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