Huge SAFETY CONCERN, DPST switch used HALF mains and HALF DC....

[peteb2]

This is a question on electrical safety and possibility of someone being electrocuted.

I have to ask is it safe practice to use an RL3-4R series rocker switch such that one set of contacts can switch mains power 230Vac while the other set can switch 12Vdc?

Here's a link to a pdf of the switch: http://www.phaseda.com/catalog/Spec_RL3-4R.pdf

The appliance is an LED lamp used in the field etc by a TV News crews. The issue of concern is that the 12Vdc connector on the appliance is a male pin XLR-4 and the pins can be easily be made contact with by the users' fingertips if the 12V is not in use.

If the light is running off mains however (via its fix-wired flex) the only isolation is the few microns of air in the space inside the RL3-4R rocker switch (which over time will reduce even further as contact wear occurs) and should the switch become wet (a very high chance) the XLR-4 male socket will go to Mains potential.

I know that this method of switching would unlikely comply for electrical safety in Australia but what about the rest of the world? The lamp is a product from Italy.

I do not want to be held responsible for this kind of setup, safety-wise because I believe it is electrically unsafe however i need some genuine evidence to back up my concern. It might be that this is perfectly OK. It might be thought that the switch is not designed to pass both DC and AC and different times because of the eventual wear to contact sets is out of spec ... something like that .

Anything would be great.

[vk6zgo]

Well, I probably wouldn't do it that way, but as such a switch is commonly used to break both sides of the 230v Mains, the insulation between the two sides should be much better than " a few microns", otherwise, equipment would be shorting the Mains out & going up in smoke every day.

Maybe you could fit a better rated switch just to be sure, or to be doubly sure, switch the 12 volts supply separately.
The News Crew would probably bitch about the latter approach, but it would ease your mind.

[Tomorokoshi]

1. One thing is a little unclear. Is the 12 V connection for switching the 12 VDC, or is it for the illumination in the switch?

2. Are there specific safety standards listed for the device? Either on the box or in the manual?

3. Is it meant for use outside of a regular office environment?

4. What is the expectation of isolation between AC and the 12V output? For instance, in the past perhaps such a lighting fixture used 240 VAC incandescent lamps where someone wouldn't be in contact with them anyway.

5. How much current is available to the 12 VDC load? I can't figure out the DC current rating of it from the datasheet.

[thm_w]

I think we need some pictures of inside the switch to know what you are talking about.

It is UL rated for 250VAC so I would be surprised if there is a lack of clearance between any of the 4 connections. Other than between the 2 LED connections, in the case of 12VDC of course.

[vk6zgo]

1. One thing is a little unclear. Is the 12 V connection for switching the 12 VDC, or is it for the illumination in the switch?

2. Are there specific safety standards listed for the device? Either on the box or in the manual?

3. Is it meant for use outside of a regular office environment?

4. What is the expectation of isolation between AC and the 12V output? For instance, in the past perhaps such a lighting fixture used 240 VAC incandescent lamps where someone wouldn't be in contact with them anyway.

5. How much current is available to the 12 VDC load? I can't figure out the DC current rating of it from the datasheet.

I think the point is, that such switches are usually used to break both sides of the Mains, so the insulation must be good enough that the Active & Neutral cannot be connected to each other at any time, as that would be a direct short on the incoming  230v supply.

As this doesn't commonly happen, if the switch is 250v rated, as the specs indicate, the OP's concern about its internal clearances is misplaced.

Whether it is a good idea to share a switch like that is another question, altogether.
It could be dangerous to someone working on  the  device who may assume that if one side of the switch is, say, +12volts DC, the other side would be the DC common.

Alternately , they may think that the DPST switch means both sides of the Mains are Isolated when it is OFF,so----not a good idea!!

[Phoenix]

I think the point is, that such switches are usually used to break both sides of the Mains, so the insulation must be good enough that the Active & Neutral cannot be connected to each other at any time, as that would be a direct short on the incoming  230v supply.

As this doesn't commonly happen, if the switch is 250v rated, as the specs indicate, the OP's concern about its internal clearances is misplaced.

Whether it is a good idea to share a switch like that is another question, altogether.
It could be dangerous to someone working on  the  device who may assume that if one side of the switch is, say, +12volts DC, the other side would be the DC common.

Alternately , they may think that the DPST switch means both sides of the Mains are Isolated when it is OFF,so----not a good idea!!

Just because a switch has functional or basic isolation rating for 250V (single point of failure) doesn't mean it will comply with double/reinforced (redundant against single failure) requirements. Particularly when he says there is likely water involved!

[jbb]

You could try contacting the OEM with this specific question. They may be able to help.

If, in the end, you determine it's unsafe, you could fit a relay to power on the 12V output.

[Muttley Snickers]

When mains double pole switching is utilised such as in mobile caravans and similar sites the user would be somewhat protected where the active and neutral are connected through the upstream RCD, MCB or ELCB device. The application described by the OP would probably not incorporate any safety aspect between the LV and SELV services so should the AC mains feed to the switch come adrift and it happened make contact with the DC side where the end user may be less cautious then a potentially dangerous hazard could result.

[peteb2]

These pictures should explain how this appliance has been wired.

The black pair on the switch are for Mains Active while the red are for the external +12V supply. My concern: a switch failure etc could see Mains Active on the Vdc input connector...

[Richard Crowley]

Your interior photos show MUCH BETTER than average design and construction (compared to your average lighting fixture).  Since the switch is rated for far higher than the voltage differential that you are concerned about, I agree with @vk6zgo that your concern is misplaced.

A lamp with open vents like that is NOT intended to be used in the rain, etc.  So your concerns about getting wet would apply to everything else in use besides the lamp.  This is why we now have warning labels that say: "Do not use toaster in bathtub."  If the people using it are that stupid, they shouldn't be allowed anywhere near the gear. 

Move along, there is nothing to see here.

[Someone]

The switch would need to be inspected to see if there is sufficient clearance+creepage internally between the contacts, hard to say without looking further into it. If thats the mains flex wired through a terminal block you've got plenty more problems to fix to meet the appliance wiring rules.

[Someone]

Move along, there is nothing to see here.

You say its neat and tidy, I'd say its a long way from meeting international safety standards.

[Richard Crowley]

You say its neat and tidy, I'd say its a long way from meeting international safety standards.

If you have worked on many theatrical/production light fixtures, you would note that this is much neater and cleaner than most of the genre.  To be sure, it is rather at the inexpensive end of the scale.  Certainly not Arri or Mole-Richardson, or even Lowell, et.al.  But for an inexpensive lighting fixture it appears to be above average compared to what I typically see.  Certainly it is built to a price-point. But it is far from the dangerous design that peteb2 is imagining.  That switch manufacturer claims approval certification from practically everyone you have heard of around the planet.

[tautech]

Move along, there is nothing to see here.

You say its neat and tidy, I'd say its a long way from meeting international safety standards.

I wouldn't be so sure.

Consider a slightly larger 3PST switch, maybe switching 3 phases.
What matters then is the dielectric strength/spec between poles.

We use DPDT switches for switching transformer taps for example without a second thought.

If a suitably spec'ed switch was chosen for the OP's application there should be no concern but the wiring colours chosen for mains and 12V in this thing are totally another thing.   

[vk6zgo]

The switch would need to be inspected to see if there is sufficient clearance+creepage internally between the contacts, hard to say without looking further into it. If thats the mains flex wired through a terminal block you've got plenty more problems to fix to meet the appliance wiring rules.

A Mains rated switch is unlikely to rely upon clearance+ creepage to isolate the two halves when it is easy to provide a moulded barrier between the two poles.
 
The screw in  feed through probably clamps the Mains flex.
I suppose it should use crimped spade lugs like on the switch, instead of the terminal block, but thousands of such connections have managed to operate safely over decades without killing people.

I dunno about the appliance wiring rules ----- some delights slip through, like the toaster with an SPST switch in the Neutral line, & one side  of the Mains (Active in this case), connected to the frame holding the heater element, which can easily be accidentally touched, from the top of the thing.

Brush against the top of the  supposedly "off" "appliance" whilst reaching for something , & then pick yourself up off the floor!

[amyk]

There is a septum between the two poles in all the ones I've opened up.

[jolshefsky]

The easy way to make it right is to have two switches: one for the AC power and one for the 12V. But that makes the user interface more complex so I bet that's why they went with this. Safety doesn't come from "very unlikely but plausible" but from "implausibly unlikely." It's plausible that under not-so-unusual circumstances that condensation or an insect could get into the single switch providing a path from mains to the 12V—low-current indeed, but high enough to kill. With two switches, unless the unit is downright wet and used without a GCFI (which, assuming safe practices, you'd not have non-GCFI and wet in the same place), there is no such danger.

[stj]

the wiring colours chosen for mains and 12V in this thing are totally another thing.   

that's the u.s. for you - American stupid black & white coding.

[mikerj]

The easy way to make it right is to have two switches: one for the AC power and one for the 12V. But that makes the user interface more complex so I bet that's why they went with this.

Wonder what happens if you hook up 230v AND 12v together...

[rs20]

I think the point is, that such switches are usually used to break both sides of the Mains, so the insulation must be good enough that the Active & Neutral cannot be connected to each other at any time, as that would be a direct short on the incoming  230v supply.

As this doesn't commonly happen, if the switch is 250v rated, as the specs indicate, the OP's concern about its internal clearances is misplaced.

This logic seems dangerously invalid, assuming the 12V DC is mains earth referenced. For example, Class X capacitors must have insulation good enough to withstand line-to-neutral, so by your logic, Class X capacitors are totally fine for line-to-ground usage as well. As anyone who knows the difference between Class X and Class Y capacitors knows, this is in fact completely unacceptable reasoning.

Even if there's no direct analogy for self-healing dielectrics in physical switches, it all boils down to probability of failure multiplied by risk of fire (line-to-neutral) vs death by electrocution (line-to-earth).

Now is this switch "Class Y"? Probably, I dunno, ask the manufacturer. But just pointing out that it's "Class X" is hopelessly insufficient.

[Someone]

The switch would need to be inspected to see if there is sufficient clearance+creepage internally between the contacts, hard to say without looking further into it. If thats the mains flex wired through a terminal block you've got plenty more problems to fix to meet the appliance wiring rules.

A Mains rated switch is unlikely to rely upon clearance+ creepage to isolate the two halves when it is easy to provide a moulded barrier between the two poles.
 
The screw in  feed through probably clamps the Mains flex.
I suppose it should use crimped spade lugs like on the switch, instead of the terminal block, but thousands of such connections have managed to operate safely over decades without killing people.

Yes, as suggested internally there is likely a fin or wall between the two contact sets but without disassembling the switch its not possible to say its 100% ok. The terminal block in the earthing connection is just the start of the wiring problems and does not meet AS/NZS basic electrical safety requirements.

You say its neat and tidy, I'd say its a long way from meeting international safety standards.

If you have worked on many theatrical/production light fixtures, you would note that this is much neater and cleaner than most of the genre.  To be sure, it is rather at the inexpensive end of the scale.  Certainly not Arri or Mole-Richardson, or even Lowell, et.al.  But for an inexpensive lighting fixture it appears to be above average compared to what I typically see.  Certainly it is built to a price-point. But it is far from the dangerous design that peteb2 is imagining.  That switch manufacturer claims approval certification from practically everyone you have heard of around the planet.

It is entertaining when people jump to conclusions about others experience, I've worked on a wide range of luminaries/instruments/lights/lanterns/(whatever the term you wish to use) including those in installations dating from the days of manual dimmers predating semiconductors. Times change and what met electrical safety standards (or lack there of) in the past are no longer safe to use in a professional setting unless they are rebuilt to modern expectations, also note the substantial difference in risk between our 240V (now 230V) regions and those with 110V supplies.

[vk6zgo]

I think the point is, that such switches are usually used to break both sides of the Mains, so the insulation must be good enough that the Active & Neutral cannot be connected to each other at any time, as that would be a direct short on the incoming  230v supply.

As this doesn't commonly happen, if the switch is 250v rated, as the specs indicate, the OP's concern about its internal clearances is misplaced.

This logic seems dangerously invalid, assuming the 12V DC is mains earth referenced. For example, Class X capacitors must have insulation good enough to withstand line-to-neutral, so by your logic, Class X capacitors are totally fine for line-to-ground usage as well. As anyone who knows the difference between Class X and Class Y capacitors knows, this is in fact completely unacceptable reasoning.

Even if there's no direct analogy for self-healing dielectrics in physical switches, it all boils down to probability of failure multiplied by risk of fire (line-to-neutral) vs death by electrocution (line-to-earth).

Now is this switch "Class Y"? Probably, I dunno, ask the manufacturer. But just pointing out that it's "Class X" is hopelessly insufficient.

It isn't any type of capacitor, so Class X & Class Y does not apply.

A closer analogy is whether the insulation between Active & Neutral in a power cord is any different to that between Active & Earth.

[Monkeh]

The terminal block in the earthing connection is just the start of the wiring problems and does not meet AS/NZS basic electrical safety requirements.

Oh no, an extra joint, we're all doomed!

Sorry, but that I just find that quite amusing.. I know it's not quite optimal, but if you can trust one screw terminal you can trust 20 of them (and already do).

A closer analogy is whether the insulation between Active & Neutral in a power cord is any different to that between Active & Earth.

No, it really isn't. If you have a CPC in a cable, it is connected to earth, or at least it should be. A class Y cap, on the other hand, does not need to be connected to earth, and can be connected to exposed metalwork which is not earthed. Ask any Macbook owner about that.

This is exactly the same issue as the creepage and clearance on an SMPS - is there adequate clearance between components of two isolated systems or not?

[Siwastaja]

Depending on actual switch construction and specs, either a real safety concern, or not. It may have required creepage, but I doubt so. Most likely doesn't conform to the regulations, but might not be far off; the actual level of danger can be only evaluated by looking at the actual switch.

I guess the gap is much more than "microns"; more likely 1-2mm, with some plastic inbetween.

In any case, not super serious due to low probability of failure; much more serious safety issues do widely exist (such as: using random caps instead of Y caps; or using creepages way below 0.5mm between L and safety isolated side).

The probability is low because, as explained above, the switch in its most typical usage case must be rated to withstand AC live-to-neutral voltage between the legs, and AFAIK, incidents of these kind of switches arcing over between L&N are extremely rare.

Hence, most likely, it won't ever happen that the 230V side would accidentally arc with the 12V side.

This being said, if not specifically specified so, this does not conform to regulations, and for a good reason: the L&N arcing is considerably less serious incident, as it "only" causes a fire hazard, most likely handled by upstream fuses & fire retardants in plastics - the analogue of X caps is the right one. Whereas, when used like the OP describes, L to safety isolated side (12V) connection doesn't give any signs of failure to anyone, and creates a very real death trap by electrocution situation.

So, in all regulations, L-to-safety-isolated-side has much more strict requirements than L-to-N.

So while the chances of a failure are extremely low, the consequences are much, much more severe than what happens when the same type of switch fails in its intended way of usage.

[amyk]

This is a 12V automotive switch. Observe the septum between the two contact chambers, which is present despite it being SPDT since this is a common mould. The ones in the 250VAC switches I've seen are even deeper. It would have to be a pretty catastrophic failure for the two sides to short together.