Help needed understanding IEC inlet filter

[helix1]

I have purchased this inlet filter http://www.farnell.com/datasheets/1511834.pdf and am in the process of testing it. There are 3 pins on the back, N (neutral), P (live) and PE. I am not sure what PE is, but it appears to be live. In addition the entire metal casing appears to be live.

Please can someone help me understand how to wire this up safely. I don't understand why PE (which I thought should be earth) and the entire casing is live.

[mariush]

Look in the datasheet at the schematic... 

PE could be short for Physical Earth .

In some countries, the mains plugs aren't keyed, so depending on how user inserts the plug into the wall,  he/she may put live into neutral and neutral into live ... which may cause issues if some device connects neutral and earth wires.

[Monkeh]

PE is Protective Earth. It should not be live!

The shell should be connected to PE.

[helix1]

I'm in the UK and we have a 3 pin system so there should be no way someone can put the plug in the wall wrongly.

I am just a bit alarmed that the whole thing is live - it seems rather dangerous, and I'm not sure how I should be wiring it up to prevent electrocution hazard!

[madires]

Please don't play with mains if you don't have the knowledge and experience yet! The Y caps between N/P and PE pass a low AC current.

[Monkeh]

I'm in the UK and we have a 3 pin system so there should be no way someone can put the plug in the wall wrongly.

I am just a bit alarmed that the whole thing is live - it seems rather dangerous, and I'm not sure how I should be wiring it up to prevent electrocution hazard!

If it appears to be live, your circuit, socket, or cable is incorrectly wired, or you're missing PE. Or you're measuring wrong.

[picandmix]

Have you tested the mains socket  with a test meter or one of the plug type testers, you could have a faulty earth ?

What are you testing the IEC socket with, a volt meter or a neon screwdriver type of device ?

What have you got the socket for ?    I believe that type of filter works best if a closer match to the load being applied.
eg you will not get the best performance from a 20A unit when the load is just milli amps, though anything is better than nothing.

[helix1]

Thanks for your help guys.

@madires, I am being careful  ... but why does it need to connect N/P and PE with caps?

@Monkeh, it couldn't be simpler. I have literally plugged a 3 pin cord into the mains socket and put it into the back of the filter so I could test it. It is not attached to anything else.

@picandmix, I haven't tested the mains socket yet. I am testing the filter with a neon screwdriver device and also a meter. I have the 1A version of this filter, which should fit my loads of up to 1A when I get that far with the project.

[Monkeh]

And what are you measuring the case of the filter as live in respect to?

[helix1]

I am touching it with the neon screwdriver, which is showing live. When I use the meter, the P pin is 240V with respect to neutral, and the casing and PE is 120V with respect to neutral.

What should I do in this case?

[Monkeh]

I am touching it with the neon screwdriver, which is showing live. When I use the meter, the P pin is 240V with respect to neutral, and the casing and PE is 120V with respect to neutral.

What should I do in this case?

You have no earth.

[Neilm]

The IEC filtered inlet has capacitors to earth to do the filtering. If it is not connected to anything, you can get some leakage. Depending on what you are measuring this could appear as a voltage.

If it is not floating then you could actually have a problem with your supply. A few years ago I was working in a building that had been rewired after a fire - the electrician had made a mistake and all the mains sockets had the earth pins live. I spent ages trying to work out why I was getting shocks off a products I was designing when I connected the earth. If you think this could be the case, there are lots of socket testers on sale. (£5 to about £20)

[madires]

@madires, I am being careful  ... but why does it need to connect N/P and PE with caps?

The Y filter caps pass high frequency noise to earth/ground.

[picandmix]

As said, nip down to b&q or other diy stores and get yourself a simple tester
http://www.diy.com/departments/bq-230v-socket-tester/178677_BQ.prd
http://www.maplin.co.uk/p/mains-socket-tester-wd53h

[helix1]

So the capacitors are acting like a voltage divider putting the PE at 120V?

Does this mean I also need to ensure that somehow there is a proper earth attached to the PE otherwise there is a shock hazard?

Some plugs don't have the earth lead attached though. Does that mean that those leads are unsuitable for this particular filter? Seems dangerous, as someone could easily grab a random 3 pin lead and plug it in without knowing.

Sounds like a fixed wire solution so there is no chance of swapping leads would be the safest way to proceed, right?

[Monkeh]

Does this mean I also need to ensure that somehow there is a proper earth attached to the PE otherwise there is a shock hazard?

Yes.

Some plugs don't have the earth lead attached though. Does that mean that those leads are unsuitable for this particular filter? Seems dangerous, as someone could easily grab a random 3 pin lead and plug it in without knowing.

No cable with an IEC C13 connector on the end should lack an earth! If you have cables like that, destroy them. They should not exist.

[Gyro]

Any UK IEC mains lead should have continuity from the Earth pin on the 13A plug to the Earth pin on the IEC filter (and therefore its case), no exceptions. You don't need to do any further earthing of the filter case... IT becomes the Earth connection to the case of whatever you're putting it into.

That means either (1) a faulty IEC lead, (2) a faulty IEC filter (no connection between Earth pin and case - very unlikely), or (3) no Earth connection to your 13A socket.

You can easily do unplugged continuity tests for (1) and (2) without exposing yourself to further risk. If they're both intact then you need to get (3) sorted immediately!    As others have said a socket tester will help - you need to go round and verify every socket in the house if this is the case as it could be on the whole ring main, or the whole house.

Edit: Just to avoid any terminology confusion, PE is the Earth pin on the mains plug.

[helix1]

Thanks guys, that all makes sense.

A final question to get fully clear on this... does it also mean that the equipment cannot be used via a travel adapter in other countries that only have 2 pin sockets?

[Monkeh]

Thanks guys, that all makes sense.

A final question to get fully clear on this... does it also mean that the equipment cannot be used via a travel adapter in other countries that only have 2 pin sockets?

Absolutely. If you require an earth, you require an earth.

[Gyro]

P.S. I think we'd all be curious at this stage to know what the fault is, have you buzzed it out yet?

[helix1]

It was a dodgy lead! IEC adapter on one end, but the plug end had a plastic earth pin - no wonder I had no earth!

Needless to say that has now gone in the bin

[Gyro]

Ughh, I hate things like that  The bin's certainly the right place!

P.S. Probably best to put it beyond use too - smash the plug or at least remove the fuse (assuming it has one!  )

[TimFox]

With 240 V line-to-neutral and neutral near ground potential and no connection to PE (protective earth that should be connected to ground), the capacitors will put the PE connection (and shell) at approximately 120 V AC from ground.  The series impedance to that PE connection is a medium capacitance (a few nF, probably) that will conduct enough current into you to be felt, but probably not enough to harm you.  If you have many such filters connected to the same line, and the shells are otherwise connected together (through an outlet strip or direct connections between equipment cases), the current can be higher.
At my former day job, we called this the "Dan effect", as in "It's hard to shock Dan, but ...".  It wasn't Dan's fault:  the site electrician had connected a large Diesel generator to the building's power distribution without grounding it.
PE is there to ensure that any metal that can be touched by the operator will be at ground potential, even with a fault inside the boxes.  Then, it is safe to touch the box, chassis, etc.  The case of the line filter is directly connected directly to the chassis of the equipment.

[jwm_]

It was a dodgy lead! IEC adapter on one end, but the plug end had a plastic earth pin - no wonder I had no earth!

Needless to say that has now gone in the bin

That doesn't sound dodgy, that sounds outright criminally negligent. can you retrieve it and chop the ends off to show what the wires are in it? If they couldn't afford the copper for a ground lead, i wonder how crappy the current carrying conductors are. Where did you get the cable? (also chopping the ends off will make sure no one finds and re-uses it.)

My parents always chopped the power cords off things they gave me to take apart as a kid thinking it would keep me from plugging them in to try to get them to work, all it actually did was teach me at a young age how to properly splice power cords.

[tggzzz]

Does this mean I also need to ensure that somehow there is a proper earth attached to the PE otherwise there is a shock hazard?

Some plugs don't have the earth lead attached though. Does that mean that those leads are unsuitable for this particular filter? Seems dangerous, as someone could easily grab a random 3 pin lead and plug it in without knowing.

Stop. Right. Now. Stay away from mains voltages. Get a qualified electrician to physically check anything you have done w.r.t. mains voltages.

You are currently a danger to yourself and, potentially (ho ho) others. Currently (ho ho), you don't even understand all the questions that need to be asked, let alone the correct answers.

The problem is that someone on this forum could provide a correct answer to one of your questions, and it would still be dangerous. Why? Because you might not have provided all the necessary information simply because you don't realise what is necessary and sufficient.

[helix1]

@tggzzz, fair point. I'm a beginner for sure. That's why I'm posting a newbie question in the beginner's forum. But if we can move beyond my own incompetence which clearly isn't in doubt , I want to understand these kind of questions.

Take the following hypothetical... For Christmas electronics enthusiast Johnny gets given 2 presents. Mum and dad buy him the latest cool bit of properly earthed kit with kosher IEC inlet and plug. They did all the research to check it was safe and everything. Uncle Bert bought a different present - a cheapo Chinese knockoff audio amplifier for Johnny's stereo collection, bought for £10 down the market complete with fake IEC lead. By complete luck the audio amplifier doesn't manage to electrocute Johnny so Christmas is awesome.

6 months later, the family needs to move house. Johnny disconnects all his gear, boxes up each bit of kit and chucks all the electrical leads in a bag, so they're all in one place. At the new house, he puts everything together again and promptly kills himself turning on the kit from his mum and dad. He unknowingly plugged the wrong lead in so it was no longer earthed and the inlet filter on the back automatically turned the whole casing live.

It just seems odd to design an inlet filter to automatically make the casing of something live when the one thing that can be easily changed by the uneducated user (i.e. swapping a good lead for a dodgy one) happens.

Ok these kind of leads shouldn't exist. But unfortunately it appears that they do, so why not design something that takes this into account?

[madires]

6 months later, the family needs to move house. Johnny disconnects all his gear, boxes up each bit of kit and chucks all the electrical leads in a bag, so they're all in one place. At the new house, he puts everything together again and promptly kills himself turning on the kit from his mum and dad. He unknowingly plugged the wrong lead in so it was no longer earthed and the inlet filter on the back automatically turned the whole casing live.

It just seems odd to design an inlet filter to automatically make the casing of something live when the one thing that can be easily changed by the uneducated user (i.e. swapping a good lead for a dodgy one) happens.

Ok these kind of leads shouldn't exist. But unfortunately it appears that they do, so why not design something that takes this into account?

The Y caps limit the current to roughly a mA by their impedance at 50Hz. It would hurt, but not kill. BTW, there are different classes of devices, please see https://en.wikipedia.org/wiki/Appliance_classes for more details.

[Gyro]

There is no guarantee that the insulation and capacitors inside the IEC filter are suitably rated for Class II double insulated operation, they may only be single insulated and have Y2 Caps. The Filter is designed to operate with a 3 core earthed IEC lead only so there is no requirement for such an insulation level.

Edit: Actually, thinking about it, there's no way that a standard potted IEC filter could ever meet theoretical Class II - the clearances on the output connections don't have sufficient clearance from the case for one thing!

@helix1:

Ok these kind of leads shouldn't exist. But unfortunately it appears that they do, so why not design something that takes this into account?

You may argue that, but such leads are illegal. It is illegal to sell them... but it is also illegal to put them into service (the only legal thing you can do is buy them  ). It's just the same as the China manufactures cloverleaf shaped mains plugs without a fuse that Trading Standards are jumping up and down about (burning Hoverboards). It's your responsibility not to use such items (your house insurance company wouldn't be very happy if you burn it down!). Remember what I said - it's not a matter of the case becoming live - the case is the earthing point for your equipment's outer case, without an earth lead the whole equipment is unprotected.

With regard to the mains filter, it is designed that way to filter some of the interference by channeling it to earth via the Y capacitors. It requires the earth lead to do this - it's part of the design. The only filters that don't include such capacitors are medical grade ones (they only have L to N filtering).

The only devices allowed to operate without an earth connection are Class II Double insulated ones. These have very specific requirements for internal construction, (two separate insulation barriers between mains and anything touchable, very specific clearance requiremenrs, captive internal mains connections etc. Trust me, you're not qualified to design such devices at your stage of experience (it's one for the professionals only, with LVD testing and certification).

The rules are quite simple - a Class II Double insulated product will be identified by a symbol on the rear panel (square within a square) and will either have a captive 2 core mains lead or a 2 pin mains input connector. Anything with a 3 core mains lead or a 3 pin input connector (like your IEC) MUST be properly earthed.

 

[madires]

Edit: Actually, thinking about it, there's no way that a standard potted IEC filter would ever meet Class II - the clearances on the output connections don't have sufficient clearance from the case for one thing!

The standard IEC filter implies class I. A filter for a class II device would lack the Y caps and any metal shielding. There are IEC connectors without PE, but for very special cases. I got an isolation transformer with a variac which has a PE-less IEC, which makes sense.

[Gyro]

Hmm, I've never come across one of those. Presumably they have the Earth (PE) pin physically removed. As you say, very special case.  Class II devices do of course quite often have Y caps  across the isolation barrier but specifically Y1 rated.

The bit I was commenting on was the:

It would hurt, but not kill

  By definition, being a non earthed Class I situation, it Could kill (you'd have to be unlucky of course).

Edit: typo

[madires]

Class II devices do of course quite often have Y caps  across the isolation barrier but specifically Y1 rated.

SMPS wall warts I assume. People love to get zapped by them.

[Gyro]

No, most Class II consumer equipment with SMPS, Set-top boxes, TVs, DVDs etc. They're needed to meet EMC. Capacitance value is limited, typically 2n2. Y1 Caps (normally Ceramic) have reinforced insulation and are rated for 4kV AC test and carry UL, VDE, SA etc approvals. The 8mm CE minimum primary-secondary clearance is always maintained, both PCB footprint and lead spacing.