In building a mains distribution box, should I get different results from connecting the shields of mains leads to the chassis of the distribution box, which in turn is connected to the earth wire vs. connecting directly to the earth wires? This older article from Rane says that for IC's to connect the shield to the chassis. Whilst the article deals with signal wires not mains, I'm wondering. Grounding and Shielding Audio Devices
Have done a bit of mains AC wiring. In standard mains, any shielding is connected to earth at the supply end. In HiFi audio, the chassis is also involved in the earth path, but is usually not a question for mains cables because plugs and sockets are involved. If doing a direct wire distribution (hydra) other options are involved and I've never seen guidelines or discussion related to the specific question I posted.
The two main wires from the net, in continental Europe blue (return) and brown/red (phase) never goes to anything but a primary circuit (transformer, SMPS with isolation etc). The yellow/green (earth) should cleverly be connected to the metallic (conductive) parts of the chassis. Then, if one of the phase/return wires get loose and touches the chassis, the safety relay will shut off.
NEVER try to connect what you believe is return to chassis.
The primary circuit is isolated and insulated from the secondary circuit with rectifiers, decoupling capacitors, electronic circuits etc. The ground wire on the secondary may be connected to chassis as well. This may reduce hum.
In continental EU we do not use shielded AC cables. If you do in UK, the shield must be connected to protective earth. Else, you risk a connection from the phase wire to the shield and then it starts getting dangerous.
Does this cover your question?
NEVER try to connect what you believe is return to chassis.
The primary circuit is isolated and insulated from the secondary circuit with rectifiers, decoupling capacitors, electronic circuits etc. The ground wire on the secondary may be connected to chassis as well. This may reduce hum.
In continental EU we do not use shielded AC cables. If you do in UK, the shield must be connected to protective earth. Else, you risk a connection from the phase wire to the shield and then it starts getting dangerous.
Does this cover your question?
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Read this https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
Then ask questions on what didn't make sense. Bill puts it very sensibly.
Then ask questions on what didn't make sense. Bill puts it very sensibly.
I have used shielded control cables aboard submarines.
The rules in the UK are similar to the EU Electricity at Work rules and there is no mention of shielded mains cables only Steel Wire Reinforced for feeds from the sub station into a property and no further.
If I was given a piece of equipment to PAT test, I would fail it if the mains cable were screened. Distro Boxes do not use screened cable!
I have just taken and passed my 18th edition so I feel qualified to voice my opinion.
The rules in the UK are similar to the EU Electricity at Work rules and there is no mention of shielded mains cables only Steel Wire Reinforced for feeds from the sub station into a property and no further.
If I was given a piece of equipment to PAT test, I would fail it if the mains cable were screened. Distro Boxes do not use screened cable!
I have just taken and passed my 18th edition so I feel qualified to voice my opinion.
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We do not use shielded mains cables in the UK. If we did, we would call them 'screened' not 'shielded'.
The mains earth conductor must have a low resistance connection through any distribution device, as it is a vital part of electrical safety.
Assuming that the shield/screen is an extra conductor (i.e. it has not replaced the earth conductor - which would probably be illegal) then you can connect it however you wish. It should have no safety implications, and it should have no audio quality implications. The only thing is that it needs to be grounded somewhere, as if left floating it would make matters worse. You will not see definitive engineering guidelines because enginners woud never use a shielded mains cable.
The mains earth conductor must have a low resistance connection through any distribution device, as it is a vital part of electrical safety.
Assuming that the shield/screen is an extra conductor (i.e. it has not replaced the earth conductor - which would probably be illegal) then you can connect it however you wish. It should have no safety implications, and it should have no audio quality implications. The only thing is that it needs to be grounded somewhere, as if left floating it would make matters worse. You will not see definitive engineering guidelines because enginners woud never use a shielded mains cable.
Hi,
Perhaps OP means something like that in the photo. I used it for some DIY power cords. The green wire connects the chassis to mains PE as it should. Amps etc are taking power from a DIY power strip, a steel box that includes EMI filters, so I thought the screened cable would help to avoid EMI pollution between the filter and the device.
Perhaps OP means something like that in the photo. I used it for some DIY power cords. The green wire connects the chassis to mains PE as it should. Amps etc are taking power from a DIY power strip, a steel box that includes EMI filters, so I thought the screened cable would help to avoid EMI pollution between the filter and the device.
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Irrespective of regs, a number of AC leads in multiple countries of the HiFi-world use screens, either as a surrounding wire weave or foil with an attached drain wire. This is found in both DIY and after-market AC leads, as referenced by MagicBus. I don't see that shields/screens are a safety issue (as long as terminated). They are a noise issue, meant to prevent RF leaking into the system. I'm not talking about the connections of the ground wires or safety earth here, just RF screening.
Both options I mentioned in the OP are grounded. One is tied directly to ground, and the other is to ground through the chassis, which is grounded.
With direct wiring, each junction box is meant to be tied to safety earth, which provides both safety from a loose phase wire, and gives RF screening properties to the junction box. If direct wiring is on both sides of the junction box and the wires involve screens, they are also connected to ground.
For screening in signal circuits and data circuits, reg code and recommended practice used to say that screens should be connected to ground only at the supply side, but then changed to say the screens should be connected at both ends. There is still a variety of practice in this regard.
Several aftermarket mains leads have a wire screen which is then tied to the earth pin of the plug on the supply side. Putting some chassis between the screen and safety earth still makes it grounded and gives RF screening, but should introduce very slight resistance between the two. You would never do this when connecting the earthing wire to protective earth as you want the lowest resistance connection to true earth possible. But in signal circuits some designers recommend connecting screens to a grounded chassis at entry. Whether this is because the increased resistance is negligible where RF screening is involved, or because the slight resistance is actually useful, I've not seen discussed.
Both options I mentioned in the OP are grounded. One is tied directly to ground, and the other is to ground through the chassis, which is grounded.
With direct wiring, each junction box is meant to be tied to safety earth, which provides both safety from a loose phase wire, and gives RF screening properties to the junction box. If direct wiring is on both sides of the junction box and the wires involve screens, they are also connected to ground.
For screening in signal circuits and data circuits, reg code and recommended practice used to say that screens should be connected to ground only at the supply side, but then changed to say the screens should be connected at both ends. There is still a variety of practice in this regard.
Several aftermarket mains leads have a wire screen which is then tied to the earth pin of the plug on the supply side. Putting some chassis between the screen and safety earth still makes it grounded and gives RF screening, but should introduce very slight resistance between the two. You would never do this when connecting the earthing wire to protective earth as you want the lowest resistance connection to true earth possible. But in signal circuits some designers recommend connecting screens to a grounded chassis at entry. Whether this is because the increased resistance is negligible where RF screening is involved, or because the slight resistance is actually useful, I've not seen discussed.
It depends. In the case of a screened mains flex why wouldn't you connect both ends?
The shielding does not loose its properties when not connected to earth.
as it is the case for airplanes.
Ground connection at one end is sometimes used to avoid ground loops at low frequencies. It is not a good practise towards EMI.
French specialist Alain Charoy has written books about electronic perturabtions. In one of them, he gives five conditions to be all fullfilled to justify a one end connection.
Alain Charoy :
Alain Charoy : livres, bibliographie de l'auteur - Librairie Eyrolles
I can see how a shield connected to PE may be useful to cats and dogs when they bite through a cable. With a bit of luck their teeth may still touch the grounded shield when they hit the hot stuff.
In the US, mains cables are often shielded and some areas require it. It's called 'metal conduit' (tubing) and may be ridge or flexible. It's a major part of the Safety Ground/Protective Earth system and adds mechanical protection. The shielding is an incidental feature.
There are strict electrical rules as to how it's connected.
There are strict electrical rules as to how it's connected.
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