Twisting Cables
- Thread starter fifty60
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Very good and deep question, which could be (and probably is) the subject of a book.
If the conducted emissions are common mode in voltage, appearing equally on both wires of the twisted pair, then the emissions arriving (conducted) at the far end of the wire will not be reduced significantly or at all by twisting. But the far end device may have common mode noise rejection. The twisted pair may help to insure that that balanced noise going into the pair is still balanced at the far end.
If the conducted emission voltage is on only one of the wires, then twisting the pair will at best increase the wire to wire capacitance, which may have a small filtering effect.
It will not even necessarily reduce radiated emissions from that wire pair if the current corresponding to the emitted signal is not equal and opposite between the two wires of the pair.
Brief digression into "conducted emissions":
Emissions could be radiated directly from the device, getting out regardless of any connected wires.
Or it could be conducted through the wires directly to the terminals of the device that is getting interfered with.
Or, and here is where you need to know the applicable definition for your regulations, it could be conducted out of the originating device and then radiated from that wiring to a sensitive device along the way.
If the conducted emissions are common mode in voltage, appearing equally on both wires of the twisted pair, then the emissions arriving (conducted) at the far end of the wire will not be reduced significantly or at all by twisting. But the far end device may have common mode noise rejection. The twisted pair may help to insure that that balanced noise going into the pair is still balanced at the far end.
If the conducted emission voltage is on only one of the wires, then twisting the pair will at best increase the wire to wire capacitance, which may have a small filtering effect.
It will not even necessarily reduce radiated emissions from that wire pair if the current corresponding to the emitted signal is not equal and opposite between the two wires of the pair.
Brief digression into "conducted emissions":
Emissions could be radiated directly from the device, getting out regardless of any connected wires.
Or it could be conducted through the wires directly to the terminals of the device that is getting interfered with.
Or, and here is where you need to know the applicable definition for your regulations, it could be conducted out of the originating device and then radiated from that wiring to a sensitive device along the way.
It is a component that has a switch mode power supply. I do not see much filtering on the input of the component. Would you agree that if it is the lack of filtering on the switch mode power supply, that it is "Emissions could be radiated directly from the device, getting out regardless of any connected wires." It is definitely coupling with the actual power wires feeding the component.
There is also a suspect HMI screen that would have a DC to DC converter. Would lack of filtering here also "get out regardless of any connected wires"?
The end goal is to reduce the conducted emissions getting back out on the mains supply from the equipment. I can install a catch all filter on the overall equipment incoming power, but would like to know if there is anything I can do with simple wiring to reduce the conducted emissions. T
he HMI screen has a grounded shielded untwisted cable. Would twisting the power cable to this HMI reduce the conducted emissions? I believe the emissions, as I stated earlier, are coming from the DC to DC power supply in the HMI circuitry. The HMI is component 1. Component 2 that is also having the conducted emission problem has an internal switch mode power supply.
There is also a suspect HMI screen that would have a DC to DC converter. Would lack of filtering here also "get out regardless of any connected wires"?
The end goal is to reduce the conducted emissions getting back out on the mains supply from the equipment. I can install a catch all filter on the overall equipment incoming power, but would like to know if there is anything I can do with simple wiring to reduce the conducted emissions. T
he HMI screen has a grounded shielded untwisted cable. Would twisting the power cable to this HMI reduce the conducted emissions? I believe the emissions, as I stated earlier, are coming from the DC to DC power supply in the HMI circuitry. The HMI is component 1. Component 2 that is also having the conducted emission problem has an internal switch mode power supply.
Last edited:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
In the case you describe, the "right" place to filter out the emissions from the switch-mode power supply is exactly where the input (and/or output) cables leave the box. Anything else will be a long chase and a painful one.
If you can conveniently put a filter at the far end of the cable only, then that cable should probably be both twisted and shielded.
So an actual filter installed at the input/output of the component would be the best route. This would prefferably be installed by the component manufacturer right, inside of the component? I cannot mitigate very much through wiring practice alone? How many dB's of filtering could I reasonably expect to reduce through wiring practices?
Last edited:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
That is far too general a question to ask.
Even a back of the envelope answer or rule of thumb guesstimate would require more information about the frequencies, noise voltages, noise mode, wire lengths, etc. just to get started.
438kHz with voltage level of 73 dBuV (average) coming from conponent with internal DC/DC converter. 514.5kHz with voltage level (average) of 72 dBuV coming from component with switch mode power supply.
How can I determine if this noise is common mode or differential?
The component with the DC/DC converter is also being powered from a Class 2 power 230V to 24VDC power supply. The component with the DC/DC converter is definitely the noise source. I do not really understand how this noise travels from the component, through the power supply, and then out to the mains wires. Probably around 4 feet of wire (VCC 2' and COM 2') between the component and the power supply. This component uses shielded cable for VCC and Com. It is not twisted. Would twisting be of any great benefit here, or twisting wire be more for radiated emissions affecting the component.
How can I determine if this noise is common mode or differential?
The component with the DC/DC converter is also being powered from a Class 2 power 230V to 24VDC power supply. The component with the DC/DC converter is definitely the noise source. I do not really understand how this noise travels from the component, through the power supply, and then out to the mains wires. Probably around 4 feet of wire (VCC 2' and COM 2') between the component and the power supply. This component uses shielded cable for VCC and Com. It is not twisted. Would twisting be of any great benefit here, or twisting wire be more for radiated emissions affecting the component.
Last edited:
Speedskater
Senior Member
- Location
- Cleveland, Ohio
- Occupation
- retired broadcast, audio and industrial R&D engineering
On why cables should be twisted, see:
****************************************************
"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing"
by Jim Brown K9YC
Audio Systems Group, Inc.
http://audiosystemsgroup.com
The basis of this tutorial is a combination of my engineering education, 55 years in ham radio, my
work as vice-chair of the AES Standards Committee working group on EMC, and extensive research
on RFI in the pro audio world where I?ve made my living.
http://www.audiosystemsgroup.com/RFI-Ham.pdf
More Jim Brown papers:
http://www.audiosystemsgroup.com/publish.htm
********************************************
"Ground Loops: The Rest of the Story"
Bill Whitlock, AES Fellow and Jamie Fox, P.E.
This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA
ABSTRACT
The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system
noise problems are well known. But what causes power-line related currents to flow in signal cables in the first
place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage
differences normally found among system ground connections, even if ?isolated? or ?technical? grounding is
used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little
has been written about this ?elephant in the room? topic in engineering literature and apparently none in the
context of audio or video systems. It is shown that simply twisting L-N pairs in the premises wiring can
profoundly reduce system noise problems.
http://xa.yimg.com/kq/groups/20963848/268252969/name/Whitlock-Fox+-+Ground+Loops+.pdf
****************************************************
"A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing"
by Jim Brown K9YC
Audio Systems Group, Inc.
http://audiosystemsgroup.com
The basis of this tutorial is a combination of my engineering education, 55 years in ham radio, my
work as vice-chair of the AES Standards Committee working group on EMC, and extensive research
on RFI in the pro audio world where I?ve made my living.
http://www.audiosystemsgroup.com/RFI-Ham.pdf
More Jim Brown papers:
http://www.audiosystemsgroup.com/publish.htm
********************************************
"Ground Loops: The Rest of the Story"
Bill Whitlock, AES Fellow and Jamie Fox, P.E.
This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA
ABSTRACT
The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system
noise problems are well known. But what causes power-line related currents to flow in signal cables in the first
place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage
differences normally found among system ground connections, even if ?isolated? or ?technical? grounding is
used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little
has been written about this ?elephant in the room? topic in engineering literature and apparently none in the
context of audio or video systems. It is shown that simply twisting L-N pairs in the premises wiring can
profoundly reduce system noise problems.
http://xa.yimg.com/kq/groups/20963848/268252969/name/Whitlock-Fox+-+Ground+Loops+.pdf
Thanks for the link Speed.
The document from Eurotherm EMC Installation Manual(now Schneider???) discussing wiring practice, etc. It is probably the best document I have been able to find over the past few days.
I still am not able to determine if twisting the cables will greatly affect the "conducted emissions" directly. I do not have a LISN and Spectrum An. to test the results. I already had a shielded wire, and failed. But the wires were not twisted. i do not think twisting the wire will have any important effect on the conducted emissions, but does have a greater effect on immunity.
The document from Eurotherm EMC Installation Manual(now Schneider???) discussing wiring practice, etc. It is probably the best document I have been able to find over the past few days.
I still am not able to determine if twisting the cables will greatly affect the "conducted emissions" directly. I do not have a LISN and Spectrum An. to test the results. I already had a shielded wire, and failed. But the wires were not twisted. i do not think twisting the wire will have any important effect on the conducted emissions, but does have a greater effect on immunity.
Last edited:
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
That, I think, sums it up well. The only way to significantly reduce conducted emissions is by filtering.
But remember that filtering includes series elements such as ferrite toroids as well as parallel elements such as capacitors.
Tapatalk!
But remember that filtering includes series elements such as ferrite toroids as well as parallel elements such as capacitors.
Tapatalk!
Speedskater
Senior Member
- Location
- Cleveland, Ohio
- Occupation
- retired broadcast, audio and industrial R&D engineering
The new 850 page book by Henry W. Ott has a 50 page chapter on Conducted Emissions. An online book search may find parts of this chapter.
"Electromagnetic Compatibility Engineering"
by Henry W. Ott,
publisher: John Wiley & Sons, hardcover 872 pages, 566 figures, 65 tables.
Publication date: August 2009, ISBN#: 978-0-470-18930-6.
http://www.hottconsultants.com/EMCE_book_files/emce_book.html
Conducted emission regulations are intended to control the radiation from the
public alternating current (ac) power distribution system,* which results from
noise currents conducted back onto the power line. Normally, these currents
are too small to cause interference directly with other products connected to the
same power line; however, they are large enough to cause the power line to
radiate and possibly become a source of interference, for example to AM radio.
The conducted emission limits exist below 30 MHz, where most products
themselves are not large enough to be very efficient radiators, but where the ac
power distribution system can be an efficient antenna. The conducted emission
requirements, therefore, are really radiated emission requirements in disguise.
"Electromagnetic Compatibility Engineering"
by Henry W. Ott,
publisher: John Wiley & Sons, hardcover 872 pages, 566 figures, 65 tables.
Publication date: August 2009, ISBN#: 978-0-470-18930-6.
http://www.hottconsultants.com/EMCE_book_files/emce_book.html
Conducted emission regulations are intended to control the radiation from the
public alternating current (ac) power distribution system,* which results from
noise currents conducted back onto the power line. Normally, these currents
are too small to cause interference directly with other products connected to the
same power line; however, they are large enough to cause the power line to
radiate and possibly become a source of interference, for example to AM radio.
The conducted emission limits exist below 30 MHz, where most products
themselves are not large enough to be very efficient radiators, but where the ac
power distribution system can be an efficient antenna. The conducted emission
requirements, therefore, are really radiated emission requirements in disguise.
We twist together wires that are considered to be sensitive to induced emissions.
For example the gate/cathode pair for an SCR.
I've heard all kinds of high-flown theories. But the main thing is that it keeps the conductors close together, minimises inductance and any external field couples with both.
If I have 230V circuit that fails conducted emissions when it is connected directly to a 230V source, and then connect that equipment to the 230V secondary of a 460V to 230V step down general purpose transformer, should I expect the conducted emissions to improve? Does the transformer isolate the conducted emissions to the secondary side?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The transformer will reduce common mode signal significantly, but the extent will depend on the exact arrangement of the primary and secondary windings.
If they are would interleaved on a common core, high frequencies can be conducted through from winding to winding by capacitive coupling. Layered windings, especially with a grounded shield in between will minimize this transmission path.
Difference mode emissions will be reduced to the extent that the transformers inductance and capacitance make it a bad transformer at the emission frequency. Although some capacitive coupling can still take place just as with common mode emissions.
A GP transformer will not help nearly as much as a shielded one.
Tapatalk!
If they are would interleaved on a common core, high frequencies can be conducted through from winding to winding by capacitive coupling. Layered windings, especially with a grounded shield in between will minimize this transmission path.
Difference mode emissions will be reduced to the extent that the transformers inductance and capacitance make it a bad transformer at the emission frequency. Although some capacitive coupling can still take place just as with common mode emissions.
A GP transformer will not help nearly as much as a shielded one.
Tapatalk!
It is actually an industrial control transformer. Here is the transformer: http://www.solahevidutysales.com/pdf/transformers/ICE.pdf
I do not see any ground on the shield. I know without the transformer I have trouble passing conducted emissions. I'm hoping with the transformer I will pass. Is this reasonable given the above transformer?
I do not see any ground on the shield. I know without the transformer I have trouble passing conducted emissions. I'm hoping with the transformer I will pass. Is this reasonable given the above transformer?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
There is no shield. The double vertical line represents the magnetic core.
Since you have problems passing the standard, I would look specifically for a shielded transformer.
If you are only over the limit by a small amount, at least the transformer would give you a good place to install a line filter. and might just make the difference in its own.
Tapatalk!
Since you have problems passing the standard, I would look specifically for a shielded transformer.
If you are only over the limit by a small amount, at least the transformer would give you a good place to install a line filter.
and might just make the difference in its own.Tapatalk!
- Status