Power plug and grounding

[GytisB]

Good day! I was wondering about one thing for a few weeks now, and I can't seem to get the "straight forward answer" anywhere. I was a bit annoyed with those old plugs on the vintage amps that don't fit into the new european 220v power outlets, because of the lacking ground pin cutouts. So on one of my amplifiers, I swapped the power chord for the computer type plug, with 3 pins. This gives also an option to use any length cable you want, which is a nice extra. When soldering, I routed the earth pin on the inside to the "GND" and soldered it there. But is this correct? or should it be left "untouched/unsoldered"? Because even the newer receivers from 2010, when using computer plug, uses two pin cable with "hot and neutral". No ground is present. Am I damaging the equipment when using GND to ground it? and does it even need the ground? should I just cut the cable and leave it only with 2 pins?
Thank you in advance!

 

[whoaru99]

Generally, I do not add equipment grounding wire to something that wasn't originally equipped. The reason you don't get a "straight forward answer anywhere" is because there isn't one. Devices are/can be certified or "listed" (as in UL listed here in the USA) with or without. Modifying the device all but certainly nullifies such a certification/listing. Some care, some don't, many think they're smarter than the mfg.; some might be, or not.

 

[Binkman]

Am I damaging the equipment when using GND to ground it? and does it even need the ground? should I just cut the cable and leave it only with 2 pins?

As @whoare99 touches on grounding of equipment. If it didn't have a ground lug then you don't need it because the unit is internally grounded. Secondly the reason 99% of amps use same is to avoid ground loops when you connect other equipment to your amp. with RCA cables, they are pos. and neg. i.e. if you've ever forgot and unplugged an rca cable with the power on you hear a humm through your speakers. that is an open ground.
No harm in using a plug w/ground but you don't need to connect the ground lug and in some conditions can be dangerous should you be touching a unit. Safety can not be more important.
Earth grounding and audio explained
https://sound-au.com/earthing.htm

 

[GytisB]

Generally, I do not add equipment grounding wire to something that wasn't originally equipped. The reason you don't get a "straight forward answer anywhere" is because there isn't one. Devices are/can be certified or "listed" (as in UL listed here in the USA) with or without. Modifying the device all but certainly nullifies such a certification/listing. Some care, some don't, many think they're smarter than the mfg.; some might be, or not.

I'm certainly not trying to be smarter than mfg, just thought it would be "smart". As I can see it might to be as smart as I thought.

As @whoare99 touches on grounding of equipment. If it didn't have a ground lug then you don't need it because the unit is internally grounded. Secondly the reason 99% of amps use same is to avoid ground loops when you connect other equipment to your amp. with RCA cables, they are pos. and neg. i.e. if you've ever forgot and unplugged an rca cable with the power on you hear a humm through your speakers. that is an open ground.
No harm in using a plug w/ground but you don't need to connect the ground lug and in some conditions can be dangerous should you be touching a unit. Safety can not be more important.
Earth grounding and audio explained
https://sound-au.com/earthing.htm

Sweet! Thank you for the link, will give it a read! And as I can see, it will be best to get rid of that grounding connection inside/leave it disconnected. As you say - safety is the most important thing here!

 

[Binkman]

@GytisB I certainly have no clue of your power grid in Norway, you could contact your local service and query about line conditioners and the like.

 

[whoaru99]

I'm certainly not trying to be smarter than mfg, just thought it would be "smart". As I can see it might to be as smart as I thought.

Nothing was directed specifically at you. It was just a general comment that on the Internet one reads lots of opinions on how things should or shouldn't be done.

 

[Hyperion]

Having read the information in the provided link my assessment of the consensus is that mains earths should be connected where possible - being more of an advantageous safety measure than a disadvantage. This is assuming the service grounding scheme at the equipment location is in good order. The only exception being equipment that is double insulated, where added earths are very strongly discouraged.

 

[gadget73]

I have added grounds to things. The usual preference is a bolted connection, usually I use a transformer screw or something else that is near the power cord entry. Should be done with a crimped eye and star washers to ensure good connection. If there are power line to chassis caps, I also remove those when adding a ground.

 

[El Rubio]

In the U.S. common household ac service 220v is provided via two 120vac lines (180 degrees out of phase) a neutral, and a ground. Most household devices use just one of the 120v legs. The neutral is bonded to ground at the electric service entrance ( main breaker panel).

When you connect your new ground lead to The chassis of your device, you created a new bond between neutral and ground. Now you have return voltage on the ground line. If your outlet is a ground fault circuit interruption type, it should trip.
I don’t know electric code in your country, but that would be against the guidelines here.

 

[whoaru99]

Well, not quite, and I'm making an effort to be less pedantic, but...

It's delivered from a 240V CT transformer. So, the power is isn't delivered by two 120V legs, it's supplied at 240V but two 120V legs are derived via a center tap in the 240V transformer. The "neutral" being the connection to the center tap.

As a side note, neutral is an interesting choice of name since the neutral (properly known as the grounded conductor, not to be confused with the grounding conductor) isn't used at all in a 240V circuit and is anything but "neutral" in a 120V circuit. LOL.

 

[Blue Shadow]

I have added grounds to things... If there are power line to chassis caps, I also remove those when adding a ground.

In this instance you are redesigning the ground scheme of the unit and most here are not qualified to do that so if folks dive into the addition of grounded power cords on the gear, they need to know what they are doing as I know you do.

 

[gadget73]

When you connect your new ground lead to The chassis of your device, you created a new bond between neutral and ground.

Most things do not connect the power line directly to the chassis. If it does happen to be one of those devices, then a grounded cord should never be used.

 

[GytisB]

I think I'm better of removing ground wire and leaving wiring original. Will just leave neutral and ground connected as usual, and ground pin will just stay there unused. Thank you for the replies, I have an answer now!

Nothing was directed specifically at you. It was just a general comment that on the Internet one reads lots of opinions on how things should or shouldn't be done.

Oh, sorry! I didn't mean that you were directing it specifically at me. I just meant that I'm far from being smarter than the engineers that made the equipment, and was just wondering if that was stupid to do or not.

 

[Bill Ferris]

I have been replacing failing 2 wire to 3 wire(aka grounded) power cords on tube equipment for decades, especially vintage guitar/bass amplifiers with no problems with the use of said electronic equipment + performing AC chassis leakage tests before releasing the repaired audio equipment to the customer..

And in one instance, by doing so probably save my customer`s life when his mid sixties Fender Deluxe Reverb guitar amp`s AC power switch developed a bazaar carbon burn through trench in the plastic housing`s back from the switched load(power transformer`s primary wire) terminal to one of two nearby rivets that held toggle switches plastic housing to the metal front of the switch and on to the chassis, which if I hadn`t power cord grounded the amp he would have had full line voltage on his body and if he touched another grounded musician, equipment, or microphone while touching his guitar strings, the resultant shock might very well have killed him !!
Instead, when he flipped the amp on, it promptly blew the 2 &1/2 amp mains fuse saving him from a nasty shock.

When I electronically restored my Mc. MC 30`s, and MC 60 yrs. ago, I replaced all three power cords with modern grounded power cords, and have no ground loop issues with them being interconnected with any other gear, or A/V systems..

Now, this was only in the 120 volt powered electronic equipment area, so other than newer 240 volt clothes driers having 4 pin power plugs, verses the older 3 conductor type, in which one pin is ground, and the other is neutral outside the normal (2) 240 volt plug`s power pins, and rewiring my brand new SS Mc MC 1201`s to 240v following the factory`s instructions, those amps were grounded @120v, and remained grounded when converted to 240v.. That is the extent of my 240v equipment`s grounding experience..

No hum, or ground loops were present when they were signal connected to the grounded 120v powered A/V rack`s equipment that sent them their audio signals..

Folks, IMHO/E have ground loop problems hooking up gear, usually because they don`t know what their doing, or are indifferent to the rules that apply, this opinion of mine is based on working in the audio field for over 45 yrs.

A good amount of those yrs. involved setting up & running PA`s for rock bands, & my band members equipment & my systems didn`t have ground loop hum, noise issues, or had any shocks touching any powered up, & grounded gear, or each other..

Ground your ungrounded metal chassis equipment, or not, it`s your life, not mine !

Ciao

 

[whoaru99]

Fear of electrocution is easily mitgated by using a GFCI and one doesn't have touch/modify the gear at all to implement one.

This gadget is especially nifty for tube amps. In addition to GFCI, it is an automatic disconnect in case of power outage so you don't get a hot restart problem on your tubey goodness.

https://www.amazon.com/TRC-14650006-6-Shockshield-Protection-Unmonitored/dp/B000XVG72G

 

[El Rubio]

Most things do not connect the power line directly to the chassis. If it does happen to be one of those devices, then a grounded cord should never be used.

Sure, there are ways to do it if you can verify that you are not making a direct connection from neutral to ground.

 

[conductivity]

Fear of electrocution is easily mitgated by using a GFCI and one doesn't have touch/modify the gear at all to implement one.

The GFCI is in case of a catastrophic failure from abnormal use of the device (i.e. someone dropped a hair dryer in the bathtub). The GFCI is therefore not a part of the normal function of a grounding scheme. It is a contingency plan when the grounding has an unforeseen consequence and is not guaranteed to work perfectly every single time there is a ground fault.

IEC 60364-4-41: "Protection for safety – Protection against electric shock" states that metal cases exposed to the user must be grounded, period.

"The fundamental rule of protection against electric shock, according to IEC 61140, is that hazardous-live-parts must not be accessible and accessible conductive parts must not be hazardous live, neither under normal conditions nor under single fault conditions.

"According to 4.2 of IEC 61140, protection under normal conditions is provided by basic protective provisions and protection under single fault conditions is provided by fault protective provisions. Alternatively, protection against electric shock is provided by an enhanced protective provision, which provides protection under normal conditions and under single fault conditions.

"In the fourth edition of IEC 60364 (2001):
– protection under normal conditions (now designated basic protection) was referred to as protection against direct contact and
– protection under fault conditions (now designated fault protection) was referred to as protection against indirect contact.

"Exposed-conductive-parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in 411.4 to 411.6.

With that said, I have found an interesting method to ground equipment that can prevent the prohibitive issue with ground loop hum and would like to get input from other members. The use of a negative temperature coefficient thermistor of 10 ohms is recommended by Nelson Pass for connecting the earth/ground wire to the chassis. Check for continuity between signal cable neutral and chassis ground, for there might be no continuity and thereby no need for the thermistor. Or what about a varistor first and then connected to the thermistor? Chassis => varistor => thermistor => ground wire.

"As commonly seen in my previous projects, you will also see a thermistor / diode bridge combination used to provide ground loop isolation between the chassis, which is hardwired to the AC outlet ground, and the circuit ground. An ordinary CL60 thermistor and a 35 amp rectifier bridge should suffice."
F5 amp by Nelson Pass
https://www.firstwatt.com/pdf/art_f5_turbo.pdf

"I have two favorite "ground loop breakers", a power Thermistor and a rectifier bridge.

The Thermistor works by being an ordinary 10 ohms or so, but in the event that a lot of current goes through the ground circuit, it reduces to a much smaller value. A tip of the hat to Frank De Luca for that invention.

The rectifier bridge will conduct a lot of current when you go over .7 volts, enough of a barrier for noise, but a good conductor in event of failure. One advantage to the rectifier bridge approach is that it can isolate to channels of ground both from each other and earth at once.

You will see the use of the Thermistor in most of my DIY amp articles, and the rectifier bridge on the
Zen lite article."
Forum post by Nelson Pass
https://www.diyaudio.com/community/threads/grounding-schemes.1819/post-13713

"The third, protective earth conductor is not for nought, though I would not wire it to chassis right away. Instead, get a Y2 class (safety) film capacitor of maybe 4.7 or 6.8 nF to connect the chassis and PE. This is (a) small enough to not cause any dramatic ground loop issues yet (b) still substantially larger than internal transformer capacitance, hence keeping the device near ground potential at all times and minimizing open input hum."
https://www.diyaudio.com/community/threads/grounded-power-cord-for-vintage-amp.358669/

"The loop breaker works by adding a resistance in the earth return circuit. This reduces circulating loop currents to a very small value, and thus 'breaks' the loop. The capacitor in parallel ensures that the electronics are connected to the chassis for radio frequency signals, and helps to prevent radio frequency interference. Finally, the diode bridge provides the path for fault currents. The use of a large chassis mounting (35A) type is suggested, since this will be able to handle the possibly very high fault currents that may occur without becoming open circuit. Note the way the bridge is wired, with the two AC terminals shorted, and the two DC terminals shorted. Other connection possibilities are dangerous, and must be avoided.

"It is not uncommon to have an induced voltage of perhaps 1V RMS between the earth connections of power outlets that are wired separately back to the switchboard. This small voltage, with a total resistance of perhaps 0.2-0.5 Ohm, will cause a loop current of 2 to 5 Amps, all of which flows in the shield of the interconnect. This is sufficient to cause a voltage difference across the interconnect, which the amplifier cannot differentiate from the wanted signal. By breaking the loop with the 10 Ohm resistor, the current is now less than 200mA, and the voltage across the interconnect will be very much smaller, reducing the hum to the point where it should no longer be audible.

"This article, including but not limited to all text and diagrams, is the intellectual property of Rod Elliott, and is © 1999. Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro- mechanical, is strictly prohibited under International Copyright laws."
Earthing Your Hi-Fi - Tips, Tricks and Techniques: "Chapter 9 – Use Of Loop Breaker Circuits"
https://sound-au.com/earthing.htm#s9

Furthermore, it is worth pointing out that fair use of text on the Internet is allowed no matter what terms of use are written at the URL. I just quoted those spurious terms from Rod for comedic effect. The use of a three-pronged power plug without connecting the ground wire is the same as a scam, so that is obviously not a good way to do it either. I am confused by the forum posts scattered around the Internet about grounding, so how about my forum post here for finding a good way to do it?

Edit: I guess that this is not a good way to do it with vintage equipment that is double insulated and has a metal chassis.

 

[whoaru99]

The GFCI is therefore not a part of the normal function of a grounding scheme.

Yeah, I understand GFCI has nothing to do with earth grounding. That it doesn't rely on connection to earth ground is, in fact, the beauty of GFCI.

Note the primary context of the thread was old/vintage gear that typically didn't include earth ground.

NEC, which is the electrical code in the USA, allows GFCI to be installed on circuits that do not have grounding conductors. Not as a replacement for grounding (because devices that incorporate grounding should be connected to grounding circuit). Rather GFCI provides effective protection against electrocution where equipment/safety ground is not present on the gear or in older premises wiring.

Further, it's not unheard of for people to defeat earth ground by using a "cheater" plug because the power circuit may not have grounding capability (or perhaps because they're trying to "fix" ground loop hum). In that case too, of intentionally defeated grounding, GFCI still provides effective protection against electrocution.

 

[conductivity]

it's not unheard of

Sure, I still think it can fall within the category of "catastrophic".

Anyway, I found out that NTC thermistors can be connected in series to increase the amperage to where a circuit breaker can trip instead of just ignoring the ground wire and relying on blind faith to prevent a catastrophic failure. Don't you think thermistors in series is a decent method for the ground wire if signal ground is coupled to chassis ground, since it's actually the only method that is not "catastrophic"?

"An NTC thermistor is always connected in series with the load to be protected. If the inrush current cannot be handled by one thermistor alone, two or more thermistor elements can be connected in series.

"Paralleling several NTC thermistors is inadmissible, since the load will not be evenly distributed. The thermistor carrying the largest portion of current will heat up until it finally receives the entire current (which may result in destruction of the device), while the other paralleled thermistors remain cold."
Siemens Matsushita Components – General Technical Information
https://www.thierry-lequeu.fr/data/Thermistors-NTC.pdf

Maybe it's just me that has a 10 amp breaker, but I could buy something like this that is really cheap:
https://www.mouser.dk/ProductDetail/EPCOS-TDK/B57236S0509M000?qs=AKDv8POSxR3vP%2B1oSg4b5Q==
https://www.mouser.dk/ProductDetail/EPCOS-TDK/B57238S0309M000?qs=E/3ZYvLbbh8XGXxMBfqGBw==

 

[gadget73]

connecting them in series increases the resistance, which decreases the amount of current that will flow through the circuit. If the goal is to trip the mains breaker, the last thing you want is to reduce the amount of maximum current that can flow from mains to ground. The lower the current, the longer it takes for the breaker to trip.