Driving a new ground spike

[JohnRoberts]

Regarding safety ground being a hazard: I was an expert called in to help in a case in a Texas church where a preacher was electrocuted (that's death, not just a shock as some folks think the word is defined) as he was handed a microphone. He was standing in a "hot tub" what used a small electric water heater to warm the water. The sound equipment, including microphone, was all properly grounded. But the amateur electrician who had replaced the water heater a few weeks earlier had neglected to fasten the green (grounding) wire to the housing of the water heater.

Since I was manager over all of Peavey's mixers and powered mixers I was more than a little aware of human safety grounding concerns.

Peavey got sued by the family of a guitar player killed by a properly grounded guitar amp, in combination with a mis-wired RPBG (reverse polarity bootleg ground) outlet. UL sat with us in court and we were exonerated (the mis-wired house was condemned).

I recall late last century a similar case of a preacher killed during a baptismal ceremony. Some other Peavey executives teased me with the news (in a bar in Germany during a trade show). The fault was an open EGC safety ground that some repair technician disconnected to "fix" a mixer hum problem. I was kept extremely uncomfortable until they finally relented and told me it was a competitor's top box powered mixer, not one of mine... The religious officiant is still dead and I don't mean to make light of that.

The wide availability of wireless mics have probably saved many from the immediate shock hazard of carrying a solid ground path (Hard wired mic) into energized water. GFCI outlets on the water pump/heater circuits are also pretty widely used now.

The heating element had developed a corrosion pin-hole which then allowed current flow into the water. This current would have been harmlessly routed back to neutral/safety ground had the wire been in place.

I have shared my personal anecdote about my home hot water heater (with completely consumed sacrificial anode) energizing my hot water and shocking (not killing) me in my shower.

Obviously, the church congregation was horrified as the preacher collapsed into the water (the current through his arm exceeded the 10 to 15 mA "let go" threshold current, so he couldn't just let go of the microphone. Which makes me wonder, how did Europeans come up with 25 to 30 mA for RCDs?

Agreed it appears 30mA is high...the "let go" threshold is generally considered 15mA. The US standard threshold for GFCI is 6mA. That can still be uncomfortable and unsafe if standing up on a ladder, but not likely to get you stuck to it.

JR

PS: I once had a lawyer call me and ask me to be an expert witness for his client who got shocked when utility power "jumped" to his aluminum ladder and shocked him. It was a 240V drop going into his residence. I told the lawyer that his ******* client must have touched the wire with his aluminum ladder. I didn't get hired for that "expert" gig.

 

[Tubetec]

Jesus , feels like Ive opened the Cenobytes puzzle box on this topic ,

Even those of us with the same(more or less ) mother tongue are coming a cropper due to the terminology and the different systems in place in differing territories . language barriers adds its own translatory losses on top .

The point about wireless mics being a better choice for preachers who like to appear in front of their congregation in a hot tub sounds reasonable , but the whole thing sounds like an affront to the basic message of religion in the first place , oximoronic?

I did premise this thread with a caveat that what may apply to one system may be totally inapropriate in another territory , sure I've swapped out a few light switches over the years , checked and re-torqued the screws on the odd outlet socket , always making sure to first isolate and test for any voltage before I touched anything .

At a premesis I once worked a 'half arsed' spark came to wire up my bench on someone elses recommendation , he wired blue to live , brown to neutral , I had an isolation transformer at my bench supply so it didnt matter much , but mains volts still appeared on the supply side blue wire even with the breaker down , I didnt discover the fault until I got rid of the iso.trans later , the ******* **** ( words which I use sparingly towards any human being ) had the gall to turn up sometime after again , suffice to say he left with his tail between his legs and never came back again . I disconnected the cable he installed to my bench and clearly labeled it faulty so no one ever used it again .

 

[ccaudle]

When an audio system is interfaced with shielded audio cable that is terminated at both ends and none of the equipment is grounded, this is exactly what is happening.
I have personally seen power supply failures that resulted in a direct short between AC Line and Chassis, resulting is 120 VAC on the audio cable shield.

Are you talking about a piece of equipment which was modified to remove a protective earth connection, or a properly UL listed double-insulated device? A line to chassis fault on a UL listed double insulated design would be a notable event, a line to chassis fault on a device with a "cheater plug" or a cut ground pin is a predictable electrocution hazard. That is the entire reason that different standards and different safety classes for line powered devices exist.

"...the Safety Ground..does not go to the ground rod ! Never ever do this."
Why not?

I think left out of that original should have been ...does not go only to the ground rod. As you point out as long as the technical ground is still bonded to neutral there is no safety concern.

As to the earth not being able to sink current, why it it that when a power line breaks and falls to the ground, it can create a 100 foot long 6 foot deep glass lined trench? (I have personally seen this).

From a 240V line? Or a 10kV volt line? I don't think anyone ever said that soil doesn't conduct at all, just that it is not a low resistance conductor, and not consistent between different geographies and different weather conditions.

If ground rods are only for lightning protection, what happens when the Neutral from the power pole is faulty or breaks? (I have personally seen this)

The line-to-neutral voltage falls far enough that most domestic equipment stops operating. You will have to be more explicit with what you are implying, I'm not sure what other effect you are saying can occur. Because of the neutral-grounding rod bond at the service entrance you will have current flow through the ground rod at the building service entrance back to the ground rod at the premise transformer, but I'm unclear how that fits into the discussion.

I don't intend to be argumentative, but the NEC (and , it would seem, other electric codes) are not written with recording studios in mind.

I think that is explicit, NEC is published by the National Fire Protection Association, not AES or SMPTE. Competently designed equipment has to take that into account and prevent reasonable levels of current on the PE connections from corrupting the audio signals.

I am curious to know if the technical ground systems you have described at actually better in some way than having isolated branch circuits for the studio equipment. If all outlets in a studio area go directly back to the distribution panel and have only audio equipment powered from those branch circuits, how is that any different than the scheme you have described where there is a separate ground rod for the audio equipment branch circuits, but those grounding conductors still have to be tied to neutral, and therefore the building primary ground rod, at the distribution panel?

 

[leadbreath]

"half arsed' spark"

Another technical term our fellow North American brothers will no doubt not be aware of.....

 

[Newmarket]

I believe it's so in all parts of the world.

In UK/SA its not at the power station but at your local supply transformer....

Yes. tbh I 'read' it as being at the local supply 'sub-station' ie transformer and I'm guessing that that is what Rob Flinn meant ?
I also note he's in Sussex and people in Sussex are always correct (apart from the Bonfire Crazies in Lewes obvs )

 

[leadbreath]

Yes agreed, just though I'd clarify as the thread is getting a bit wild with "half arsed sparks" and preachers getting electrocuted.....

 

[leadbreath]

 

[Newmarket]

"Relying on cable shields for safety grounds is dangerous "

I think everyone agrees with this.

When an audio system is interfaced with shielded audio cable that is terminated at both ends and none of the equipment is grounded, this is exactly what is happening.

Not really. In the case you outline there is no 'Safety Ground' since "none of the equipment is grounded" . In case of Live to Chassis short the chassis will be at the Live Voltage. But in the case that a piece of equipment does not itself have a 'Safety Ground' connection/wire then it should be "Double Insulated" and the Live to Chassis fault should not be possible if the kit is designed and built to standard and not damaged/tampered with.

As to the earth not being able to sink current, why it it that when a power line breaks and falls to the ground, it can create a 100 foot long 6 foot deep glass lined trench? (I have personally seen this).

It certainly can conduct current to varying degrees. As evidenced:
Earth Return

But the term 'sink' is usually used to describe a current 'sink' (similarly "Current Source") rather than the ability to simply act as a conductor.

 

[Newmarket]

I should really go and do some actual work now
It involves measuring a system that can generate tens of kVs.
Let's hope it's properly 'Earthed' !

 

[JohnRoberts]

Yes agreed, just though I'd clarify as the thread is getting a bit wild with "half arsed sparks" and preachers getting electrocuted.....

I have been interested in electrocution deaths for years and the last time I looked more closely a significant number of deaths are professionals (including sparks) who should know better but behaved too casually around lethal hazards.

JR

 

[Matt Syson]

I'm still at a loss as to the function of the connection marked "FE". But at least the breaker only interrupts L, and not N.
I have a feeling that FE would be a reference to Frame Earth, thus the chassis (presumably metal).
@rob You need 'specialised' electricians, and probably a crate of beer in France. The 'Official' and regulation techniques may vary. The websites of electrical component (switches/wall sockets/breakers etc have latest regulation information easily available. My place has an intriguer power connection, presumably original, being 4 terminals with 'thumbscrews' like on laboratory power supply for 'low voltage use with spaced at about 2 inches apart. Being 3 live phases and Neutral. the cover is fixed with 2 finger releasable screws. I 'upgraded to usual PVC/plastic coated wiring from the cotton covered rubber and other wires that were in place when I moved in. There is a 3 phase switch/500 milliamp master ELCB which THEN goes through the meter. Both of these are sealed. I then have 30mA RCDs on each phase. I had to provide my own earth connection. a 1.5 metre spike connected with 16mm csa wire. Of all the several hundred studios I have been involved with (as commissioning engineer for 3 mixer manufacturers), I have never seen an isolation transformer used. A UPS in Spain because the studio is half way up a mountain and the voltage dips from time to time. Abbety Road and broadcasters worldwide haven't needed isolation transformers except safety regs in the UK (BBC) called for them for 'casual equipment' (dodgy guitar amps from visiting musicians) as well as checking they have valid PAT test certificates. All of which reminds me that in the morning I have to go and investigate the damage caused by lightning at a friends house. Orange telecom text me if lightning is expected where I live suggesting I unplug the phone/internet.
ITN (The UK Independent Television News) had a 100KVA transformer in the room under a mixing desk.
The patch was wired unbalanced (Bantam) at -10dB and was a 'problem' to get through ''code'.
I spent a night working to disconnect (link out) the patch for the duration of the ITN compliance team, and a day later rewire the whole lot. Things have changed since 1982.

 

[Rob Flinn]

I'm still at a loss as to the function of the connection marked "FE". But at least the breaker only interrupts L, and not N.
I have a feeling that FE would be a reference to Frame Earth, thus the chassis (presumably metal).
@rob You need 'specialised' electricians, and probably a crate of beer in France. The 'Official' and regulation techniques may vary. The websites of electrical component (switches/wall sockets/breakers etc have latest regulation information easily available. My place has an intriguer power connection, presumably original, being 4 terminals with 'thumbscrews' like on laboratory power supply for 'low voltage use with spaced at about 2 inches apart. Being 3 live phases and Neutral. the cover is fixed with 2 finger releasable screws. I 'upgraded to usual PVC/plastic coated wiring from the cotton covered rubber and other wires that were in place when I moved in. There is a 3 phase switch/500 milliamp master ELCB which THEN goes through the meter. Both of these are sealed. I then have 30mA RCDs on each phase. I had to provide my own earth connection. a 1.5 metre spike connected with 16mm csa wire. Of all the several hundred studios I have been involved with (as commissioning engineer for 3 mixer manufacturers), I have never seen an isolation transformer used. A UPS in Spain because the studio is half way up a mountain and the voltage dips from time to time. Abbety Road and broadcasters worldwide haven't needed isolation transformers except safety regs in the UK (BBC) called for them for 'casual equipment' (dodgy guitar amps from visiting musicians) as well as checking they have valid PAT test certificates. All of which reminds me that in the morning I have to go and investigate the damage caused by lightning at a friends house. Orange telecom text me if lightning is expected where I live suggesting I unplug the phone/internet.
ITN (The UK Independent Television News) had a 100KVA transformer in the room under a mixing desk.
The patch was wired unbalanced (Bantam) at -10dB and was a 'problem' to get through ''code'.
I spent a night working to disconnect (link out) the patch for the duration of the ITN compliance team, and a day later rewire the whole lot. Things have changed since 1982.

Fortunately (in some respects I don't have to deal with flakey wiring at my place in Aude. The previous owner self built it and his father in law was an electrician. The report on the wiring when we bought the place was excellent. The estate agent said he's never seen one so good before.

The barn where my studio will be going has no mains wiring at present so I have a blank canvas in terms of the mains. Fortunately my other halfs family are all plumbers, roofers & electricians, so I have quite a bit of professional help/advice available. However it's quite difficult understanding & being understood by them, because although the other half is French & has fluent English she doesn't translate technical info very well.

The reason I was asking about the isloation transformer is that I happen to have a 32A one, that I was planning to use. Maybe overkill but I live in quite a rural area & there are quite a few farms in the immediate vacinity with heavy electrical kit so I thought it might provide a bit of immunity from them. I was going to hang all the technical outlets from it. Maybe a waste of time, but it's not going to cost me anything much to implement it.

 

[scott2000]

The estate agent said he's never seen one so good before.

lol

However it's quite difficult understanding & being understood by them, because although the other half is French & has fluent English she doesn't translate technical info very well.

This app is pretty great. I can vouch for the Spanish translation. Use it often.

https://play.google.com/store/apps/details?id=com.hawsoft.mobile.speechtrans&hl=en_US&gl=US

 

[abbey road d enfer]

The reason I was asking about the isloation transformer is that I happen to have a 32A one, that I was planning to use. Maybe overkill but I live in quite a rural area & there are quite a few farms in the immediate vacinity with heavy electrical kit so I thought it might provide a bit of immunity from them. I was going to hang all the technical outlets from it. Maybe a waste of time, but it's not going to cost me anything much to implement it.

An iso xfmr won't do much for cleaning your mains distro. Its main purpose is to create a new Neutral that can be made equipotential with the actual earth (read "soil"). In areas where the soil does not have good conductivity, it provides a superor degree of safety.
The xfmr, due to its restricted BW, filters out some RFI/EMI, but it's not sufficient nor reliable.
Beware that an iso xfmr, being designed for safety, does not care about studios, hum and S/N ratio. It generates a large level of magnetic hum, so you have to install it far away from sensitive equipment.
One very important spec is the stray capacitance. Do you know it?

 

[moamps]

I'm still at a loss as to the function of the connection marked "FE". But at least the breaker only interrupts L, and not N.
I have a feeling that FE would be a reference to Frame Earth, thus the chassis (presumably metal).

Here is an explanation:
"Why does the unit have a white tail?
This is an earth reference lead. This is a backup in case of loss of neutral. The RCD function is disabled without a voltage
reference if the Neutral is lost.

Why is the earth lead white?
This is not an earth. The white lead is only a voltage reference “functional earth” for the operation of the electronics of the
RCD which is common in 1 pole width RCBOs.

Do we have to connect the white wire “tail”?
The unit will still operate with the earth reference disconnected. However, if the neutral is lost with the white lead
disconnected the unit will not trip on an earth leakage."

https://www.nhp.com.au/-/media/Proj...-Protection/MOD6EarthLeakageFAQ-FL-001-EN.pdf
P.S.
I hope this site I linked isn't hosted in Serbia.
I can only imagine what a shame it would be if it is hosted in Croatia.

 

[Rob Flinn]

An iso xfmr won't do much for cleaning your mains distro. Its main purpose is to create a new Neutral that can be made equipotential with the actual earth (read "soil"). In areas where the soil does not have good conductivity, it provides a superor degree of safety.
The xfmr, due to its restricted BW, filters out some RFI/EMI, but it's not sufficient nor reliable.
Beware that an iso xfmr, being designed for safety, does not care about studios, hum and S/N ratio. It generates a large level of magnetic hum, so you have to install it far away from sensitive equipment.
One very important spec is the stray capacitance. Do you know it?

Yes, I'm aware of stray capacitance. I was reading the presentation notes that Bill Whitlock kindly shared on this subject earlier in the thread. In this he highlights the effects of stray capacitance, & how they can negate the benefits. However, there is an apparent possible benefit if one installs them in the right place in the system.

First, when any line filter, conditioner, or
isolation transformer is used, Code requires
that the device as well as its load still be
connected to safety ground as shown.
Because transformer winding capacitances
and/or filter capacitors divert additional 60 Hz
and high-frequency noise currents into the
safety ground system, they frequently
aggravate the problem they claim to solve.
Second, the touted noise attenuation figures
for virtually all these power line devices are
very unrealistic. Measurements are made with all the equipment (generator, detector, and device
under test) mounted on a large metal ground plane. Although the resulting specs are impressive,
they simply don’t apply to performance in a real-world situation where grounding is via safety
ground wires or conduit. But such devices can be very effective when installed at the power
service entrance, where all system safety grounds are physically very close to a common
reference point (usually the ground rod).

 

[abbey road d enfer]

I hope this site I linked isn't hosted in Serbia.
I can only imagine what a shame it would be if it is hosted in Croatia.

???

 

[moamps]

post 159:
"The page that moamps linked to is hosted in Serbia. For any safety-critical information I would consult a qualified and NICEIC registered electrician in your locality, not some random website written by goodness-knows who, or what."

 

[abbey road d enfer]

Yes, I'm aware of stray capacitance. I was reading the presentation notes that Bill Whitlock kindly shared on this subject earlier in the thread. In this he highlights the effects of stray capacitance, & how they can negate the benefits. However, there is an apparent possible benefit if one installs them in the right place in the system.

When I wrote "Do you know it?", I meant do you know the stray capacitance of your xfmr?

 

[Rob Flinn]

When I wrote "Do you know it?", I meant do you know the stray capacitance of your xfmr?

Ah right, sorry I misunderstood. Not off hand, I would have to look and see if there are some makers mrks on it. It came from a hospital installation.