Getting a shock off of my power amp.

[Arpangel]

Strange this, it’s just started to happen, I’ve checked wiring, earthing, all seems fine, I had a bit of a change around here, moving the amp, a Quad 405, it started after I moved it, I touched the case and got a bit of a whack off of it, there is no noise in the audio, buzzing etc, it all sounds fine, I haven’t got around to having a look inside yet, needless to say I’m not using it, I’ll investigate today, any pointers welcome.

[Hugh Robjohns]

The standard quad 405 is supposed to have an earthed chassis, so if you're getting belts off it you are missing an earth somewhere.

The problem is unlikely to be inside the Quad amp itself if it was working fine and you've just moved it, although a quick check with a multimeter for earth continuity between the chassis and the middle earth pin on the IEC mains inlet would confirm.

Much more likely to be a dodgy mains cable, power plug board or wall socket....

Of course... this fault could have been present previously but masked because the amp was being grounded via some other piece of equipment which is now absent!

[Arpangel]

The standard quad 405 is supposed to have an earthed chassis, so if you're getting belts off it you are missing an earth somewhere.

The problem is unlikely to be inside the Quad amp itself if it was working fine and you've just moved it, although a quick check with a multimeter for earth continuity between the chassis and the middle earth pin on the IEC mains inlet would confirm.

Much more likely to be a dodgy mains cable, power plug board or wall socket....

Of course... this fault could have been present previously but masked because the amp was being grounded via some other piece of equipment which is now absent!

Thanks Hugh, I’ve checked continuity on the IEC, all is fine. Strange this, I was using the 33 preamp before, but I’m now using the 405 direct off of my control room out, I’m not using the 33.
However, I am using an ART Clean Box to match the +4 of the mixer to -10 of the 405, as the level was way too high before.
I don’t know if this is causing an issue, I’ll put back the 33 later and see if there is still voltage on the case.

[Hugh Robjohns]

Thanks Hugh, I’ve checked continuity on the IEC, all is fine.

If the case has earth continuity to the iec socket, that's good and as it should be... So you need to check the iec cable and the earth a the wall socket (and plug board if used).

The bottom line is that there can not be any voltage on the case if it is being correctly earthed. Obviously.

The other possibility, of course, is that the voltage you sensed wasn't 'on the amp' at all, but was on you as a static charge, and you discharged yourself to the earthed amp case... Have to stop wearing those nylon thongs....

[Folderol]

Indeed. Jolt or buzz?
Jolt = static
Buzz = AC (mains)

[Nazard]

Interesting. I used to drive my 405 from by 33, but use my own homebrew preamp now. Then, the 405 was grounded by the 33. Quote from the manual: "...the 405 will be earthed via the audio lead and should not be coonected to the earth lead in the mains cable".

When I first rebuilt my Mk I 405, I am almost sure I added a solid ground chassis connection to the IEC connector, as there wasn't one present! But you have checked the IEC connector.

[Hugh Robjohns]

My own QUAD 405 is grounded via the mains inlet and the audio ground is tied to the chassis too. And all the schematics I've checked for both the 405 and 405-2 show a grounded chassis via the mains inlet.

[ManFromGlass]

Nylon thong? I almost peed myself! Today’s chuckle award. Leather is always safer, especially if it comes into contact with unearthed metal. . . .

[Arpangel]

Thongs aside, I’m a bit worried, I unplugged the 405 and took it to another room to have a look at it, with nothing plugged in and the unit powered up, there was no evidence of a voltage on the case at all, and no shocks.
The wiring in our house is terrible, we are discovering horrific things all the time, and slowly putting them right, like no earthing to sockets etc.
This house should be rewired, we got a quote for £15,000 which given the fact that we may be downsizing at some point just isn’t worth it.
The house was bodged up by my partners father, who was a wartime radar engineer, he just added bits and pieces as he went along, terrible.
I’m going to check the sockets in the studio room today, and trace them back, just to make sure we have earth continuity.

[Folderol]

Ouch!
Are there actual ring mains, or are they all just daisychained spurs? If you do decide to downsize you may not be able to get the wiring certified - which would take a significant lump off the house value.

[Arpangel]

Ouch!
Are there actual ring mains, or are they all just daisychained spurs? If you do decide to downsize you may not be able to get the wiring certified - which would take a significant lump off the house value.

That’s disturbing, thanks for telling me, I didn’t realise you had to have a certificate.
We had the house valued recently, and the figure quoted was based on a visual assessment of the house as it stands, no mention by the estate agent concerning the condition of wiring, plumbing etc. The chances are high that it will be bought by a developer, so the place will be gutted anyway.

[BillB]

he just added bits and pieces as he went along, terrible.

It looks like you have answered you own question, and it doesn’t have much to do with the amplifier.

Can the experts hereabouts confirm whether one of those light-up mains plug testers https://www.screwfix.com/c/tools/socket ... cat7910008 would help Arpangel to usefully identify problem sockets?

[Mike Stranks]

The cheaper ones are OK, I used to use one for basic testing of sockets at venues...

... but for more serious fault-finding work something from the Martindale range is preferred:

https://martindale-electric.co.uk/?device=c&utm_source=adwords&medium=cpc&utm_campaign=772878644&gclid=CjwKCAjwlZf3BRABEiwA8Q0qq-ocflJ4-NAVWiRaSM40GF-VdV0KlRKgO8zubg-nbK2kZRUSwhf9thoCQUAQAvD_BwE

[wireman]

The cheaper ones are OK, I used to use one for basic testing of sockets at venues...

... but for more serious fault-finding work something from the Martindale range is preferred:

https://martindale-electric.co.uk/?device=c&utm_source=adwords&medium=cpc&utm_campaign=772878644&gclid=CjwKCAjwlZf3BRABEiwA8Q0qq-ocflJ4-NAVWiRaSM40GF-VdV0KlRKgO8zubg-nbK2kZRUSwhf9thoCQUAQAvD_BwE

They seem quite coy about the "28" faults their basic testers can check for.

Now as a non expert what would I like from a tester, how about tell me if any combination of the wires are swapped. Will these tell me? — no.
I do have one of these testers, which I use as a quick way to spot the most dangerous issues (earth connection disconnected, LN swap) for example if I use a borrowed extension lead.

[Sam Spoons]

The cheaper ones are OK, I used to use one for basic testing of sockets at venues...

... but for more serious fault-finding work something from the Martindale range is preferred:

https://martindale-electric.co.uk/?device=c&utm_source=adwords&medium=cpc&utm_campaign=772878644&gclid=CjwKCAjwlZf3BRABEiwA8Q0qq-ocflJ4-NAVWiRaSM40GF-VdV0KlRKgO8zubg-nbK2kZRUSwhf9thoCQUAQAvD_BwE

They seem quite coy about the "28" faults their basic testers can check for.

Now as a non expert what would I like from a tester, how about tell me if any combination of the wires are swapped. Will these tell me? — no.
I do have one of these testers, which I use as a quick way to spot the most dangerous issues (earth connection disconnected, LN swap) for example if I use a borrowed extension lead.

Even the basic 'Buzz-It tester shows L/N reversal and L/E reversal. In the UK neutral is connected to earth at the sub-station.

[wireman]

The cheaper ones are OK, I used to use one for basic testing of sockets at venues...

... but for more serious fault-finding work something from the Martindale range is preferred:

https://martindale-electric.co.uk/?device=c&utm_source=adwords&medium=cpc&utm_campaign=772878644&gclid=CjwKCAjwlZf3BRABEiwA8Q0qq-ocflJ4-NAVWiRaSM40GF-VdV0KlRKgO8zubg-nbK2kZRUSwhf9thoCQUAQAvD_BwE

They seem quite coy about the "28" faults their basic testers can check for.

Now as a non expert what would I like from a tester, how about tell me if any combination of the wires are swapped. Will these tell me? — no.
I do have one of these testers, which I use as a quick way to spot the most dangerous issues (earth connection disconnected, LN swap) for example if I use a borrowed extension lead.

Even the basic 'Buzz-It tester shows L/N reversal and L/E reversal. In the UK neutral is connected to earth at the sub-station.

I keep hearing this but then wonder why electricians have to learn about multiple types of earthing arrangements (TN-S, TN-CS, TT).

[Folderol]

I keep hearing this but then wonder why electricians have to learn about multiple types of earthing arrangements (TN-S, TN-CS, TT).

For the common or garden house basher it's pretty much irrelevant, but for a proper electrician who may be wiring an indoor jacousy one day, a garden swimming pool the next and an industrial distribution the following week, this very much matters!

[Sam Spoons]

+1, it's a bit like if your a guitarist in a rock and roll band you may only need to know three chords but if you make your living playing orchestra pits and sessions it helps to know all of them*.

* Though not many guitarists risk killing their clients if they got it wrong,

[Hugh Robjohns]

They need to know because the different arrangements exist for historical reasons, and because some arrangements are not allowed in specific situations.

The system descriptions come from the IEC and thus are based on French words. So the 'T' in these mains supply system codes refers to 'terre' -- French for Earth. 'N' refers to the Neutral connection, and the 'C' and 'S' indicate that the supply Earth is either Combined (combiné) with the Neutral or Separate (séparé) from it.

So, a TT system provides Line and Neutral connections from the supply substation (or pole transformer) to the building (and the Neutral is bonded to Earth at the substation in the standard way). But there is no separate Earth connection to the building from the substation -- only the Neutral and Line are connected. Instead, a local earth is provided via an earth spike or underground plate at the building.

This arrangement is fairly common in older properties and in rural buildings fed by overhead cables, but as the earth impedance back to the substation via the soil is inherently variable (and higher than a direct connection) an RCD (GFCI) is required on incoming supply for shock protection.

Most modern UK installations use the TN-C-S system (sometimes called a PME or Protective Multiple Earth system). The Neutral is bonded to Earth at the substation, and only the Neutral and Line are provided in the supply distribution to the building -- but at some point at or near the building a separate Protective Earth is created from the Neutral.

Typically with this distribution system, multiple consumers share the supply feed, and so the resulting high current flow along the Neutral conductor will cause a rise in voltage (due to the cable resistance) at the consumer end relative to the supply end.

As the local Protective Earth is derived from this Neutral conductor the Earth potential at the consumer unit won't be at the same potential as the substation's Earth.

To overcome this problem, the Neutral supply line is Earthed at frequent points along the supply/installation route -- hence its alternate name of PME. This TN-C-S arrangement is in widespread use around the world, where it is also known as a Multiple Earth Neutral (MEN) or Multi-grounded Neutral (MGN) supply.

There is a risk with this system that if the Neutral feed becomes open-circuit for some reason (the cable gets dug up, for example), there would be no direct current path back to the substation, and for that reason the TN-C-S system cannot be used in a specific set of 'at risk' installations (these include building sites, caravan parks, petrol stations and some others).

A variation of this supply arrangement is called TN-C, but this is used mainly only for mains supply distribution systems, where the Neutral conductor also serves as a Protective Earth, without the additional interim bonding. It is not normally found in consumer building supplies.

The TN-S system provides all three connections -- L, N and E -- between the substation and building. The Neutral is bonded to Earth at the substation as normal, but a separate Earth connection from the same point is also extended to the building, along with the Neutral and Line feeds.

So the Protective Earth and Neutral conductors are physically separate things, connected only at the supply source.

There's a good explanation of all this here: https://electricalapprentice.co.uk/an-introduction-to-earthing-and-bonding/ which is also where I borrowed (and modified) the diagrams from.

[Arpangel]

Thanks for all the info, I've got the usual neon screwdriver, for a simple polarity check, and my God, haven't we had a few surprises there! lighting circuits have had switches placed in the neutral side, there is no ring, just endless spurs.
Our attitude here is to strip out issues as we find them, and replace where needed. We've done loads of work, my partners brother is an electrical engineer, I did three years with Plessey, but that was a long time ago, her brother does all the wiring, and I work as his mate.
It's a compromise, keeping it safe, and functioning, but not a total rewire, as we don't know the future yet.
I'm just going to check earthing continuity today, back to the board, there are earth bonding clips to copper water pipes, at least.

[Hugh Robjohns]

...there are earth bonding clips to copper water pipes, at least.

But apparently not helping the socket you used...

[wireman]

For those interested in this level of detail, JWs videos on Youtube are quite understandable...

For example:

https://www.youtube.com/watch?v=AWxeb2MI37c
https://www.youtube.com/watch?v=JRHyqouJPzE

[Arpangel]

...there are earth bonding clips to copper water pipes, at least.

But apparently not helping the socket you used...

Thanks again, there are 3 core 2.5mm cables in the studio sockets, I've buzzed them back to the main earth, all OK. So that's not the problem. This room was a complete hospital ward, for my partners parents when they were ill, the wiring was installed by NHS contractors, it had to be safe as it was supplying medical equipment, which is very surprising given the standard of the workmanship.

[Hugh Robjohns]

Clearly something doesn't add up here.

If the earthing arrangements for the amp, the mains cabling and the wall sockets are all good you obviously cannot have received an electric shock from the case of the amp becuase it was properly grounded.

Therefore the 'belt' you felt must have been going the other way -- grounding a static charge you were carrying around on your own body.

[pk.roberts]

I don't claim to be any kind of expert on this; but I am aware that apart from the more common earthing arrangements outlined by Hugh, there is a arrangement know as 'IT' or 'isolated earth' which is used in some medical locations (designed to allow systems to 'float'). Given the history of the space, I really think it's time to call in a real expert.