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[I’m not sure if this is the right place to ask or if I should ask over in the electrical SE but…]

I have outdoor speakers in my backyard that are all connected via the same copper run (speaker wire 14/2 iirc), which comes into the house and connects into a sonos amp. The sonos amp then is also connected to a few other things but does not have ground on the power input. That being said, should I ground the speaker wire before it connects to my sonos amp or is that not really a thing? My main concern is how to protect my amp and networking equipment (amp is connected to a networking switch) from a surge (ESD, lightning, etc - granted I know if lightning hits my house or near by, nothing really stands a chance).

If it matters, my speaker wire outside is 99% ran through buried pvc conduit.

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  • That's not really a thing. how to protect from a surge : a $10k battery backup system with built-in surge protection. But that only saves everything else in your house when the Sonos gets set on fire. You could isolate it with Ethernet-over-power adapters. But I'm not sure if that would be even worse w/o expensive surge protection.
    – Mazura
    Sep 16 at 9:22
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No

You should ground the amplifier itself, although in most cases this is automatic as part of the power cable and safe domestic wiring. You should not ground the speaker cables though.

The amp may drive both speaker wires (the so-called "push-pull" or "bridged" arrangement). This delivers 4 times the power for the same voltage output from the amp, because driving each side of the speaker with an equal and opposite signal gives you double the voltage across the speaker. In this case you would be shorting out one side of the amp, which would likely cause damage or at least blow a fuse.

If it doesn't use a push-pull, grounding the "low side" wire might not cause immediate damage. However anything causing a shift in voltage between the earth stake which grounds your house (which the amplifier is connected to) and the speaker will cause a voltage shift at the amplifier output. Generally this isn't a good thing for electronics. Something as simple as rain could cause a voltage shift through electrolysis and kill your amplifier.

And more than all this, you just plain don't need to, because the voltages aren't high enough to pose a hazard. In the UK, anything under 50V is considered "low voltage", which (using Ohm's Law) covers you for anything putting out up to 300W RMS into an 8-ohm load for a single-ended amplifier, or 1200W RMS for a bridged amplifier. Double those figures for 4-ohm speakers. I seriously doubt your Sonos amp is doing any more than this.

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  • The amplifier is not grounded. With this advise he has nothing grounded. ESD from lightning strike can be a real hazard depending on where/how he runs the wires and where the speakers are located.
    – P2000
    Sep 16 at 13:37
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    @P2000 I covered that in the first paragraph, if the amp isn't already grounded. But you can't randomly pick any wire in the system and bolt it to ground, as the OP is suggesting. That's not going to work.
    – Graham
    Sep 16 at 14:31
  • Then I suppose you'd have to explain how to ground the amplifier. Even then, it seems that doing so relies entirely on grounding inside, and still exposes the house and inside electronics to ESD or any faulty mains outside. I'm willing to learn, but see no path to safety yet.
    – P2000
    Sep 16 at 16:04
  • I agree with this from a safety standpoint, there is not enough amps drawn to worry about it. I have held live speaker wire many many times before... Tickle at best. (yes I had a huge box speaker in the back of my car when I was younger). The other thing is if you ground it there is a high high chance for interference and degradation of sound.
    – DMoore
    Sep 16 at 18:25
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    @P2000 I see no path to a hazard. If you're talking about a lightning strike, earthing a wire will actually conduct any hazardous voltage from a ground strike into the house, so you'd be making things worse. (As well as breaking the amplifier, of course.) Even if lightning actually struck the cable, how do you imagine earthing would make anything better? I don't understand where you think any hazard could possibly come from. Talk us through the failure modes you're imagining.
    – Graham
    Sep 16 at 20:23
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Yes, Protect!

In short, to be thorough: if speakers are mounted above ground, ground the speaker housing, guide the wire through grounded galvanized metal tubing until under ground, and install a surge protector in the audio path.

What NEC/CEC, IEEE and ARRL say...

Most buildings now have many additional outside connections—exterior lighting, remote gate controls and security monitors, electronic dog fences, auxiliary buildings, etc., which are often not dealt with in the codes. Any of these connections can bring damaging lightning currents into the building.

Finally, and most significant for many people, modern houses have from $5,000 to, in rare cases, $500,000 of electrical/electronic equipment, such as in utility systems, home entertainment systems, computers, security systems, and building automation systems. All of these are extremely vulnerable to lightning surges brought in on power or signal cables, and the basic NEC/CEC requirements do little to protect them.

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Ref: How to Protect Your House and Its Contents from Lightning, IEEE Guide for Surge Protection of Equipment Connected to AC Power and Communication Circuits, Published by Standards Information Network, IEEE Press

And if you don't:

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Source: Lightning and the Radio Amateur, Glenn R. Cate N4GRC

http://www.arrl.org/lightning-protection

Grounding around Speakers

In general, speakers mounted under the soffit against the house don't need protection. Speakers in the garden, especially close to trees or mounted near/on high poles should be protected.

Underground wiring does not require protection since it is already wrapped in earth. What's relevant is where the speakers are mounted, and what's nearby.

External electrical systems above 48V (or so, depending on region) require grounding. If your amplifier produces a voltage under that threshold, you don't need grounding. Speaker voltages for home systems like yours are generally under 30V. High-power audio systems have different requirements.

So the amp's voltage on the speaker wire is not the issue. Rather, it's ingress, incl. ESD, that should be taken care of, as you rightfully ask about.

Proper grounding will to some degree protect your equipment from ESD and other ingress of high voltage, incl. accidental shorts to mains voltage, when a speaker housing shorts to a nearby light that is improperly grounded. Spades and lawnmowers are your enemy.

In the event of a lightning strike you'd want a fault/short/path to be created from whatever metal is struck to a grounding wire bonded to house earth. If it doesn't save the electronics, grounding still stands a chance at saving the house. The point is to guide as much energy to ground as possible before it reaches electronics inside.

Amateur Radio operators know this best, and they earth the coax shield of their antenna wires before entry and also bond it to the house ground. Binding prevents voltage differentials between external ground and house ground, that result from nearby strikes that cause a so called "ground lift". Of course, their needs are much tougher due to the use of tall or or high placed antennas, but the principle is the same for other outdoor electronics wired into the house.

To be clear (and thanks to an important point made by user Triplefault), in your audio application you ground the metal housing and tubing, not the audio wires like the "black" wire of your amplifier's speaker output.

For one, you don't want to expose the amplifier to residual ESD or use speaker wire as your discharge conductor, and second, you don't want to possibly create a ground loop that produces hum and other noise.

The details of what happens depend on the specifics of your amplifier, but best to avoid altogether.

Surge Protection in the Audio Path

Additionally a surge protector installed outside, just before the audio wiring enters the house, will protect your interior electronics (and anything flammable around it). This is common practice for telephone / DSL and cable wiring. It will not always protect your amplifier, but it will shunt away dangerous energy as soon as possible.

How loudly do you play your music outside? Whether you can use a telephone/DSL surge protector depends on the required current feeding the speakers. The internal resistance is perhaps 3 or 4 Ohm, so you may produce heat that needs to be dissipated. Alternatively you can use a mains surge protector to connect your speakers through. They are designed for higher currents (read the specs). Note the audio wattage and required current.

Dedicated surge protectors for audio speakers are available for precisely this purpose, for up to 1000W power and impedances from 8 Ohm down to as low as 2 Ohm.

Alternatively you can place your amplifier outside away from flammables, having only a discharge path through the mains into the house ground.

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  • 1
    'Speaker wires surrounded by earth' - true, but insulated by plastic conduit. Most speakers will be housed in plastic or wooden cabinets, which cannot be earthed.
    – Tim
    Sep 16 at 8:09
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    All this is true, and is good advice. But the OP particularly asked about grounding the speaker wire, not other parts of the system.
    – Graham
    Sep 16 at 8:37
  • Speaker voltages are generally under 30V, except for high-power systems. This is a Sonos amp, and they're not high power. The other exception is constant voltage systems which are rare, extremely so in domestic cases (years ago I worked on a 100V line system)
    – Chris H
    Sep 16 at 10:35
  • yes @Tim, so I don't see issues with ESD or lightning happening IN the earth and that portion of the wiring. OP can run it in PVC if he wishes.
    – P2000
    Sep 16 at 13:21
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    @ChrisH, thanks, I edited my answer!
    – P2000
    Sep 16 at 15:56
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I am not familiar with static or lightning protection concerns and will have to defer to others. However, I would not ground the actual wires running between the amp and the speakers.

Some amplifiers run push-pull, that is, both wires to a single speaker are active amplifier outputs delivering power signal 180 degrees out of phase. If you ground one of the wires, you will at least get only half of the output signal, at least be short-circuiting the other output, and possibly destroy the amp.

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no, there's a safety issue with separate grounds

Note: I'm not an electrician. This is something I learned when setting up an amateur radio station which I think applies. But please defer to experts.

If you ground some equipment to Earth and that equipment is connected to the house's electrical supply, that equipment's ground must be properly bonded with the house's electrical ground. The reason for this is that a nearby lightning strike can set up a voltage differential in the ground, such that the different grounds see different voltages, and therefore a current will flow through them. You could have a high current flow into one ground, through the equipment you are trying to protect, through your house wiring, and then out the other ground. But if the grounds are bonded together, then the current has a low impedance path from the one ground to the other, so you won't introduce a dangerous current into the equipment and house wiring.

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  • Yes agree, ask amateur radio folks and they have their outside metal wires/antennas grounded and bonded. Some also have surge protection. Although the risks for radio folks are much higher, the same principle applies. They also don't rely only on their amp's ground inside to take care of the discharge.
    – P2000
    Sep 16 at 17:54
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Try to keep an ethernet line the only connection to your outdoor equipment. You are then able to use fibre optic cabling (you will need media converters and a fibre optic cable. Obviously, two separate power supplies), which will give you perfect electrical separation (except whatever the power supply provisions for both sides of the connection have in common).

Addendum: Solutions for carrying other signal types (audio and video, digital and analog) over fibre cables exist - but these will likely be more expensive (practically all current fibre stuff is designed for professional use - but fibre Ethernet is used in a lot of places, so the parts and materials for it are produced in volume and comparatively inexpensive).

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