Earthing of PA Speakers

[Paul Smith]

Hi, can anyone help?
On a 100v line PA system, do the speakers require an earth?
It is above 50v so the cables are routed in the same containment as 230v circuits, but the circuit is fed in a 2 core cable with no earth. Some PA amps have a 1 amp fuse on the output for overload, but not all
Generally, these systems are not earthed, but what is the reason why not? Is it anything to do with it being frequency agile and 7671 refers to 50Hz systems? Is there an exemption from 7671 for Audio systems? Does it make any difference if the PA is linked to the fire alarm and forms part of a PAVA system?
If no earth is required what is the method of fault protection? The voltage is greater than 50v so it's not SELV, there is more than 1 speaker per circuit so it can't be Electrical Seperation

 

[SirKit Breaker]

As i am not an expert in the audio visual field, i can only apply my electrical head to this one.

My guess is that an earth is not required because your speaker equipment is class 2, and double insulated displaying the small box within a large box symbol. As i stated this is not my field but i'm always willing to be corrected.

If your speakers have a metal frame within and even if it is completely enclosed i would put in a 3 core cable and earth it anyway, daisy chaining all the speakers on your circuit and terminating at the amp.

Running your 100v system alongside the 230v cabling i would think may introduce noise if your speaker cables arn't screened.

Regards.......Howard.

 

[Paul Smith]

Thanks.

The speakers aren't class 2.
There have been no noise issues on other projects where cables have been run in the power trunking. The only noise issue are usually if the microphone cables aren't segregated

Paul

 

[pennywise]

I would agree they must be double insulated. look at the plate on the backs of the speakers for the square within a square symbol. We have just done a church with the same system, we didn't do the PA system that was done by a ex radar engineer he was more worried about interference with the inductive hearing loop and our ring final circuits CPC. All the speakers were wired in 2 core flex but obviously speakers aren't all the same cheers. wasn't quick enough bang goes my theory then.

The transformer for the speakers could it be center taped down to 50v like a site transformer?

there might be some relevant information here I haven't read it all.

Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

 

[Paul Smith]

Thanks

No, it's 100v to 0v, no centre tap.

I think we could call it Electrcial Seperation, but the regs only allow this for 1 item of current drawing equipment. There are normally multiple speakers on a circuit.

 

[pennywise]

I would personally just contact the manufacturer and ask, or if you can see an earth terminal present on the backs of the speakers you then must provide an earth cheers.

 

[Golden_Boy]

As i am not an expert in the audio visual field, i can only apply my electrical head to this one.

My guess is that an earth is not required because your speaker equipment is class 2, and double insulated displaying the small box within a large box symbol. As i stated this is not my field but i'm always willing to be corrected.

If your speakers have a metal frame within and even if it is completely enclosed i would put in a 3 core cable and earth it anyway, daisy chaining all the speakers on your circuit and terminating at the amp.

Running your 100v system alongside the 230v cabling i would think may introduce noise if your speaker cables arn't screened.

Regards.......Howard.

Are you running a low frequency sine wave at full output continuously ?? I reckon not. Thats the only time you will get 100 volts on a 100 volt line output from an amp. Under normal circumstances there will be MUCH less than 100 volts on any of the conductors. Also of course is the question of any earthing at the output transformer inside the Amp. There is usually none or at most a centre tap ( that would be 50-0-50 volts at full output on the two conductors.
In the past I worked on 1000 watt ( 1Kw) audio amps running a 55 volt and a 220 volt line output. the outputs where never earthed and as far as i know no-one was ever badly hurt from the ouput ( it did tingle a bit if you got your hand in the wrong place !! )

 

[Guest123]

I've done numerous PA sytems in schools, offices etc, and have only ever installed a 2core YY cable for them, no earth.

Never had any issues with it and the systems were always passed by the powers that be.

Dont think I've ever seen an earth terminal on a speaker TBH???

 

[Doomed]

Its a 100V rated signal wire for the speakers, the actual voltage will never reach this value.

Ack! my curiosity just made me measure the voltage on our 100V PA system that is playing background music. Between tracks a reading of 0V, ranging up to 5V during a song. We only have the music playing quietly though.

 

[Toonlad]

The way i understand it is, for arguements sake you have a 120w amplifier and take it to maximum load, ie 120w worth of speakers tappped at various settings. Then drive the amp at 100% Then you will achieve the 100v. But if you didnt crank it up then the voltage will be lower.

So on a fully optimised amp and running at max then 100v will be acheived. Very rarely do i put in any pa systems at full load, i would normally split it and zone it through a slave amp.

I hope ive come accross in trying to explain this for you, if not then its another epic fail by me lol

 

[Golden_Boy]

The way i understand it is, for arguements sake you have a 120w amplifier and take it to maximum load, ie 120w worth of speakers tappped at various settings. Then drive the amp at 100% Then you will achieve the 100v. But if you didnt crank it up then the voltage will be lower.

Did I not mention this earlier?

 

[Toonlad]

Did I not mention this earlier?

Always Two. master and an apprentice