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Old 26th June 2008, 06:18 PM   #1
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Default Please help with safety earth using wood enclosure

Hi,

I am finally wiring my system and want to play very safe in terms of wiring the safety earth. Please see attachment.

The PSUs (one per channel) and the amps are in separate boxes. The PSUs' box is a metal one and the amp is in a wood and acrylic box.

I have attached the safety earth to the PSUs' chassis and to the power ground line just after the PSUs.

The mains Live is fuesed (anti-surge slow buring 1.6A)

The amps have separate power and signal star grounds which are linked by thin longish copper cables.


Now the question is: since the amp's box isn't a metal one I do not know if I should nevertheless connect the safety earth to the signal an/or power star grounds or if none of this is needed in this case.


Many thanks in advance.

Regards
Antonio
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Old 26th June 2008, 06:43 PM   #2
Nuuk is offline Nuuk  United Kingdom
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First off Antonio, you say wooden box but are there any conductive parts like knobs?
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Old 26th June 2008, 06:48 PM   #3
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None at all Nuuk. There isn't any knob switch or conductive parts at amp level

I will use a preamp and the on off swicth will be at the PSU level.

Basically there will be no metal parts whatsover that one could touch, apart form the RCA terminals.

Regards

Antonio
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Old 26th June 2008, 07:11 PM   #4
Nuuk is offline Nuuk  United Kingdom
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You say that you have connected the power ground to the chassis case. Have you used the circuit that AndrewT showed us or is it a direct connection?

Strictly speaking you should also have a connection to ground from the amp case to safety ground in the PSU case.
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Old 26th June 2008, 10:16 PM   #5
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Quote:
Originally posted by Nuuk
You say that you have connected the power ground to the chassis case. Have you used the circuit that AndrewT showed us or is it a direct connection?

Strictly speaking you should also have a connection to ground from the amp case to safety ground in the PSU case.

It is a direct connection but I'm planning to do Andrew's circuit later.

What I will do is to run an earth cable to the amp and I will connect the signal and power ground to it - forming a safety earth star- and I will see how it goes with hums and humps. The I will move from there.

Regards

Antonio
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Old 27th June 2008, 07:48 AM   #6
Nordic is offline Nordic  South Africa
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I use wooden cases often....

I use the ground tab of the IEC socket as a star ground... if anything is exposed/needs grounding, I run a wire from there to it.

Wood offers some insulation (if it is dry), but you realy want a proper earth to protect your house from burning down, without it an error could fail to trip the mains fuse, and get ugly....
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Old 27th June 2008, 08:51 AM   #7
dnsey is offline dnsey  United Kingdom
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When wooden enclosures were common in commercial gear, they were often lined with foil, which was earthed in the usual way. This not only gave a greater degree of safety, but provided screening too.
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Old 27th June 2008, 09:25 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
the important safety feature is that:

all exposed conductive parts must be connected to Safety Earth.

The connection to Safety Earth MUST SURVIVE longer than it takes the fuse to rupture and the arc to extinguish. A resistor cannot achieve this, a direct connection using adequate copper area should easily meet this requirement.

Keep in mind that an interconnect may be disconnected at the other end.
Does that result in an exposed conductive part?
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