use IEC or dont?

[mich]

hi,
how do you feel about using or not using the iec conector?
what i realy mean is ,do you use the ground conection from mains power (conected to chassis)-or not?
i know sometimes using the ground means more 50-60 Hz hum, but on the other hand safety is important too....whats your aproach? :?

 

[mcs]

It's much easier when you live in an old house with no grounded outlets... :green:

Best regards,

Mikkel C. Simonsen

 

[pucho812]

Safty first use the ground. I have only been in one studio my wholelife where they didn't use that ground and that was because the building had old wiring. So they would use 50 cent 3 prong to 2 prong ground lifts that you can get at any local hardware store. It worked good till it burnt out a few channel/track cards on the multitrack. Not to long ago I bought a used urei graphic EQ from cherokee studios and they actually cut to ground plug off. Good thing I only paid 50 bucks for it. in a perfect world you should never have to ground left but for whatever reason you need to buy the plug it's cheap and you can go back as necessary.

 

[MikoKensington]

IEC where your coming from...

...(crickets chirping)

Aside from an IEC looking "pro" you can always install a ground lift.

 

[Mark Burnley]

Hi,

As far as the world of electrical safety is concerned, there are only TWO types of installation-

1. Fully grounded

2. Un-grounded double insulated

This classification depends upon the MAINS safety ground. Nothing to do with other system grounds, but upon the inherent need for a connection from the socket in the wall to the equipment.

Within the first type of installation I would count most "pro audio" gear. Look inside any metal cased equipment, and you'll see the incoming Mains Ground lead connecting directly to the chassis. This is an electrical SAFETY connection.

Imagine this scenario- you place a metal cased piece of equipment onto a wooden bench. You plug the mains lead into the wall and flick the power switch. Due to a fault internally, the Live (Hot) lead of the incoming mains has come adrift and is touching the metal case.

There are two possibilities here- I've come across both- firstly, if the chassis is grounded to mains ground, there will be a low-resistance electrical path from the case/chassis, through a bonding wire, to the IEC or cable inlet, down the mains cable, and to the mains socket in the wall. This is (hopefully) electrically connected to the ground at the incoming mains at the consumer unit (fusebox). Eventually, depending on where you live, this Mains Ground connects to Mains Neutral, and The Planet.

So, when the Mains Live cable in the faulty equipment touches the chassis, because of this unbroken chain of Grounding conductors, it effectively becomes shorted with the Neutral conductor. This causes a current to flow Which causes the lowest value fuse in the system to BLOW!....

This will either be the fuse in the Live input of the equipment (I like those combo IEC fuse/connector units- no excuse for no fuse!) or the fuse in thye mains plug (in the UK!) or the last line of defense- the Supply Fuse for the mains circuit you've plugged the equipment into. Note the increase in fuse size here- the equipment fuse will often be ~1A or so, a fuse in a plug can be anywhere between 3A and 13A (in the UK) and a Mains Supply fuse in thye Consumer Unit will be 10 to 16A (or up to 30A for a large ring main)

Obviously, the larger the fuse the larger the "fault current" will flow-and if any of your Ground wires in the chain can't handle the fault current, they may fuse before the Mains fuse- so as a rule of thumb, always use ground wires of equal or greater size as the Live input wire to the equipment.

As soon as the fuse blows, the equipment is made safe- the chassis/case is no longer at Live potential.

But lets look at the second case- no Mains Safety Ground connection to the chassis/case, or else a disconnected Mains Safety Ground (sadly too common in studios as a quick "hum fix" :shock: ....

With no path for the fault current, the case stays at Live potential- no fuse will blow. So when you come to touch the equipment, YOU become the conductor from the Live chassis/case toGround (you'll be standing on the ground, or touching a Grounded piece ofmetal/equipment/structure) and therefore recieve a shock.

So a safety ground is ESSENTIAL!

The second method of grounding is common to domestic/prosumer gear and some pro digital gear- a double insulated piece of equipment is designed to operate safely with no Mains Safety Ground. Have a look at CD players, VCR's, DVD players etc- they come with a twin-conductor mains cable. The design of this equipment is such that it is impossible within reason for any live conductor to touch ANY part of the equipment accessible to the user.The mains transformers also have to pass more stringent regulations for safety and leakage. This type of equipment has a "double insulated" symbol on the back by the spec/mains requirement badge. It is a small square inside a larger square.

Equipment with a "Ground Lift" switch does NOT remove Mains Safety Ground- this is continually connected to the chassis/case and any other safety connection, but the switch breaks the connection between Mains Safety Ground and the 0V or Commonn terminal in the equipment.

Just had to get that off my chest, I'm fed up of seeing unsafe equipment. And electric shocks.

:thumb:

Mark

 

[robomatique]

Thanks Mark!

Great post and very informative, exactly what we newbies need!!

So how do I choose mains fuse? And what is slow blow (Tfuse)? When should I choose that?

Robert

 

[mich]

thanks a lot mark and everyone! great information ! :thumb:

 

[franklinh]

What a great thread!

My question is, in trying to improve the safety (and noise performance?) of older tube gear that plugs in with only hot and neutral, what do you do then? I remember hearing someone refer to these as "hot chassis" gear, that it can be dangerous, and that there was a reasonably simple way (in DIY terms) to remedy this condition, making it safer to use and interface with modern gear. Any takers?

In the case of my revox G36 it only has hot and neutral which hit a transformer (no center tap). 0v from the bridge rectifiers on the other side of that transformer hit the chassis, which is ground for EVERYTHING, including audio (unbalanced I/O). Is that a detriment to my health, noise floor, or both?

Frank

 

[Kev]

I always use the IEC inlet
I always tie the IEC ground to chassis

after that some PCB's may end up at chassis and many don't
PCB or Audio ground is at the XL3 and a losely star ground method will be employed

vary rarely have I had a loop/hum issue and I think a second look at the PCB layout or grounding Pot externals has fixed the problem