video grounding and bonding

[caldesac]

I have some questions as well as a plan that I would like commenting on if anyone has any experience or thoughts with such a setup. The environment is an audio/video facility.

The racks that the equipment is mounted have a ground stud in the bottom of the rack to bond the chassis of each piece of equipment to and to bond the racks together. There are copper buss bars that are sold which serve the purpose of bonding individual pieces of equipment to and then having one connection to the grounding stud. Can I get rid of the stud altogether and just do runs from each piece of equipment to the grounding stud? I?m having a hard time thinking of what the difference would be except for the ability to get a good connection (ie. 1 connection from buss bar vs. many from each piece of equipment). I just don't want to unnecessarily spend money, but I don't want to cut corners that will put me in a bad place either.


In general I?m trying to finalize plans on a facility bonding/grounding scheme and am going back and forth having had my own past experiences as well as having done a lot of reading on the subject lately on the method of grounding and bonding. There?s a lot out there from specialists that seem to imply that IG isn?t really worth it in A/V facilities. Then there?s star grounding vs. non-star grounding, and not much definitive information on the proper methods for grounding and bonding an A/V facility. The last facility I was involved in (not the grounding scheme thank god) had IG receptacles throughout, dedicated technical panels, isolation transformer, technical star bonding and grounding and still had major noise issues. That has put a bit of fear into me about how to move forward on a project that I am responsible for. Not to mention trying to look at cost/benefit factors. I don?t want to spend a bunch of money on wiring up IG if it?s not going to improve the system performance.


Here?s what I?m looking at doing now. Maybe someone can comment on this ?

1. Right now I?m looking at bolting together the racks using ?? bolts (sanding down to bare metal at the bolting points) and lock washers to bond them together.

2. Having the copper buss bars mounted inside the rack using insulated posts with each piece of equipment tied to the buss bar using insulated ground wire, and the buss bar tied to the bonding/grounding stud.

3. Having a main technical ground strap running past my equipment racks to the technical panel IG buss bar. There will be an additional grounding strap from the grounding stud of each rack tying into the main grounding strap. The main grounding strap will be run inside of EMT conduit or Greenfield.

4. I?m also looking at doing IG circuits and running the isolated ground back in the conduit with the main lines. Mounted on the inside of each rack would be an IG power strip using insulated posts. Can I tie power strips from multiple racks together if the amperage doesn?t exceed the capacity of the circuit? Is there a recommended method of doing this if so?

5. I?ve also heard mixed things about HAVING to tie all equipment to one phase for an a/v facility. The approach seems logical for small setups, but a significant setup would throw the power system way out of balance if it were all on one phase. I?ve had people swear that if this isn?t done things will go all wrong though. Does anyone have any experience with this?

6. I?m not doing computer flooring and was just going to mount the racks on 4? x 4? wood beams to give me room to run cables. Would this potentially cause any issues?


Thanks for your thoughts!

Chris

 

[dereckbc]

First, why would you even want to use an external ground, or even ground the equipment, you are just asking for noise and trouble

Second if you want to do it right, do what all A/V studios do and use balanced power and forget about any special grounding techniques.

http://www.equitech.com/

 

[dereckbc]

caldesac I should have taken some more time to elaborate.

The trick or secret to noise free power is to use a single dedicated circuit from an isolation transformer. Isolation transformers made for the purpose can attenuate up to 140 db of common mode noise. Even a typical dry type will provide a minimum of 40 db of common mode noise.

Now here is the catch, most A/V applications require more than one dedicated branch circuit. So what do you do? Well you use a dedicated system such as one I mentioned from Equi-Tech. It is everything you need in a box. There are several manufactures for the balanced power systems like Monster, Trip-Lite, and others, but Equip-Tech is the original and best out there.

I suspect you are not a qualified electrician, so I will not tell you how to do a hardwired system for premises wiring, but I can guide you to a rack mounted plug-n-cord system.

First thing to do is determine what size in terms of KVA you need like 1, 2, 3, 5, 7.5, or 10 KVA. If you do not know how to do this, sorry, I will not help unless you can convince me you are in the electrical trade.

2. Purchase the isolation transformer (balanced power system), install it in the bottom of the center equipment rack if more than three are used.

3. Have a qualified electrician install you a 240 circuit of the right size according to the manufactures requirements. These can range from 20 to 50 amps. They will look just like the receptacle you use at home for an electric dryer, welder, or something similar to it depending on the current size.

4. Route all your A/V AC power cords to the transformer and get to work recording.

That?s it. If you use one of the specialized isolation transformers like Equi-Tech, you will have top of the line, state of the art, A/V studio AC power system used in all professional studios everywhere. No special grounding, no IG receptacles (waist of time and money), and NO NOISE whatsoever.

 

[caldesac]

Thanks for the reply. Have you worked on A/V facilities yourself? I'd be interested in hearing more about your experiences. Maybe we can chat offline. I've worked on and in many great facilities and my experience has differed greatly from your statement that "all" a/v facilities go this route. You've got my attention though. I'll read up on the Equitech site.

To answer your question, my understanding of the external ground (I'm assuming you're referencing the chassis ground) is that it's purpose is twofold. 1) Bonding of the equipment to ensure that they share a common reference. 2)to provide a route for noise from the chassis of the equipment other than over the signal cable that's connected to another piece of gear (particularly important in unbalanced systems). I'm more than willing to be corrected if this is wrong. Please tell me what trouble I'm inviting.

Best!

chris

 

[caldesac]

caldesac I should have taken some more time to elaborate.

The trick or secret to noise free power is to use a single dedicated circuit from an isolation transformer. Isolation transformers made for the purpose can attenuate up to 140 db of common mode noise. Even a typical dry type will provide a minimum of 40 db of common mode noise.

Ahhh... Isolation Transformer. Yes, I'm very familiar with isolation transformers. I wasn't used to the term Balanced Power System in place of isolation transformer. Right, I have worked with hardwired K-rated isolation transformers in A/V systems.

I suspect you are not a qualified electrician.

You suspect correctly...

First thing to do is determine what size in terms of KVA you need like 1, 2, 3, 5, 7.5, or 10 KVA. If you do not know how to do this, sorry, I will not help unless you can convince me you are in the electrical trade.

Thanks for the challenge, but fortunately I don't need your help there. I'm afraid I already gave myself up there anyway.

clip...

That?s it. If you use one of the specialized isolation transformers like Equi-Tech, you will have top of the line, state of the art, A/V studio AC power system used in all professional studios everywhere. No special grounding, no IG receptacles (waist of time and money), and NO NOISE whatsoever.

Thanks for the advice. That's helpful. I really appreciate it. Is this something you have had personal experience with. I would be interested in getting your response to Bill Whitlock's take on balanced power in this article.

http://svconline.com/mag/avinstall_safe_power/index.html

Best!

Chris

 

[dereckbc]

Chris, isolation transformers and balanced power systems both use isolation transformers, but blalanced system is quite a bit different as there is no grounded circuit conductor involved (aka neutral). Instead it uses two line phase conductors (L-L) of 120 VAC, and line to ground is 60 VAC.

Since you are not a qualified electrical professional, I cannot give you much advice on this forum other than to use Plug-N-Cord connected equipment as I referenced earlier.

I have had quite a bit of experience with balanced power systems, however not in the A/V world, I have used them quite a bit in the engineering and design of Data Centers. I worked closely with Equi-Tech in designing what is called a PDU (Power Distribution Unit) used to distribute branch circuits in Data Centers. The PDU is a self contained balanced isolation transformer fed from a UPS on the primary, and circuit breakers on the secondary with modular construction. Much like what you see in the Plug-N-Cord units just on a much larger scale and different input voltages.

I have read Bill's writing before, and if you notice he reflects/supports what I was telling you in regards to elaborate grounding systems only adding trouble, and you get the most bang for your buck using either balanced power or isolation transformer techniques.

I did perform some work in recording studios back in the late 70's early 80's, and today am still an audiophile. I own an Equi-Tech unit for my home theater.

I won't be able to help you much more than I already have, as there is legal issues offering non-professionals advice. My best is advice is what I already gave you to use a Plug-N-Cord connected equipment such as the Equi-Tech or some other manufactures equipment, and have a qualified liscensed electrician run the dedicated circuit for its use.

If you wish to discuss away from this forum, you may PM me with some contact info. I will do what I can within limits.

Good Luck

Dereck