ground strap thickness

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fm-engineer
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ground strap thickness

Post by fm-engineer » Wed Mar 07, 2018 6:47 pm

Is 0.022 still industry standard on 4" inch ground straps? I'm getting ready to rebuild an indoor ground system and it appears there are now four different thicknesses of copper strap available from most suppliers. The thick or heavy duty one is 0.032. Me thinks 0.022 is what most of us have used for years. Kintronic use to sell it in 50' rolls.

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kkiddkkidd
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Re: ground strap thickness

Post by kkiddkkidd » Wed Mar 07, 2018 7:24 pm

For almost all indoor applications, .020 (usually 2in wide) copper strap is the norm for lower power AM, FM and light duty lightning grounding. We use .032x4in for high power, high current and main lightning grounding applications. Occasionally a consultant specifies thicker than .032 or wider than 4in but I fail to see the advantage in either for most grounding applications.

.020 thick copper is about 10x skin depth at AM frequencies and about 100x skin depth at FM frequencies.

In most studio or indoor applications the decision for .020 strap is based on thinner strap or NO strap due to the obvious work-ability problems with thicker. I always vote for strap...

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

fm-engineer
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Re: ground strap thickness

Post by fm-engineer » Sun Mar 11, 2018 9:37 am

Thanks for the info

TPT
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Re: ground strap thickness

Post by TPT » Sun Mar 11, 2018 7:32 pm

Local college got a grant to build a fancy recording studio--I got involved rebuilding the radio station studios in the same building.
Recording studio guy wanted separate panel and isolated grounds from the lighting and HVAC circuits--I suggested running 2" strap from that panel to an outside ground.

Electrician was horrified--"if you lost the neutral all the current would go through that strap!!"

At least the fancy studios (and the radio station in the former dark room) are in the basement. Need to figure out how to ground some strap for the protection on the STL coaxes.

Lee_Wheeler
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Re: ground strap thickness

Post by Lee_Wheeler » Sun Mar 11, 2018 11:37 pm

Depending on the way the electricians and, more importantly, the inspectors read code then most broadcast operations can be out of compliance.

Code wants one, and only one, bond between ground and neutral and that bond is to be located in the main service entrance panel. Adding ground straps off of the equipment to ground can always provide an alternate path if the main bond was to fail. The answer to the electrician is tell him to make damn sure they do a good job on the service grounding. I can usually explain things well enough to the electricians that they get it but I have had a couple of inspectors that gave me trouble so I typically run any exposed strap after the final electrical inspection - at the same time as I am removing and replacing all of the GFCI outlets that code made the electricians install to power the racks.

...Lee

fm-engineer
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Re: ground strap thickness

Post by fm-engineer » Mon Mar 12, 2018 10:55 am

Yep,

I had an electrical inspector recently require us to cut loose the connection between the transmitter reference ground and the service entrance panel ground. He said the service entrance can only be attached to a designated ground rod and nothing else. When he saw the 4 inch strap inside the building going to each transmitter, he became verbally agitated. The inspector said the strap was a violation of NEC for bonding or grounding, and everything had to go through the main panel. He then saw additional 4 ground rods and strap ring outside (as shown in the Nautel grounding manual). I showed the inspector the Nautel grounding manual (which has nice diagrams), and he said following that manual would result in multiple violations of NEC.

TPT
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Re: ground strap thickness

Post by TPT » Mon Mar 12, 2018 3:41 pm

Why the NEC is full of //manure....

There is no understanding or consideration of RF---or that matter, of lightning, which is really more RF than DC.

radio_guru
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Re: ground strap thickness

Post by radio_guru » Mon Mar 12, 2018 6:15 pm

Your best bet is to connect the service panel to a well beyond NEC minimum enhanced earthing system ring which is also the RF and tower ground. In Chicago, that's called a Hogan Ground where the panel is bonded to a much larger ground system covering multiple devices and services as well as structural elements. Including generators.

I agree with the inspectors opinion however. There can be only one ground node and anything else had best be capable of carrying the service's fault current. Especially in a large building with multiple panels and 1000A service. Bad news otherwise.

The only way around that is to create or derive a new service which then requires it's own ground and neutral separate from the house. Now many AHJ's will still insist the ground go to the house ground. That's not entirely necessary for newly derived systems as there is a DC disconnect from the originating service. Especially if you place a dielectric fitting on the conduit going into the transformer enclosure and only have the two or three servicing conductors with no neutral.

It's wildly difficult to comply with the NEC and work effectively with RF and high quality audio. But it can be done with very careful thought and practice.

FWIW, I use .032" exclusively. I have found .020 burns up too easily when using oxy/acetelyne and 15% silvaloy. And I've seen the result of 0.020 shattering during an extreme lightning hit. What a mess.

RG

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kkiddkkidd
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Re: ground strap thickness

Post by kkiddkkidd » Tue Mar 13, 2018 7:07 am

NEC is a good thing for occupied residential and commercial protection but really gets in the way of solid lightning protection at transmitter sites.

I once had a new TX site electrical inspection fail because the electrician had left the neutral shorting bar in the breaker box. The inspector made him remove it and was about to break it into pieces it when we started a conversation about how this was an unmanned site and we were standing under a 499ft lightning rod AND would he rather have a bizillion volts & amps of lightning current flowing on the equipment cases for all to touch or shorted semi-safely to a good solid ground that was bonded to everything.

He thought about it a minute and laid the shorting bar in the bottom of the box and said "if that thing gets installed back in that box it would be an NEC violation" and left. The shorting bar was back in the box before his dust settled and is still there 20ish years later. Lightning damage at that site has been very, very minimal.

Later,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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kkiddkkidd
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Re: ground strap thickness

Post by kkiddkkidd » Tue Mar 13, 2018 7:51 am

radio_guru wrote:
Mon Mar 12, 2018 6:15 pm

FWIW, I use .032" exclusively. I have found .020 burns up too easily when using oxy/acetelyne and 15% silvaloy. And I've seen the result of 0.020 shattering during an extreme lightning hit. What a mess.

RG
Unless you are trying to braze .020 outside in strong, cold winds, you are using way too much heat or at least too much direct heat. We braze .020 to all manner of other materials and have little problem with it burning or carbonizing when using appropriate heat.

I have seen soft solder melt between sections of strap but never seen an undamaged strap (of any thickness) blow up in a lightning strike. If you had even a piece of .020x2in strap blow up in a mega strike... That was probably the least of your worries.

Regards,
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

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RFWarrior
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Re: ground strap thickness

Post by RFWarrior » Wed Mar 14, 2018 6:48 am

fm-engineer wrote:
Mon Mar 12, 2018 10:55 am
I had an electrical inspector recently require us to cut loose the connection between the transmitter reference ground and the service entrance panel ground. He said the service entrance can only be attached to a designated ground rod and nothing else.
Your inspector was wrong. NEC 250.4 was revised heavily in 2011 and very clearly states that equipment and facility grounds MUST be tied to entrance ground and that having separate grounds with earth as the common connection is NOT a viable option. Unfortunately, it takes awhile for any change in "the rules" to trickle down through the rank and file.
Jeff Welton, CBRE
Regional Sales Manager - Central U.S.
Nautel
Toll free: 1-877-662-8835, ext. 5127
Halifax Number: 902-823-5127
Quincy Number: 217-919-0189
Cell: 902-489-1635
jwelton@nautel.com

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