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Author Topic: metal table  (Read 3206 times)
KB3ASA
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« on: June 07, 2013, 07:38:01 PM »

Hello Elmer
    I'm setting up a Ham Shak and need some words of wisdom. I have a metal work bench that I plan to use as my radio table,and all other radio equipment,will this be a problem? Can I cover the top with wood or rubber,or static mat?
   Al KB3ASA
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WB6BYU
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« Reply #1 on: June 07, 2013, 08:00:11 PM »

No, it isn't a problem.  You can ground the table then bond the ground connector
on each piece of equipment to the table with a short wire jumper if you want.
If you are building / repairing equipment on it, then having a static dissipative
mat will prevent unintentional short circuits when you put something down on it.
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K8AXW
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« Reply #2 on: June 07, 2013, 09:18:58 PM »

I would be terrified to have a metal operating desk or workbench.  Especially if it's grounded.

Almost invariably you will have an arm or elbow on the table and if you accidentally touch something that is defective you just might wind up dead.

At the very least I would cover it with plywood or a rubber mat. I would then cover part of the plywood with plate glass which can be available from a plate glass window outlet.  They have large shards of plate glass from which they can cut you a specific size. 

Then you will have something to put operating aids, photos and or QSL cards under.

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KE3WD
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« Reply #3 on: June 08, 2013, 04:48:29 AM »

Hello Elmer
    I'm setting up a Ham Shak and need some words of wisdom. I have a metal work bench that I plan to use as my radio table,and all other radio equipment,will this be a problem? Can I cover the top with wood or rubber,or static mat?
   Al KB3ASA

Insulated top such as wood, rubber would be a good idea.  

I wouldn't go with the Static Mat, which is conductive.  

As to those claiming that a steel workbench, grounded, is dangerous, well I'm thinking of all the years at various jobs where I've sat behind the standard steel construction test benches, working day in and day out with stuff that makes ham radio gear look like low voltage toy train sets.  Those benches almost invariably had some sort of insulating top on them, in a lot of cases just a piece of  ~1/4"  thick particle or "masonite" board bonded to the steel top.  Then there's the stint where the job consisted of testing 480VAC elevator gear, the benches all had steel tops and were grounded to the electrical panels.  Still alive. 

73
« Last Edit: June 08, 2013, 04:52:47 AM by KE3WD » Logged
K8AXW
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« Reply #4 on: June 08, 2013, 10:12:21 AM »

WD:  I understand.  I also worked around a plant electrical shop and a motor winding shop so I'm somewhat familiar with what can and can't be done on a metal workbench. 

No doubt the reason you're still alive is because of your professionalism and the total understanding of what you could and couldn't do on the metal bench.

However, the question was posted by an ham asking a question about his operating position.  I think, other than perhaps a service technician, a ham will have more equipment; more opportunity to do something that would be very dangerous if he has a grounded metal table.

This includes defective equipment that is setting there just looking for a way to get to ground.



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AC5UP
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« Reply #5 on: June 08, 2013, 11:01:12 AM »

OTOH, if there was any RF in the shack a metal table would definitely tickle your fancy.........

I like a work surface that's durable but easily replaceable, non-conductive, and never feels like a brass toilet seat in January.
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KE3WD
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« Reply #6 on: June 08, 2013, 12:00:57 PM »

WD:  I understand.  I also worked around a plant electrical shop and a motor winding shop so I'm somewhat familiar with what can and can't be done on a metal workbench. 

No doubt the reason you're still alive is because of your professionalism and the total understanding of what you could and couldn't do on the metal bench.


Actually, back then I was young and still rather wet behind the ears. 

And I've always been able to make mistakes. 

But, like I said, if you leave the steel operating desk ungrounded, but of course, star ground the radio equipments, not very likely to encounter the big problem of encroaching death.  At least, not as direct consequence of operating desk material choice. 

And, yes, I once ran my full power qro ham station on a surplus but nice looking metal school lab type testbench.  With shortened legs and a big comfortable oak swivel chair and a pad for the seat made by the xyl.  The floor was hardwood. 

73
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K7MH
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« Reply #7 on: June 08, 2013, 01:37:50 PM »

The Johnson killowatt desk was a metal desk with the amplifier built in. Apparently they did not see it as a problem.
Very cool piece of gear. I would love to have one. Rather expensive when you find one!
 
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KB3ASA
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« Reply #8 on: June 08, 2013, 06:19:47 PM »

KB3ASA Al
Thank you gentelmen,this question appears to be more serious than I realized when I posted.
I want to understand your answers.I will drive a copper rod into the earth under my table the crawl space,then cover the table top with .25 mason board?
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K8AXW
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« Reply #9 on: June 08, 2013, 07:27:18 PM »

Al:  My opinion once again.  I would cover the table top with at least a 1/4" of either Mason board or plywood.  I would run heavy copper braid (RG-8 coax braid is an excellent source) from each piece of equipment (ones that are AC line powered) to a common ground bus bar which in turn is grounded through a ground rod.  I still wouldn't ground the metal desk.

I've only seen pictures of the Johnson Kilowatt so many years ago I can't remember if other gear was placed on it or not.  So I can't comment on that. 

Quote
feels like a brass toilet seat in January

This is a good point Al.  I have plate glass on my desk and as I pointed out I have operating aids and a few special QSL cards under the glass.  However, as 5UP points out, this glass does feel like a brass toilet seat in January!  Especially when the house A/C is on.

Al - K8AXW
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KE3WD
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« Reply #10 on: June 09, 2013, 07:42:38 AM »

...I will drive a copper rod into the earth under my table the crawl space,...

Please tell me that is a joke, right? 

If it isn't, it should be. 

Do. Not. Ground. the metal bench unless it is one of those metal benches that already has grounded electrical outlets installed in it and those outlets get grounded via the third prong ground of the electrical system. 

A separate grounding rod, when used as an antenna safety ground outside the shack building, should be bonded to the house grounding system. 

A separate Ground Rod connected to the bench is a recipe for disaster. 


73
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KD6KWZ
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« Reply #11 on: June 09, 2013, 08:09:16 PM »

Quote
A separate grounding rod, when used as an antenna safety ground outside the shack building, should be bonded to the house grounding system.

*One* of many reasons not to use an exclusive ground, where it's not tied to other grounds, is Single Wire Earth Return (SWER) power systems, found in various places in the world:

http://en.wikipedia.org/wiki/Single-wire_earth_return

Earth conductivity can be all over the map, so, you may get unlucky with untied grounds under some conditions.

Static mats are supposed to be fairly resistive, a charged ESD sensitive device can be blown out on a straight grounded metal table.
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