NEC 640.22

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NEC 640.22 metal equipment racks and enclosures shall be grounded. Bonding shall not be required if the rack is connected to a technical power ground. I have metal equipment racks in auxiliary room and broadcast room for audio and video purpose. Do they need to be grounded or bonded?
 
Audio guys need a lot of special attention and the NEC is doing a lousy job of appeasing them. Here is my interpretation of what that section is trying to say

Grounded- A physical connection to the earth.

Bonding- Connecting everything together.

Technical power ground- (I didn't even know those words existed in the NEC) Making sure that there is a real, actual, NEC compliant equipment grounding conductor in circuit that powers a piece of audio equipment.


1) you must connect your racks to mother earth = grounded (that part is there to appease the dirt worshipers, maybe)

2) you don't have to run a jumper wire from every metal object in the room to every other metal object in the room = bonding

3) you absolutely must run a proper equipment grounding conductor to every piece of equipment that uses electric power even if you really, really don't want to = technical power ground
 
Not a reference to the ground of a technical power system, described elsewhere, which delivers 120V as balanced 60V to ground rather than a 120V ungrounded conductor and a grounded conductor?
It is typically delivered by an SDS having a 120V secondary with a grounded center tap. That transformer used typically has a high quality electrostatic shield between primary and secondary.

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GoldDigger said:
Not a reference to the ground of a technical power system, described elsewhere, which delivers 120V as balanced 60V to ground rather than a 120V ungrounded conductor and a grounded conductor?
It is typically delivered by an SDS having a 120V secondary with a grounded center tap. That transformer used typically has a high quality electrostatic shield between primary and secondary.

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:? You lost me.
 
GoldDigger said:
I am saying that I do not see the term as "technical" power ground, like "effectively" grounded modifies grounded in PV. I see it as "technical power" ground, the EGC of a no longer widely used distribution system.

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So you are saying a "technical" power ground is exactly the same as a "technical power" ground only different.

I'm still lost even though I think we might agree.
 
ActionDave said:
So you are saying a "technical" power ground is exactly the same as a "technical power" ground only different.

I'm still lost even though I think we might agree.
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What I am trying to say is that a technical power ground only exists as part of a (rare) technical power system.

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GoldDigger said:
What I am trying to say is that a technical power ground only exists as part of a (rare) technical power system.

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OK.

Now help a wire pulling grunt out a little more. What is a technical power system?

btw just to make sure there is no misunderstanding, I'm not being sarcastic in any way.
 
ActionDave said:
OK.

Now help a wire pulling grunt out a little more. What is a technical power system?

btw just to make sure there is no misunderstanding, I'm not being sarcastic in any way.
Click to expand...
As I said in my first post, a technical power system is one in which the two 120 volt conductors are balanced at 60V to ground instead of being at 120V and 0V to ground. Note that this is NOT the same as the "balanced" 60V Modified Square Wave output of some cheap battery powered inverters! (Although the effect of trying to bond the supposed "neutral" to ground will be similar in both cases!)
The goal is to minimize 60Hz hum in audio equipment and capacitive ground current leakage in medical devices.

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GoldDigger said:
As I said in my first post, a technical power system is one in which the two 120 volt conductors are balanced at 60V to ground instead of being at 120V and 0V to ground. ....
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OK. Now I'm starting to understand. I have seen isolated transformers 60 0 60 used for audio, but I ain't never seen the term "technical power system" until today. Is it somewhat widely accepted and I'm late getting up to speed?
 
ActionDave said:
OK. Now I'm starting to understand. I have seen isolated transformers 60 0 60 used for audio, but I ain't never seen the term "technical power system" until today. Is it somewhat widely accepted and I'm late getting up to speed?
Click to expand...
Whether or not it is a widely accepted term, I believe it is defined (by usage if not explicitly in Section 100) in the NEC.

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