810/820 mast/coax grounding v.s.250.54

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cbrown

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I was recently managing the install and cutover of network hardware at a remote facility and ran across something that struck me as wrong. I of course got into a -discussion- with the facility power journeyman on site. I am just that darn network eng :), but in this case I think the local power crew is in error.


There is a peice of radio comms gear (PtP 802.16 bridge) mounted in a weathertight enclosure on the outside of the building. The enclosure metal, and has a non-conductive feed-thru the the inside (concrete wall).

The radio unit chassis is bonded to the enclosure.

The radio unit power is standard grounded 120v to a recep inside the building on the wall, the recep is a std #12 H-N-G to a dedicated breaker.

There is a #6 run from the enclosure to a 5/8" 10' rod directly below the enclosure.

This seems OK under 250.54 (I think that is the right article) as an additional ground, as rod to enclosure to radio chassis to #12 egc seems to qualify.


The argument was about the mast and coax bonds.

The mast is #10 green insulated bond to the enclosure.

The coax has a bulkhead style protecter, bonding the braid to the enclosure.


By my understanding, the mast and coax bonding runs must terminate on the grounding electrode system, or an extension of such. *NOT* the additional electrode allowed under 250.54

Am I totally off here?
 
The critical concept you must keep in mind is to create a single point ground.
See Art 100 definition intersytem bond and 250.94
Art 810 is for the mast, it must be bonded to a location listed in 810.F(1) or (2)
Art 820 is for the coax, it must be bonded to a location listed in 820.100B 1 or 2.
Also the rules in Art 250 don't apply to a chapter 8 rule, unless referenced by chapter 8, see 90.3
So get your answer from chapter 8 first.
 
offff

offff

cbrown said:
I was recently managing the install and cutover of network hardware at a remote facility and ran across something that struck me as wrong. I of course got into a -discussion- with the facility power journeyman on site. I am just that darn network eng :), but in this case I think the local power crew is in error.


There is a peice of radio comms gear (PtP 802.16 bridge) mounted in a weathertight enclosure on the outside of the building. The enclosure metal, and has a non-conductive feed-thru the the inside (concrete wall).

The radio unit chassis is bonded to the enclosure.

The radio unit power is standard grounded 120v to a recep inside the building on the wall, the recep is a std #12 H-N-G to a dedicated breaker.

There is a #6 run from the enclosure to a 5/8" 10' rod directly below the enclosure.

This seems OK under 250.54 (I think that is the right article) as an additional ground, as rod to enclosure to radio chassis to #12 egc seems to qualify.


The argument was about the mast and coax bonds.

The mast is #10 green insulated bond to the enclosure.

The coax has a bulkhead style protecter, bonding the braid to the enclosure.


By my understanding, the mast and coax bonding runs must terminate on the grounding electrode system, or an extension of such. *NOT* the additional electrode allowed under 250.54

Am I totally off here?
Click to expand...

Please correct me if what I interpret is off....There is no bonding conductor from the outside metal enclosure going to the main disconnect terminal grounding bar. If there was, then the mast #10 green would be properly bonding the mast. Additionally, coax grounding is presently bonded to the same (802.16 bridge gear) enclosure that is connected to a ground electrode only.

In comm gear, the coax braid grounding must be at the signal source equipment chassis and not elsewhere. The radio chassis ground would be at the 120Vac power connection grounding...unless it is using a non-grounding connector with a chassis ground strap to the EGC.

If the above is not the case, then I would agree with you. rbj
 
Also keep in mind the purpose of grounding these items near the entrances is to route lightning to/from earth, there is no other purpose. This is why these 800 Articles specify no more than 20' length. If additional electrodes are installed they do have to bond to each other to form a electrode system.
If lightning strikes without a good route to/from earth it will flash throughout the systems, the electrode connection is supposed to eliminate flashing.
 
Egc

Egc

tryinghard said:
Also keep in mind the purpose of grounding these items near the entrances is to route lightning to/from earth, there is no other purpose. This is why these 800 Articles specify no more than 20' length. If additional electrodes are installed they do have to bond to each other to form a electrode system.
If lightning strikes without a good route to/from earth it will flash throughout the systems, the electrode connection is supposed to eliminate flashing.
Click to expand...

The original post may have confused me and some others on the intent of looking at the overall lack of bonding to the single point ground that Tom was referring. The Lightning hazard is of major concern also, but the poster is looking for confirmation of improper equipment to source bonding at this facility. It would be helpful if the OP would have additional remarks to our responses. rbj
 
It?s easy to think the EGC with the power circuit would provide an effective ground fault path (bond), but I do see there is more to these situations.
 
Installing it their will create two potential differeonces in the case of a lightning strike nearby. The two electrode systems should be bonded together at the service with a #6
 
mcclary's electrical said:
Installing it their will create two potential differeonces in the case of a lightning strike nearby. The two electrode systems should be bonded together at the service with a #6
Click to expand...

My thoughts are on two differant functions 1) equipment grounding & 2) grounding. Two differant functions and purposes (fault path to source and earthing for static).
 
Reply to Gndrod

Reply to Gndrod

The weather enclosure is bonded to a rod below, the radio chassis is bonded to the enclosure *AND* the grounding conductor of the 120V supply for the radio.

This would seem to be approved as an _extra_ ground for signal ref/RF purposes.

The argument was about the mast/coax/antenna.

The mast is bonded w/ #10 to the enclosure, the antenna is bonded both through the mast and through the coaxial bulkhead protector running the the enclosure wall.

By my reading the mast and protector must be bonded *directly* to the grounding electrode system, and the extra 250.54 rod does not count as it is only conntected to the facility ground via the #12 egc running the the sub-panel.


The root question would be

Can an additional ground rod installed per 250.54 be treated as part of the GES or not.

I said no, the rod must be bonded to the nearest part of the system, *or* to the building wide grounding bus (telco type building, massive grounding bars that do tie to the GEC via conductors much larger than #6).

The local sparky claimed that a rod installed under 250.54 counts as part of the GES for the purposes of 810/820, becaus it is an allowed rod, and is connected to the facility ground via the #12 egc on through the electrical panels to the GEC.


Note, this is not an actual safety argument, just a code one. This is about as far from a lightning area as possible, there are no overhead power lines, and there is a several hundred foot tower (properly grounded/bonded) about 40 feet down the wall. The only functional reason for the grounding and protector is static suppression (static from dry powder snow blowing at 50+ mph at -40 is an issue).
 
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