Cable Tray Bonding

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Boutch

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A communication cable tray is installed below a false ceiling and supported by continuous threaded rods which are screwed in the concrete ceiling using hollow core inserts.

The cable tray is not bonded to ground and the resistance between the cable tray and the AC ground is near zero ohm.

Does that mean the rods are acting like bonding conductors using a UFER ground? and is this an acceptable bonding technique?
 
IV. Grounding Methods 800.40ish

IV. Grounding Methods 800.40ish

Normally we run a ground cable in the tray and bond tray to tray or tray to box or pipe, and each end of the tray etc. Art 800.40 gives requirements of the com wire itself, doesn't say a lot about cable trays. I'm sure you've read this Art. I mention it mainly because you have had a lot of lookers and no offers, thought I would give support, feel bad for you low voltage guys. The NEC is not there yet.
 
Cable trays - Article 392
grounding - section 392.7

if your wiring is only com wiring, you'll have to read thru article 800 and see if it mentions 392 (I don't remember), but we always ground cable trays anyway (best practice)
 
Are communications cables "electrical conductors"? 392.7 only requires that cable tray that support "electrical conductors" has to be grounded.

On a side note if we apply the difference between conductors and cables as often done for the Article 725 rules, does this mean that cable trays that support electrical cables do not have to be bonded?
Don
 
Equipment groundings (250-118) purpose is to provide an effective ground fault current path to the electrical source so in the event of a fault high current will flow to source opening overcurrent protection on the way, clearing the fault.

Equipment grounding should be a known path not assumed in other words an electrician should not see some conduit or frame entering concrete and simply assume it is bonded. Conduit can stub between points and if it is not physically bonded it may tone on an ohm meter but it's path is unknown therefore it is not bonded because it is unknown if it can handle any amount of fault current. Table 250-122 is used to size equipment grounding and larger circuits require larger equipment grounding conductors to enable fault current routing effectively without blowing in half or be disabled from voltage drop.

No the rods connecting to concrete are not equipment grounding. No this is not an acceptable technique to bond cable tray.

Bond this tray as if it did have 110V circuitry, my suggestion is follow the guidelines of 250-104(B) the reasoning is the same.
 
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