Bonding Cable Tray to Ground

[Machiavelli999]

Is there any NEC guideline as to what size conductor is needed to bond a metal cable tray to ground? Does it depend at all on the size of the circuits within the cable tray?

 

[petersonra]

Is there any NEC guideline as to what size conductor is needed to bond a metal cable tray to ground? Does it depend at all on the size of the circuits within the cable tray?

since when does a cable tray have to be bonded to ground?

or are you talking about an EGC connected to the cable tray?

 

[weressl]

since when does a cable tray have to be bonded to ground?

or are you talking about an EGC connected to the cable tray?

Since forever or even slightly before that........:happyyes:

392.60 Grounding and Bonding.(A) Metallic Cable Trays.​

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.......... Metallic cable trays that support electrical conductors shall be grounded as required for conductor enclosures in accordance with 250.96 and Part IV of Article 250. Metal cable trays containing only non-power conductors shall be electrically continuous through approved connections or the use of a bonding jumper not smaller than a 10 AWG.​

 

[petersonra]

Since forever or even slightly before that........:happyyes:

392.60 Grounding and Bonding.(A) Metallic Cable Trays.​

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.......... Metallic cable trays that support electrical conductors shall be grounded as required for conductor enclosures in accordance with 250.96 and Part IV of Article 250. Metal cable trays containing only non-power conductors shall be electrically continuous through approved connections or the use of a bonding jumper not smaller than a 10 AWG.​

I got the impression he wanted to connect it to a ground rod or other grounding electrode.

 

[weressl]

I got the impression he wanted to connect it to a ground rod or other grounding electrode.

...and would not that be one way to comply with the paragraph I have cited?

 

[don_resqcapt19]

...and would not that be one way to comply with the paragraph I have cited?

A connection to a grounding electrode, without a connection to the EGC(s) for the circuits in the tray would not be a way to comply with the code section you cited.

 

[petersonra]

A connection to a grounding electrode, without a connection to the EGC(s) for the circuits in the tray would not be a way to comply with the code section you cited.

I concur, although it would like work adequately.

 

[weressl]

A connection to a grounding electrode, without a connection to the EGC(s) for the circuits in the tray would not be a way to comply with the code section you cited.

So you're telling me that either at the load or the line side of EACH circuit I MUST make a connection from the EGC to the tray?

 

[don_resqcapt19]

So you're telling me that either at the load or the line side of EACH circuit I MUST make a connection from the EGC to the tray?

You must make a connection to the EGC that supplies the circuits. If those circuits have multiple sources, you must have an EGC connection to the tray from each source. Multiple cables from a single MCC would be a single source. You must have a fault clearing path in the event that a circuit in the tray faults to the tray. That path cannot be via the earth.

 

[weressl]

You must make a connection to the EGC that supplies the circuits. If those circuits have multiple sources, you must have an EGC connection to the tray from each source. Multiple cables from a single MCC would be a single source. You must have a fault clearing path in the event that a circuit in the tray faults to the tray. That path cannot be via the earth.

OK I keep forgetting that there are places where there are standalone ground rods. Our ground rods are always interconnected to form an as much as possible homogeous and equipotential field as possible, and in turn all separately derived sources and all electrical equipment are connected/bonded to it. So indeed the earth is never the(main) fault path.

 

[don_resqcapt19]

OK I keep forgetting that there are places where there are standalone ground rods. Our ground rods are always interconnected to form an as much as possible homogeous and equipotential field as possible, and in turn all separately derived sources and all electrical equipment are connected/bonded to it. So indeed the earth is never the(main) fault path.

I don't even see a connection to a grounding system like that as meeting the intent of the code rule. I see the rule as requiring an EGC to be run with the circuit conductors from the circuit source to the tray. I guess it doesn't make any real difference until you get to circuits above 400 or 500 amps where a remote fault clearing path (one not run with the ungrounded conductors) may have enough additional impedance as a result of the inductive reactance to increase the trip time of the OCPD.

 

[weressl]

I don't even see a connection to a grounding system like that as meeting the intent of the code rule. I see the rule as requiring an EGC to be run with the circuit conductors from the circuit source to the tray. I guess it doesn't make any real difference until you get to circuits above 400 or 500 amps where a remote fault clearing path (one not run with the ungrounded conductors) may have enough additional impedance as a result of the inductive reactance to increase the trip time of the OCPD.

I appreciate your point, but if THAT would be the goal and objective of the NEC, shouldn't all electrical equipment be isolated/insulated so that ALL ground currents flow through the EGC? So either the premise is false or NEC outlined requirements do not meet that goal.

 

[don_resqcapt19]

I appreciate your point, but if THAT would be the goal and objective of the NEC, shouldn't all electrical equipment be isolated/insulated so that ALL ground currents flow through the EGC? So either the premise is false or NEC outlined requirements do not meet that goal.

I don't see a reason to isolate. Parallel paths are fine, the current will divide in inverse proportion to the impedances. I just see an issue with a remote path when there is not also a path that is run with the ungrounded conductors.