Does the bond conductor have to go back to the source Grounding Point?

[majesus]

I can't find this detail in the Canadian Electrical Code. Does the bonding conductor for a fixed equipment have to run back to the power source grounding point, or can I run the bonding conductor just to a grounding point?

For instance, if I have a switchgear in one electrical room and I'm running a 1200A feeder to an MCC in a different electrical room, do I have to run a bonding conductor back to the source or can I just bond the MCC to the ELEC room's grounding bar and be done with it?


I am being told (locally) I must run the bonding back to the source ground point. I can't find in the CEC a clause stating "yes you must" or "no, not necessary."

 

[dpc]

That sounds like an equipment grounding conductor in NEC terms, if I understand correctly. It needs to run back with the phase conductors to establish a good low impedance path for ground fault current.

I don't know about CEC, but NEC covers this in 250.134

NEC Staff Note:

One of the functions of an equipment grounding conductor is to provide a low-impedance ground-fault path between a ground fault and the electrical source. This path allows the overcurrent protective device to actuate, interrupting the current. Section 250.134(B) requires the equipment grounding conductor to run in the same raceway or cable as the circuit conductor(s). This configuration allows the magnetic field developed by the circuit conductor and the equipment grounding conductor to cancel, reducing their impedance.

David Castor

http://www.cvoes.com

 

[waross]

I don't have my CEC to hand but as I remember there is a table listing minimum ground conductor size depending on the size of the breaker feeding the phase conductors.
If the electrical rooms grounding bar is grounded back to the source via a suitable conductor it is possible that it be used.
If the electrical rooms grounding bar is connected to a "Magic Triangle" to provide grounding for instruments and data equipment, it also must be connected to the source ground with a suitable conductor.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[majesus]

Thanks Guys,

For folks using the CEC... bonding size is determined using Table 16. By the way Waross, FYI: the CEC states that the bonding conductor must be the based on the ampacity of the largest ungrounded conductor in the circuit or equivalent for multiple parallel conductors.

Anyways, I could not find in the CEC the equivalent NEC rule stating that the bonding conductor must be ran back to the source grounding point. By the way, the NEC does not use the term Bonding? It wasn’t mentioned in the reply.

 

[dpc]

Yes, "bonding" is used in the NEC. It just means establishing electrical connectivity and continuity. The conductor you are talking about is not called a bonding conductor in the NEC.

David Castor

http://www.cvoes.com

 

[majesus]

Appreciate the NEC info DPC. I'm going to call it the bonding conductor in this post just because that's what it is called in the Canadian Electrical world. Interesting enough, I just asked the Engineer who questioned the return path of the bonding conductor. Sure enough he is from the States. Ah... now I know where the question originates.

To elaborate, I understand that the NEC requires the return to the source, I am glad to know that. However, I am curious to know how it is done in CEC world. I looked at a few typical installation detail drawings involving single conductor TECK cables terminating at the MCC. For those that don't know, single conductor Teck comes with a concentric cable for bonding. What is shown in the installation drawing is the single conductors entering the MCC via a Micarta gland plate. The armour and bonding conductors are not terminated, they are left isolated. The armour and bonding conductors are only grounded at the source PDC. This practice is to isolate a ground loop where circulating induced currents can cause the conductor to overheat.

The installation drawing does not show an extra conductor entering the MCC for bonding purposes. Note, the MCC is bonded in two sepearte places using #2/0 pigtailed directly to the electrical room's grounding grid.

 

[waross]

There are different rules for an equipment bonding conductor and a system grounding conductor in the CEC.
The concentric conductors in a single conductor TECK cable are for the protection of the cable only. A separate ground conductor must be run. If the same conductor is used as an equipment bonding conductor and a system grounding conductor, the minimum requrements of both types must be followed.
Re: equipment grounding; The equipment grounding conductor must go to the panel from which the circuit is fed, and be based on the appropriate table. Each switch or panel from the source to the last sub panel must be grounded with an equipment grounding conductor sized in accordance with the proper table. I believe that covers the matter without a specific rule.

Bill
--------------------
"Why not the best?"
Jimmy Carter