To Bond or Not to Bond

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lauraj

Senior Member
Location
Portland, Oregon
Sorry if this has been discussed before, I could not find anything.

My question deals with bonding requirements of flexible metal conduit going from the secondary side of the transformer to the disconnecting means. It seems that the different inspectors here have varying interpretations of how that should be done. Some require bonding on both ends, some on just one end, and others not at all.

Really, the only code reference I can cite for this is the requirement for an Effective Ground Fault Current Path in 250.4(A)(5), but that of course is totally up to interpretation as to what is effective or not.

Personally, I think bonding one end or the other would be sufficient.

Does anyone else have some ideas about this?
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
I'm at the airport, so don't have my code book accessible. You are on the right path. Services are the only place where the bonding gets "over the top" on bonding out - it is unprotected from the utility. After the first OCPD, things are protected. If you have Mike Holt's "Grounding vs Bonding" book, he covers it nicely.
 
Bonding on one side of the FMC, such as terminating the EGC to the frame of the transformer (considering the transformer is properly installed), and bonding it to the fitting on the other side of the FMC connection to the panel.
 

Rockyd

Senior Member
Location
Nevada
Occupation
Retired after 40 years as an electrician.
1236111162.jpg

This is the book I'm referring to. Call 1.888.NEC.CODE (1.888.632.2633).
One of the best pieces of lierature for your library!​
 

raider1

Senior Member
Staff member
Location
Logan, Utah
And there's no equipment grounding conductor in that conduit from the xfmr to the disconnect.

Where is the system bonding jumper installed?

If you are trying to use the conduit as an EGC remember that FMC can only be used as an EGC for circuits protected by a maximum 20 amp overcurrent protective device.

How is the transformer grounded and bonded?

Chris
 

lauraj

Senior Member
Location
Portland, Oregon
Where is the system bonding jumper installed?

If you are trying to use the conduit as an EGC remember that FMC can only be used as an EGC for circuits protected by a maximum 20 amp overcurrent protective device.

How is the transformer grounded and bonded?

Chris

I was just mincing words, I would certainly pull an equipment bonding jumper with the feeds. I still don't feel like my question is addressed though. How would I respond or argue the point to an inspector that requires a bonding bushing on both ends of the conduit?

As far as where the system bonding jumper is located, would the requirement be different for either case?
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I was just mincing words, I would certainly pull an equipment bonding jumper with the feeds. I still don't feel like my question is addressed though. How would I respond or argue the point to an inspector that requires a bonding bushing on both ends of the conduit?

Ask the inspector what code section requires a bonding bushing on the conduits for the secondary conductors of a transformer. There are no special rules for bonding on the load side of a transformer. The FMC can be bonded by just using the connector, a bonding bushing is not required. 250.97 could come into play for over 250 volts if concentric knockouts are encounter that are not listed as suitable for grounding.

As far as where the system bonding jumper is located, would the requirement be different for either case?

No, the requirement would not change depending on the location of the system bonding jumper.

Chris
 

hurk27

Senior Member
Wow, I totally forgot about the change from the "99" to the "2002" that stopped allowing FMC to be used for grounding for 20 amp circuits and below.

I started to say if the fittings was listed, or a bonding bushing installed, but now thats out.
 
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