Grounding of seperately derived systems...

[xformer]

Where a transformer is set and fed with FMC, and an equipment grounding conductor is installed in the FMC, are grounding bushing required?

 

[infinity]

Not unless you you have concentric or eccentric KO's and the voltage is over 250 volts to ground. FWIW they won't do anything since the FMC is probably not a usable EGC.

 

[xformer]

Not unless you you have concentric or eccentric KO's and the voltage is over 250 volts to ground. FWIW they won't do anything since the FMC is probably not a usable EGC.

Rob,
Can you point me to where the NEC addresses that??

Thanks for your input...

 

[infinity]

In most cases FMC is not considered an EGC so the bonding bushing is somewhat useless. b. and d. would likely apply to a transformer installation.

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
(5) Listed flexible metal conduit meeting all the following conditions:
a. The conduit is terminated in listed fittings.
b. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
c. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
d. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.

For over 250 volts:

250.97 Bonding for Over 250 Volts.
For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).
Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:
(1) Threadless couplings and connectors for cables with metal sheaths
(2) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(3) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(4) Listed fittings

 

[tommy]

For some reason I thought on the secondary side of the transformer a bonding bushing or bonding lock nut is required for a new service.If I worded that right but the Primary is not needed. I do not have my code book right now but I'm thinking right in the beginning before 250.66. Any help

 

[ActionDave]

250.30 is where to look. I think there are some graphics on the Mike Holt main page.

You can bond the XO in the transformer or in the first disconnect. I usually bond in the first disconnect and run a EGC from there to a bond bushing and back to the transformer.

 

[jwelectric]

I can?t resist this one;

It is a supply side bonding jumper not an equipment grounding conductor and is sized from Table 250.66. Equipment grounding conductors are sized from Table 250.122 and are size by the overcurrent device that is ahead of them. The secondary of a transformer does not have overcurrent on the secondary so they can?t be EGCs.