# bonding transformers



## Chris Kennedy (Nov 19, 2007)

Kind of vague, did you look at 250.92 and 250.97?


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## chicken steve (Mar 22, 2011)

when in doubt, ground it

~CS~


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## kaboler (Dec 1, 2010)

That's interesting man, that's interesting. If you aren't pushing a grounding conductor through, I suppose a grounding bushing is the way to go. That's probably what they make em for.


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## cabletie (Feb 12, 2011)

Apparently you don't need them. I have always used them on the secondary side and treated it like it was a new service. Then some of the very intelligent and code savvy electricians on this site have shown me otherwise. I just did two last week and used bonding locknuts and knew that I did not have to. Old habits die hard, and conversations of this site kept rushing through my head!
Review all of sec. 250.30

Here is 2011 250.30(a)(2)
*(2) Supply-Side Bonding Jumper. *If the source of a separately
derived system and the first disconnecting means are
located in separate enclosures, a supply-side bonding jumper
shall be installed with the circuit conductors from the source
enclosure to the first disconnecting means. A supply-side
bonding jumper shall not be required to be larger than the
derived ungrounded conductors. The supply-side bonding
jumper shall be permitted to be of nonflexible metal raceway
type or of the wire or bus type as follows:
(a) A supply-side bonding jumper of the wire type
shall comply with 250.102(C), based on the size of the derived
ungrounded conductors.
(b) A supply-side bonding jumper of the bus type shall
have a cross-sectional area not smaller than a supply-side
bonding jumper of the wire type as determined in
250.102(C).

So the supply side bonding jumper can be a wire or a nonflexible metal raceway system with no wording on the need for bonding locknut/bushing. If this is your typical step down transformer 480v. to 120/208v. the genral bonding requirements of 250.97 (over 250v.)would not apply for the secondary.

See also 250.102 
Here is 2011 250.102(c)(1)

*Size — Supply-Side Bonding Jumper.*
*(1) Size for Supply Conductors in a Single Raceway or*
*Cable. *The supply-side bonding jumper shall not be smaller
than the sizes shown in Table 250.66 for grounding electrode
conductors. Where the ungrounded supply conductors
are larger than 1100 kcmil copper or 1750 kcmil aluminum,
the supply-side bonding jumper shall have an area not less
than 121⁄2 percent of the area of the largest set of ungrounded
supply conductors.


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## chicken steve (Mar 22, 2011)

good shootin' cabledude, not to digress into semantics but, i would be refering to an <MBJ> there.....~CS~


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