Grounding vs Bonding Online Training

This article was posted 11/18/2005 and is most likely outdated.

Grounding vs Bonding: 250.34 Generators—Portable and Vehicle-Mounted

November 18, 2005

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Grounding versus Bonding

PART II.

Page 12 of 13

Sections

250.34 Generators—Portable and Vehicle-Mounted

(A) Portable Generators. The frame of a portable generator isn’t required to be grounded to the earth if: Figure 250–88

(1) The generator only supplies equipment or receptacles mounted on the generator, and

(2) The metal parts of the generator and the receptacle grounding terminal are bonded to the generator frame.

(B) Vehicle-Mounted Generators. The frame of a vehicle-mounted generator isn’t required to be grounded to the earth if: Figure 250–89

(1) The generator frame is bonded to the vehicle frame,

(2) The generator only supplies equipment or receptacles mounted on the vehicle or generator, and

(3) The metal parts of the generator and the receptacle grounding terminal are bonded to the generator frame.

(C) Grounded Neutral Conductor Bonding. If the portable generator is a separately derived system (transfer switch opens the grounded neutral conductor), then the portable generator must be grounded and bonded in accordance with 250.30.

Author’s Comment: When a generator provides the sole power for a building or structure, it’s a separately derived system even though no transfer switch is present.

Figure 250–88
(Click on image to enlarge)

Figure 250–89
(Click on image to enlarge)

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Table of Contents

Sample Pages

Sample Graphic

Comments

Just looking at this issue....portable generators....from a logical point of view.....

Portable genny not a structure; ground rod for lightning protection; therefore, no ground rod necessary.

Portable genny comparable to "service" in that it is source of power...therefore neutral should be bonded to case (before any OCPD on genny).

Portable genny providing only power to bldg....even if no utility connection (yet), building is 'structure,' so bldg should have ground rod. As genny powering building- and not just ext cords powering portable tools being used in bldg- then genny ought to be bonded to bldg.

Lack of standards? As I understand NEC 90.2, this is beyond scope of NEC. Beyond the scope of AHJ as well. Possibly under jurisdiction of OSHA. So far, there has not seemed to be a need or market value to any NRTL listing- but no reason that one couldn't develop a standard for them.

John Steinke
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