larry cad
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vermilye wrote:Quote:A neutral conductor shall be bonded to the generator frame if the generator is a component of a separately derived system. The definition of "separately derived system" is complex but a portable generator that supplies power to a cord-connected RV is one. But, to add a bit more confusion - You only have a neutral in a dual voltage system (ie a 120/240 volt generator). Since many of the generators we are using for powering RVs are single 120v devices, there is no neutral & bonding is not required.
Not true. Neutral is the grounded conductor. Even in a two wire system, there is a hot and a neutral and the neutral is to be connected (bonded) to the ground.
Someone earlier claimed that by not grounding the neutral you minimize the chance of receiving a shock. That also is not true.
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Wayne Dohnal
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Quote:
Not true. Neutral is the grounded conductor. Even in a two wire system, there is a hot and a neutral and the neutral is to be connected (bonded) to the ground.
A 120 volt 2-wire system does not have a neutral. "Everybody" calls the white wire a neutral by convention, but when it comes to being technically correct, there is no neutral, and regulations about a neutral simply do not apply.
NEC article 100 "Definitions" for neutral:
NEUTRAL CONDUCTOR:
The conductor connected to the neutral point of a system that is intended to carry current under normal circumstances.
NEUTRAL POINT:
The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.
FPN: At the neutral point of the system, the vectoral sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutal point, is zero potential.
From OSHA interpretation:
"The intent of 1926.404(f)(3)(iii) becomes very clear when one considers that the term "neutral" is used in its technical sense. A 120/240 volt system has a neutral and therefore must be bonded to the generator frame. A 2-wire 120 volt system has no neutral and therefore bonding is optional. Recall that neither side of a 2-wire derived system is a neutral and when one grounds either side, it becomes a grounded terminal or conductor, but it is not a neutral."
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Salvo
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Looks like you got everything mixed up Larry. A unbonded system is twice as safe as a bonded system. In order to receive a shock in an unbonded system 2 faults need to occur. In a bonded system just one fault causes a shock.
If your house were unbonded, you can take your hairdryer in the bathtub without fear of electrocution.
Sal
larry cad wrote:Someone earlier claimed that by not grounding the neutral you minimize the chance of receiving a shock. That also is not true.
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hwybnb
Southern California
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Wayne: I have been struggling with the bonding issue for some time and apparently had reached the wrong conclusion. After reading the OSHA letter in the link you provided I am convinced you are correct. Thank you for clearing that up.
* This post was
edited 11/07/09 03:16pm by hwybnb *
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vermilye
Oswego, NY, USA
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Quote:If your house were unbonded, you can take your hairdryer in the bathtub without fear of electrocution. Only if you had your own power source. Because the utility does ground their systems to limit over voltages due to lightning strikes, crossed high tension wires, etc, you must ground/bond the neutral if your power is supplied by a utility.
The shock path in the case of the hair dryer in the bathtub would be through the drain back to the first point where the utility grounded the system, usually at the power pole transformer. Even with plastic pipe, tap water is conductive (distilled is not) so the path exists.
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john&bet
North Vernon,in.
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Will someone put this argument to bed already. Nuff said.
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Salvo
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I realized my comment was open to interpretation after I sent it off. I should have been more clear.
We're in this mess because of lightning strikes. If there were no strikes, utilities would not bond to earth ground, and individual homes would not need to bond. Now it's "safe" to bathe with your hairdryer.
I feel safer in my MH than at home. The MH generator is not bonded. I can touch Hot to chassis without getting a shock. That's great!
Sal
vermilye wrote:Quote:If your house were unbonded, you can take your hairdryer in the bathtub without fear of electrocution. Only if you had your own power source. Because the utility does ground their systems to limit over voltages due to lightning strikes, crossed high tension wires, etc, you must ground/bond the neutral if your power is supplied by a utility.
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larry cad
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Wayne Dohnal wrote:Quote:
Not true. Neutral is the grounded conductor. Even in a two wire system, there is a hot and a neutral and the neutral is to be connected (bonded) to the ground.
A 120 volt 2-wire system does not have a neutral. "Everybody" calls the white wire a neutral by convention, but when it comes to being technically correct, there is no neutral, and regulations about a neutral simply do not apply.
NEC article 100 "Definitions" for neutral:
NEUTRAL CONDUCTOR:
The conductor connected to the neutral point of a system that is intended to carry current under normal circumstances.
NEUTRAL POINT:
The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.
FPN: At the neutral point of the system, the vectoral sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutal point, is zero potential.
From OSHA interpretation:
"The intent of 1926.404(f)(3)(iii) becomes very clear when one considers that the term "neutral" is used in its technical sense. A 120/240 volt system has a neutral and therefore must be bonded to the generator frame. A 2-wire 120 volt system has no neutral and therefore bonding is optional. Recall that neither side of a 2-wire derived system is a neutral and when one grounds either side, it becomes a grounded terminal or conductor, but it is not a neutral."
Wayne, I never thought about it like that, but it seems you are correct. It seems that in the very narrow area of a 120v generator supplying power to an RV, there is no requirement for "neutral" to ground bonding.
Now a further question: given that a generator mounted within a motorhome, and supplying 120/240 volts in a three wire system is properly bonded per code requrements, what is your thought regarding bonding of a 120v 2 wire portable generator connected to an RV? Should the generator be bonded for safety as a separately derived system, or is it better to leave it un-bonded as suggested by others here?
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Wayne Dohnal
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My own opinion on bonding a 120 volt generator with an RV is that it's a toss up. With some types of failures you're better off bonded, with others your better off unbonded. I look at it as analogous to determining the location of the safest seat on an airplane, where the answer depends on what type of accident happens. This was hashed out a in another thread Grounding Generators, all 40 pages of it. Obviously a popular subject.
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Salvo
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Please list the failures where it's better to have a bond (in RV). I know of none.
Sal
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