Portable Generator Grounding

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We use portable welding machines (on rubber tires) as source of power (120 VAC) for hand tools (grinders and pipe cutters). NFPA70 has been interperted as not requiring grounding of the portable generator if equipment is connected to the generator through extention cords. If a person is using a hand tool to demo conduit and accidently cuts into a live circuit how is he protected from electrocution since the generator is isolated from ground ?

Am I missing something ?
 
Attaching the generator to ground will not do anything for personnel safety.

If a cord is cut or any bolted type of fault occurs the on-board circuit breaker will be the protection.

GFCI protection would be a good idea IMO.

As far as cutting into a live circuit that is derived from another source, grounding the generator would not make this scenario any safer, it may actually increase the danger.

Roger
 
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In the accident you describe grounding the generator to earth would not help the worker in the least.

The only way to protect the worker from the accident you describe would be to bond the generators EGC to the EGC of the source supplying the conduit being cut and even than if you grind into live wires you are likely to get hurt by shock or burns.
 
If I am using a hand tool and the hand tool is grounded through the ground wire on the hand tool (to earth ground) and I accidently cut into a conduit (AC that is referenced to earth ground) would the current flow be through the path of least resistance.. ie. the grounding wire and not my body!
 
Adrian Fitzgerald said:
If I am using a hand tool and the hand tool is grounded through the ground wire on the hand tool (to earth ground) and I accidently cut into a conduit (AC that is referenced to earth ground) would the current flow be through the path of least resistance.. ie. the grounding wire and not my body!

That is a common false hood.

1) Electricity does take the path of least resitance......it also takes every other available path in varying amounts. Your body would still be getting enough current through it to take you down.

2) Running a ground wire into the earth is not even remotely the same as having a power tool connected to the power sources grounding conductors.

The reason the NEC does not require ground rods for this application is simply because they do not increase safety and may actually decrease safety in some circumstances.

Edit; By the way, the last paragraph is just my opinion of why.
 
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Adrian, along with Iwires post, another misconception is electricity seeks the ground (earth), this is not true, it seeks (must return to) its source, which is the generator windings in this case.

The term "ground" used for bonding a device back to this source is incorrect and a big source of confussion. One of the other moderators here, don_resqcapt19, has been trying to get this changed in the NEC for some time.

The extension cords green wire will take a fault back to the generator as a bonding wire and this is the safety valve, the earth will not do anything.

Roger
 
I can understand not grounding a "Vehicle Mounted Generator" if " All Equipment is mounted on the vehicle or powered through extention cords mounted on the vehicle and " ANY EQUIPMENT POWERED THROUGH EXTENTION CORDS ARE ON THE VEHICLE". I do not understand why grounding a portable generator which is used as a source of power for cutting into conduit (that may ACCIDENTLY be live) can do anything but save the person from electrocution.

If you read the section of the NEC that addresses this issue it seems very ambigous. If you read it carefully it states that "All equipment MUST be on the vehicle or on the ground connected through extention cords plugged into the generator on the vehicle.

If reasearch is done, It would conclude that this section was intended for using equipment that is ONLY on the Vehicle. Through revisions the period (.) that sould be behind the first "... equipment mounted on the vehicle" has been removed due to a "Typo" error.

The only "LOGICAL" reason not to ground a portable generator would be if you are using it in and enviorenment where " NO OTHER SOURCE OF POWER IS GROUND REFERENCED (earth ground)" ie. new construction, inside a vessel, or on the vechicle where the generator is located.
 
Adrian, take a few minutes and read this thread.

Page 5 is where it starts to parallel this thread.


Roger
 
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Adrian, I feel we are getting off on the wrong foot here.

It appears you are not in the electrical trade but have great intentions as a member of a safety committee.

I have spent 25 years using the NEC, Roger a bit more.

The section you are quoting I am quite familiar with.

Rest assured it doe not apply only to the equipment on the vehicle.

Ground rods DO NOT protect workers from electrocution.

If you are interested in learning some truths than I and many others here will be happy to help you...but you must approach this with an open mind and enough interest to pay attention through a complicated subject.

I will finish this post by adding that when you are using tools supplied by permanent power it is not the connection of the tools EGC to a ground rod that saves you bacon it is the connection of the tools EGC to the neutral of the service supplying the tool.

Bob
 
Adrian,
I do not understand why grounding a portable generator which is used as a source of power for cutting into conduit (that may ACCIDENTLY be live) can do anything but save the person from electrocution.
Can you explain exactly how this would work to provide protection for the person?
Don
 
Please help me.The source of the electricity cut into is not supplied by the generator. It is supplied by the power company and is referenced to earth ground through the neutral. I agree that it will seek its source through the path of least resistance and that would be through the person since the portable generator is not the source of the power.

I am sorry for not being clear in my original posting.
 
I agree that it will seek its source through the path of least resistance...
And through all other available paths. That is the reason that an earth connection does not protect a person. The current doesn't all go to the path of least resistance...it goes on all available paths. The only way to provide shock protection by the use of bonding and grounding is to force enough current to flow so that the overcurrent protective device opens the circuit. In the real world, grounding never accomplishes this, only bonding does.
Don
 
Adrian, the earth is a poor conductor, so even if two sources are both earthed, the chance of it completing a fault clearing path to either is far stretched at best.

This is where a "Bonding" connection from the tool to the other source would be a safety.

If the current from the POCO source were to be applied to the tool in the way of a fault as you describe, the earth resistance between the two sources would simply be seen as a small load from the POCO source, it would travel through the tool and the operator.

A "bonding" connection from the tool to the POCO neutral would help in that it would be a much lower resistance to the POCO source.

(edited for speeling)

Roger
 
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