Generator Neutrals

Ed MacLaren · Jan 16, 2005

Re: Generator Neutrals

So you just used a safety switch and then used another panel for your gen circuits?

Yes.

I think the DPDT safety switch would have to say something about being OK as transfer equipment.

Another clip from the same catalog item -

"Supplied as standard for switching one load between two power sources, and may be field converted to switch one power source between two loads."

Ed

[ January 16, 2005, 07:18 PM: Message edited by: Ed MacLaren ]

ddderek · Jan 17, 2005

Re: Generator Neutrals

Originally posted by Ed MacLaren:

So you just used a safety switch and then used another panel for your gen circuits?

Click to expand...

Yes.

I think the DPDT safety switch would have to say something about being OK as transfer equipment.

Click to expand...

Another clip from the same catalog item -

"Supplied as standard for switching one load between two power sources, and may be field converted to switch one power source between two loads."

Ed

NOW YOU ARE GETTING EXPENSIVE... YOU ARE ADDING AN ENTIRELY NEW PANEL INTO THE PURCHASE... THAT SIEMANS PANEL SOUNDS LIKE THE BEST ALTERNATIVE, BUT STILL LEAVES ME WONDERING...

how can U.L. approve these isolated neutral generators for stand alone portable use if we all agree that it not up to code nor safe...???

(yes I know they don't have to answer to the NEC but if an isolated neutral gen IS unsafe for stand alone use, why isn't the U.L. stopping it?)

Ed MacLaren · Jan 17, 2005

Re: Generator Neutrals

YOU ARE ADDING AN ENTIRELY NEW PANEL INTO THE PURCHASE..

No need to shout, ddderek,

How else would you add a generator to an existing dwelling, where only selected critical circuits are to be picked up by the generator?

Here is a method I've used in the past that is perfectly safe, but would probably be frowned upon by most authorities.
Mount a 14-30R or 14-50R receptacle, as applicable, adjacent to, and supplied from, the main panel.
Install a similar receptacle on the end of the generator cord or cable.
Supply the critical load panel by means of a short cord with a matching plug.
During a power outage, simply un-plug the critical load panel from the main panel receptacle and plug it into the generator cord.

if an isolated neutral gen IS unsafe for stand alone use, why isn't the U.L. stopping it?

I wouldn't put much faith in the bureaucrats to keep me safe. Knowledge is power.

Ed
(edited typo)

[ January 17, 2005, 07:33 AM: Message edited by: Ed MacLaren ]

George Stolz · Jan 17, 2005

Re: Generator Neutrals

Aren't you concerned about damage to the SO cord, Ed? In a couple of years you might be back out because their critical circuits are out!

I can't spell.

[ January 17, 2005, 08:46 AM: Message edited by: georgestolz ]

petersonra · Jan 17, 2005

Re: Generator Neutrals

Originally posted by Ed MacLaren:
Here is a method I've used in the past that is perfectly safe, but would probably be frowned upon by most authorities...

By the time you did what you are suggesting would it not be almost as cost effective to just add in a small transfer switch and CBs? You can getbthem for a few hundred bucks.

Ed MacLaren · Jan 17, 2005

Re: Generator Neutrals

would it not be almost as cost effective to just add in a small transfer switch

Of course, the transfer switch is the correct way to do the job, if the customer will pay for it.

Cost effective? No. Two range receptacles, 6 feet of cord, and a 14-50P plug are much less expensive, and much safer than the hook-up the home owner would likely use if I left him to his own devices, such as a double-male cord plugged into the dryer receptacle.

Aren't you concerned about damage to the SO cord, Ed?

No. Tell me what is likely to happen to it.

Ed

[ January 17, 2005, 06:38 PM: Message edited by: Ed MacLaren ]

ddderek · Jan 17, 2005

Re: Generator Neutrals

That's a good idea Ed, a bit backwoods but safe just the same...

Can someone explain to me why the Generator is unsafe to use without the Neutral bond as a stand alone unit... I am having this same discussion in another group and the discussion has gotten to where there is actually no code declaring that a GENERATOR neutral shall be bonded... all the sections of bonding refer to premises wiring. I am so confused in this subject now that my theorey all mixed up...

Ed MacLaren · Jan 17, 2005

Re: Generator Neutrals

Can someone explain to me why the Generator is unsafe to use without the Neutral bond as a stand alone unit..

On a "stand-alone" (portable) generator serving cord-connected loads only, the frame is permitted to serve as the grounding electrode.

The neutral-to-frame bonding connection serves the same functions as the Grounding Electrode Conductor and Main Bonding Jumper do in a premises wiring system.
Without it, the equipment bonding conductor (EGC) in the load cords will not perform it's intended function.

Check this alert, in particular the last paragraph regarding some Honda generators.

Ed

[ January 17, 2005, 11:09 PM: Message edited by: Ed MacLaren ]

don_resqcapt19 · Jan 18, 2005

Re: Generator Neutrals

Ed,
I'm not sure what happened to create a shock hazard in the link that you gave. I don't see how a current path can be created by reversing the neutral and the EGC even if there is no bonding jumper.
Don

George Stolz · Jan 18, 2005

Re: Generator Neutrals

Wouldn't the simplest solution to this problem be a switch that connects the grounding and neutral system on the generator?

They could have a picture on it, "house" mode and "portable" mode."

I've never dug into a generator to find the bonding jumper, but I can imagine it's a pain to find and get to! I bought a generator a few years back, let it sit for too long, and the carb got dirty. I got to looking and that sucker would be a pain to remove and rebuild!

[ January 18, 2005, 07:48 AM: Message edited by: georgestolz ]

Ed MacLaren · Jan 18, 2005

Re: Generator Neutrals

Don,
How about this for a current path. This is for a load plugged into one of the 115 volt receptacles.

* From generator hot through GFCI to hot side of load.
* Through the load and back to gen on mis-connected EGC.
* From gen frame to earth.
* Through earth to victim's feet.
* Through victim to load device enclosure.
* Back to gen through the mis-connected neutral and GFCI.

The GFCI sees this as normal load current.

Got to go now, I will try to post a sketch later.

Ed

crossman · Jan 18, 2005

Re: Generator Neutrals

Excellent forensic thinking, Ed. That is certainly a possibility. Essentially the frame of the generator would be "hot" in respect to the unbonded "neutral" wire which is attached to the enclosure of the connected equipment.

don_resqcapt19 · Jan 18, 2005

Re: Generator Neutrals

Ed,

From gen frame to earth.

If there is no bond from the generator windings to the frame or earth there is no current path and no shock hazard. I have done some experiments on the generators on our rescue trucks using 2 wire cords and GFCIs. These generators do have the neutral to frame bond, but the truck tires provided isolation. I tried every thing that I could think in the way of creating "ground faults" to get the GFCI that was feeding the two wire cord to trip. I was not able to make that happen. If I used a three wire cord to feed a portable metal light stand placed on wet ground, then in some cases I was able to make the two wire cord trip the GFCI, but the combination of the three wire cord and the metal light stand provided a connection to earth, a path for small amounts of current, and a path for a shock hazard. I could also make the GFCI trip if I set the portable generator on wet earth. Again these generators have the neutral bonded to the frame and that creates a connection to earth. Without the connection to earth, I could not make 5 mA of current flow back to the GFCI at the generator. This would be the same case with your example and an unbonded generator...there is no ground fault current path.
It appears to me that the code requirement to bond the generator to the frame actually creates a slight decrease in safety.
Don

crossman · Jan 18, 2005

Re: Generator Neutrals

post the diagram, Ed!

ddderek · Jan 18, 2005

Re: Generator Neutrals

Originally posted by Ed MacLaren:

but the bonding jumper is not sized large enough.

Click to expand...

Why would it need to be #6?

Ed

OK, back to the bonding jumper SIZE... according to 250.28 (D) the main bonding jumper shall not be smaller than sizes shown in Table 250.66 for grounding electrode conductors. (That states for minimum number 8 conductor size) (was looking at alluminum for # 6 ref. earlier) But the point is the Gen bonding jumper is NOT sized according to code for the Seperately derived system being used. So may not be sufficient in and of itself... Thus isolating becomes necesary rather than three pole transfer switch?

Ed MacLaren · Jan 18, 2005

Re: Generator Neutrals

If there is no bond from the generator windings to the frame or earth there is no current path and no shock hazard.

Don't you think there would be enough conductivity through the earth for them to feel a tingle, under any soil conditions?

The GFCI wouldn't see this scenario as anything but normal load current, even if it was over 6 ma.

Also, they didn't specify how severe the shock was.

Ed

[ January 18, 2005, 04:19 PM: Message edited by: Ed MacLaren ]

don_resqcapt19 · Jan 18, 2005

Re: Generator Neutrals

Ed,

Don't you think there would be enough conductivity through the earth for them to feel a tingle, under any soil conditions?

I don't see a circuit between the white and the green. Where is the current path? Under the conditions shown, I don't think that there is any current flow on any of the conductors. There is not a complete circuit.
Don

crossman · Jan 18, 2005

Re: Generator Neutrals

In this south texas coastal plain damp black clay, I am sure that a shock would be felt.... if the guy is barefoot...

At other locations with different earth characteristics, the path through the earth is certainly debatable, but the fact that full potential would exist between the equipment housing and the generator housing is undeniable.

don_resqcapt19 · Jan 18, 2005

Re: Generator Neutrals

crossman,

At other locations with different earth characteristics, the path through the earth is certainly debatable, but the fact that full potential would exist between the equipment housing and the generator housing is undeniable.

How? It is an isolated system. Neither winding conductor has any potential to the generator frame or earth. I still don't see a current path here.
Don

don_resqcapt19 · Jan 18, 2005

Re: Generator Neutrals

Guys,
I'm being dense today. I keep overlooking the generator frame itself is connected to the earth. That completes the path. Isolate the generator from earth and there is no path.

Don

Generator Neutrals

Senior Member

Member

Senior Member

Moderator

Senior Member

Senior Member

Member

Senior Member

Moderator

Moderator

Senior Member

Senior Member

Moderator

Senior Member

Member

Senior Member

Moderator

Senior Member

Moderator

Moderator