Portable Generator GEC & EGC

[doug glasscock]

277/480-125KW generator on wheels
Are most portable generators wired as SDS or not?
If SDS,
Questions:
1. Do you drive a ground rod solely for the portable generator to be connected to?
2. If so, do you connect this ground rod to the ground rod for the pump house OR can you just provide a place on the Pump House utility service ground rod to connect the generator?

[bennie]

A generator is a generator, a transformer is a transformer, there is nothing else.

The premises wiring may, or may not, be a separately derived system.

A transfer switch, ahead of the main service switch, and disconnecting the utility MGN, will create a separately derived system.

[doug]

[ March 05, 2003, 10:21 PM: Message edited by: doug ]

[dereckbc]

If you switch the neutral at the transfer switch, or if the generator neutral is bonded to the frame, then it is considered SDS by code.

If it is configured SDS then you must provide a GEC to the service ground electrode. By code you cannot simply drive a ground rod for the generator without bonding it to the service electrode.

[Ed MacLaren]

As Dereck stated (he types faster than I do :) ), the determining factor is whether the generator is connected to a fixed wiring system by means of a transfer switch, and how that switch is configured.

If the generator is the only power source, and is not interconnected with another (utility) source, the term Separately Derived System does not even apply.

Assuming it is interconnected, the type of transfer switch (3-pole or 4-pole) selected, and the grounding/bonding required, depends on whether or not the generator winding wye point (neutral) is bonded to the generator frame.

The sketches below may help.
Note- They do not represent actual installations, and are offered to illustrate basic principles only.

Some of the other people here can help with the applicable NEC rules.

http://www.electric-ed.com/images/Gen10.gif

http://www.electric-ed.com/images/Gen9.gif

Ed

[ March 05, 2003, 11:02 PM: Message edited by: Ed MacLaren ]

[bennie]

Read carefully the definition of a separately derived system, in Section 100.

A premises wiring system can be a separately derived system. A generator, transformer or the other power sources are not separately derived systems.

[Ed MacLaren]

Hi Bennie, glad to hear you're health has improved.

"A rose by any other name is still a rose"

No matter what we call them, there are power sources that are "separate" from the main service, and a stand-by generator is one of them. In Canada we call them "isolated systems"

I am using the term Separately Derived System here because that is what the NEC calls them, and this is an NEC forum.

Ed

[bennie]

Hello Ed, thanks for the thoughts. I don't mean to appear rude, my comments may be taken that way. I don't have a flowered writing style :) .

My only concern is that the erroneous application of the phrase, Separately Derived System, is causing a lot of objectionable common mode current and EMF.

Grounding a system in one earth location, is correct, grounding a transformer in two locations is an error.

[charlie b]

A rose by any other name would smell as sweet. A carnation can also smell sweet, but that doesn’t make it a rose.

My contribution here will relate to language only, not to code. A generator is not, and cannot ever be, a “Separately Derived System.” Nor can a transformer, nor any other power source. The reason is simply that none of these is a “system,” in the context of the NEC definition of SDS. The “system” is the premise wiring system. It can be powered by a transformer or by standby generator, but it is the wiring system that constitutes the SDS, not the power source.

Let’s be careful with words. The NEC is full of them, and therein lies the hazard. If you look up the word “separately” in a common dictionary, you will find such concepts as isolated, divided, disconnected, and detached. But can’t go from these meanings directly to an understanding of a “Separately Derived System,” even though that phrase does contain the word “separately.” You need to do as Bennie suggests, and look up the phrase in Section 100.

[dereckbc]

Bennie, I agree with your statement: "Grounding a system in one earth location, is correct, grounding a transformer in two locations is an error". This can be practiced if the electrician or engineer plans carefully. It is rarely practiced however. I agree this is the major cause of common mode noise on ground systems.

The problem is by code the transformer or any SDS can be grounded from multiple points. (The points have to be bonded, but not single point) One is from the EGC on the primary of a transformer, and another from the GEC on the secondary Xo. By code they are not required to come from the same central location (SPG). In addition the equipment being served by the transformer probable has incidental contact to ground via concrete anchors, and contact with other metallic objects forming multiple paths to ground through the EGC.

Glad to see you back and share your knowledge.

Dereck

[bennie]

Gentleman: You have made my day. This is an area that really needs interest from learned professionals on this forum.

I have researched this topic back to when it went sideways. My information indicates that after 1984, when the handbook was written by J.F. Mac Partland, the equipment ground wire was added to a transformer primary.

A lot of problems in grounding will go away when the true definition of a separtely derived system is considered.

I have puzzeled over this subject, for a long time. The answer I needed was in plain sight, Article 100.

My Email is: palmerbenray@aol.com if anyone wants more data.

[Ed MacLaren]

How often have any of you ever installed a transformer or generator and not connected some circuit conductors and a load to it?
That makes it a "system" and the grounding of that system is what Doug asked about in his post.

Doug, this is what OSHA has to say about the grounding of portable generators in one of their interpretation publications.

QUOTE "OSHA Standard 29 CFR 1926.404(f)(3)(i) and NEC 250-6(a)(1) and (2) states the conditions where portable generators do not have to be grounded.
Specifically, 29 CFR 1926.404(f)(3)(i)states "Under the following conditions, the frame of a portable generator need not be grounded and may serve as the grounding electrode for a system supplied by the generator: (A) The generator
supplies only equipment mounted on the generator and/or cord- and plug-connected equipment through receptacles mounted on the generator, and (B) The
noncurrent-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame." END QUOTE

However when a so-called "portable" generator is connected to a fixed wiring system it would then not meet the definition of a portable generator, and then the system it supplies should be grounded and the equipment "bonded to ground" by the same methods as any other system.

The sketches illustrate the way I believe it should be done, from an engineering point of view. Perhaps someone will comment on NEC compliance.

Ed

[ March 06, 2003, 12:08 PM: Message edited by: Ed MacLaren ]

[bennie]

Ed: I know we have walked this dog before, it still won't hunt. :)
From an engineering aspect the two switches are electrically the same.

This drawing appears in the handbook, and in Chapter 12 of the Soares Book of grounding.

This drawing is as ludicrous as the statement " All transformers, except an auto-transformer, are separately derived systems".

[Ed MacLaren]

Bennie,
But she's a hard dog to keep under the porch. :)

Could you tell me, and the other good people, in technical laymans's terms, just what is wrong with the installation as sketched.

Ed

[bennie]

Trace the path of the green wire, in the switch, indicated as a separately derived system.. The switch is shunted.

[david luchini]

Bennie,
As I read the definition of separately derived systems in the NEC, it is a premise wiring system with no direct electrical connections, including a solidly connected grounded circuit conductor, to SUPPLY conductors originating in another system. I do not see how the green wire in the sketch could be considered a SUPPLY conductor of either system. What does it supply, and would the system stop supplying power if that conductor is disconnected? The definition of an SDS appears not to address grounding conductors as you indicate.

Dave

[don_resqcapt19]

We will have an official panel statement on this in July. I have submitted a proposal to add the following words to the Article 100 definition of SDS:
"For the purposes of this section, a connection between the grounding conductors on the primary and secondary side of a transformer shall not be considered a direct electrical connection". This is proposal 1-134. A similar proposal, 1-135, has been submitted by Mr. Stromberg of Dow Chemical. These proposals will put this question to rest, as they will result in an offical position statement by the code making panel.
The 2003 proposals (http://www.nfpa.org/nec/TheNEC/ROPsROCs/2003ROP/2003ROP.asp) are on line. These are just the proposals, without any panel action or comment.
Don

[Ed MacLaren]

Trace the path of the green wire, in the switch, indicated as a separately derived system. The switch is shunted.Yes, I agree, it is. And what is wrong with that? What problem or hazard does that cause?

Ed

[bennie]

The reason for disconnecting the MGN during an emergency situation, such as a storm, is due to the unknown state the neutral may achieve.

A broken MGN from the distribution system, back to the source, can cause the medium voltage to appear on all grounded conductive surfaces of the premises.

A transfer switch must be before the main service switch to insure disconnecting the utility MGN system. With the MGN disconnected, the premises wiring is then a separately derived system. Grounding must be done, if the system is required to be grounded.`

[bennie]

The Soares book implies that current does not flow in green wires.

The article also states that auto-transformers are not separately derived systems. Who ever wrote that does not know anything about transformers. A grounded wye/grounded wye, has a neutral connected.

No power source is a separately derived system. The power source may supply a separately derived system.

A transformer supplying a separately derived system must have an ungrounded primary supply.

An isolation transformer has a grounded primary with an ungrounded secondary.

[doug]

ED,
On your diagram for SDS, what does the dotted blue line represent?

Doug Glasscock

[hurk27]

I think what the intent of the NEC is that there is no solid connection between the generator/transformer and the primess wiring as it says if the second part of the definition:

Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
and in a FPN that also discribes it:

250.20
D) Separately Derived Systems.
FPN No. 1: An alternate ac power source such as an on-site generator is not a separately derived system if the neutral is solidly interconnected to a service-supplied system neutral.
So if a transfer switch switches the neutral then it would be a separately derived system, and would be required to be bonded as per 250.30

FPN No. 2: For systems that are not separately derived and are not required to be grounded as specified in 250.30, see 445.13 for minimum size of conductors that must carry fault current.

[ March 06, 2003, 11:48 PM: Message edited by: hurk27 ]

[bennie]

Correct, provided the switching is done before the equipment ground wires are in the equation.

Install a conductor of any color, or name, across a switch and the switch will not function. Why switch the neutral when the equipment ground conductor is in parallel.

The switching, as shown, must have been designed by the auto-transformer expert. :)

[Ed MacLaren]

Doug, the dotted blue line represents the alternative location to connect the generator grounding electrode conductor.

Install a conductor of any color, or name, across a switch and the switch will not functionBennie and I have been through this before, but I think it should be addressed again in case the new folks are interested.

A double throw switch (transfer switch) is actually two switches in one, and in this SDS installation it’s purpose is to completely isolate the circuit conductors of the two systems.

There are actually two separate systems and it helps to visualize them one at a time.
Note - The sketches below are for a single-phase installation, but the principle applies to three phase also.

When the load is on utility power, it is as if the generator does not exist. Diagram 4 The unbalanced load (neutral) current path is from X to Z, and there is no parallel path.

Likewise, when the load is on generator power, it is as if the service (utility) does not exist. Diagram 5 The unbalanced load (neutral) current path is from X to Y, and again there is no parallel path.

Each system is grounded and each system’s EGC lands at the point where it’s GEC is connected, (Single Point Grounding) and the function of the transfer switch is not impaired by the EGCs.

Ed

http://www.electric-ed.com/images/Gen7.gif

http://www.electric-ed.com/images/Gen6.gif

[bennie]

Visualize the utility neutral (MGN) becoming 13 KV to ground, during a storm, when the MGN is broken upstream.

Basic electrical theory, a shorted switch is no switch.

Bennie...palmerbenray@aol.com

[ March 07, 2003, 08:10 AM: Message edited by: bennie ]

[bennie]

Another reason the MGN must be disconnected is to prevent the ground electrode system from conducting fault current from non-related, near by power lines, during a LG fault.

[bennie]

Regardless of the Soares Book on Grounding, a green wire will carry current, it's presence excludes the premises wiring from the definition of being a separately derived system.

Place the transfer switch ahead of the service switch. Switch the neutral. Install equipment ground conductor from the transfer switch to the service switch. You now have a separately derived system when operating in the generator mode.

[david luchini]

Bennie,
Out of curiousity, where would the service Main Bonding Jumper (NEC 250-28) be installed on the system you just described, and where would the SDS bonding jumper (NEC 250-30(a)(1)) be installed?

Dave

[bennie]

Hello David. The intertie to the earth, equipment, and MGN, will be at the service switch.

The ground electrode system for the utility service will serve the generator. There is not as much concern with a lightning strike transient.
A lightning strike can affect the neutral.

Another reason for disconnecting the neutral (MGN) is...During storm conditions and ice buildup on power lines the lines break and make first contact with the MGN below the lines. The premises service elevates to the high voltage. This is also part of the reason for the speed requirement of a generator starting and coming on line. Voltage on the conductive surfaces is quickly removed.
Compares to the GFCI principal.

[david luchini]

Bennie,
I'm not sure I understand. Are you saying that there is no SDS bonding jumper as defined in NEC 250-30(a)(1)? If so, what is the purpose of that section?

Dave

[bennie]

David: The premises wiring is the separately derived system. The same service intertie serves the same purpose for both the utility and generator.

Alternating-current Systems Without External Connections Section 2514, now Separately Derived Systems, originated during the REA era of electrical distribution.
As power lines started appearing in the rural areas. Many farm houses had generators for electrical power.
This premises wiring system is a separately derived system, it is separately derived from the utility system, and not grounded to the utility grid MGN.

The code statement is to point out this feature, and require the separately derived system to be grounded according to proper procedure.

The definition in Article 100 is quite clear and substantiates this statement.

[bennie]

Another fact: Dairies were powered by a transformer supplied by an ungrounded secondary power line. The derived neutral was not electrically connected to the supply MGN.

This premises wiring is a separately derived system, the transformer is a transformer, nothing else.

This system is not used due to through fault containment problems.

[david luchini]

Bennie,
I think the definition in article 100 is quite clear that the SDS involves the interconnection of SUPPLY conductors (including the grounded circuit conductor) and not of the grounding system.

If the SDS is also the service entrance, then why give instructions on how to ground the SDS in section 250-30. It is already grounded by section 250-28. The SDS grounding section is completely redundant under this example. It seems to me that under your definition that every three phase service fed from a utility padmount transformer is also an SDS (whether or not there is a generator and transfer switch) because there is no connection from the primary system to the secondary system.

Dave

[Ed MacLaren]

I am mystified by Bennie’s statement-
Another reason the MGN must be disconnected is to prevent the ground electrode system from conducting fault current from non-related, near by power lines, during a LG fault.Why would the (Multiple Grounded) Neutral have to be "disconnected" in this particular system, and not in others.
The neutral conductor, in virtually every residential and three phase four-wire service in North America, is not switched.

In my house, my workplace, and in most building services that I have seen, the multiple grounded utility neutral extends un-switched, and un-fused, all the way to the load devices.

The purpose of switching the neutral conductor in the transfer switch, in the systems illustrated above, is to prevent a parallel path created by the internal bonding of the generator neutral to the frame.

If the generator neutral is bonded to the frame, and the neutral were not switched, a portion of the unbalanced (neutral) current would flow in the EGC. Diagram 6.

Generators that do not have their neutral bonded to the frame (floating neutral) can be used with a solid neutral transfer switch. Diagram A – Page 1

http://www.electric-ed.com/images/Gen8.gif

Ed

[hurk27]

If we look closer at 250.30 (1) it says that we can bond the gec at any point eather at the supply or the first means of disconect and a transfer switch could be the first means of disconect. but it does say that The point of connection shall be the same as the grounding electrode conductor as required in 250.30(A)(2). (point is singler)
Now where does it say that we have to bond the EGC at both the generator and the disconect?

(4) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system.
Again the word connection is singler


Now here it even permits us to have a single connection
Except as permitted by 250.24(A)(3),

250.24(A)(3) Dual Fed Services. For services that are dual fed (double ended) in a common enclosure or grouped together in separate enclosures and employing a secondary tie, a single grounding electrode connection to the tie point of the grounded circuit conductors from each power source shall be permitted.

I might be wrong on the intent but after rereading it over and over it seems to not allow a second connection.
And the bonding would seem to serve as both the egc and gec after the connection and this would comply with 250.20 FPN No. 1: An alternate ac power source such as an on-site generator is not a separately derived system if the neutral is solidly interconnected to a service-supplied system neutral.

Grounded Conductor. A system or circuit conductor that is intentionally grounded.

Grounding Conductor. A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Grounding Conductor, Equipment. The conductor used to connect the non–current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.
Grounding Electrode Conductor. The conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, at each building or structure where supplied from a common service, or at the source of a separately derived system .

[ March 07, 2003, 10:08 PM: Message edited by: hurk27 ]

[dereckbc]

Bennie, I am trying to follow along with you, but I am still not clear what you are trying convey.

Are you saying if the service has a MGN, it is not SDS?

For example: If the sevice was a 480 ungrounded delta.

It looks to me like you are trying to say if there is a grounded conductor involed it is not SDS.

[doug]

Remember me,
I started all this.
My generator is 125KW, 277/480 on wheels.

Kohler says that a customer can specify whether to bond the neutral to the frame or not when it is ordered.

So lets say I order it with the neutral not bonded to the frame.

If I were to install a service rated transfer switch with utility and generator 3-POle main breakers built in to the transfer switch (Cutler Hammer makes this type of switch). I would then carry five wires (L1,L2,L3,N,bonding G) from the generator to the transfer switch and only four wires from the utility (L1,L2,L3,N) to the transfer switch. The GEC would be bonded at the transfer switch which would work for both services with a single ground rod.

1. Does this sound right?

2. Since the generator can be moved from site to site and it will have a cable with a large plug to connect to the pump house. Is it also safer/redundant to provide a place to hook on to this same ground rod, a connection from the generator frame?
I am thinking about this in the unlikely event that the operator starts the generator prior to plugging it in for operation.

Doug Glasscock

[ March 07, 2003, 11:23 PM: Message edited by: doug ]

[ronaldrc]

I'm not siding with anyone here but I did find these in my old 1971 NFPA NEC Handbook.

These where a direct scan from the pages and unedited.

Article 700-15 Please read paragraph #2 Solid Neutral on A-C and D-C Systems

:)

[ March 09, 2003, 09:57 AM: Message edited by: ronaldrc ]

[hurk27]

Doug glad to see your still around but if you order the generator with the neutral to ground bonded then you must provide a 4-pole transfer switch look at ED's last diagram in his last post as this explaines it best. but if you order it without the bond then you can use a 3-pole transfer switch but you must run a egc along with the feeders from the generator fram to the transfer switch now you can bond the neutral at the transfer switch or at the service but where you do this bond you must bond your gec too. and the service is treated like a subpanel and will not have a neutral to ground bond. a neutral to ground bond can only be done at one location in a non sds system.

Wayne

[hurk27]

Ed In the first post of the two diagrams (A&B) the B (SDS) will have a parallel path of the neutral between the generator and the transfer switch. I think this is why we have to connect the gec at the same point that we bond the neutral?

But I have learned alot from these post as the way I was thinking with the gec connecting to both sides of the transfer switch neutral contact that there had to be a paralleling of the neutral but after tracing the current path's I see now that it wouldn't since when the transfer switch is in the generator position the current would not flow back through the bond at the service disconect. even though there is an electrical connection accross the contact it is because that the connection is broken between the two neutral connections (poco&generator) at the transfer switch.

this could be duplcated by taking a dpdt switch and aranging the circuit with the supplys and loads with the same grounding to mimic the same circuit and an amp probe could be used to show which way the current goes when the switch is changed.

And as per the definition goes the neutral of the premiss wiring is not solidly connected to the service neutral or to the generator's neutral there just connected together (the service to generator) by the gec's
Ed Thanks again
Wayne

[ March 08, 2003, 01:46 AM: Message edited by: hurk27 ]

[bennie]

Hello Ronald, I got your message sent to the webmaster, thanks a lot.

You have submitted a good article. The ground current flow in a MGN system will also affect the GFP zero sequencing of the generator, when the neutral is not disconnected. The sensor sees this as a fault and will dump the unit off line.

This, of course is on units with GFP protection.

The transfer switch, as shown, will not disconnect the MGN (neutral).

[Ed MacLaren]

Doug,
1. Does this sound right?Sounds good to me. By using a generator with an "unbonded" neutral, and a solid neutral transfer switch, no further "earth grounding" is required at the generator. (Diagram A, Page 1)

2. Is it also safer/redundant to provide a place to hook on to this same ground rod, a connection from the generator frame?It wouldn't do any harm, but I don't see a purpose for it, unless you think lightning might strike the generator.


hurk27,

The broken line in the SDS - (Diagram B, Page 1) is an alternative connection point for the GEC(blue). One or the other would be used.

Because Doug is using a cord-connected generator, it would be more practical to connect the GEC at the transfer switch, if his system was configured as an SDS. If it was connected at the generator, the connection would have to be made each time the generator was used.

Do you still see a path in parallel with the neutral?

Ed

[ March 08, 2003, 07:54 AM: Message edited by: Ed MacLaren ]

[doug glasscock]

Wayne,
Thank you for your response. That further clarified things for me about the pump house panelboard requiring an isolated neutral so you don't get parallel current paths.

So, the pump house panelboard is 277/480-4W.
This panelboard would have to be ordered with both an isolated neutral bus and a ground bus.

Correct?

[hurk27]

Posted by Doug "My generator is 125KW, 277/480 on wheels."
do they make a cord that big?

doug
you cant have the ground bar isolated as it wouldn't serve the perpose.
only the neutral has to be isolated. you could just do the bonding at the panel just like in a normal service and just keep the neutral isolated from ground in the transfer panel and in the generator this will allow you to bring the gec to the service and keep it at the same poimt of bonding the neutral but you will still have to run a ground wire with the current wires to ground the cases of the generator and the transfer switch.

Ed if the gec is bonded at the transfer switch and the neutral to case bond is done at the generator then the neutral in the cord connecting the generator would be paralleled, with the gec also connecting at the service disconnect.

In diagram "B" if you follow the path from point of the gec/neutral connection in the transfer sw then to the neutral bar in the service disconnect then back through the ground bonds to the generator you will see that the neutral is infact parralleled. but just from the generator to the transfer sw.

[ March 08, 2003, 01:15 PM: Message edited by: hurk27 ]

[Ed MacLaren]

hurk27,

Yes, I see it now, thanks for pointing that out. This type of installation (generator with bonded neutral used with transfer switch) would require that the GEC always be connected at the generator to avoid that problem. I will change Diagram B, Page 1, accordingly.

By the way, this is a good reason for always using a generator with a floating (unbonded) neutral when it will be connected to a fixed wiring system by means of a transfer switch, and when it must be portable.

Sh*t, now I will have to go back and fix one I just installed last week. :o
The guy wanted to store the generator in his garage, and just haul it out in the driveway when needed, and plug it in.

On second thought, maybe I'll leave it as is. I used an oversized feeder cable from the service panel to the transfer switch, and the green EGC in the generator cord is the same size as the neutral.

Ed

[ March 08, 2003, 03:11 PM: Message edited by: Ed MacLaren ]

[dereckbc]

Doug, I think it has been beaten to death now. Your best way for a portable generator used the way you plan to use it provided no GFP is involved:

1. Do not to bond the neutral to the frame.
2. Use a 3-pole transfer switch.
3. Use a 5-pole plug-connector at the generator P-P-P-N-EGC.
4. Forget about a ground rod at the generator. If you insist on using a ground rod you will have to bond it to the service electrode and connect it to the generator. But it just cannot float unless you completly disconnect from the service.

Good luck

[doug]

Everyone,
Thankyou for all the input. This has been truely helpful.

[ March 09, 2003, 01:02 AM: Message edited by: doug ]

[doug]

Wayne,
I didn't mean to say that the ground would be isolated, now that I have read my post again, I see it reads that way.
Thanks for everything.

[dan19403]

i believe that i am right, please correct me if wrong, but in an industrial application -- wouldn't 2/4 SOOW cord be sufficient for say a 150' run for this generator -- not even plugged in but wired directly into the disconnect.

I know we installed a 60kVA 3 phase unit using 4/4 SOOW at a demo site and we were required to install a seperate ground.

Originally posted by hurk27:
Posted by Doug "My generator is 125KW, 277/480 on wheels."
do they make a cord that big?

doug
you cant have the ground bar isolated as it wouldn't serve the perpose.
only the neutral has to be isolated. you could just do the bonding at the panel just like in a normal service and just keep the neutral isolated from ground in the transfer panel and in the generator this will allow you to bring the gec to the service and keep it at the same poimt of bonding the neutral but you will still have to run a ground wire with the current wires to ground the cases of the generator and the transfer switch.

Ed if the gec is bonded at the transfer switch and the neutral to case bond is done at the generator then the neutral in the cord connecting the generator would be paralleled, with the gec also connecting at the service disconnect.

In diagram "B" if you follow the path from point of the gec/neutral connection in the transfer sw then to the neutral bar in the service disconnect then back through the ground bonds to the generator you will see that the neutral is infact parralleled. but just from the generator to the transfer sw.

[gwz2]

Last time I looked at Diagram B, Ed had corrected as he said he would.
The Green (GEC) does not tie to the Grounded Conductor at the Transfer Switch.
The GEC is now at the Generator Common Terminal.

[doug glasscock]

Crouse Hinds makes the 200amp reverse plug (with female connections) and a mounted reverse receptacle (with protected male pins) that will work for this application. Seeing the question about the availability started me digging for the answer. Still looking for a 5 conductor cable.

[ March 11, 2003, 11:25 AM: Message edited by: doug glasscock ]