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Posted By: dave4242 generator wiring woes - 11/21/02 11:07 PM
We have a 5000 watt Coleman generator. When the house was built, the electrician placed a 100 amp doublepole breaker at the base of our panel and from that ran wires to a subpanel that powers the circuits which can be fed by the generator. There is a three position transfer switch (positions are: electrical utility(normal)/off/generator). All the neutral wires are screwed to a bar in this transfer box(it appears that only the hot wires are switched). The ground wires are all screwed to a separate grounding lug in the transfer box.
So much for the background info. Now here's the basis of my 4 questions:
In the garage, the electrician installed a twist-lock plug that has separate neutral and ground(4 prongs). The generator outlet has only 3 connectors. It is 220v and looks somewhat like a duplex outlet.
1: I was told to just connect the neutral and ground wires in my cable that goes from the generator to the house together at the ground pin on the plug that inserts into the generator. Is this correct?
2: The generator also has an internal wire that bonds the neutral to the case/frame of the generator. Should that be disconnected so that the neutral is no longer bonded to the case.
3: Do I need to hook this the external grounding lug of the generator to a ground rod if the neutral is no longer bonded to the case?
4: If the neutral is no longer bonded to the case and I want to run a tool appliance directly by plugging into the 110v oulet on the generator, do I have to do anything special?
Thanks very much,
Dave
Posted By: txsparky Re: generator wiring woes - 11/21/02 11:27 PM
Dave,
If you do a search on generators in this forum,you will find alot of threads on this subject.Hope this helps.
Posted By: dave4242 Re: generator wiring woes - 11/21/02 11:44 PM
I'm sorry. I did read some of the threads on generator hookups, but I really had a hard time applying it to my situation.
Posted By: electric-ed Re: generator wiring woes - 11/22/02 12:19 AM
Portable generators that have the winding center-tap (neutral) bonded to the frame by the manufacturer are primarily intended for use where not connected to a building wiring system.

Generators that are designed to be permanently connected to a building wiring system through a transfer switch are usually manufactured with the neutral isolated from the frame (floating), as shown in Diagram 1.

Note - These diagrams do not represent actual installations, and are intended to illustrate basic principles only.

[Linked Image from electric-ed.com]

Because the grounded (neutral) conductor is not switched in the transfer switch, no other grounding electrode connection is required at the generator.

If a generator that has the winding center-tap (neutral) bonded to the frame is used with a transfer switch, as in Diagram 2, the switch should break the grounded (neutral) conductor, which will require the generator neutral to be grounded to an acceptable grounding electrode.

[Linked Image from electric-ed.com]

Ed

[This message has been edited by electric-ed (edited 11-21-2002).]
Posted By: dave4242 Re: generator wiring woes - 11/22/02 01:14 AM
Ed,
What could conceivably happen if the generator does not have the floating ground (neutral is bonded to frame) and the neutral is not switched at the transfer switch.
Posted By: electric-ed Re: generator wiring woes - 11/22/02 01:52 AM
Quote
What could conceivably happen if the generator does not have the floating ground (neutral is bonded to frame) and the neutral is not switched at the transfer switch?
When on utility power the neutral is in parallel with the equipment bonding conductors (green). The unbalanced load current, which should be flowing in the neutral only, will divide, and some will flow in the equipment bonding conductors.

[Linked Image from electric-ed.com]

Ed
Posted By: dave4242 Re: generator wiring woes - 11/22/02 03:30 AM
sorry for not understanding, but could this potentially feed back into the line and shock someone working on the downed power lines?
Wouldn't it preferentially go to the ground circuit/ground rod for the house?
Posted By: electric-ed Re: generator wiring woes - 11/22/02 02:52 PM
Quote
could this potentially feed back into the line and shock someone working on the downed power lines?
No, the transfer switch will prevent this. In Diagram 3 the generator is not connected and would not be operating. The problem is that the EGCs (green) are not sized for, and therefore not permitted to carry, the unbalanced load current.
Quote
Wouldn't it preferentially go to the ground circuit/ground rod for the house?
No, this current should flow back to it's source, the utility transformer winding, by way of the grounded (neutral) conductor.

Ed


[This message has been edited by electric-ed (edited 11-22-2002).]
Posted By: Ron Re: generator wiring woes - 11/22/02 03:19 PM
The portable gen in this application may not be used as the grounding electrode conductor (GEC) per 250.34(A). Provide a GEC.
Posted By: dave4242 Re: generator wiring woes - 11/22/02 04:26 PM
How would I rectify this situation with my current setup? The grounding conductor from the twistlock oulet in the garage to the transfer switch is 6 gauge.
My electrician told me that technically everything should work fine, but the ground connection in the generator (bonding wire or generator outlet) may be undersized.
The wiring from the generator back to the panel is oversized for the load (possibly 20 amps max).
Posted By: dave4242 Re: generator wiring woes - 11/22/02 04:41 PM
I called Coleman, and they said that I can buy a new end bell assembly that will have a 4 prong twistlock plug and would be compatible with my generator's internal wiring. It would then have a separate neutral and ground.I think that would solve all my wiring woes. Does this ound ok with my setup?
Posted By: Ron Re: generator wiring woes - 11/22/02 04:47 PM
The 4 wire plug is a great start. You will need to unbond the n-g in the gen.
Posted By: electric-ed Re: generator wiring woes - 11/22/02 05:17 PM
Why spend money to change the end-bell?

Get a competent electrical contractor (not the one who did the original installation) to hardwire the generator and disconnect the neutral-to-frame bonding jumper.

Because your transfer switch does not switch the neutral conductor, no GEC is required at the generator. Refer to Diagram 1 above.

Ed



[This message has been edited by electric-ed (edited 11-22-2002).]
Posted By: dave4242 Re: generator wiring woes - 11/22/02 06:42 PM
Ed,
What do you mean when you say hardwire the generator?
The end-bell is about $100 from Coleman.
I would think the electrician's bill would be higher.
Posted By: electric-ed Re: generator wiring woes - 11/22/02 07:21 PM
By the term "hardwire" I meant to connect the cable directly to the generator terminals without using the receptacle and plug.
Of course, there will be some who will say that this will violate the UL listing, but it will actually be safer.

There is no need for a receptacle in this type of installation, unless you want the generator to remain portable.

It will not be possible to safely use cord connected tools by plugging into the generator receptacle if you disconnect the neutral-to-frame bonding jumper.

Ed

[This message has been edited by electric-ed (edited 11-22-2002).]
Posted By: dave4242 Re: generator wiring woes - 11/22/02 08:30 PM
okay,
last 2 questions, i swear.
If I buy the new bell housing from Coleman for $100, and I connect that so it has a floating ground (neutral no longer bonded to frame/ground),
1. When I connect the generator to the house with the 4 prong twist lock plugs on each end,do i need to ground the generator to a grounding rod with the external grounding lug or will it be grounded through the house wiring that goes to the transfer switch (6 gauge)?
2. When plugging in tools directly (which we never do), any special considerations (e.g. attach grounding lug to ground rod)?
Posted By: electric-ed Re: generator wiring woes - 11/22/02 10:14 PM
Dave,
Answers to your two questions, based on circuit principles. There may be NECode rules that take precedence.

1. As I stated above, because the generator winding center-tap (neutral) is solidly connected to the house service grounded (neutral) conductor in your transfer switch(see Diagram 1 above), it is already grounded, and should not be regrounded.

2. Connecting the frame of the generator to a ground rod will not protect you from shock caused by a fault in a power tool!!
Don't plug outdoor tools and appliances directly into the generator receptacles, after it has been modified by "unbonding" the neutral.


The bottom line is - The grounding/bonding requirements for the safe use of a portable generator are different from those for a generator that is wired to a building wiring system.
I recommend that the receptacles in the generator be disabled if it is wired to your building system using a transfer switch. Plug your outdoor tools into the house receptacles which should be GFCI protected.

If you must use the generator receptacles, the system should be wired as shown in Diagram 2 (above) using a three pole transfer switch, and leaving the neutral-to-frame bonding jumper in place.

Ed

[This message has been edited by electric-ed (edited 11-22-2002).]
Posted By: sparky66wv Re: generator wiring woes - 11/23/02 04:02 AM
Electric-Ed,

If the grounding electrode conductor in diagram two is bonded to both the generator frame (and the generator neutral) as well as the service neutral (at bonding jumper), what is opening the neutral accomplishing?

Would seperate electrodes (and conductors) be better?

(I'm following the blue line representing the EGCs)

It just doesn't seem to be isolating the noodles at all to me...

[Linked Image]

Other than that, I'm glad that I've actually been putting them in right!
Posted By: txsparky Re: generator wiring woes - 11/23/02 04:57 AM
Virgil,
Mine's hooked up like your neighbors(the miner) [Linked Image] [Linked Image]
Posted By: electric-ed Re: generator wiring woes - 11/23/02 01:38 PM
sparky66wv,

1. Separate systems in the same facility are required to be grounded to the same grounding electrode, or, the grounding electrodes are required to be interconnected.

2. The reason that the transfer switch in Diagram 2 is required to switch the neutral is to prevent the neutral being in parallel with the equipment grounding path (green), when the generator neutral is bonded to the frame, which would create the problem shown in Diagram 3 (above).

3. When the transfer switch breaks the neutral, as in Diagram 2, we have, in effect, two separate systems, only one of which is active at any time.

4. Look at each system individually.
a. Load on utility power (Diagram 4 – this post). Unbalanced load current flows from the load neutral bus (X) back to the source it came from (Z).

[Linked Image from electric-ed.com]

b. Load on generator power (Diagram 5 – this post). Unbalanced load current flows from the load neutral bus (X) back to the source it came from (Y).

[Linked Image from electric-ed.com]

Ed


[This message has been edited by electric-ed (edited 11-23-2002).]
Posted By: Ron Re: generator wiring woes - 11/23/02 02:29 PM
For this application we are dealing with Diagram #1. I believe that the generator case should be connected to the GEC per NEC 250.34(A).
Posted By: electric-ed Re: generator wiring woes - 11/23/02 03:00 PM
Ron,
It is quite possible that you are correct if there have been changes in the 2002 NEC.

The following is a quote from an issue of the newsletter called "Electrical Currents" published by the office of the Chief Electrical Inspector, US Dept of Labor.
(I believe it refers to the '99 NEC. The emphasis is mine)

(Quote) "Ground rods at generators-
A premises wiring system whose power is derived from a generator and the generator has no direct electrical connection, including a solidly connected grounded circuit conductor (neutral), to supply conductors originating in another system, must be grounded as specified in Section 250-26. This requires a bonding jumper to connect the equipment grounding conductors to the grounded conductor and a grounding electrode conductor to connect the grounded conductors to a grounding electrode. This is a separately derived system, and a grounding electrode system must be properly established at the generator location.

NEC 250-5 (FPN No. 1) states: "An alternate alternating-current 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." The most common example of this is an on-site generator installed as a backup source of power. This is the type that
would employ a transfer switch to transfer utility and generator power. The transfer switch does not break the connection between the generator neutral and the utility grounded circuit conductor (neutral). The generator is required to have an equipment grounding conductor to ground any exposed noncurrent-carrying metal parts. This
equipment ground must be a type specified in NEC 250-91(b) and run from the normal system ground to the generator frame. It should be noted that a supplementary grounding electrode at the generator location is allowed under NEC 250-91(c). A grounding electrode is not required by the NEC, but could be recommended by the generator manufacturer." (End quote)

Ed
Posted By: dave4242 Re: generator wiring woes - 11/23/02 08:47 PM
I spoke with the Coleman people, and have ordered a new prewired bell-housing which will allow me to simply replace the oulets I have now with a 4 prong Twistlock 220v and a regular 110v. The whole housing simply connects via a snap-on wiring harness.
Then it sounds like we'll be up to code as far as having a separate ground and neutral.
And as far as I understand this thread, i will not need to connect the generator to a separate ground rod when using it through my transfer switch since the neutral is not switched.
Posted By: Ron Re: generator wiring woes - 11/24/02 01:24 PM
I'm not suggesting another grounding electrode, just a grounding electrode conductor and it interconnection with the existing grounding electrode system. Just driving a rod for the gen. would require it also to be connected to the existing grounding electrode system anyway.
BTW, great graphics!
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