Separately Derived System and Generators

[360Youth]

We received this letter from Generac after their determination that the installation of a ground rod at the standby generator is at best unnecessary and at worst detrimental....

January 17, 2013

To whom it may concern,

UL 2200 14.1.6 requires that a terminal for a grounding electrode conductor must be provided on the outside of all generators even though it may not necessarily be connected because of the type of installation the generator is being installed for. For example, if you are bonding the ground to the neutral at the service, the grounding electrode would be optional as it is a non-separately derived system. In situations where the bond is made at the generator, the grounding electrode terminal would be used and this would be considered a separately derived system. All Generac generators, except the industrial product are non-separately derived systems and would not require a ground rod.

Because UL doesn?t know how the generator will be installed in the field, the standard appears as such and it requires the terminal to be installed at the time of manufacturing in the event it is used as a separately derived system.

Best Regards,



Bob Cramer
Master Electrician/Electrical Inspector
Generac Power Systems, Inc.

We distributed that letter to various municipalities for their information and received this response back from one of the inspectors (names left to protect the "innocent" )...

It is my understanding and also the
Electrical Division of DOI, that where there may be a potential of the neutral being severed on the line side (due to storm, etc.) the system would become separately derived.
thus requiring the terminal on the generator to be connected to the grounding electrode in all cases.

Please run this by Mr. Bob Cramer.

Thanks

Does the loss of utility service (eroded line, downed powerline, etc) constitute a separately derived system or is defined and contained within the service equipment itself? Thanks.

 

[don_resqcapt19]

The loss of the neutral on the line side of the main bonding jumper does not change anything. There is still an connection to the generator neutral and the building grounding electrode system.

 

[360Youth]

The loss of the neutral on the line side of the main bonding jumper does not change anything. There is still an connection to the generator neutral and the building grounding electrode system.

That's what we thought, but I prefer to field opinions more experienced than my own before I react. I see a phone call in my future.

 

[sandsnow]

Assuming a grounded system supplied by the utility. Assuming it is a single phase or wye connected system. The type of transfer switch dictates if the genset is an SDS. If transfer switch has switched neutral, then SDS and bond and ground neutral at genset. If solid neutral transfer switch then leave the neutral insulated at the genset. And what Don said.

 

[ceb58]

It is my understanding and also the
Electrical Division of DOI, that where there may be a potential of the neutral being severed on the line side (due to storm, etc.) the system would become separately derived.
thus requiring the terminal on the generator to be connected to the grounding electrode in all cases.

Please run this by Mr. Bob Cramer.

Thanks

In my job we must install them as a SDS per DOA's requirement, but that is state government work. The understanding above is about the third different explanation I have heard come from DOI. They can't come up with a good explanation but they refuse to back down. But look at it from the installed perspective. From service disconnect the neutral and grounding electrode conductor are bonded. From there to the ATS is 4 wire where the neutral and the Equipment Grounding Conductor are separated and isolated with the EGC bonded to the can. From the generator is the same 4 wire. Neutrals tied together and isolated with the EGC bonded to the gen. frame and ran to and bonded to the can. Very simple I know you know this, but it is to make a point from the above statement. Even if the line side neutral were severed you will still not break the bond between the neutral coming from the gen and the systems Grounding Electrode system. So driving a rod would be at best a supplemental rod. Even in a case of setting up the generator as a SDS because of the EGC you will still never break the bond. And DOI has admitted that that is true but are willing to "overlook it" as to do different would be violations of the code. The only way this would change is if a storm took the service disconnect off of the house along with the GEC, as you and I have seen due to where we live, but in that case you have more to worry about than a generator