Keepin it Simple Understand Generators

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brother

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Just reading the 2008 code. Looks like they TRIED to make it simple for the generators when it needs bonding or not. Well the only thing i see someone debating is the 'PERMANENLY INSTALLED GENERATORS' seeing how they didnt DEFINE 'premanently installed'. (I know it sounds simple but i know someone would argue about any definition, ie. 'depends on your definition of sex')

Lets see if i got it now, PLEASE correct me if im wrong, For simplicity we will call the grounded conductor the NEUTRAL. This is for a simple house/dwelling when the power goes out. ;)

Seperately Derived System is basically just a SWITCHED NEUTRAL. So if the transfer switch , switches the neutral when the generator is on then you got to drive ground rods and you bond the FRAME of the generator to the ground rods (via a gec) but you do NOT connect the neutral and grounds together at the generator since in most cases they are bonded together at the panel (service disconnect). Am i correct??

A NONseperately Derived System is when the neutral is NOT switched AT THE TRANSFER SWITCH, so the generator neutral and the UITILITY neutral are bonded together (assuming you pull a neutral from the generator) but the equipment grounding conductor(ground) is attach to the frame of the generator and ran to the Panel and connected to the GROUND bus of the panel(service disconnect). NO GROUND rods are driven for the generator because you are useing the UTILITY grounds (for lightning etc). And that neutral at the UTILITY is used to clear a fault path(trip a breaker)

The size of the Equipment bonding jumper on the SUPPLY side of the generator will be based on table 250.66 So assuming you have little over 5kw generator with a 30 AMP breaker then you need a # 8 copper. Seeing when the generator is on the transfer switch (hot)conductors are the temporary SERVICE ENTRANCE conductors (assuming they are sized accordingly to feed a30 amp).

The size of the LOAD side of the equip. bonding jumper is in accordance with table 250.122. so a 30 amp ocp would need a #10 copper.

So have i got this correct now for the 2008 code?? OR NO. Thanks for the help.Always learning.
 
Pretty close. But what you are missing is the system bonding jumper, for a SD generator, it connects the neutral to the frame of a generator. It provides the path for fault current back to the generator windings. You must have it on a SD generator or someone could die. You must not have it on a non SD generator, other wise you get neutral current on the generator frame.
And for the 2008 NEC the grounded conductor is now a neutral.
 
tom baker said:
Pretty close. But what you are missing is the system bonding jumper, for a SD generator, it connects the neutral to the frame of a generator. It provides the path for fault current back to the generator windings. You must have it on a SD generator or someone could die. You must not have it on a non SD generator, other wise you get neutral current on the generator frame.
And for the 2008 NEC the grounded conductor is now a neutral.
Click to expand...


Ok i got ya. But it was my understanding that since the NEUTRAL and and Grounds were BONDED at the panel(service disconnect) (Remember this is just regular house not commercial) , then you Do NOT bond them at the SD generator. I was told it was like a TRansformer, where you do ONE or the OTHER but NOT both. So The current would always return to the source.

Since as you say it should be Bonded together at the SD generator, and the Panel (service disconnect) is BONDED as well (in most residences) then would you not have a PARRELL path of current on those 2???? I wish i knew how to draw pictures here but I not good at that yet.

Im looking at 2008 code articles 250.35 (A) Separately Derived System and 250.30 (A) (1) System Bonding Jumper

250.35 (A) SDS . where the GENERATOR is installed as a SDS, the requirements in 250.30 SHALL APPLY.

250.30 (A) (1) System Bonding Jumper
An unspliced system bonding jumper in compiance with 250.28(A) thru (D) that is sized based on the derived phase conductors shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor. This conection shall mbe MADE at ANY SINGLE POINT on the separately derived system from the source to the FIRST system DISCONNECTING MEANS or overcurrent device, OR it shall be made at the SOURCE of the separately derived system that has no disconnecting means or overcurrent devices.

Exception No. 2: A system bonding jumper at both the source and the first disconnection means shall be permitted where doing so does NOT establish a PARALLEL path for the grounded conductor. Where a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection thru the EARTH shall NOT be considedred as providing a PARALLEL path.
 
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What you may be missing is that in the separately derived system, the transfer switch has disconnected your generator neutral from the house neutral/ground bond. It sounds like it is possible in some instances to have that bond remain, but I can't picture how to do it without creating the parallel paths they say you can't create.

So you need to have that N-G bond somewhere on the generator side too in an SDS.
 
suemarkp said:
..........It sounds like it is possible in some instances to have that bond remain, but I can't picture how to do it without creating the parallel paths they say you can't create.

So you need to have that N-G bond somewhere on the generator side too in an SDS.
Click to expand...


Well in residential, that is EXACTLY whats happening, the BOND between the neutral buss and ground buss is remaining in the House panel when that transfer switch is thrown. Like i said i wish i could draw a picture to show, but havent figured out how to post that yet on this site. So assuming that Tom Baker is correct in saying a sds generator is to ALSO be bonded at the generator too., then you got a parrell path that is clearly a code violation.

Would love to hear from others, i noticed that its really quiet on my post. ;) LOL
 
But the neutral in the house panel is not connected to the generator neutral or the transfer switch output neutral when the neutral is switched to the generator feed. So yes, the house N-G are bonded, but that does no good for a fault path because you need the generator neutral connected to the grounding wire.

I'm curious on your drawing how the generator neutral is getting connected to the grounding conductor when in generator mode. I don't think it can happen unless you've got a bonding jumper on the generator side of the switch.
 
Brother,

What type of transfer switch are you using? If the T.S. does not open the

neutral, you can't have a SDS.

Your system does not warrant a SDS, so let's just drop that for now.

From your gen. you need to bring the two 'hots' and one neutral and one

equipment grounding conductor ( green). I have the feeling that the T.S. is

part of the Main panel,ie., interlocking circuit breakers , so connect the two

'hots' from gen. to T.S. gen. terminals, run the gen. neutral to the neutral

bus in the Main panel run the EGC from gen. to EG bus in the Main panel,

at the gen. keep the neutral and EGC seperated with the EGC going to the

gen. frame.

Wheather or not this is residential or commercial makes no difference!!

Hope this helps you out.

One more thing, make sure the MBJ is installed in the Main panel.
 
Keepin it Simple Understanding Generators

Keepin it Simple Understanding Generators

benaround said:
Brother,

What type of transfer switch are you using? If the T.S. does not open the

neutral, you can't have a SDS.

Your system does not warrant a SDS, so let's just drop that for now.

From your gen. you need to bring the two 'hots' and one neutral and one

equipment grounding conductor ( green). I have the feeling that the T.S. is

part of the Main panel,ie., interlocking circuit breakers , so connect the two

'hots' from gen. to T.S. gen. terminals, run the gen. neutral to the neutral

bus in the Main panel run the EGC from gen. to EG bus in the Main panel,

at the gen. keep the neutral and EGC seperated with the EGC going to the

gen. frame.

Wheather or not this is residential or commercial makes no difference!!

Hope this helps you out.

One more thing, make sure the MBJ is installed in the Main panel.
Click to expand...

That is a good explanation, when the TS has a solid neutral ( does not open the neutral to the panel )

If the TS does open the neutral to the panel then you have no GES at the generator, so you must provide one and bond the neutral to the casing, just as you would at the service main.
 
benaround said:
Brother,

What type of transfer switch are you using? If the T.S. does not open the

neutral, you can't have a SDS.

Your system does not warrant a SDS, so let's just drop that for now.

From your gen. you need to bring the two 'hots' and one neutral and one

equipment grounding conductor ( green). I have the feeling that the T.S. is

part of the Main panel,ie., interlocking circuit breakers , so connect the two

'hots' from gen. to T.S. gen. terminals, run the gen. neutral to the neutral

bus in the Main panel run the EGC from gen. to EG bus in the Main panel,

at the gen. keep the neutral and EGC seperated with the EGC going to the

gen. frame.

Wheather or not this is residential or commercial makes no difference!!

Hope this helps you out.

One more thing, make sure the MBJ is installed in the Main panel.
Click to expand...


Im not actually installing anything, just doing reasearch to get a better understanding of things. Been reading this 2008 code. Thanks for the info.
 
I explained it this way in a thread the other day and think it helps.

The answer depends on the transfer switch.

If the transfer switch does not switch the neutral you do not bond at the generator as it will be bonded by the bond at the service panel. It is not considered an SDS (Separately Derived System) by the NEC.

If the transfer switch does switch the neutral you do bond at the generator as it will not be bonded by the bond at the service panel. It is considered an SDS (Separately Derived System) by the NEC.
 
brother said:
Well in residential, that is EXACTLY whats happening, the BOND between the neutral buss and ground buss is remaining in the House panel when that transfer switch is thrown. LOL
Click to expand...

The typical residential TS does not transfer the neutral. It would almost be safe to say that none do.
 
tom baker said:
The typical residential TS does not transfer the neutral. It would almost be safe to say that none do.
Click to expand...

We've got some 100, 200, 400, and an 800a transfer switch at the warehouse, waiting to be installed, maybe next week... depending on when we get all the houses re-metered for the City [/FEMA].

None of these transfer the neutral, not even the 800. I'm not sure I'd know the difference between a "commercial" TS and a "residential" one, but these are all pretty hefty boxes. We're putting some on houses and some on businesses.

One goes to the owner of our company- his house was without poco power for 12 days so he bought himself a 13kw 120/240 1o nat gas genset for Christmas. I think he got tired of making gas runs for the generator this time. Maybe our thhn run across the garage floor was the tipping point... (hey, you do what you gotta do sometimes)
 
I know this thread is pretty well dead but I wanted to say that Generac sponsered a webcast on 12/07/07 that covered generator installs pretty thoroughly. They allow you to download a pdf of the presentation they did. Anyway it has great diagrams and NEC articles. If anyone wants the presentation I am happy to email it. It's 41 color pages about 1MB
 
brother said:
Ok i got ya. But it was my understanding that since the NEUTRAL and and Grounds were BONDED at the panel(service disconnect) (Remember this is just regular house not commercial) , then you Do NOT bond them at the SD generator. I was told it was like a TRansformer, where you do ONE or the OTHER but NOT both. So The current would always return to the source.
Click to expand...
brother said:
Since as you say it should be Bonded together at the SD generator, and the Panel (service disconnect) is BONDED as well (in most residences) then would you not have a PARRELL path of current on those 2???? I wish i knew how to draw pictures here but I not good at that yet.
Click to expand...

Using the underlined statements above I think that you are not installing the TS properly. If the TS is between the meter and the main disconnect then all the bonding MUST take place in the TS and the TS MUST be rated as service equipment and the house panel is treated as a sub-panel.
Switching the neutral in this service rated TS will also disconnect the bonding to the grounding electrode system of the house.

If the TS is on the load side of the main and switches the neutral it again disconnects the grounding electrode system from the house.
 
generators grounding

generators grounding

I'm installing a genset,400 amp,4-pole ATS 480 volt 3 phase. Do I drive a ground rod at generator ? Do I pull a green and white wire?
 
jwelectric said:


Using the underlined statements above I think that you are not installing the TS properly. If the TS is between the meter and the main disconnect then all the bonding MUST take place in the TS and the TS MUST be rated as service equipment and the house panel is treated as a sub-panel.
Switching the neutral in this service rated TS will also disconnect the bonding to the grounding electrode system of the house.

If the TS is on the load side of the main and switches the neutral it again disconnects the grounding electrode system from the house.
Click to expand...

This is an old post, I was not installing anything, just trying to get a better understanding. And after good research and the good responses from mike holt guys, I got it. ;)
 
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