Generator (again)

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augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
Situation: Service rated ATS and the neutral is switched by the ATS Generator, 25 ft from the building, has a built in 1200 amp disconnect. Supply to building is in PVC.
On this job the 2005 Code applies.
The problem is that there is no equipment ground run with the phase condcutors from the generator. The engineer says they are not needed.
I first looked at it as simply a SDS. My first thought is we have to have an equipment ground , but then I considered the follwing:
Since the generator has a main, install a bonding jumper and electrode there and consider the supply to the building as a 250.32 feeder and since there is no metallic connection, bond the neutral at the building
(With that neutral bond the gen would no longer be an SDS and we will run that by the engineer,but I don't see that as a requirement)
Comments, please.
 
auggie -
Just for my own curiosity, Wha is the system?

13.8kv impedance grounded? (that's about a 20MVA gen :roll:)
480Y solidly grounded? (that's maybe and 800kw)
480Y impedance grounded?

208Y?

Are there any line to neutral loads at the generation voltage?

cf
 
So, the install is 350kw, mostly 120V high harmonic loading (computers, servers, lighting), and no metalic conduit - and you verified there is:

1. No ground mat between the gen pad and the building grounding system;

2. Fuel piping system does not have any metalic path to building;

3. No water at the gen with a metalic path back to the building:

You are not asking if this is a good design - you are asking if it is legal (meets code).

From that point of view I think you nailed it. It's under the 2005, so it is, by definition, a good design and perfectly safe.

cf
 
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Cold Fusion said:
So, the install is 350kw, mostly 120V high harmonic loading (computers, servers, lighting), and no metalic conduit - and you verified there is:

1. No ground mat between the gen pad and the building grounding system;

2. Fuel piping system does not have any metalic path to building;

3. No water at the gen with a metalic path back to the building:

You are not asking if this is a good design - you are asking if it is legal (meets code).

From that point of view I think you nailed it. It's under the 2005, so it is, by definition, a good design and perfectly safe.

cf
Click to expand...

Thank you for taking the time to review this with me.

I have two mental stumbling blocks left:
(a) The ATS was purchased with a switched neutral. Once the generator neutral is bonded to at the ATS as is the Utility the generator is no longer a SDS. Not sure if this effects anything
(b) There will obviously be some interconnection between the ATS & the generator for starting, etc. It seems if you ran a EGC with those you would have created a "path" other than your neutral and it seems you would have to have an EGC for those circuits if they are over 50v.
 
aug -
Shame on you for making me think:roll:
augie47 said:
...(a) The ATS was purchased with a switched neutral. Once the generator neutral is bonded to at the ATS as is the Utility the generator is no longer a SDS. Not sure if this effects anything...
Click to expand...
I may not understand the installation :confused:. I'll describe what I think I'm hearing.

The gen is in a separate structure, and has a OCP on the gen. The feed from the gen to the building ATS is 4 wire. The fourth wire is a neutral/ground and is switched by the ATS. This conductor also has a connection to the ATS grounding lug - which gets us the connection to the building grounding electrode system.

The utility feed is also 4 wire to the building disconnect. The N/G conductor is bonded to the grounding electrode system at this first disconnect. The utility feed to the ATS is 5 wire - separate ground and neutral. The neutral is switched, but not the ground.

Before I go any further, tell me if this is true. If it is, I need to think about this a bit to give you a decent answer.

augie47 said:
...(b) There will obviously be some interconnection between the ATS & the generator for starting, etc. It seems if you ran a EGC with those you would have created a "path" other than your neutral and it seems you would have to have an EGC for those circuits if they are over 50v.
Click to expand...
This one seem simpler - which likely means I don't understand:roll:. It okay if you tell me I'm all wet.

But in any case, The ATS is likely open transition, no synchronizing capability and the only control connection from the ATS to the gen is a pair of dry contacts in the
ATS for the gen start signal - which could be 12V or 24V from the gen controls. Unless there is a shore power connection from the utility service, there is no 120V at the gen. So this is likely okay. Even so, there is still the Gen N/G conductor that has to be bonded to the building grounding system at the ATS (If what I said above is true).

Two comments not on topic to follow:
1. You have an interesting one here.

2. Probably no chance to dope slap the engineer and tell him to put in the 5wire feed - bummer:mad:

cf

PS A "dope slap" is not necessarily a bad thing. In my case it is generally applied by my co-workers in a gental manner to get my attention focused of something extremely simple that I keep stepping over. :)-)
 
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Cold Fusion said:
aug -
Shame on you for making me think:roll:
I may not understand the installation :confused:. I'll describe what I think I'm hearing.

The gen is in a separate structure, and has a OCP on the gen.Yes The feed from the gen to the building ATS is 4 wire. The fourth wire is a neutral/ground and is switched by the ATS. YesThis conductor also has a connection to the ATS grounding lug - which gets us the connection to the building grounding electrode system.
Yes.

The utility feed is also 4 wire to the building disconnect. The N/G conductor is bonded to the grounding electrode system at this first disconnect. The utility feed to the ATS is 5 wire - separate ground and neutral. The neutral is switched, but not the ground.
Almost..utility actually is a 4 wire to the Service Rated ATS

Before I go any further, tell me if this is true. If it is, I need to think about this a bit to give you a decent answer.
Question: Once the generator neutral was bonded to the ATS (which is also bonded to the utility neutral) is the generator still a SDS ? (would the two bonded neutrals constitute a soildly connected grounded circut conductor ? (don'k know that anything actaully changes either way)
If the generator is no longer and SDS, but in a seperate building can we still bond the neutral from the main buiolding to the frame ?

This one seem simpler - which likely means I don't understand:roll:. It okay if you tell me I'm all wet.

But in any case, The ATS is likely open transition, no synchronizing capability and the only control connection from the ATS to the gen is a pair of dry contacts in the
ATS for the gen start signal - Probaly true definitely open transition..which could be 12V or 24V from the gen controls. Unless there is a shore power connection from the utility service, there is no 120V at the gen. So this is likely okay. Even so, there is still the Gen N/G conductor that has to be bonded to the building grounding system at the ATS (If what I said above is true). Agree

Two comments not on topic to follow:
1. You have an interesting one here.
Been working with it for two days now
2. Probably no chance to dope slap the engineer and tell him to put in the 5wire feed - bummer:mad:
Lot bigger and younger than me :) wiring installed before I saw it

cf

PS A "dope slap" is not necessarily a bad thing. In my case it is generally applied by my co-workers in a gental manner to get my attention focused of something extremely simple that I keep stepping over. :)-)
Click to expand...

.....................................................
 
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Auggie -

Is this what you have?:confused:

4W ATS, switches the three phases and the N/G conductor. The building main is after the ATS - that's the only way that I could see that the utility could get to the ATS as 4W.

Note that I show the N/G conductor is bonded at the building Main CB, after the ATS.

The picture is kind of sloppy looking. I'll redraw is it is not clear what I have in mind

cf
 
Cold Fusion said:
So:
The transfer switch is two circuit breakers. These two are your utility service disconnect and building generator disconnect?

What (Where) is the N/G bond when the transfer switch is in the "GEN" position?

cf
Click to expand...

Good question... I will have to look closer. In that it is service rated, I assumed (bad) that it was bonded at the utility service termination but I am not positive.
If the generator Neutral is bonded does that create a "solidly connected" tie to the utility neutral (thus making the Generator not a SDS) ?

(p.s. I do apprecite your input and hope you don't charge me by the hour:))
 
RUWired said:
And where is the generator panel feed from and is there an equipment ground with that feeder.
Click to expand...

That part is incomplete and can be handled either way as allowed by 2005 (I am still checking to assure no metallic path).
In either event I think you may have found another "fly in the oinment", the block heater, etc equipment ground will result in a ground path thru the
generator panel whether it be by a bonded neutral or a separate equipment ground.

This would all have been avoided if there had been a grounding conductor installed, but there wasn't so now we have dumb electrical inspector vs educated engineer and, if I am right, I need ammunition for the battle.
 
Gus - I don't ever recall putting in a 4W gen connection. They are always 5W. This one is going to be tough.

Continuing on:
Could be you will also need an NG bond on the output of the transfer switch. See the attachment. That way the gen NG conductor is both switched, and also gets its N/G bond. I had originally thought that the utility N/G bond at the transfer switch would have to come out, but now I think not. There is likely a meter at the utility entrance and there will be an N/G bond there. If so, no use taking the one at the transfer switch out.

RUWired said:
Augie, isn't there a battery charger and block heater circuit to the generator?
Click to expand...

augie47 said:
yes from a panel in the generator house
Click to expand...
oh-oh. I had asked about a shore power connection is post 10.

So there is a panel in the gen house that supplies a battery charger, block heater, probably some lights and convenience recetpacles. And it is fed 5W from a building panel after the transfer switch?

As RUW alluded, I don't know how to keep the grounding conductor for the panel feed from being a parallel path for any generator neutral current.

edit to add: Even if 4W, the N/G conductor will be parallel path for the gen neutral current.

cf
 
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I think the "ut-oh" is going to drive the last nail in the 4 w coffin.
With that connection, we have a second path which will prohibit the
4w "separate building" allowance.
Also I would have some concern about relocating the bonding point to the load side. There would be no bond on the ATS from the generator until the switch closed. Possibly no problem, but seems like a potential one.

cf, just for informations sake..what's you take on the sidenote question.
If both the utility neutral and generator neutral are bonded at the ATS (line side) does that remove the status of the generator as a SDS ?
 
As it stands now, I don't see any way to justify not having the equipment grounds.
It also seems like if we removed all other obstacles, without the EGC, the requirement to bond the neutral is going to cause GF problems.
 
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