service disconnect for stanby system

[benwieland]

i have a customer that has a 200a 3p service and i am adding a 30kw stanby generator and ats. the meter is on the outside wall and nipples through to the main panel directly on the other side. the ats and generator are going to be directly next to the meter base and the ats is going to nipple through the wall and re-feed the main panel. the gen-set comes with a service disconnect(integral main breaker)---i dont need to set a service disconnect between the meter and the ats -- do i ---the main panel is directly on the other side of the wall.

 

[George Stolz]

Re: service disconnect for stanby system

The ATS would have to be rated as Service Equipment.

 

[coppertreeelectric]

Re: service disconnect for stanby system

Just a question, why are you choosing to install the ATS next to the meter and not the main?

Usually we only install a ATS next to meter if the meter and main are located on a pedestal.

Steve

 

[tx2step]

Re: service disconnect for stanby system

Without looking up and siting specific code references, these are the immediate practical considerations that I see right off:

1. You are planning on the generator assuming the full load of the building -- the entire panel? You have a 200 amp 3-phase 4-wire service, right? Probably 120/208Y, possibly 120/240 Delta? A 30 KW generator has a maximum rated output of what? Maybe 85 Amps at 208Y or about 75 amps at 240 Delta? It probably doesn't have the capacity to carry the entire building load!

You may need to rethink this and figure out how to limit the maximum load that the generator can assume, so that it stays within it's maximum rated output.

2. You don't say what size ATS you are installing. To carry the entire panel, it would have to be rated at least 200 amps.

3. It is not normal to install an ATS ahead of the service entrance main overcurrent protection/disconnect means. A fault in the wire between the ATS and the panel would not have any protection. You also have no means to kill the power to the ATS to service it, except by pulling the meter or killing the transformer.

4. As George pointed out, the ATS would have to be rated and labeled as Service Equipment. Otherwise, you would certainly need to have a rated service disconnect/overcurrent protection device between the meter and the ATS. The service overcurrent device amp rating couldn't exceed the amp rating of the ATS.

5. Is the ATS 3-pole or 4-pole (i.e. solid neutral or switched neutral)? This affects whether it is considered a "separately derived system".

6. Make sure the grounding system is done correctly.

 

[iwire]

Re: service disconnect for stanby system

Originally posted by benwieland:
i dont need to set a service disconnect between the meter and the ats -- do i ---the main panel is directly on the other side of the wall.

It is a code violation to install a transfer switch ahead of the service disconnect.

230.82 Equipment Connected to the Supply Side of Service Disconnect.
Only the following equipment shall be permitted to be connected to the supply side of the service disconnecting means:

(1)Cable limiters or other current-limiting devices.

(2)Meters, meter sockets, or meter disconnect switches nominally rated not in excess of 600 volts, provided all metal housings and service enclosures are grounded.

(3)Instrument transformers (current and voltage), high-impedance shunts, load management devices, and surge arresters.

(4)Taps used only to supply load management devices, circuits for standby power systems, fire pump equipment, and fire and sprinkler alarms, if provided with service equipment and installed in accordance with requirements for service-entrance conductors.

(5)Solar photovoltaic systems, fuel cell systems, or interconnected electric power production sources.

(6)Control circuits for power-operable service disconnecting means, if suitable overcurrent protection and disconnecting means are provided.

(7)Ground-fault protection systems where installed as part of listed equipment, if suitable overcurrent protection and disconnecting means are provided.

Notice transfer switches are not in the list.

This is why a transfer switch used in the manner you want to must be rated as service equipment and that will add significantly to the cost of the switch.

A service rated transfer switch must have an external manual means to disconnect both the utility and generator power from the building.

Also if you did this the service disconnect has now been relocated outside to the ATS and the indoor panel will have to have the neutrals and grounds isolated from each other.

An equipment grounding conductor will need to be run into the 200 amp panel from the ATS.

Any grounding electrode conductors will have to be moved from the 200 amp panel out to the ATS.

As tx2step pointed out the generator capacity vs the service size seems to be a problem also.

Can I make a suggestion?

Forget the original plan, which would require an expensive 200 amp service rated ATS, all the EGC, GEC work and would probably trip the generators main when the ATS switches.

Use a standard 100 amp ATS mounted inside beside the existing panel and feed a 100 amp MLO panel beside that. Run a large raceway between the existing 200 amp panel and the new 100 amp sub panel and move the circuits over to the 100 amp sub panel that the customer needs to run on the generator.

The code allows 'overloading' an optional generator (in a way) however it makes little sense to do so with an ATS.

[ June 17, 2005, 02:49 PM: Message edited by: iwire ]

 

[shelco]

Re: service disconnect for stanby system

Bobs suggestion is exactly the correct way to do this. A seperate panel for critical circuits that is run via the generator upon an outage. The other way may negate the purpose of emerg. back up when the gen. or transfer switch over loads and quits.

 

[tx2step]

Re: service disconnect for stanby system

I agree with Bob and Shelco-

What good would it do to overload the generator such that it trips its circuit breaker -- what have you gained? Now you're without power again.

I'd use a wireway between the 2 panels to move the branch circuits over that need to stay on during a power outage.

Keep the total load (on each phase) that you move over to the new panel (that can operate simultaneously) within the capacity of the generator , so you won't trip its circuit breaker.

You would feed "Normal Power" to the ATS from a new 100/3 circuit breaker that you install into the existing main panel. You should have room for a new 100/3 because you have moved circuits over to the new panel.

This is the standard way that you add a new generator into an existing installation.

 

[coppertreeelectric]

Re: service disconnect for stanby system

Usually we only install a ATS next to meter if the meter and main are located on a pedestal.

This comment I stated was in ref to residential properties. On commercial applications the ATS will only feed emergency and priority ckts. I am only correcting my own statement here.

As everyone has said before, check your load v.s. your output. I would not in any case install the ATS prior to the main panel, but thats just me.

Good luck, Steve

 

[George Stolz]

Re: service disconnect for stanby system

 

[iwire]

Re: service disconnect for stanby system

Cool sketch George but that is not what I had in mind.

I will try to type a one line riser diagram.

Service Point > Service Conductors > meter socket > Service Conductors > 200 amp service panel > 100 amp breaker > 100 amp feeder > ATS > 100 amp main lug subpanel.

Generator > ATS > 100 amp subpanel.

The branch circuits would be handled as you showed.

 

[George Stolz]

Re: service disconnect for stanby system

Okay, so like this:


Now I'll think about how to ground this.

 

[iwire]

Re: service disconnect for stanby system

George you got it now.

Grounding and bonding can be handled one of two ways.

The generator can have it's neutral bonded to it's frame and the grounding electrodes.

In this case the transfer switch must switch the neutral along with the hots.

This is a common way of doing it on commercial jobs that have GFP (Ground Fault Protection) on the main and large feeders.

OR

The generators neutral is left isolated from the grounding and you use a transfer switch with a solid neutral.

This is the easer, cheaper, common way to do it on smaller applications.

Bob

[ June 18, 2005, 12:39 PM: Message edited by: iwire ]

 

[tx2step]

Re: service disconnect for stanby system

Cool sketches George -- what software are you using to do that?

The "solid neutral" method is the most common installation. Also the least expensive. you would run an EGC (equipment grounding conductor) from the panel to the ATS to the Generator, like you would do for a feeder. As Bob said, keep the ground and neutral isolated. It would NOT be considered a "separately derived system". See "Exhibit 250.6" on page 250.21 of the 2005 NEC HANDBOOK if you have one, which shows how it should be installed. You do NOT install a "Grounding Electrode" for the generator.

If you do have a switched neutral in the ATS, then you DO have a separately derived system. See "Exhibit 250.7" on page 250.21 of the NEC 2005 HANDBOOK for a one-line diagram showing how it should be installed. In that case, you do have to bond the generator to the "Grounding Electrodes" and install a "Bonding Jumper" (neutral to ground) for the generator.

[ June 18, 2005, 12:29 PM: Message edited by: tx2step ]

 

[George Stolz]

Re: service disconnect for stanby system

Tex, Appleworks 6, I have an iMac.

Both of you, thanks. That's actually pretty easy to remember, I don't know why it hasn't stuck up to now.

 

[benwieland]

Re: service disconnect for stanby system

thanks to everyone for posting. after i posted i read into my code book a little further and found what i needed. what i didnt mention is that the 30kw and the 200a ats are customer supplied. he had already purchased them through a dealer for another electrical contractor to install and after 2 months of the ec jerking him around he asked me to see what i could do. the final decision is this. install a nema 3r enclosed se rated breaker outside next to the meter, from there run 3/0 to the solid neutral non se rated ats, 1/0 to the gen set that has integral main breaker, and then 3/0 to what was the main breaker panel on the inside. seperate the grounds and neutral inside(just a matter of removing one main bonding jumper) and re-route the grounding electrode to the breker outside. this is actually the easiest way upon more investigation at the site. as far as the gen-set not being large enough, i made the customer well aware of that but he has already purchased it and it is a 3phase model and they had to order it so he cant really upgrade you know.

 

[iwire]

Re: service disconnect for stanby system

Sounds like you got all the bases covered.

If in the future the customer ends up having trouble with the generator not carrying the full load you could come up with some load shedding schemes using the aux contacts of the ATS to drop out some contactors.

Anyway welcome to the forum and good luck.

 

[tx2step]

Re: service disconnect for stanby system

Originally posted by georgestolz:
Tex, Appleworks 6, I have an iMac.

George... Hmmmmm

Well, that won't work on my DELL.

I wonder what fairly inexpensive software that I can use on my DELL (Windows XP) that would be easy to do those kind of drawings on? That would be pretty useful.