Generator install question.

[Saywatt]

Looking to install a 20kw generator at a home that has a 3-wire service to a 200amp MB panel.

The ATS is service rated with a 200amp breaker/dico. that I'm installing between the meter and the panel.

Does the service to the panel then become a feeder? Do I need to replace the 3-wire seu with 4-wire ser and separate the grounds and neutrals?

 

[iwire]

Looking to install a 20kw generator at a home that has a 3-wire service to a 200amp MB panel.

The ATS is service rated with a 200amp breaker/dico. that I'm installing between the meter and the panel.

Does the service to the panel then become a feeder?

Yes

Do I need to replace the 3-wire seu with 4-wire ser and separate the grounds and neutrals?

Yes

The grounding electrode connections will also have to be relocated to the transfer switch.

Is 20 KW large enough to comply with 702.5(B)?

 

[Saywatt]

I didn't sell them the generator.

I guess a load calculation is in order.

 

[LarryFine]

Do I need to replace the 3-wire seu with 4-wire ser and separate the grounds and neutrals?

Yes

The grounding electrode connections will also have to be relocated to the transfer switch.

Additionally, you're supposed to replace any 3-wire major-appliance feeds with 4-wire.

 

[LarryFine]

I guess a load calculation is in order.

And an automatic way of shedding large-enough loads, such as interrupting the 24v HVAC control voltage.

 

[iwire]

Additionally, you're supposed to replace any 3-wire major-appliance feeds with 4-wire.

Good point Mr Fine.

 

[tryinghard]

Looking to install a 20kw generator at a home that has a 3-wire service to a 200amp MB panel.

The ATS is service rated with a 200amp breaker/dico. that I'm installing between the meter and the panel.

Does the service to the panel then become a feeder? Do I need to replace the 3-wire seu with 4-wire ser and separate the grounds and neutrals?

Yes adding the ATS as the service disconnect between the meter and panel causes its load to be feeders, (was service entrance now feeder). And yes you need to separate the grounds and neutrals downstream past the service disconnect to eliminate a neutral parallel path (comply with 250.142(B) and such).

 

[LarryFine]

Good point Mr Fine.

Danke!

I do that sometimes.

 

[tryinghard]

I didn't sell them the generator.

I guess a load calculation is in order.

The inspector may give you grief with proving its size, make sure your customer accepts the responsibility and your pay does not hinge on this issue. Some areas require sound control measures (through ordinances) your customer should qualify this specific type generator before buying it.

I?m an advocate for sizing supplies at least per 220 in your case I recommend following one of three examples of D2 in Annex D (pgs 763-764). The results of this could be submitted with your bill and posted in the ATS. Interesting to see this application at minimum could include 2/0cu service entrance, 2/0cu feeder, #6cu feeder from gen set (200a service disconnect 70a +/- gen ocpd) ? at a glance it?s a weird mix.

 

[Saywatt]

So basically the install will cost more than the generator.

Spoke to the customer today and got some more info:

-1100 sq ft.
-New 2 ton heat pump.
-gas range.
-standard electric water heater.
-electric dryer.
-no garage, well pump or out building.
-two people residing in the house.

The generator is fueled by natural gas and according to what I've read, that brings the generator down to 18kw.

18kw=75 amps.

I'm going to do a load calculation as well as an on sight, real time ,calculation with the amp meter Monday.


It will be close, but I'd bet that house never sees 75 amps other than when the compressor starts.

 

[Saywatt]

And an automatic way of shedding large-enough loads, such as interrupting the 24v HVAC control voltage.

I'm told the ats has load shedding capability which i'm not familiar with.

Do you simply split the t-wire inside the ats?

 

[tom baker]

Generator companies have software to help you size the generator for motor and compressor starting applications,

 

[tryinghard]

So basically the install will cost more than the generator...The generator is fueled by natural gas and according to what I've read, that brings the generator down to 18kw.
18kw=75 amps.
I'm going to do a load calculation as well as an on sight, real time ,calculation with the amp meter Monday.

It will be close, but I'd bet that house never sees 75 amps other than when the compressor starts.

The generators OCPD will be mounted on the unit, and may not be 75A. I think you could use maximum demand from their utility as permitted in 220.87 (1yr data - thought it was 3 months), but I believe the load cal is easier and more accessible.

 

[jxofaltrds]

Additionally, you're supposed to replace any 3-wire major-appliance feeds with 4-wire.

Good point Mr Fine.

Reference?

 

[Saywatt]

Reference?

Bump.

Good grief. Do I need to install arc faults, smokes, and two kitchen counter top circuits too?

And people wonder why permits are shrinking in numbers?

 

[LarryFine]

Reference?

250.140.

It is arguable that an insulated neutral obviates the requirement.

 

[iwire]

Additionally, you're supposed to replace any 3-wire major-appliance feeds with 4-wire.

Good point Mr Fine.

Reference?

The code has not allowed 3 wire feeds to dryers and ranges from sub panels for many years, maybe always.

In this case the OPs design means the old main panel has becomes a sub panel.

 

[iwire]

Bump.

Good grief. Do I need to install arc faults, smokes, and two kitchen counter top circuits too?

And people wonder why permits are shrinking in numbers?

I don't see anything that will require any of that but there is a chance that the existing panel is listed as 'Service Equipment Only' which would mean you would have to replace it.

 

[jxofaltrds]

250.140.

It is arguable that an insulated neutral obviates the requirement.

Yes I would argue that.

The code has not allowed 3 wire feeds to dryers and ranges from sub panels for many years, maybe always.

In this case the OPs design means the old main panel has becomes a sub panel.

We did not start running a 4-wire until 1996 or 1999. But I do not have my books in front of me.

 

[iwire]

Yes I would argue that.

You would fail

We did not start running a 4-wire until 1996 or 1999. But I do not have my books in front of me.

You are thinking of when we were prohibited from running 3 wire at all from any panel

We were never allowed to run 3 wire from sub panels.