New Standby Emerg. Generator for a residence.

[Luis De Castro]

Doing engineering plans for the installation. The generator is a new 60KW generac 120/240v single phase with floating neutral. I understand that is a non-separetely derived system. Is t ground rod required. The automatic transfer switch is a2p- 400a with a 400a circuit breaker main. already installed in the house. The generator breaker will be a 2p-300a. IM a little confused about thye grounding

 

[augie47]

The determination of SDS vs non SDS is based on whether the neutral is switched in the transfer switch.
If your TS is a two pole with solid neutral connections then the system is not and SDS and the generator neutral will be floating and have a EGC from the system to the generator.

 

[tom baker]

And please review generator definitions in Art 700-791-702. For a residence you are designing an optional standby system.

 

[gadfly56]

And please review generator definitions in Art 700-791-702. For a residence you are designing an optional standby system.

Not to mention, 60kw is a heck of a lot of e-power for a residence.

 

[roger]

Not to mention, 60kw is a heck of a lot of e-power for a residence.

Not to mention why does a Generac installer need engineered drawings?

 

[tom baker]

Many are confused about generator grounding and bonding. Mike Holt once was working with generac about ground rods at generators, he gave up on that.

 

[Birken Vogt]

Many are confused about generator grounding and bonding. Mike Holt once was working with generac about ground rods at generators, he gave up on that.

Well they stopped including exterior ground lugs and making mention of ground rods years ago. Thankfully. Ignorant inspectors used to make us install a ground rod.

 

[marmathsen]

Many years ago I drove a ground rod for a generator only to find out months later that I hit the water line feeding to the dock. Serves me right.

Rob G - Seattle

 

[retirede]

Mike Holt once was working with generac about ground rods at generators, he gave up on that.

That is troubling.

 

[Seven-Delta-FortyOne]

Virtually all residential home standby generator are wired with floating neutral and are intended to be installed as a non-SDS. There is not really any good reason to do otherwise.

Ground rods are not required at the genset at least in my area.

I did bid a couple larger diesel commercial units a couple weeks ago, in the 150kW range, and they had ground rods spec’ed on the plans. No idea why, but I’m often left scratching my head over things I seen drawn on plans.

 

[gene6]

I did bid a couple larger diesel commercial units a couple weeks ago, in the 150kW range, and they had ground rods spec’ed on the plans. No idea why, but I’m often left scratching my head over things I seen drawn on plans.

I have seen that in plans also, they spec'ed them in a large underground vault (on 2 corners of the vault), I got to ask the engineer and he said he needed a 'ground reference' at the vault, he also mentioned a 'I triple E' book, it was over my head. They were not tied into the neutrals though.

 

[kwired]

I have seen that in plans also, they spec'ed them in a large underground vault (on 2 corners of the vault), I got to ask the engineer and he said he needed a 'ground reference' at the vault, he also mentioned a 'I triple E' book, it was over my head. They were not tied into the neutrals though.

They shouldn't be tied to the neutral especially if a non SDS. There is no general NEC prohibition of connecting "supplemental electrodes" to any point desired along the EGC conductor throughout a premises. There could be other technical reasons to desire to connect something to an electrode, where some go wrong is they think they need to isolate whatever they are concerned about and connect to an electrode but not to an EGC.

 

[David Castor]

I just came by to emphasize that you should NEVER refer to a standby generator as an EMERGENCY generator. You are just asking for a lot of issues and headaches. The NEC has very different requirements the different types of local generator systems (as defined in the NEC of course.).

 

[JoeStillman]

I've always considered a generator sitting on a pad to be a 250.32 "Structure", requiring a grounding electrode. 250.32(B)(1) requires the equipment grounding conductor to be bonded to the Structure's grounding electrode.

Without the local grounding electrode and bonding to the main building grounding electrode system, a lightning stroke closer to the generator than the house could cause a rise in potential at the generator unequal to the rise in the house, causing a flashover somewhere, probably the ATS.

An inspector once judged that a trash compactor sitting on a concrete pad 100' away from the main building was just such a "Structure" and made us bond to the rebar and drive a rod.

 

[don_resqcapt19]

I've always considered a generator sitting on a pad to be a 250.32 "Structure", requiring a grounding electrode. 250.32(B)(1) requires the equipment grounding conductor to be bonded to the Structure's grounding electrode.

Without the local grounding electrode and bonding to the main building grounding electrode system, a lightning stroke closer to the generator than the house could cause a rise in potential at the generator unequal to the rise in the house, causing a flashover somewhere, probably the ATS.

An inspector once judged that a trash compactor sitting on a concrete pad 100' away from the main building was just such a "Structure" and made us bond to the rebar and drive a rod.

That is one of the reasons the definition of structure was changed a few cycles ago. A generator on a pad is equipment just like an air conditioning unit on a pad is.

Structure.
That which is built or constructed, other than equipment. (CMP-1)

 

[JoeStillman]

That is one of the reasons the definition of structure was changed a few cycles ago. A generator on a pad is equipment just like an air conditioning unit on a pad is.

Good point. But couldn't the pad be considered a Structure, on which the Equipment is mounted?

If I wanted to know how much rebar to put in the pad, I would ask a Structural Engineer, not the Equipment manufacturer.

 

[don_resqcapt19]

Good point. But couldn't the pad be considered a Structure, on which the Equipment is mounted?

If I wanted to know how much rebar to put in the pad, I would ask a Structural Engineer, not the Equipment manufacturer.

Not in my opinion.

 

[gadfly56]

Good point. But couldn't the pad be considered a Structure, on which the Equipment is mounted?

If I wanted to know how much rebar to put in the pad, I would ask a Structural Engineer, not the Equipment manufacturer.

From what I've seen around, those pads are pre-cast and dropped in place. If you're lucky, they put down a couple of inches of 3/4" stone. No one is engineering these pads for generators this small.

 

[Seven-Delta-FortyOne]

From what I've seen around, those pads are pre-cast and dropped in place. If you're lucky, they put down a couple of inches of 3/4" stone. No one is engineering these pads for generators this small.

Well, technically the QuikPad is. County even makes me submit the engineering with it. It’s stamped by an engineer out of Florida. Meets all their hurricane requirements

Still, a slab of concrete or fiberglass little bigger than a stepping stone is not a “structure” in anyone’s book.

 

[gadfly56]

Well, technically the QuikPad is. County even makes me submit the engineering with it. It’s stamped by an engineer out of Florida. Meets all their hurricane requirements

Still, a slab of concrete or fiberglass little bigger than a stepping stone is not a “structure” in anyone’s book.

Well, color me impressed. I just took a look at the PDF's of the drawings. The seal's no good outside Florida, but it might serve to convince an AHJ anyway.

I'm used to seeing more of this:

EZ-EQPAD Universal Equipment Pad – EZ-CRETE

www.ez-crete.com

I didn't bother to sign up to get the spec sheet.