Stand by gen and ATS questions and confirmations

[mark32]

I will soon install my first service rated ATS and need some opinions/ideas/help.

1) I will size the ATS's feeder according to the gen's on board breaker (100a) as opposed to the gen's output (72a). Even though this gen will "supply" the entire house (House has 200a service), it's very likely it will shed some loads so I cannot use 310.15 to size these conductors. In addition, this gen has an oil heater so I need to supply 120v's to it, using the same raceway (Over 24"), so I now have to derate. I'm looking at #2 cu and #6 egc here. Correct on sizing to the breaker size here?

2) I've never had to shed loads before so I'm kind of in the dark. I haven't seen the ATS's install manual or the ATS yet, are these shedding relays typically supplied from the manufacturer? (This is a Cummins Onan gen set by the way) Please correct me if my understanding is wrong. If these relays are in the ATS I bring in the loads to be shed from the MDP. Not sure how many I'd need to do, but it could get crowded in there if more than a few are done in this manner I'd gather. Perhaps, considering A/C's, just bring in the t-stat cable(s) and break it there? Is there a priority to these loads and how long does it take before they are re-energized? I just got off the phone with the customer, said the salesman told him he'd be able to run both of his A/C's, which the customer expects without fail to operate, so A/C's are a priority. I'm going to stop by the job tomorrow and see what large loads he has and get a better look at the ATS.

3) I will need to move the GEC's to the ATS, can I extend the GEC that goes to the waterline by connecting the new GEC to the existing GEC in the MDP by terminating it to the ground bar or will I have to re-pull an entirely new line?

I'll get a pic of the existing service tomorrow, more questions to come.

 

[templdl]

Have you given some thought about adding a panel that would be limited to the dedicated loads that you intent to supply with the generator? I think the goal should be to make the installation as simple as possible.
In doing this you would install the ATS just ahead to this 100a(?) panel for all of the important loads instead of attempting to use a bunch of load shedding relays making the system complex.
I would go back to as simple of an installation as you can and then justify the importance and cost to accommodate some of these other features.

 

[mark32]

That's a cool idea, I like it templdl, but the salesman got to this customer before I did and this packaged was sold with the idea he would be able to run the entire house, except for loads like the pool, etc, during an outage.

 

[weressl]

Have you given some thought about adding a panel that would be limited to the dedicated loads that you intent to supply with the generator? I think the goal should be to make the installation as simple as possible.
In doing this you would install the ATS just ahead to this 100a(?) panel for all of the important loads instead of attempting to use a bunch of load shedding relays making the system complex.
I would go back to as simple of an installation as you can and then justify the importance and cost to accommodate some of these other features.

So explain to the Customer that a more complex system, with load shedding relays and contactors would be less reliable and would tend to fail when it is needed. Explain that you would be more than glad to come out for a service call during outages, but is that he really wants?!

 

[templdl]

So explain to the Customer that a more complex system, with load shedding relays and contactors would be less reliable and would tend to fail when it is needed. Explain that you would be more than glad to come out for a service call during outages, but is that he really wants?!

Give the reasonable explanation a shot. I you run into resistance back off, keep your mouth shut and install it like the home owner was sold on. Don't try to fight it.
Where the heck does this guy live where he would anticipate a power outage frequently enough and of an extended length of time to warrant such a complex setup?

 

[mark32]

I just got back from the customers house, he's got a 40 circuit panel and a 24 circuit panel, both full, gas appliances though. Two A/C's, one RLA 18a, the other 16.5a. The only other large loads would be two floor heating systems and a pool, which the owner has no problem turning off. So, do you think this gen with an output of 72 amps would have a problem starting these two at the same time? What are the chances they both start at the very same time? I'm going to call the salesman and ask him a few questions. Also, here is a pic of the service. The ATS has a height of 23", there is 36" from the bottom of the window to grade level, notice the basement window directly below where I'd like to put the ATS. The ATS has KO's only in the bottom, wondering if there would be an issue if I punch my own holes in the side? If I can't do that, any ideas on how you'd run from the meter to the ATS and from the ATS to the existing entrance hole for the service cable/raceway?

 

[mark32]

Doh, I could just mount the ATS inside near the panel, however, I'd have about 5'-7' of service cable coming down the basement wall, probably have to install a disc outside.

 

[qcroanoke]

Two A/C's, one RLA 18a, the other 16.5a. two floor heating systems and a pool, So, do you think this gen with an output of 72 amps would have a problem starting these two at the same time? What are the chances they both start at the very same time?

Yes! The Locked rotor amps will be much higher than RLA.
I once killed a 30 KW Onan genset when I dropped 2- 4 ton ach units on it at the same time.
You can lock one or both of them out by simply opening the R lead of the control xfmr when the genset is running. Or install adjustable time delays in each unit that prevents them from starting at the same time.

 

[electricguy61]

Perhaps you already know this, but the load shedding of AC's can be accomplished by simply breaking the low voltage wires that feed the compressor. In most Automatic Transfer Switches (ATS), the loading shedding is 1 or more relay's that change state when the genet starts up. I had a home with a 400amp service, but with load shedding was able to use a 20KW Onan genset.

 

[mark32]

Thanks guys for the replies. I like the idea of installing an adj time delay (On make) in the condensing units. Something like this yes? http://www.zorotools.com/g/00055088

 

[qcroanoke]

Thanks guys for the replies. I like the idea of installing an adj time delay (On make) in the condensing units. Something like this yes? http://www.zorotools.com/g/00055088

Yes, we order them in all of our wallmount units for that very reason. Set 1 timer on 1 minute and the other on 2 minutes.
I would still look at locking out 1 of the units unless the owner insists on having it available.

 

[mark32]

Thanks qcroanoke, are you saying there maybe an issue starting one unit while the other is running? How would I lock the one out? This guy dropped a lot of dough on this setup, telling him he'll only have one A/C won't go too well but I will if need be.

 

[qcroanoke]

Thanks qcroanoke, are you saying there maybe an issue starting one unit while the other is running? How would I lock the one out? This guy dropped a lot of dough on this setup, telling him he'll only have one A/C won't go too well but I will if need be.

Maybe not, it may run both units ok, but very little else while they are both running.If you lock one out you just need to break the R lead between the unit and the t'stat. open it only when the generator is running.

 

[nollij]

Thanks qcroanoke, are you saying there maybe an issue starting one unit while the other is running? How would I lock the one out? This guy dropped a lot of dough on this setup, telling him he'll only have one A/C won't go too well but I will if need be.

The GenSet manufacturer should be able to provide a load step simulation depending on the GenSet that is being supplied and the loads that you specify.

 

[mark32]

Well most of this is ironed out, now I'm just looking for a couple of opinions on the placement of the ATS.

1) If I mount it outside underneath the window and use SE and SER it wouldn't be too bad, but visually, eh.

2) Extend the SE to inside (See pic) and mount a 200a disc just to the right of that alarm enclosure, flex out of that to the ATS (w/main) mounted just to the right of the MDP and flex out of that to the MDP.

3) Instead of using the disc, mount the ATS in the same spot and make my own holes in the top. SE comes in the top and flex out the top to the MDP.

You read posts here where a guy shows what he did and you hear the comments, "Well you should have done this or that". I'd like to avoid those comments if at all possible, probably not though