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Discussion Starter · #1 · (Edited)
So i recently sold a job for a 20Kw Generator and the customer was informed that the ATS can only handle 2 AC units at most, He asked me what were his options if he wants to operate 5 Condensing units plus house loads:blink:? As a contractor myself, what options should i Give him to get this job going smoothly and give him his 5 Condensing units working off a Generator. Thanks,
 

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Giorgio.g said:
So i recently sold a job for a 20Kw Generator and the customer was informed that the ATS can only handle 2 AC units at most, He asked me what were his options if he wants to operate 5 AC units plus house loads:blink:? As a contractor myself, what options should i Give him to get this job going smoothly and give him his 5 AC units working off a Generator. Thanks,
. 5 outside condensing units , or 5 window units ? That's a big difference . If it's 5 condensing units and a lot of house loads , I'm questioning the size of the 20 KW ? Have you done a load calc for what they want to have running ? That's step one .
 

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NJ Electrical Contractor
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Discussion Starter · #3 · (Edited)
. 5 outside condensing units , or 5 window units ? That's a big difference . If it's 5 condensing units and a lot of house loads , I'm questioning the size of the 20 KW ? Have you done a load calc for what they want to have running ? That's step one .
Fixed! Condensing units*, Well, here is the thing, I did mentioned to him that the 20Kw unit will handle 2 Condensing units at most plus general house hold loads and he was fine with that, A 20Kw unit will handle just that without a problem, once i sent him the estimate he was happy with it but he gave me that curve ball of having his 5 CU on one Generator, I can simply sell him a 25Kw unit and call it a day.
 

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... I did mentioned to him that the 20Kw unit will handle 2 Condensing units at most plus general house hold loads and he was fine with that....
We did a job where there are 3 outside units, on a 20 kW generator set.

Did a load test, and it handled all 3 of `em just fine. We did put them on the load shedding relays, however.

How large are those outside units?
 

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yes, I wouldn't be in business if i didn't, Just want to gather other peoples thoughts regarding this approach.
being in business has nothing to do with knowing how to properly size a generator. It does not sound like you have a clue so your customer will have an installation that will fail when he needs it. If the customer is telling you what his transfer switch will handle it sounds like you don't know how to install a generator much less size it.
 

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Discussion Starter · #10 ·
being in business has nothing to do with knowing how to properly size a generator. It does not sound like you have a clue so your customer will have an installation that will fail when he needs it. If the customer is telling you what his transfer switch will handle it sounds like you don't know how to install a generator much less size it.
Go back and read what i wrote,I never mentioned that he is telling what a transfer switch will handle, He asked to run 5 units on a 20kw generator, I asked a questioned and not to have someone tell me that an installation is going to fail, I thank you for your information and input if you decide to share it.
 

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Go back and read what i wrote,I never mentioned that he is telling what a transfer switch will handle, He asked to run 5 units on a 20kw generator, I asked a questioned and not to have someone tell me that an installation is going to fail, I thank you for your information and input if you decide to share it.
who informed the customer his ATS will only handle two condensors
 

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So i recently sold a job for a 20Kw Generator and the customer was informed that the ATS can only handle 2 AC units at most, He asked me what were his options if he wants to operate 5 Condensing units plus house loads:blink:? As a contractor myself, what options should i Give him to get this job going smoothly and give him his 5 Condensing units working off a Generator. Thanks,

I really think 5 x condensing units off one 20Kva is pushing it !
Even your own instinks tell you that !
You would have to find some way of controling the start ups,
Starting them one by one with a pause in between might just do it !
But the genny will be working its ring off !

As for the A T S ! well it wont do at all !
Check the amp ratings for the ats and the condensors
and advise the customer to upgrade !
 

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Sounds like the customer thinks the issue is a matter of debate or negotiation. Like Scottie says "I cenna change the laws of physics!
 

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Giorgio.g said:
Single 200A service coming in.
. Sounds like that may even be undersized ? Regardless , if the deal was he only wanted to be able to run 2 units along with most household loads , and he signed a contract for a 20kw unit , he needs to know , that if he expects the whole house to run seamlessly , then a bigger unit is recommended . You can do the load shedding relays , but you're still gonna be pushing that thing past it's capabilities , I think ? This person spins like they want something to run the whole house , period . Size the generator and transfer switch according to that . 20kw is a lot , but not when you start adding in ac condenser inrush current .
 

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5 condensing units rated at about 24a's per....all 5 on a 20kw? I wouldn't.

So you can do low voltage load shedding on two of the units and put another unit on the relay load shedding.

....just syaing, you could. I think you need to properly size the genset though, as you didn't provide nearly enough information.
 

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There's a lot of confusion here...

When selling a generator, you should know exactly what is in the house, every single load. IMO, that is part of the electrician's job to find out. It sounds like you might have priced this one over the phone and then the customer told you more later?

Second, the Generac ATS has built in load shedding for 2 AC units. That does not mean that the generator you attach to the ATS can handle 2 AC units nor does it mean that the ATS or generator is limited to only 2 AC units.

It's up to the electrician to figure out how many units the generator can handle. That's not an easy thing to figure out because AC units require a lot of current to start. One thing I can say for sure is that 5 units is way to many for a 20KW or even a 25KW.

Generac's ATS has the ability to easily add 4 more relays which can be used to switch 120/240V but if you need to you can also use them to switch the low voltage AC units. So you would be able to load shed up to 6 units in total. Chances are the load shedding will be keeping those units off. As long as all the AC units are on the load shed, you will be code compliant because I assume everything else in the house in natural gas and the total load of the house is less than the 20 kw could handle.
 

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5 condensing units rated at about 24a's per....all 5 on a 20kw? I wouldn't.....
Not likely to have that much load.

On the 20 kW installation we did, there was 32 Amps being used when 3 outside units were all running at the same time.

If they are all started up at different times, then it's possible to run 5 of `em at the same time.... depending on the size of each ....
 

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Discussion Starter · #19 ·
There's a lot of confusion here...

When selling a generator, you should know exactly what is in the house, every single load. IMO, that is part of the electrician's job to find out. It sounds like you might have priced this one over the phone and then the customer told you more later?

Second, the Generac ATS has built in load shedding for 2 AC units. That does not mean that the generator you attach to the ATS can handle 2 AC units nor does it mean that the ATS or generator is limited to only 2 AC units.

It's up to the electrician to figure out how many units the generator can handle. That's not an easy thing to figure out because AC units require a lot of current to start. One thing I can say for sure is that 5 units is way to many for a 20KW or even a 25KW.

Generac's ATS has the ability to easily add 4 more relays which can be used to switch 120/240V but if you need to you can also use them to switch the low voltage AC units. So you would be able to load shed up to 6 units in total. Chances are the load shedding will be keeping those units off. As long as all the AC units are on the load shed, you will be code compliant because I assume everything else in the house in natural gas and the total load of the house is less than the 20 kw could handle.
Hack i actually went to meet the customer and take care of the load calc myself, We had agreed that a 20KW will be handling 2 AC units at most and all other loads, He knew he has 5 units and that the 20kw will not be enough to handle all 5 plus general house hold loads. With that said, my price to him was for a 20KW of which now it will have to change to a 25Kw or higher to accomplish what he really intends to do, Customers think that a 20Kw is a "Whole house" generator, It is on certain homes with minimal loads and want to saty under the $15k price range, once you go over 25Kw the unit alone is close to $9k not including the ATS.

Again, I am not asking questions to get bashed or anything like that, Just wanted to hear different opinions but it seems here that some members here instead of helping are quick to jump the gun and make you feel stupid.
 

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Something to keep in mind about heat pumps with resistance backup heat. When they go into the defrost cycle during heat mode, the resistance heat will also be turned on to counteract the cold air from the air conditioning running in the winter (which is what the defrost cycle is). In my case I have 15 or 20kw of resistance heat and IIRC half of it turns on during defrost. Maybe the newer units are different but my resistance heat during defrost can't be disabled unless you go inside of the air handler. Of course you can load shed the resistance heat but the customer should be told about the cold air every so often.
 
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