Whole house load shedding transfer switch

Status
Not open for further replies.
A

adagys

Member
Location
SW of Chicago
I have a customer who wants to install either a 17kw generac to be located approx. 60 feet from the main panel or a 20kw with a whole house transfer switch. Can anyone tell me what size pipe/wire I would have to install from the generator to the 14 position transfer switch and are there any other wires(control) I would need to bring?

Also, I have never wired in a whole house transfer switch and I really don't understand how this load shedding switch is wired.

thanks

Al
 
adagys said:
I have a customer who wants to install either a 17kw generac to be located approx. 60 feet from the main panel or a 20kw with a whole house transfer switch. Can anyone tell me what size pipe/wire I would have to install from the generator to the 14 position transfer switch and are there any other wires(control) I would need to bring?

Also, I have never wired in a whole house transfer switch and I really don't understand how this load shedding switch is wired.

thanks

Al
Click to expand...

For a load-shedding ATS, IIRC, the loads to be shed are landed on special breakers in the ATS. These breakers are relay controlled. When the emergency generator kicks on, the unshed loads come on immediately. The sheddable loads then come on in a timed sequence. If the controller senses that the generator is bogging down on a particular load when it first comes on then it's immediately dumped. It may automatically retry a few times before finally giving up. You could try starting here for more info.
 
adagys said:
Thanks. Are the circuits controlled by low voltage control wires. I see the A/C is but what about the others?
Click to expand...

Depending on the calculated load and the generator size, the A/C may be the only branch circuit that needs to be shed.
The panel does not by default provide load shedding for all branch circuits.
If more loads (such as resistance heating) needed to be shed, additional modules (e.g. relay breakers) would have to be installed.
There also is probably a limit to the number of branches or groups of branches that the control module can switch independently. (Like as low as 1).
 
The Generac load shed module in their ATS sheds when generator drops to 58hz I believe, then there are 4 load sheds positions available. 1 and 2 has set of dry contacts to break any 24 volt circuit, ( a/c, auxilary heat relays etc.) AND a voltage output set of contacts also. Voltage output on 1-4 is decided by jumpers (field provided) to send 120v or you can ( field provide) a transformer and send out 24 volt to operate contactors that break loads ( water heaters etc.) in remote locations. Need 6 control wire in addition to your 4 generator output wires to operate ATS and load shedding. Ensure T1 is wired and fuse good, these generators have no alternator and rely on built in battery charger (T1) to keep battery charged even when running. Also don' t forget to pull the 3 control fuses in ats if wiring up generator after ats is energized, will send 3- 120v circuits out to gen hot, where your buddy is, (or you will be) connecting other ends
 
Thanks for the info. Does anyone know what size pipe and wire I will have to run if I am installing the generator 60' from the sub/transfer switch. My customer is buying a 17kw with the pre-wired transfer switch and I am not sure what size wires it comes with and would like to get a jump on the install. I know it comes with a 30' whip but that won't nearly be long enough. I am going to have to cut that whip down to about six feet and pipe the rest,
 
adagys said:
I have a customer who wants to install either a 17kw generac to be located approx. 60 feet from the main panel or a 20kw with a whole house transfer switch. Can anyone tell me what size pipe/wire I would have to install from the generator to the 14 position transfer switch and are there any other wires(control) I would need to bring?

Also, I have never wired in a whole house transfer switch and I really don't understand how this load shedding switch is wired.

thanks

Al
Click to expand...

adagys said:
Thanks for the info. Does anyone know what size pipe and wire I will have to run if I am installing the generator 60' from the sub/transfer switch. My customer is buying a 17kw with the pre-wired transfer switch and I am not sure what size wires it comes with and would like to get a jump on the install. I know it comes with a 30' whip but that won't nearly be long enough. I am going to have to cut that whip down to about six feet and pipe the rest,
Click to expand...

If you're installing the prewired ATS with the load center, it does not have the load shedding capabilities. If it's the one I'm thinking of, you are supposed to install a 70A breaker in the main panel to feed/protect the load center in the ATS. Then wirenut the circuits to be protected to the 6' whip that comes with the ATS. The 6' whip contains the branch circuit wires and the power feeder from the main panel to the ATS load center.

The 30' whip just has the control wires and the feed from the generator. I think the power feed from the generator was #4, not sure of the control wires, maybe 14-16AWG.
The 30' whip is just 3/4" flex so you could run 3/4" pvc. But with a 60' run and if there are turns/bends, you might want to run at least a 1".

You need to either have some number labels or use the ends of the supplied wires with the labels for your splices. Or someway to make sure you keep all the control wires labeled/marked the same on both ends so they don't get crossed when connecting to the generator junction block and in the ATS. The genny junction block must be placed close enough to the genny that the cable from the genny will reach.
 
The 20kW is rated at 83.3 amps when fueled by LP and is protected by a 90 amp OCP. As far as the load shedding goes, the most recent itineration of the Generac switch has four 24v dry contacts that can be tied into the HVAC controls or to a separately purchased mag starter for appliance shedding. (i.e., water heater, range, etc, depending on what size module you get.)
 
Thanks for all the info. That is exactly the pre-wired transfer switch I will be installing. Are there (2) #4 wires and a neutral and ground? If so does anyone know the size of all the wires in the whip? We have to put everything in EMT here and I am trying to figure out if I can run all the wires in a 3/4" pipe or 1". There will not be a lot of 90 degree bends. Also, can the control wires be in the same pipe or do I have to run a separate pipe?
 
adagys said:
Thanks for all the info. That is exactly the pre-wired transfer switch I will be installing. Are there (2) #4 wires and a neutral and ground? If so does anyone know the size of all the wires in the whip? We have to put everything in EMT here and I am trying to figure out if I can run all the wires in a 3/4" pipe or 1". There will not be a lot of 90 degree bends. Also, can the control wires be in the same pipe or do I have to run a separate pipe?
Click to expand...

I already stated that the 30' whip is only 3/4" and it contains all the wires to the generator.

But since your run is over 30' you will have to run the control wires in a separate conduit from the power wires. In this case I would think (2) 3/4" conduits would be fine.

I don't know (remember) if the box that comes with the kit that contains the junction block will accept two conduits or not. You might have to install a different outdoor rated box for the junction block if it won't accept two conduits.

If you don't know what I mean by " box with a junction block" I will explain. There is a box that mounts on the house close to the generator, I think within 6'. It is already connected to a whip from the genny. It contains a junction block. The block is for the power wires. You land the (3) power wires, L-L-N from the ATS on the block. Then the power leads from the genny land on the corresponding terminals for each wire. Then there is an EGC block to land the EGCs from each on.
The control wires from the genny & ATS are connected together by the matching connector ends on each.

Since these units usually are sold as a kit, you will have to do some modifying to get things to fit together.

It's supposed to go like this:

ATS is supposed to be mounted beside the main panel. I mis-spoke before when I said "6' whip" because now that I think about it, the whip was only 2'.
The ATS is a surface mount box and that presents a problem if you're mounting beside a flush mount panel.
Anyway, the short whip contains all the branch circuit wires plus the power feed that goes to the 70A (17kw) breaker.

The 30' whip is already attached to the ATS. You find where you need to exit the house and drill a hole for the whip.
On the outside where you just drilled the hole is where the box with the junction block is mounted. You run the connector from the whip into the back of it.

Then the whip from the genny is run to the box/junction block.

This is how it is supposed to be set up. But with your situation, you will have to do it different.
 
The 30' whip has #6 cu conductors for generator output, and 5-#16 control wires. The 17kw generator has a 65 amp main breaker, even though output is 70+ amp (LP) I guess Generac does this to save money, and put smaller wire in the whip.
 
Shanky said:
The 30' whip has #6 cu conductors for generator output, and 5-#16 control wires. The 17kw generator has a 65 amp main breaker, even though output is 70+ amp (LP) I guess Generac does this to save money, and put smaller wire in the whip.
Click to expand...

If I had to guess, they're probably just trying to build in some head room so that you're not tempted to run the generator at the hairy edge of its capacity.
 
Status
Not open for further replies.
Top