# Adding a Sub Panel for Transfer Switch



## wirenut1110 (Apr 26, 2008)

Code requires they be routed together and terminate in the same panel.

Someone else may be able to cite a a code article.


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## hayewe farm (Mar 15, 2009)

Have you actually checked you usage to see if at any time you are actually using more than 100 amps?


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## 300zx (May 24, 2009)

*circuits*



hayewe farm said:


> Have you actually checked you usage to see if at any time you are actually using more than 100 amps?


I was thinking the same thing. 22 circuits can add up quick.


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## ScottR (Oct 6, 2008)

dcopps said:


> I am using a 2-1/2 “conduit from the main to the sub. If I move the neutrals I would have 3-#2, 1-#6(g), 5-#8, and 40-#12.


I could very well be wrong, but isn't that too much fill for 2 1/2"?*

*EDIT: At least without derating all 49 conductors.


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## dcopps (May 16, 2009)

300zx said:


> I was thinking the same thing. 22 circuits can add up quick.


I checked it two ways.

First using the large loads (20amp ac, frig, ect) plus lighting and small appliances based on sf of house. Came to 79amps plus 20% overload = 95 amps.

Second by adding up all the watts assuming everything is on (Lights, coffee pot, hair drye, etc.). It came to 94 amps but i don't see this ever happening.


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## InPhase277 (Feb 9, 2008)

A conduit nipple can be filled to 60% before derating, but I haven't done the math. And yes, the neutrals should be routed with the hots. The grounds can stay.

P.S.: 22 essential circuits? Really? We have different definitions of essential then! The fridge, a couple lighting circuits, the furnace blower, the well pump, and a couple receptacle circuits are essential. But 22?


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## dcopps (May 16, 2009)

ScottR said:


> I could very well be wrong, but isn't that too much fill for 2 1/2"?*
> 
> *EDIT: At least without derating all 49 conductors.


I checked it without the neutrals (28 conductors) and it was plenty but I need to recheck to include the neutrals. The conduit is less than 24” long so do I still need to meet the max fill requirements.  
The main panel is recessed in sheet rock in my garage. I placed an 8x8x8 JB below the panel with a short 2 ½” nipple that resulted in 4” of the JB protruding out of the wall. That allowed me to put in a 2 ½” el to the sub panel. Each one of the conduits is less than 24”. The total length of each conductor from main to sub is 7.5’. I’ll try to take a photo tonight to show this monstrosity.


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## dcopps (May 16, 2009)

InPhase277 said:


> A conduit nipple can be filled to 60% before derating, but I haven't done the math. And yes, the neutrals should be routed with the hots. The grounds can stay.
> 
> P.S.: 22 essential circuits? Really? We have different definitions of essential then! The fridge, a couple lighting circuits, the furnace blower, the well pump, and a couple receptacle circuits are essential. But 22?


We were without power for 13 days during Hurrican Ike. After that long you want a lot of essentials. I attempted to attach the spreadsheet showing the panel. Hope it works.
SUB PANEL 1Small AC (240)20120Microwave (240)3220220410Frig - Kitchen20115Master Bedroom1223Frig - Utility20215Bedroom 2 & 3136Kitchen GFI (1)20115Garage & Ulility Light57Furnace (Large)2015Bath 2, Entry & Front Light168Kitchen GFI (2)20215Family Room & Fan179Disposal/Dishwasher2015Sprinkler1811Garage GFI (Work Bench)20115Kitchen / Breafast Lights1914Master Bath GFI2015Bath Light / Floor Plug & Outside2115Washer / Dryer20215Tv/Porch/Study & Outside2024Vent Hood2015Furnace (Small)22


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## hayewe farm (Mar 15, 2009)

It seems to me that you are going through a lot of extra work. Why not just install a main transfer switch. The chances of you actually using more than 20KW at one time is generally pretty slim. You can then us the breakers in the panel to turn off circuits not in use but still have them available if you need them.


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## dcopps (May 16, 2009)

hayewe farm said:


> It seems to me that you are going through a lot of extra work. Why not just install a main transfer switch. The chances of you actually using more than 20KW at one time is generally pretty slim. You can then us the breakers in the panel to turn off circuits not in use but still have them available if you need them.


This would work but I am trying to do it to code.

If I had a whole house transfer switch (without load shedding) Code would require the generator to be sized for the whole house and that includes two A/Cs, pool pump, oven, electric dryer, ect. I want this system to work automatic even when no one is home.


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## dcopps (May 16, 2009)

OK, here are the the photos of the project. As you can see I have already moved the a/c and microwave circuit. The main is going to take some clean up. I haven't ordered the TS yet. Let me know if I am on the right track.


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## 300zx (May 24, 2009)

Looks good, Is that a pvc j-box or metal ? I would put a ground lug in if metal :thumbsup:


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## dcopps (May 16, 2009)

300zx said:


> Looks good, Is that a pvc j-box or metal ? I would put a ground lug in if metal :thumbsup:


It's metal. But the nipple to the main is also metalic so i figured it would do for the ground. It would be simple to add a ground for the JB (if the 2 1/2" nipple is not already full)


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## InPhase277 (Feb 9, 2008)

I might have done things a little different, but overall, it seems compliant. The metal box doesn't need to be bonded by a wire unless there is a splice in it, but as it is painted metal, the nipple may not be making a good connection. It would be easy to add an open lug in there and land the largest ground on it.

Also, you will save yourself a headache later if you square those wires up in both panels. Right now they are banjo'd as the crow flies. A neat panel is safer and easier to work in. Zip ties are your friend.


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## dcopps (May 16, 2009)

InPhase277 said:


> I might have done things a little different, but overall, it seems compliant. The metal box doesn't need to be bonded by a wire unless there is a splice in it, but as it is painted metal, the nipple may not be making a good connection. It would be easy to add an open lug in there and land the largest ground on it.
> 
> Also, you will save yourself a headache later if you square those wires up in both panels. Right now they are banjo'd as the crow flies. A neat panel is safer and easier to work in. Zip ties are your friend.


I agree it needs a cleanup. My biggest worry is how to trace which neutral to move over to the sub panel. With all the clutter it will be difficult. Any suggestions?


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## InPhase277 (Feb 9, 2008)

dcopps said:


> I agree it needs a cleanup. My biggest worry is how to trace which neutral to move over to the sub panel. With all the clutter it will be difficult. Any suggestions?


Man, honestly, since you are doing all that work any way, just disconnect _everything_ and go from there. Pull all the wires off the ground and neutral bars, label or mark the wires on the breakers, and start fresh. Find the neutrals you need and get them out of the way, then re-terminate everything nice and neat. Then make your taps and tie everything up. You will be much more satisfied when you're done.


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## dcopps (May 16, 2009)

Well, I finished the sub panel over the weekend. Took a lot longer than I thought. The main panel is cluttered more than I would like but what can you say with 45 wire nuts. I attached a finshed. Next project will be the transfer switch. Thanks for the help.


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## masterklu (Aug 17, 2009)

I have just aquired a Kohler 12res generator and a Asco 165 100amp ATS . I also have a 200 amp service., I am not a electrician but have some elec. understanding, but would like more. My intent is to do the same install as yours, with the help of a elctrician friend. Have you installed the ATS yet ? I would like to hear and see the install, follow up with some pictures if possible. I would like to do the wiring and set up myself if possible with help of course. Your post is much appreciated. Thanks


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## dcopps (May 16, 2009)

I just finished the intall yesterday. Everything works great. I also installed a watt meter below the TS. You can see the current transformers in the photo of the TS.


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## wirenut1110 (Apr 26, 2008)

Looks good:thumbsup: I just have 2 things. Where is the power (120V) to the battery charger coming from? It looks like the gas line doesn't have a drip leg on it (IFGC 408.4, IRC G 2419.4)


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## dcopps (May 16, 2009)

The supply for the battery charger is from a 15amp breaker in the sub panel. The install gave two choises. 1) using taps from the ATS with a 5 amp fuse 2) using 15 amp breaker from panel that is hot when generator is active. My ATS did not have the taps so I picked option 2.

It seems drip legs are not used in this area. Houstons NG must be dry?


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## spark plug (May 5, 2009)

*Issue of capacity Vs. (actual) usage!*



300zx said:


> I was thinking the same thing. 22 circuits can add up quick.


He just wants to have the capacity, not necessarily the actual usage on the ATS! (Now more than ever) :yes::no::drinkon't Drink and Drive!!!


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## wirenut1110 (Apr 26, 2008)

dcopps said:


> My ATS did not have the taps so I picked option 2.
> 
> It seems drip legs are not used in this area. Houstons NG must be dry?


Good deal, just wanted to check to make sure it was being served by generator power too. As far as the drip leg, I'm not sure, I just wanted to point it out.


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## dcopps (May 16, 2009)

Another issue is grounding the gen set. Currently I have it grounded with an EG back to the main panel. The gen set does have a ground lug on the outside cabinet but I did not use it. It seems the best way to protect the gen set is through the EG vs a ground rod (some say the controls of the gen set can be damaged easy with the direct connection to the ground rod). BTW, the main panel ground rod is located just a few feet from gen set so it would be very easy to connect but would be a circular connection. Would that cause any ground falts to go throuth the gen set and cause damage to the controls?

I hope this make sense.

My vote is to use the EG and no ground rod


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## Stubbie (Jan 7, 2007)

dcopps said:


> Another issue is grounding the gen set. Currently I have it grounded with an EG back to the main panel. The gen set does have a ground lug on the outside cabinet but I did not use it. It seems the best way to protect the gen set is through the EG vs a ground rod (some say the controls of the gen set can be damaged easy with the direct connection to the ground rod). BTW, the main panel ground rod is located just a few feet from gen set so it would be very easy to connect but would be a circular connection. Would that cause any ground faults to go through the gen set and cause damage to the controls?
> 
> I hope this make sense.
> 
> My vote is to use the EG and no ground rod


The key to determining if your generator needs to have a driven ground rod is at the transfer switch. If the neutral is not switched (as yours ) then the generator is not considered a separately derived system. In which case you are not required by code to drive a ground rod as it has a solid connection thru the transfer switch to the neutral of the dwellings electrical system and therefore would be effectively grounded to the the service equipment for the dwelling and the grounding electrode system of the dwelling. 

There should be no neutral to case/ground bonding in your sustem or objectionable current will flow on the eg. This neutral to case bonding will occur only in the service equipment of the dwelling.

However if you just want to have the ground rod NEC 250.54 allows it as an auxiliary ground rod for equipment/generator. Remembering that the ground rod is in no way intended to be used to clear ground faults and has no effect on touch potentials or stray voltage. It's intention is strickly to provide an earth path for high voltage events like lightning to protect the generator. A ground should never be driven as the sole path for fault current. If fault current cannot find its way to the source over a very low impedance path to the generator or utility transformer... then circuits breakers cannot clear/trip and open the circuit.

Also the generator could have had instructions to bond the neutral and ground at the generator if the transfer switch was 3 pole switching the neutral and to drive a ground rod. As yours is with neutral not switched the neutral and ground should be separate at the generator to prevent a parallel path for neutral current. 

My vote is to save yourself the labor it would serve no point to drive a ground rod with an unswitched neutral type transfer switch.


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## wirenut1110 (Apr 26, 2008)

The case of the generator needs to be grounded. If you take a look on page 5 section 6 of your install manual, it shows this.
Installation manual


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## Stubbie (Jan 7, 2007)

I don't think the generator needs to be grounded but you could install a ground rod and be in compliance with code. However the instructions do say install a ground rod as specified by local codes. I fail to see the point for local code to specify a ground rod for the system if it isn't separately derived. 

This is an ongoing issue of controversy across the industry. Ground rods are to protect equipment/property from damage. He already has that without the ground rod at the generator. But I will agree that if local code says drive a rod then you must install it if you cannot get them to agree with you on what is required by code.

I'm glad you brought up the manual. That helps in clearing up what the manufacturer wants and is a good thing to consider to protect your warranty. Cause if local code wants one you better drive it and get some sleep that your warranty will be honored.

I still say it serves no substantial protection in this case.


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