# Subpanel installation in outbuilding



## fls (Feb 7, 2008)

I've read many questions here relating to my situation, but still have questions. Since this installation will be permitted and inspected by the county, I'd like not to have any major errors in my plan. Here's the situation: I need to provide a 240V 40 amp circuit to a small greenhouse about 50 feet from my house. The main panel in the house is a 200A Square D. I purchased an outdoor Square D 100A panel to use as a subpanel in the greenhouse. The circuit will be fed from a 40A breaker in the main panel and will be powering a 240 volt portable heater (rated at 23.3 amps, with a 30A socket), a 15A 120V convenience outlet (GFI in the subpanel), and a 15A 120V dedicated circuit (no outlets) powering a couple of small air circulation blowers (2.4A total load). The total distance from the main panel to the subpanel is 85 feet, of which 45 feet will be underground and 40 feet will be through the house crawlspace to the main panel.

The underground section will be 1" schedule 40 PVC buried 18 inches. I plan to run individual #8 THWN wires (black, red, white) and a #10 green insulated ground wire through the conduit. I spoke to the chief inspector for the county (he's NOT an electrician and doesn't do the actual inspections) and he didn't think that I needed a ground rod and to separate the neutral and ground connections at the subpanel. Answers I've read here lead me to believe that might not be correct. 

There are other 240 volt circuits in my house right now, including A/C, and 
those plus many of the 120V circuits are NOT in conduit nor are they run through holes in the floor joists. They're just stapled to the joists, so thought I'd do the same with the new circuit. But, this seems to be at odds with other answers I've read. 

So - what are the problems with what I plan to do? Thanks for any help.


----------



## handyman78 (Dec 29, 2007)

_"There are other 240 volt circuits in my house right now, including A/C, and those plus many of the 120V circuits are NOT in conduit nor are they run through holes in the floor joists. They're just stapled to the joists, so thought I'd do the same with the new circuit. But, this seems to be at odds with other answers I've read."_

So what part are you questioning? You can run the conduit as stated but the individual conductors cannot be run exposed to the main panel without protection of conduit. You can run conduit all the way back to the main (much work!) or alternately, you could terminate the individual wires at a junction box where you convert from the conduit to the appropriate cable to go to the main panel. 

Regarding the ground rod, you would have a ground conductor running from the subpanel back to the main and the main should have the only connections to ground rods so this should be fine. You must keep the neutral and ground seperated in the subpanel.

You might want to locate the electrical inspector to see if the plan is acceptable there.

Electricians on this board may have some other ideas.


----------



## fls (Feb 7, 2008)

I had planned on a junction box in the crawl space to terminate the individual conductors and then run a jacket cable from there to the main panel. Regarding the ground in the subpanel, I guess I'll have to find a ground bar for the subpanel as it didn't come with one. There's a bar for the neutrals, but not for the ground wires. Are the ground bars unique to the particular make/model of subpanel, or can I use any of the ground bars sold at Home Depot for this? I believe that they must be attached to the housing using a threaded screw hole.


----------



## handyman78 (Dec 29, 2007)

I was in Lowes the other day and saw that ground bars are offered by different manufacturers for their own panels so this shouldn't be a problem. Make sure that there is a bond from the subpanel to the ground bar only, not to the neutral bar.


----------



## HouseHelper (Mar 20, 2007)

The greenhouse is a detached structure. If you are installing a subpanel, you are required to also install a grounding electrode (rod). This will attach to the grounding bus.
Use a grounding bus specific for your panel. It should fit in holes already in the panel.


----------



## J. V. (Jun 1, 2007)

The 240 volt circuits in your house (dwelling) are branch circuits. The wires running to the sub panel are feeders. That is why it is a different circumstance.
As handyman said, seperate the grounds and neutrals in the subpanel. Drive one ground rod at the sub panel and bond the rod to the ground terminal strip in the sub. Connect the ground from the source to this terminal strip also. If you have metal water lines at the green house bond to them and land them on the ground terminal. No action needed if the water pipes are plastic.
You must have four wires running to the sub. 2 Hots 1 Neutral and 1 Ground.
Green houses are wet environments. You may need to protect the feeder with a GFCI breaker. For sure you will need GFCI for any recepts in the green house. Also you may need to drive 2 ground rods. Might need a weather resistant panel enclosure? Talk to the inspector about wet locations.


----------



## handyman78 (Dec 29, 2007)

Thanks Househelper and J.V. for the correction and clarification re: ground rods at the subpanel.


----------



## Stubbie (Jan 7, 2007)

I don't think they will flag you but the minimum feeder in your situation must be 60 amps. 

Copied section Art. 225 Outside feeders and branch circuits

Note the below requirements are talking about the number of branch circuits that supply utilization equipment within the structure unless otherwise noted.

The feeder or branch-circuit disconnecting means for a structure must have an ampere rating not less than the calculated load determined per Art. 220 [225.39]. But observe the following:

*One-circuit installation* The disconnecting means must have a rating at least 15A.
*Two-circuit installation* The feeder disconnecting means must be rated at least 30A.
*One-family dwelling* The feeder disconnecting means must be rated at least 100A, 3-wire.
 *For all other installations, the feeder or branch-circuit disconnecting means must be rated at least 60A.*


----------



## borninpa (Jan 15, 2008)

*why not just run for 60A subpanel?*

Since code states that 60A is minimum for sub feeder... why not just run a #6 for 60A. You will pay a little more but will be within code and never have to worry about not having enough power.


----------



## chris75 (Aug 25, 2007)

Stubbie said:


> I don't think they will flag you but the minimum feeder in your situation must be 60 amps.
> 
> Copied section Art. 225 Outside feeders and branch circuits
> 
> ...



Stubbie, those are disconnect ratings not feeder sizes... No where does it state what size feeder to pull only what the minimum disconnect must be...

I can easily pull # 10's out to a shed install a 60 amp disconnect and meet code... the OCP would be installed at the house...


----------



## Stubbie (Jan 7, 2007)

I thought that is what I was trying to say and I quickly read over this (my mistake for the day) and read it to say 40 amp breaker at the main panel feeding an mlo 100 amp sub panel. Feeder in the first sentence was a real bad typo should have been disconnect. I was trying very badly to say a 40 amp breaker for a disconnect also serving as the ocpd for the feeder was not going to be compliant for a 3 branch circuit installation. The six handle rule under my understanding doesn't apply to a detached building like this..... 225.36 requires the disconnecting means to be marked as suitable as service equipment. Most panelboards have instructions that they are suitable as service equipment when less than six handles are installed and the panelboard is not used as a Lighting & Appliance Branch Circuit Panelboard .... often overlooked on feeders to detached structures. A panel containing three branch circuit handles would make the panel not suitable for service equipment, and a main disconnect would be required.
In most shed type installations this will limit the disconnect to one handle and in this case it would need to be 60 amps not 40.

That being said.. good catch and I apologize for really goofing that one up.


----------



## fls (Feb 7, 2008)

HouseHelper said:


> The greenhouse is a detached structure. If you are installing a subpanel, you are required to also install a grounding electrode (rod). This will attach to the grounding bus.
> Use a grounding bus specific for your panel. It should fit in holes already in the panel.


OK - thanks to all for comments on the grounding. I understand and will handle that properly.


----------



## fls (Feb 7, 2008)

Stubbie - I'm afraid I don't follow your point. I just read through the section of the NEC you referenced and that seems to apply to situations where the subject circuit will be outdoors or on the outside of a building. I don't understand how it applies to this situation. According to the inspector I talked to, I don't need any other disconnect than the 40 amp breaker in the main panel that will feed my greenhouse circuit. No one else has brought up the point about the breaker or feeder size for this circuit having to be 60 amps. Seems to me that if that were true in every case, there wouldn't ever be a need for UF cable of #8 size. Maybe I'm just not interpreting the terminology used correctly.


----------



## Silk (Feb 8, 2008)

J. V. said:


> You must have four wires running to the sub. 2 Hots 1 Neutral and 1 Ground.
> quote]
> 
> 
> ...


----------



## goose134 (Nov 4, 2007)

All true, but I'll bet being a greenhouse, there is a water pipe in there somewhere. Even if the water is piped in PVC, he's running conduit, why NOT throw a EGC in? Still though, you are thorough.:yes:


----------



## Silk (Feb 8, 2008)

Just giving him the option. This way he could just buy some triplex and forget about the conduit. Them he could also forget about the separation of the grounds and neutrals. Just like to KISS (Keep It Simple Stupid). Not any attempt at being derogatory towards anyone, I just like the saying and it seems to work for me since I'm no Einstein.


----------



## Stubbie (Jan 7, 2007)

Article 225 provides the installation requirements for outside branch circuits and feeders that run on (or between) structures, buildings or poles. Branch circuits would generally be on a building in most cases coming from a panel in the building or on the outside of the building or there is an exception allowing one branch circuit between buildings. Feeders between buildings whether they originate inside or outside or terminate inside or outside require a disconnect at the detached building at the nearest point of entrance of the feeder conductors to the detached building and readily accessible.

Where you will find controversy is whether or not the 6 handle rule is allowed as the required disconnect at the building. I assume your inspector is allowing it but he is incorrect if he is saying the breaker in your main panel is the disconnect for the shed. He may allow no more than six throws of the hand in the 100 amp sub-panel to be the disconnect but not the ocpd of the feeder back in the main panel, this is not the detached building disconnect. Bottom line is if he says it is ok then he is satisfied and you can move on. You will get all kinds of argument over this this section of code. A main lug only panel in most residential settings is only allowed if it is installed in the same building as your main panel or properly called the service equipment. The disconnects for power to multiple panels in a single building must be grouped together in a single location and in this case this will satisfy code. This is because your main breaker will kill all power to that single building including the sub-panel that is also located in that building.. However for a detached structure being powered from a feeder originating from a separate building where the service equipment is located cannot have its disconnect located in the other building it must be located at the structure being served by the feeder. SEE NEC 225.31 and 225.32

As Chris75 correctly pointed out the 40 amp breaker in the main panel is the ocpd for the feeder but it is not the required disconnect for the shed. You must have a single handle 60 amp disconnect or larger at the shed IMO. However your inspector says otherwise but I believe he is using the *six handle rule* for your sub-panel in the shed not the 40 amp ocpd in the main panel. This is where I disagree with the inspector. However this rule is commonly used and there are thousands of installations like yours is going to be. I'm simply saying that because your shed sub panel is not a power panel and is a lighting and appliance branch circuit panel with 10% of its breakers supplying lights and appliances the six handle rule does not apply and the structure requires a single handle disconnect or a main breaker or back fed breaker in the sub-panel rated 60 amps or more. 
Remember a panelboard is allowable as service equipment (which is the requirement of the disconnecting means from Art. 225.36) if less than 6 throws of the hand (handles) are installed and it is not a lighting and appliance branch circuit panel board. Your sub panel is a lighting and appliance branch circuit panel because it has more than 10% of those six throws using lights and appliances. This makes it not suitable for service equipment under the 6 handle rule so some form of main disconnect that is service rated is required at the shed that has one handle... not six or less.
I have recently come to believe this a commonly misapplied section of code allowing the six handle rule at a detached structure using a sub panel that meets the definition of a L&A&BCP.

EDIT: My explanation for the 6 handle rule is paraphrased in my words from the source that changed my opinion located here.....

http://forums.mikeholt.com/showpost.php?p=649523&postcount=12


----------



## InPhase277 (Feb 9, 2008)

Article 225 is mostly directed at non-residential premises. The 60 A rule is for the size of the disconnect, not the circuit.

You must run four wires, 2 Hot, 1 Neutral, and 1 Ground. You can get away with running only three, but this is NOT a good way of doing it, as some neutral current must return through the earth. USE FOUR WIRES.

Having said that, you are required to install a grounding electrode (i.e. a ground rod) at your out building and connect it to the ground bar in your subpanel, which you can purchase at the same place you bought the panel. If you have metal water piping in your building, you must bond that to the ground in the panel. Same goes for concrete rebar and the metal structure if you have one. And grounds and neutrals must be kept separate.

Also, given the distance, you might consider increasing the size of the conductors to compensate for voltage drop.

InPhase277


----------



## mrdave (Mar 16, 2008)

*similar set up*

I am installing similar out building circuit.

40 amp 2 pole breaker in 200 amp house sub panel with seperated neutral/ground

the main ground bonding jumper is at meterbase/diconnect/elcetrode location at driveway

#2 wire to 100 amp sub in pump house (#2 used for voltage drop)
4 wires to this panel with ground and neutral seperated at pump house subpanel as well

100 amp Sub panel in pump house to have backfed 60 amp main breaker/disconect
2- 2 pole breakers -1 for each pump (well-20amp)&(pressure pump-15 amp)
1- 1 pole breaker - for general lighting/receptacle circuit 20 amp
(demand @ 25 amps total)
Second grounding electrode at pump house.

Does this sound to code


----------



## 220/221 (Oct 9, 2007)

> Sub panel in pump house to have backfed 60 amp main breaker


The main breaker need to be secured via screw to the panel. It will function but not pass close inspection.


----------

