another grounding question...sorry!

houser

Hi All,
The set-up: I have installed a 125A main lug panel in my detached garage with a 35 foot run (underground) of 6/3 in conduit and a 100A breaker in the main panel (that's enough for my needs). I called a buddy of mine (elec. contractor) and asked him if I should ground rod the new panel, and he (very busy) told me "Naaahh, don't worry about it! Bye!!"

I have tried to learn more about the subject, and read most of the threads I can find on the garage sub-panel ground rod vs. no ground rod issue.

So, without trying to troll up more contention here , I would like to pose this question again. I don't have evidence for my stance on this (other than the posts here and my buddies advice). I have seen comments (and websites) that say you MUST ground!! But here is how I am trying to understand the situation:

If this new panel were installed 3 feet from the main panel in my basement, most would agree that, if wired correctly, it would'nt need its own ground rod, right? So what is it about a 35 foot run, into a detached building, that warrants a rod?

And it is NOT about the materials cost or time to install...both are obviously inconsequential... I'm just trying to understand what the controlling factors are here...

thanks for listening!

HouseHelper

Any detached building that has more than one circuit run to it must have its own grounding electrode. That electrode must be connected to the grounding bus in the panel. If you ran a separate neutral and ground, then the neutral bar must be isolated and the grounding bar must be bonded to the panel enclosure. That is the code.

Andy in ATL

Anyone want to comment on the wire size versus breaker size? Was that #6AWG copper?

Edit to add: I know that it wasn't your original question but there is a light hearted debate on a pro's forum talking about "unsafe and against code" or "not necessarily unsafe but still against code." Assuming you were protecting #6 copper with a 100A breaker that would fall into the "unsafe and against code" category.

P.S. I liked the way you worded your post--got me tickled.

houser

Househelper,
Killer answer! Short, sweet, and full of info. Thanks! So its the fact that it is in its own environment (detached) that sets all of the other code in motion.


Andy,
I got the #6/3 AGW + 100A combo from the aforementioned buddy (yeah, thats right, the electrical contractor). At least I didn't just dream it up...

First, I'm not going to run new wire unless absolutely necessary.
But if you are saying I should back off on the available amps to this panel, then what is a safe and "in code" breaker for this set-up? Then I'll know what I can do wiring-wise in the garage itself (nothings done yet)

Thanks for the heads up

And if someone wanted to actually do their homework and look this type of information up before they went and spent money and time on a project, they would looookkk .... where? Something online perhaps?

thanks again to all... great forum!
houser

HouseHelper

Good catch Andy. I got so focused on the grounding issue, I missed the breaker size.

Houser: If you have 6/3 NM on a 100A breaker, you have two problems:
1. NM is not rated for wet locations and therefore should not be used in underground conduit.
2. The 100A breaker is too large for the #6 wire. You should be using a 60A breaker or, if you really need 100A, be using #2 copper wires.
EDIT:
3. You need a main breaker on the subpanel in a detached garage if the panel allows more than 6 breakers.

chris75

6-3 NM is only good for 55 amps....

HouseHelper

But since there are no 55A breakers available, you can "upsize" to a 60A.

chris75

If you meet the requirements, yes... which in most cases is a given.

J. V.

Wheres the main in the sub panel? You did say lug panel?
I assume you have several breakers and the sub panel is "out of sight" of the main panel?

Andy in ATL

In my opinion--and my opinion only the nm (romex) pulled into the PVC kind of falls into the category of "I'm gonna tell you to rip it out ond pull in THWN #2AWG copper for 100A or THWN #6AWG for 60A" Are you going to do it? I doubt it and I'm sure that your electrian buddy will tell you you will be alright. Is it unsafe and against code or just against code? ( the nm in the pipe) Lets see what others say. If you PM me I'll tell ya what I think.

Stubbie

Speaking strictly about the 6/3 cable in conduit. We would first have to know if it is indeed NM type cable. If it is then it needs to come out of that conduit. It cannot be ran underground in conduit or anything... it is not rated for wet location.
Now anywhere else in conduit it takes a while to explain or you could debate it for a long time until the NEC decides to make it more clear. My personal way of looking at it is if the area where the nm (romex) is installed in conduit (outside of a wet location) is not considered to be an area where physical protection would be required...it would not be code compliant.

The rest of the debate..ie..conduit fill for one cable as calculated by note 3 chapter 9 and other stuff is irrelevant in this situation if the cable used is nm cable. It cannot be in that conduit. The conduit will eventually over time flood with water. Plus the op doesn't state what type conduit he put underground probably pvc but we don't know that.


Stubbie

Andy in ATL

I agree

frenchelectrican

you have to understand this part the 6/3 conductor if you say NM [ Romax ] type you can not run this in the conduct pipe at all if this is a UF wire that no issuse with that without conduct but if you allready put in or plan to put in conduct in there you have to run the THHN/THWN [ typcally it will be dual rated so just make sure it have both of it on the wire itself ]

the other thing is you can not use 100 amp breaker with #6's at all.
the wire is too small for this size of breaker

typically useally 60 amp breaker will do this. i say useally there are some areas we have to use 50 amp breaker [ they dont make 55 amp breaker anyway ]

the other thing is grounding system IMO it will be wise to run full 4 wire to subfeed box [ black, red , white , green or bare copper wire ]
the other thing is when you hook up the subfeed box make sure you dont tie the netural with ground keep them sepearted if that box have a jumper band or green screw on netural bussbar please do remove it,

unforetally with most i say most subfeed box dont useally have grounding bar with it so you have to buy in kit they are few bucks and pretty easy to put it on.

i think this will cover it pretty well

Merci , Marc

oh by the way if in subfeed if have more than 6 breaker " handles " there you have to installed backfeed breaker with proper sized breaker. [ this is in the NEC code ]