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I am wiring my shop (loving spouse insists on calling it a garage, but what can I do?) and have run into a question I can’t find an answer to in my research. (Yes, I could hire an electrician, and I will, but I want an idea if I am getting correct info from him or her later.)
I have a 200 amp main panel and have connected (with my father-in-laws help) it to a 100 amp sub panel.
Leaving the Main Panel via a 50 amp breaker is a #6 – 3 with ground (4 stranded wires in a single cable). The Neutral bar and ground bar in the main panel are joined by a bar.
Incoming to the 100 amp-rated Sub panel are: 2 – #6 hot feeds connected to the hot terminals; 1 – #6 neutral connected to the neutral bar; and 1 – #6 ground connected to the ground bar. The ground bar and neutral bar are NOT connected to each other in this sub panel. The ground bar has a #6 solid copper wire going from bar to an 8ft. grounding rod.
Leaving the sub panel for the run to the shop (garage) are three stranded wires. In the box is a 50 amp breaker. Out of the breaker are 2 – #6 stranded wire lines (hot), and 1 – #8 stranded wire neutral, running underground in metal conduit 12″ below ground (these are single wires, not, cable). The sub-panel is itself grounded to an 8ft. rod.
At the garage (shop – now she’s got me doing it!) there is a 100 amp-rated sub-sub panel. I know its not really necessary, but my father-in-law put it in while I was at work. It has the 2 – #6 host going to the hot terminals, and the neutral going to the neutral bar. There is a ground bar in this box.
In this box are breakers for lights (2- 20 amp breaker runs) outlets (2 – 20 amp breaker runs) and compressor (1- 20 amp 220 run).
Now the question: Is this sub-sub panel wired correctly? Does it have to be wired like the main panel (neutral bar and ground bar joined?) or is it once a sub panel, always a sub panel (be: don’t join the neutral and ground?).
Jeff
Replies
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No bar.
PS, your inside-the-house sub-pannel is now redundant (maybe it always was ?).
*I'm b notan electrician, and would really like it if you'll post what you find out from your electrician, but I think the answer is "No" the "sub-sub" panel isn't wired correctly by current standards.FWIW, I've spoken with several electricians, though, and gotten differing opinions as to how important it is to keep the neutral and ground separate back to main panel.
*Bob: What about the "sub-sub panel isn't wired correctly by current standards"?jprice: The ground and neutral should be connected in the main and not connected in any sub-panels, which sounds like what you have. You only have one main panel. Everything else is a sub panel. -David
*Universal code says separate Neutral and Ground except in the main panel. They recently allowed separate grounding for subpanels, though. I'm fuzzier on whether subsubpanels are allowed, but I would think it was a bad idea on the basis of wire length and extra connections alone.
*David,I i thinkit's the lack of the 4 wire lead from the sub to the "sub-sub" which doesn't meet current standards, but again, I'm not an electrician so I don't know for sure.
*I would normally only run 4 wire to a sub panel...I do not know if a ground rod is OK...it might be. I would need to ask my electrical code genius friend.near the stream,aj
*The ground and neutral in ALL subpanels should be separate, they are to be tied together only at the main panel. The metal conduit between the subpanel and the sub-subpanel should act as the ground connection between these two panels, providing all joints are made correctly. It would have been better to run a ground wire also. You did not state the distance between the sub and sub-sub panels. I assume they are relatively close so that voltage drop is not a problem.
*Bob: I'm with AJ and Norml, the metal conduit provides an approved ground, but it would be better to have run 4 wires. There are different connectors for the metal conduit that create a better connection with the subpanel, I'm forgeting the name just now, but they run about $4-6 instead of $0.79. -David
*jprice, If you look in the Jan.2001 issue of Fine Homebuilding there is an article on common electrical mistakes, with a pretty good illustration on the neutral/ground connection in sub-panels.They are NOT to be connected, if they were they would be in parallel and you would have neutral current flowing back to your main panel on the metal conduit.A ground rod is required for each separate building.The neutral and ground are connected in the service panel only, then isolated no matter how many sub-panels you add.One other thing,do you have water or gas piping to your shop?They have to be bonded to the grounding conducter also.Sounds like your father-in-law did well.
*David;> the metal conduit provides an approved ground....This might be one of those areas subject to local interpretation. Some electricians have told me that metal conduit can function as ani effectiveground, but that it is not technically correct because of the possibility of corrosion developing in the mechanical connections. I don't know how accurate that information is.OTOH, there is a county near me where I very commonly find (in older houses) main panels which are grounded with a copper line running only from the ground bar to a clamp on the conduit leading to the meter, and a ground wire from the meter box to a driven rod. Many of those boxes bear inspection stickers, so I've concluded that it was accepted in that area in the past.
*Bob: Agreed, many things are subject to local interpretation. On one level, it matters what the pros and cons of different approaches are. But if an inspector is involved then his/her interpretation is the one that matters. At least until everything is finalled. -David
*The distance between the sub panel and sub sub panel is 80 feet. The metal conduit was asembled properly and there are tight metal to metal connections between the conduit and both sub panels. As to the lack of 4-wire between the sub and sub-sub panel, I plead guilty. I SHOULD have run a separate ground just to be on the safe side, but I didn't. It may be overkill, but there is NOW an 8ft.ground rod at EACH sub panel, connected to the panels.I did read NH and the wiring article (that's why I'm here). I will have an electrician looking at the set up late this week and I will post the results. It appears the consensus is that there is one and only one main panel, and every panel after that is a sub panel. Further, no sub panel should have the ground and neutral bar connected. [At Home Depot I looked at all the various brands of sub panels (< 125 amps) and not one had a ground bar attached. But, all the 200 amp panels had bars connecting the neutral and ground bus bar attached.]Finally, I want to thank all of you for your assistance. This is the first list I have ever been part of where there was ACTUALLY some helpful advice. THANKS.
*jprice, you need to take the grounds all of the way back to the main panel. NEC section 250-33 to 44. If you are using EMT (thin wall0 under ground, you are going to have trouble down the road. I've pulled a lot of wire out of burried thinwall, and it was usually muddy,wet and cover in rust. Even aluminum thinwall leaks undergound. It may last 20 years, or you could have trouble next week if you nicked a wire on you pull-in. I would use plastic, and pull the ground.Dave
*When you run a feeder to a separate building, technically you do not need or want to run a ground wire, but rather make the panel at the separate bldg. a main panel as well, by driving 2 gnd rods and connecting a bond to the cold water pipe if applicable. at this point you would land all your grounds and neutrals together as a main service. As for your sub - sub panel if they are in the same bldg, a separate ground bar and termination would be required
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I am wiring my shop (loving spouse insists on calling it a garage, but what can I do?) and have run into a question I can't find an answer to in my research. (Yes, I could hire an electrician, and I will, but I want an idea if I am getting correct info from him or her later.)
I have a 200 amp main panel and have connected (with my father-in-laws help) it to a 100 amp sub panel.
Leaving the Main Panel via a 50 amp breaker is a #6 - 3 with ground (4 stranded wires in a single cable). The Neutral bar and ground bar in the main panel are joined by a bar.
Incoming to the 100 amp-rated Sub panel are: 2 - #6 hot feeds connected to the hot terminals; 1 - #6 neutral connected to the neutral bar; and 1 - #6 ground connected to the ground bar. The ground bar and neutral bar are NOT connected to each other in this sub panel. The ground bar has a #6 solid copper wire going from bar to an 8ft. grounding rod.
Leaving the sub panel for the run to the shop (garage) are three stranded wires. In the box is a 50 amp breaker. Out of the breaker are 2 - #6 stranded wire lines (hot), and 1 - #8 stranded wire neutral, running underground in metal conduit 12" below ground (these are single wires, not, cable). The sub-panel is itself grounded to an 8ft. rod.
At the garage (shop - now she's got me doing it!) there is a 100 amp-rated sub-sub panel. I know its not really necessary, but my father-in-law put it in while I was at work. It has the 2 - #6 host going to the hot terminals, and the neutral going to the neutral bar. There is a ground bar in this box.
In this box are breakers for lights (2- 20 amp breaker runs) outlets (2 - 20 amp breaker runs) and compressor (1- 20 amp 220 run).
Now the question: Is this sub-sub panel wired correctly? Does it have to be wired like the main panel (neutral bar and ground bar joined?) or is it once a sub panel, always a sub panel (be: don't join the neutral and ground?).
Jeff