I have a wiring question that is probably simple but I just want to make
sure I do this right. I have a subpanel in my shop that was installed by a
professional. He ran #8 AWG from a 60 A breaker in the main panel to
another 60 A cutoff breaker in the subpanel. This was my request as he
stated that it wasn't necesarry and it probably isn't.
Anyway he tied the neutral and the ground together at the ground bar. Is
this correct? When adding 110 circuits would I then do the same, place the
neutral and the ground both in the ground bar? This just seems
counterintuitive somehow. Second but related question: If I do this I will
probably run out of spaces on this bar. Can I add a second bar or should I
just pigtail a a bunch of the grounds together (which seems like a bad
idea) or,...? If I add a second bar how do I secure it in the panel?
Any suggestions , in particular what the correct way to do this so it
meets code, from those with actual knowledge of the code and relevant
material would be greatly appreciated.
On Wed, 25 Feb 2004 10:18:55 -0600, Secret Squirrel wrote:
The neutral (grounded conductor) and ground (grounding conductor) should
be seperate in the sub panel, the ground busbar bonded to the panel and
the neutral busbar isolated from the panel. The only place neutral and
ground should be tied together is in the service entrance. Also, the
length of #8 wire for a 240V run should not exceed 60'. You should invite
him back to bring your subpanel up to code.
On Wed, 25 Feb 2004 10:18:55 -0600, Secret Squirrel <Secret> wrote:
|I have a wiring question that is probably simple but I just want to make
|sure I do this right. I have a subpanel in my shop that was installed by a
|professional. He ran #8 AWG from a 60 A breaker in the main panel to
|another 60 A cutoff breaker in the subpanel. This was my request as he
|stated that it wasn't necesarry and it probably isn't.
|Anyway he tied the neutral and the ground together at the ground bar. Is
If this is a separate building with an added grounding electrode then
it is correct. Otherwise, the grounding conductors and neutral should
be separated in the panelboard. (Ref 250-24 & 384-27 NEC 1981)
He made 2 mistakes. The neutral and ground must be isolated in a sub panel
unless this is a separate building with no other metalic paths. In thet case of
a separate building you also need a ground rod or other electrode.
The other problem is the #8. You need at least #6 copper for 60a.
The feeder should be 4 wires with an insulated white that goes to the isolated
neutral bus and you add the grounding bus. That gets screwed directly to the
enclosure in the holes provided.
The green insulated or bare grounding wire goes to the new ground bus.
I can provide the code references if you need them
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I may be wrong about the wire size. I will verify that, and if necessary
will have the breaker reduced in size. This not a seperate building.. it
is an attached garage so according to what you, and several others have
told me, I should have a seperate neutral and ground bar. I assume then
that I can just purchase an additional bus and install it.. either
isolated for neutral or connected to the box for ground(whichever I dont
already have) and I'll then be correct?
As long as he pulled the 4 wire feeder the ground bus is a minimal cost and
effort. They are in a little baggie next to the panels in the Home store. Just
be sure you get the right one for your panel. They are usually standard across
a brand name. You may have to move a set screw to get access to the right
holes. They are usually all tapped. Get the longest strip that will fit. You
will appreciate the extra holes later.
The two busses you are currently concerned with in your sub-panel (besides
the two incoming hot legs) are a neutral bus bar, and a ground bus bar.
(Often panels/sub-panels don't come with the ground bus bar, and they must
be purchased separately ... sounds like your case)
There is generally a "bonding screw" on the neutral bus bar that must be
screwed down so that it contacts the metal of the sub-panel, which in effect
bonds the neutral and ground busses together.
Since your sub-panel is not in a separate building, the neutral bus bar in
the sub-panel is not normally "bonded" to the metal panel, and thence to
ground, but floats instead.
IOW, in your case, as you have described it, the bonding screw on the
neutral bus bar would NOT normally be screwed down.
You should be able to buy a ground bus for your particular panel at the same
place you got the sub-panel. It should be just a few bucks and is not
difficult to install as long as you do it before you have the panel full.
(Be sure to flip the breaker at both the main panel and your sub-panel
insure that they can't be flipped on without your knowledge.)
Others have covered the technical shortcomings of your panel. You indicated
you used a professional but from the mistakes made, he surely did not have
the work inspected. Its unfortunate that he shorted you one the wiring
feed. The cost to have used the correct #6 wiring would have been nominal.
<Secret> wrote in message
Is the shop a separate building? If it is, and has it's own grounding rod
then it sounds fine.
If the shop does not have it's own grounding rod this is wrong. You need to
buy a separate grounding bar for the sub panel and hook only the ground
wires to it. Leave the neutral wires attached to the original. A sub panel
without a separate grounding rod is like another circuit in a way. The
neutral and ground must remain separated.
In any event, and others may correct me here, isn't a #8 wire a little light
for the application?
On Wed, 25 Feb 2004 15:30:18 -0800, Howard Ruttan wrote:
#8 can be used to a max of 60' for a 240V application with a voltage drop
od 2% with a 60A breaker. #6 would be better and is required for over 60'
or 30' for 120V @ 60A.
Source: Practical Electrical Wiring.
#8 copper is not suitable for a 60a feeder under any circumstances.
Source: National Electrical Code 310-16
If this is a branch circuit serving a pure motor load it might be OK for an
even bigger breaker but not if it is a feeder to a sub panel.
If this is using Romex (Type NMb) you really need #4 for 60a but if it is
THHN/THWN in conduit #6 is OK.
It has to do with the insulation rating of the wire.
"The drop in the feeders then should not exceed 2%, and in branch circuits
no over 3%. A lower drop is desirable. A commonly accepted figure is 2%
from the beginning of the branch-circuit wires to the farthest outlet,
with an additional 1 to 2% in the feeders, depending on their length.
This means that on a 120-volt circuit the voltage drop from the
branch-circuit panelboard (in the service entrance) to the most distant
outlet should not exceed 2.4 volts; on a 240-circuit it should not exceed
The 60' is for type TW wire in free air. If in conduit or cable, shorter
distances/heavier wire/different wire type is required. As always, size
matters - bigger is better.
This is not the test in the National Electric Code. In fact "voltage drop" is
only referenced in a fine print note which does not have any enforcability.
The rule is based on the ampacity defined in 310.15 and the table 310.16 is the
usual guide assuming you don't have engineering supervision. That limits 6 ga
Romex to 55a and 6 ga THHN/THWN to 65a.
8 ga Romex is only 40a and 8 ga THHN/THWN is 50a
That is code
Well then, someone should tell the publishers of "Practical Electrical
Wiring" - Herbert P. Richter & W. Creighton Schwan - based on the NEC, A
McGraw Hill book to correct the information in their book.
I guess they should, since this has been the code and the law in any place that
has adopted it for about a century.
There are lots of sources of bad information out there.
I just looked at their web ad and they gave me this reference
"Chapter 7. Selecting Conductors 98
Choosing a type of wire insulation 99
Understanding wire sizes 101
Understanding ampacity and the NEC ampacity tables 103
Reducing voltage drop 107"
What does it say about "NEC ampacity tables" It should reference 310.16
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