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.
Thanks
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
<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. ... <snip>
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?
--
Cheers,
Howard
----------------------------------------------------------
Working wood in New Jersey - [email protected]
Visit me in the woodshop - www.inthewoodshop.org
Below is correct. Call the electrician back.
"Greg" <[email protected]> wrote in message
news:[email protected]...
> 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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On Wed, 25 Feb 2004 15:30:18 -0800, Howard Ruttan wrote:
> In any event, and others may correct me here, isn't a #8 wire a little light
> for the application?
#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.
--
-Doug
>#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.
On Thu, 26 Feb 2004 01:07:24 +0000, Greg 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
4.8 volts."
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.
--
-Doug
>"The drop in the feeders then should not exceed 2%, and in branch circuits
>no over 3%. A lower drop is desirable
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
On Thu, 26 Feb 2004 03:42:44 +0000, Greg wrote:
>>"The drop in the feeders then should not exceed 2%, and in branch circuits
>>no over 3%. A lower drop is desirable
>
> 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.
--
-Doug
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.
>Well then, someone should tell the publishers of "Practical Electrical
>Wiring"
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
This is 310-16
Paste this to an 80 column wide screen
Table 310-16. Allowable Ampacities of Insulated Conductors Rated 0 through
2000 Volts, 60ø to 90øC (140ø to 194øF) Not More Than Three Current-Carrying
Conductors in Raceway or Cable or Earth (Directly Buried), Based on Ambient
Temperature of 30øC (86øF)
Size Temperature Rating of Conductor. See Table 310-13 Size
_________________________________________________________________________
60øC 75øC 90øC 60øC 75øC 90øC
(140øF) (167øF) (194øF) (140øF) (167øF) (194øF)
_________________________________________________________
TYPES TYPES TYPES TYPES TYPES TYPES
TW*, FEPW*, TBS,SA, TW*, RH*,RHW*, TBS,
UF* RH*,RHW*, SIS,FEP*, UF* THHW*, SA, SIS,
THHW*, FEPB*,MI, THWN*, THHN*,
THW*, RHH*, XHHW*, THHW*,
THWN*, RHW-2, USE* THW-2,
AWG XHHW*, THHN*, THWN-2, AWG
kcmil USE*,ZW* THHW*, RHH*, kcmil
THW-2, RHW-2,
THWN-2, USE-2,
USE-2,XHH, XHH,
XHHW*, XHHW,
XHHW-2, XHHW-2,
ZW-2 ZW-2
_____________________________________________________
ALUMINUM OR COPPER-CLAD
COPPER ALUMINUM
_________________________________________________________________________
18 .... .... 14 .... .... .... ....
16 .... .... 18 .... .... .... ....
14 20* 20* 25* .... .... .... ....
12 25* 25* 30* 20* 20* 25* 12
10 30 35* 40* 25 30* 35* 10
8 40 50 55 30 40 45 8
_________________________________________________________________________
6 55 65 75 40 50 60 6
4 70 85 95 55 65 75 4
3 85 100 110 65 75 85 3
2 95 115 130 75 90 100 2
1 110 130 150 85 100 115 1
_________________________________________________________________________
1/0 125 150 170 100 120 135 1/0
2/0 145 175 195 115 135 150 2/0
3/0 165 200 225 130 155 175 3/0
4/0 195 230 260 150 180 205 4/0
_________________________________________________________________________
250 215 255 290 170 205 230 250
300 240 285 320 190 230 255 300
350 260 310 350 210 250 280 350
400 280 335 380 225 270 305 400
500 320 380 430 260 310 350 500
_________________________________________________________________________
600 355 420 475 285 340 385 600
700 385 460 520 310 375 420 700
750 400 475 535 320 385 435 750
800 410 490 555 330 395 450 800
900 435 520 585 355 425 480 900
_________________________________________________________________________
1000 455 545 615 375 445 500 1000
1250 495 590 665 405 485 545 1250
1500 520 625 705 435 520 585 1500
1750 545 650 735 455 545 615 1750
2000 560 665 750 470 560 630 2000
___________________________________________________________________
CORRECTION FACTORS
_________________________________________________________________________
For ambient temperatures other than 30øC (86øF), multiply
Ambient the allowable ampacities shown above by the appropriate Ambient
Temp øC factor shown below. Temp øF
_________________________________________________________________________
21-25 1.08 1.05 1.04 1.08 1.05 1.04 70-77
26-30 1.00 1.00 1.00 1.00 1.00 1.00 78-86
31-35 .91 .94 .96 .91 .94 .96 87-95
36-40 .82 .88 .91 .82 .88 .91 96-104
41-45 .71 .82 .87 .71 .82 .87 105-113
46-50 .58 .75 .82 .58 .75 .82 114-122
51-55 .41 .67 .76 .41 .67 .76 123-131
56-60 .... .58 .71 .... .58 .71 132-140
61-70 .... .33 .58 .... .33 .58 141-158
71-80 .... .... .41 .... .... .41 159-176
*Unless otherwise specifically permitted elsewhere in this Code, the
overcurrent protection for conductor types marked with an asterisk (*) shall
not exceed 15 amperes for No. 14, 20 amperes for No. 12, and 30 amperes for No.
10 copper; or 15 amperes for No. 12 and 25 amperes for No. 10 aluminum and
copper-clad aluminum after any correction factors for ambient temperature and
number of conductors have been applied.
Copyright 1995, NFPA
Also, change to fixed width font (Courier New is good).
"Greg" <[email protected]> wrote in message
news:[email protected]...
> This is 310-16
> Paste this to an 80 column wide screen
310.16 is the one you use for virtually all building wiring. The 75c column can
only be used if the wire is 75c rated and the terminals are also 75c rated. The
90c column is only used for derating purposes. Romex must be used with the 60c
column and there is a footnote that limits "small" sizes of any conductor type.
That is #14 (15a) #12 (20a) and #10 (30a) unless otherwise permitted.
"Greg" writes:
> #8 copper is not suitable for a 60a feeder under any circumstances.
<snip>
I'm not going to get into a pissing contest about wire size, wire insulation
grade, etc, etc; however, if you learn nothing else from this thread,
remember the following:
Trying to use the smallest allowable wire size is an example of the just
about the worst economic model possible.
The lowest cost wire(AKA: Smallest size) results in higher power losses (ie:
power loss = I^2*R) over the life of the installation which get lost in the
monthly power bill, but are included anyway.
The only people who benefit from small conductor sizes are the people who
are selling you the power you use.
HTH
--
Lew
S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: <http://home.earthlink.net/~lewhodgett> for Pictures
>Trying to use the smallest allowable wire size is an example of the just
>about the worst economic model possible.
Absoluely correct. In the above scenario with 60' of #8 @ 60a you may only be
dropping 2.2% of a 240v load but that is still 330 watts in 60'. That is about
the same as a string of rope light except you get no benefit from the heat. You
might even be compromizing the insulation of the wire.
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.
Bob
<Secret> wrote in message
news:[email protected]...
> I have a subpanel in my shop that was installed by a
> professional.
<Secret> wrote in message
> 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?
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.)
--
www.e-woodshop.net
Last update: 2/13/04
[email protected] (Greg) wrote in
news:[email protected]:
> 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
>
>
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.
"Swingman" <[email protected]> wrote in
news:[email protected]:
> <Secret> wrote in message
>
>> 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?
>
> 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.)
>
Thats exactly the piece of info I was missing.. And you're right the
ground bar was like $4.50 for a 20 slot bar. I'll get it set up this
weekend.
Thanks
On Wed, 25 Feb 2004 10:18:55 -0600, Secret Squirrel 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
> 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.
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.
--
-Doug
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
|this correct?
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)
<Secret> wrote in message
> Thats exactly the piece of info I was missing.. And you're right the
> ground bar was like $4.50 for a 20 slot bar. I'll get it set up this
> weekend.
>
> Thanks
You're most welcome. Don't forget that the green/bare ground wire from your
feed from the main panel needs to be attached to the new ground bus bar.
--
www.e-woodshop.net
Last update: 2/13/04