Yet another wiring - subpanel Q

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

Reply to
Secret Squirrel
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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.

Reply to
Doug Winterburn

|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)

Reply to
Wes Stewart

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

Reply to
Greg

Below is correct. Call the electrician back.

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Reply to
TeamCasa

I love your politically correct "invite him back..."

dave

Doug Winterburn wrote: Also, the

Reply to
Bay Area Dave

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

Reply to
Bob Davis

snipped-for-privacy@aol.com (Greg) wrote in news: snipped-for-privacy@mb-m04.aol.com:

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?

Reply to
Secret Squirrel

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.

Reply to
Greg

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.)

Reply to
Swingman

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?

Reply to
Howard Ruttan

#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.

Reply to
Doug Winterburn

#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.

Reply to
Greg

BTW your mileage may vary on this one. Some AHJs will take it, others won't.

Reply to
Greg

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.

Reply to
Greg

"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.

Reply to
Doug Winterburn

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

Reply to
Greg

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.

Reply to
Doug Winterburn

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

Reply to
Greg

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

Reply to
Greg

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