Sub-panel project advice

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  #1  
Old 09-18-06, 04:11 PM
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Sub-panel project advice

Hi there folks - new to the forum. I've already searched quite a bit and found some pretty applicable threads. I'd still like to lay out my plan for a sub-panel application and get some advice, feedback or suggestions.

My current service installed in 1999 is 100A. The feeder cable installed will support an upgrade to 150A if I need to down the road (verfiied with utility). I have two open spaces and an UNUSED 50amp dble breaker used for a range circuit. I have gas appliances.

I am installing a sub-panel in the garage for a mini-workshop. I want to have the ability to run a welder (230v), air compressor (120v) and another circuit for outlets for msc hand tools.

So far this is where I am. Installed a Homeline 100A panel in the garage (HOM612L100F) and, since I scored a good deal, have 6-3 w/ground SER cable run between the main and sub. Nothing is hooked up yet. My plan is to wire the main via a 50/60amp double breaker. I may remove the unused 50amp range circuit OR utilize those spaces.

On the sub-panel end I plan on running the two hots to the main lugs, nuetral to nuetral bar and ground to the ground bar kit I installed in the sub-panel. I'll run a seperate ground chord out to a stake on the outside of the garage.

Sound OK so far?

As far as circuits from the sub panel - the welder mfg recommends a 240v circuit with a 30amp breaker. I plan on a 2 -20 amp circuits for the other two applications.

Please feel free to give me any suggestions, comments, things I might do different, on my plan. I've done a couple different electrical projects in the past (one sub-panel), but that one only involved a couple 110v circuits.

A good picture/wiring diagram would be really helpful as well if anyone has a good reference.

Thanks, Mike
 
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  #2  
Old 09-18-06, 04:23 PM
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If your garage is a detached structure then that SER cable is no good.

If you go underground you need type USE and If you go overheaad you will need a triplex cable.
 
  #3  
Old 09-18-06, 04:36 PM
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Sorry...it's an attached garage. The cable will be routed on the basement ceiling and run out through the garage sill plate into the garage wall. It's never exposed to the outside.
 
  #4  
Old 09-18-06, 05:38 PM
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If the #6 SER is aluminum it is good for 50 amps so you can use a 50 amp breaker... no more. If it is copper you may use a 70 amp breaker even though the ampacity of #6 SER for your situation is 65 amps. Since there is no 65 amp breaker code allows you to go to the next size breaker. Either should be plenty for your needs. Of course you may use smaller breakers if you wish from the maximum allowed.

Be sure you do not bond the neutral and ground bars in the sub-panel.

You will not run a seperate grounding electrode conductor out to a seperate ground rod. The gec system installed with the main panel is all you will need. The sub- panel will not require a grounding electrode.

Roger
 

Last edited by Roger; 09-18-06 at 06:55 PM.
  #5  
Old 09-18-06, 07:20 PM
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Thanks Roger,

On other advice, I was told that I should install another ground pipe, but I'll certainly skip it. So I just need to run the ground from the 6-3 to the grounding bar then?

Thanks for the heads up on the 6-3 aluminum ampacity. Just double checking here; should I have purchased the copper 6-3NM-B for feeder .vs. the SER aluminum to get the extra protection?

Mike
 
  #6  
Old 09-18-06, 09:25 PM
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It really isnt a protection issue as for breaker size or whether the cable is copper or aluminum it is mostly an ampacity issue Cu allows for more power to the sub-panel. But you dont need anywhere near 70 amps. In a one man operation you will only have one piece of equipment operating at one time, unless you have figured out how to weld and run that air compressor at the same time. Remember though that an air compressor if left powered will automatically start at low pressure limit. So if it leaks off a little it is possible that it may start while you are welding but this still isnt an issue at 50 amps or more to the sub panel.

6/3 G NM-b copper would have given you 60 amps...55 amps ampacity for the cable and 60 amp breaker.....next size up rule since no 55 amp breaker is made. Depends on the cable type and whether copper or al.

Remember on the Al to use a anti-oxidant paste on the stripped bare wire of the cable before connecting it to the lugs of the circuit breaker and sub-panel. I like to wire brush the bare till it is shiny then apply the paste. Ideal No-Lox is an example of what you need.

When a sub-panel is in the same structure with the main panel (attached building) no extra ground rod is driven. If it is in a detached building than generally you will drive a ground rod.

Are you clear on not bonding the neutral and ground bars at the sub?

Yes you will connect the equipment ground wire of the 6/3 SER to the ground bar of the sub-panel.... not the neutral bar of the sub. All your branch circuit equipment grounds going out of the sub will attach to the ground bar.... all neutrals (usually white) will go to the neutral bar.

roger
 
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Old 09-18-06, 10:37 PM
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Roger,

I wanted to clarify the bonding issue - thanks. I always assumed that bonding the ground/nuetral required a physical wire run between the two. Since I installed the ground bar kit, I'm assuming I'm ok - no connection between nuetral and ground. Is it possible to purchase a sub-panel where this is already built in?

The model Homeline panel I have is a HOM6-12L-100

Yeah, I have trouble figuring out how to do one thing at a time, much less two! Point well made about potential max amp draw. It may be a slightly different story if I'm plasma cutting for a period of time and the compressor kicks in. They will both be running on seperate 20amp, 115v circuits. (I already have another 20 amp circuit in the garage off the main.)

I've seen advice on actually abrading the wire with the anti-oxidant compounds in place. Is that right? Seems like you'd just be rubbing it off. Thanks for the reminder, I remember seeing it on current connections on the unused range circuit in the main box.

Thanks for the time and advice!
Mike
 
  #8  
Old 09-19-06, 03:52 AM
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Yes you are correct to keep the ground/neutral seperate at the sub panel.

The extra ground rod is only needed if you are installing the sub panel in a seperate building or structure. That is how I got confused about the ser cable. something about ser and ground rod didnt sound right.

You can install a ground rod if you like.. it is just not required, nor does it bennifit you. It also will not hurt anything either.
 
  #9  
Old 09-19-06, 08:51 AM
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Just to clarify.... your homeline panel came with a green bonding screw, usually not installed (square d uses the bonding green screw). You add the ground bar kit (Part#PK7GTA I believe) but do NOT install the bonding screw, This will keep the ground bar and neutral electrically seperated. If the panel came with the green screw installed you must remove it.

Roger
 
  #10  
Old 09-19-06, 11:21 AM
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jwhite/roger

Yes, my panel came with w green screw - not installed. The ground bar kit you quoted Roger is exactly what I purchased. I installed it using two screws to the panel box surface (bottom/left on the back panel). It would still take a strap/chord of some kind to bond nuetral/ground together. I think I'm clear on the sub-panel end. As far as wiring at the main, I assume that nuetral/ground will NOT be bonded as well - two hots to the breaker, nuetral/nuetral and ground to ground bar on main?

Thanks for the help guys......
 
  #11  
Old 09-19-06, 12:17 PM
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At the main panel your neutral and ground WILL be bonded, this is the only place this should occur in your situation. So it does not matter if grounds and neutrals are seperated in the main panel. Some MAIN panels will have all the grounds on a bar and all the neutrals on a bar but dont let this confuse you. They are bonded if it is the main service rated panel, this is what you want. This bonding can be of different design depending on the maker of the panel. Might be a green screw installed or a metal bar between the bars, and so forth.
Some Mains only have one bar and the grounds and neutrals are just landed on that same bar. So it just depends on the panel bonding design.
So to summarize at the main panel you will connect your two hots of the SER to the double pole breaker terminals, your neutral will go to the bar with the white wires landed on it and your ground of the SER cable will go to the same bar or they may have a seperate ground bar, none the less the two bars are bonded in some way. There may also be bare grounds or green insulated grounds on the bar with the neutrals (whites). This is normal for the MAIN panel but not sub-panels in the same structure. At the sub the two hots will connect to the main buss lugs, the neutral to the neutral bar and the ground of the SER to the ground bar. No bond between these two bars in the sub.

In your panel IF a bond were required you would install the green screw, that screw threads into the metal of the panel back bonding the metal of the panel to the neutral bar....anything else attached to the panel metal (like that ground bar) will be bonded via the metal of the panel and the green screw then neutral bar.

I'll try to explain the reason for this. The ground wire is for safety it is not normally a current carrying wire. It only carries current in the event of a fault. So if you had a short to ground from a hot wire somewhere in the feeder or branch circuits of the sub-panel, the ground wire of the SER cable would carry the fault current back to the bonded neutral/ground of the MAIN.for a split second allowing the breaker to trip out. This is due to the massive flow of amps thru the breaker created by the fault. Otherwise no current should ever be on the equipment ground wires of the branch circuits or feeder.
If we were to bond the neutral (a current carrying wire) and ground in that sub-panel and we had an open neutral event with the SER cable or if it came apart then objectionable neutral current from the sub's branch circuits would begin using the ground wire of the SER to return to the main panel and then out to the center tap of the transformer. So in simple terms the ground is now playing neutral when it shouldnt be and you would not know you had a problem necessarily. At the main you want fault current (IF ANY) and neutral current to join so that either will flow back to the center tap of the transformer. Remember the service neutral is connected to the neutral lug in the main panel allowing the return path back to the transformer. The ground rods and water pipe electrode play no role in this they are there primarily for giant voltage events like lightning.

Many people think that the return neutral current flows to the grounding electrodes via the gec grounding wire, this is not true. The earth just doesnt magically absorb all this return current at almost no voltage.
The neutral current takes the lowest impedance path which is out the service neutral to the neutral center tap (midpoint) of the transformer which is the source of the electrical supply.


Roger
 

Last edited by Roger; 09-20-06 at 07:55 AM.
  #12  
Old 09-19-06, 08:43 PM
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So let me understand, in my case - on my sub panel, if I needed to bond the nuetral and ground, the green screw would thread through the NUETRAL bar and into the rear panel. I think it's getting clear. For some reason, I kept thinking "how does that bond the two if I thread the green screw through the GROUND bar and into the back panel" sheesh. I need to wake up. I see said the blind man...

Thats a great explanation Roger. I really appreciate you taking the extra time to explain it like you did. And its making more sense the more I think about it.

One more question if you don't mind. When I wire my 6-50R from the sub-panel, I think it's only a requirement for the welder to run 6-2. Can I use the 6-3 SER, since I have about 15ft extra?

Thanks again for the time..
Mike
 
  #13  
Old 09-20-06, 06:51 AM
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Sure you can use that cable. You will just wirenut the neutral wire on each end and dont use it. Be sure to leave enough length in case you would like to convert the outlet someday to 120/240 volt single phase use from only 240 volt use.

Your SER will have the wires color coded most likely with continuous stripes. The one with the white stripe is the designated neutral which of course is the one you dont need for the welder.

Yeah I should have said the green screw has only one place that it is installed. This location is provided by the factory and is usually identified in the installation instructions.
On Square d panels it is normally either thru the neutral bar itself thru a designated pre-drilled hole and then a threaded hole in the panel back. Or there will be a metal strap that has the pre drilled hole for the green screw and that metal strap is bonded to the neutral bar.

The purpose of bonding is to connect all metal parts so they are at the same potential and provides for electrical continuity so that the joined metal will conduct any current likely to be imposed on it.

Notice that neutral bar/bars are on insulated stand-offs from the metal of the panel... therefore the green screw must provide the bond to the metal of the panel to the neutral bar in order to provide a path of continutiy to the neutral bar.

Roger
 

Last edited by Roger; 09-20-06 at 07:39 AM.
  #14  
Old 09-20-06, 11:11 AM
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It just occurred to me that your welder is 30 amps assuming this is correct a homeline 30amp breaker will not accept #6 awg wire. So I think it might be best to just spring for the copper #10 awg in NM-b (romex) would be fine.
Could you share the manufacteruer and model number of your welder? It is possible that you could put it on a 35 amp breaker and you would then be able to use the #6 SER as a homeline 35 will accept #6. We need to verify this otherwise you will not be able to increase breaker size.

Roger
 

Last edited by Roger; 09-20-06 at 11:25 AM.
  #15  
Old 09-20-06, 12:01 PM
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Roger,

The welder is a Miller Dynasty 200DX. According to their manual, using a time delayed fuse (RK-5), they recommend a 30amp (100% duty cycle), normal operating fuse a 40amp. At 60% duty its 25a & 30a. I've actually talked to them as well, and they said the same thing on the phone.

No biggie if I have to use a smaller wire for the short run to the outlet either, but I appreciate you raising the point. It would save some bucks.

Any other suggestions are appreciated! Thanks again...
Mike
 
  #16  
Old 09-21-06, 06:50 AM
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If the breaker won't accept a #6 conductor you can pig-tail a piece of #8 copper to the end to attach to the breaker.
Make sure the connector (split bolt, wire-nut, etc) is rated for joining aluminum and copper (marked AL/Cu) and follow the instructions.
steve
 
  #17  
Old 10-09-06, 05:05 PM
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Hey all - just a big thanks to all who contributed to helping on this project. It's finished and most surpringly of all - it works - with no fires!

One other question here;
In reviewing my "equipment list" for this small shop, it seems advantageous that I have 2 -240V circuits - both 30amp - to utilize a compressor and plasma cutter at the same time - given my restrictions (I have a 50amp breaker at the main) would it be advisable to add a second 240 circuit? I do have one, 120V -20 amp circuit to a couple plugs, but would manage/monitor the use of the all devices.

thnaks again!
 
  #18  
Old 10-09-06, 07:33 PM
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Yep you can add another 240 circuit. You mentioned earlier you had a 120 volt air compressor, so are you saying that your going to add another 240 volt air compressor?

If you use good common sense and load management I dont see a problem.

Your welder has maximum amp input with the "stick" configuration operating at rated output... and that is 20 amps.

So I'm not seeing anything glaring that would prevent both the cutter and compressor from being in operation at the same time. Unless of course you have a godzilla plasma cutter but these are usually 3 phase.

Roger
 
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Old 10-09-06, 07:44 PM
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Thanks Roger,

I haven't actually purchased the compressor yet. Initially I was planning a compressor running off 120. However, after researching more, I find more options for compressors requiring 240. I'm still contemplating the purchase but, if I do go that route, I can run both devices (plasma & compressor) if I keep the draw from both at a reaonable level.

I'll probably just duplicate the wiring, breaker and 6-50R receptacle to keep it simple.

This was a fun project - I know its not over yet - but I feel good about the choices I've made based on all the input from you and the rest of the folks!

Mike
 
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Old 10-09-06, 07:49 PM
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Ok I see now. Yeah, you arent going to experiene any problems with both operating on a 50 amp sub at the same time.

Glad things worked out to your liking

Roger
 
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Old 10-09-06, 08:05 PM
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You dont want to duplicate the wiring.... wire the compressor according to its plug unless it is a hard wire. Go by the manufacturers instructions.

Roger
 
  #22  
Old 10-09-06, 10:20 PM
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Will do - thanks again.

I'm sure I'll have more questions down the road.

Mike
 
  #23  
Old 01-11-09, 12:28 PM
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Roger - Another sub-panel question!

Hello folks -

I am the original poster of this thread and a few of you helped me out a great deal (Roger!) - its served me well.

As some of my later posts eluded too - I FINALLY purchased an air compressor. Its a slightly used IR SS5L5 - 220V, 5HP. According to the motor plate, the FLA (full load amps) is 22.5A. THe past owner purchased an off the shelf 50A dryer cord with 4 pole cord/plug. It was running fine for him. Only two legs and G were wired to the starter switch on the compressor (the white nuetral was wired nutted off). My question, I'd like to be able to just change the plug on the compressor to match the receptacle I installed (30amp breaker) referenced in this thread.

I have two outlets for 220. One has a 6-50R receptacle that I use for my welder. I'd like to duplicate it for the compressor.

See any issues with that? THe other option would be to purchase the 4 prong receptacle for the 2nd outlet and just plug it in.

Thoughts?

Thansk, Mike
 
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