Wiring help please

[Roger Turnbough]

Morning all,

Ok, so yesterday I roughed in a bunch of elec boxes for the shop. Ive added a 220 leg for the big stuff that will have 3 outlets. I bought 20amp breakers for the 220 line, but am now thinking that this breaker will be to small, to say, run the DC and TS or BS at the same time. This circuit will be pulled in with #10 wires.

I am also adding a lot of new outlets for the small stuff, 110. This I was thinking of pulling 2 new circuits for. I want to pull a red, black and a common (white) for this, and have each duplex outlet in each quad box on a diff circuit. Can I use this single common wire to go across each outlet in the box? Or do I need to pull an extra common (one for each circuit?) These will be put in on 20 amp breakers, with 12ga wire.

Am I on the right track here or am I looking for alot of popped breakers? Or Worse?

Thanks for all your help.

Roger

[Kevin Gerstenecker]

Roger, you can share neutrals with differents circuits, but I prefer to have each circuit on it's own neutral. Sharing neutrals is done a lot, but anymore it is more common to find each circuit with it's own. That is the code around here, and I would imagine that is the case most places today. I am not sure what the National Electric Code says about sharing neutrals, my NEC Book is at work. If it isn't too much trouble to pull another white, do it. If you are using 12/3 Romex with a ground, I would just share the neutral for those 2 circuits.........it won't hurt a thing to do so.

[Mike Evertsen]

if I read you post right you want to run three machines at the same time on the same 220 circuit I don't think you can,,,,even running three machines on one 110 circuit won't work,,,,you can put the DC on it's own circuit then run one for the TS and BS but only run one machine at a time,,,,lights should be on a dedicated circuit ,,,,air compressor should be on a dedicated circuit,,,

[Kevin Gerstenecker]

Roger, it was EARLY when I first read your post, and I missed the 220V section at the top..........actually, I read it, but it didn't sink in. (I had no coffee in me then!) If you are running a 220V circuit using #10 Wire, you MUST use a 30 Amp Breaker. What will the amperage draw be on the 220V circuit? The amp draw will determine the condutor size. Usually, higher voltage items have a lower amperage draw, but it you are using 10 wire, use a 30 amp breaker. I don't think you will be able to run the BS, TS and DC at the same time, even on a 30 Amp circuit. I agree with Mike on this point...........run a dedicated circuit for the DC, for sure. You may be able to get by with the TS and BS on the same 220V circuit, if the chances are that they will not both be running at the same time. The DC will be running whenever the TS or BS is, so that is for sure a dedicated circuit situation. If it were me, I would run a dedicated 20A, 220V circuit to each of these items.........TS, BS and DC. That would be the overall best setup. Check the Amperage Draw on each of the items.......the amp draw should be on the spec plate of the motor...that will tell you the size circuit you need. Good Luck, and remember, Electrical work is no place to cut corners.......and be safe too! :)

[Roger Turnbough]

if I read you post right you want to run three machines at the same time on the same 220 circuit I don't think you can,,,,even running three machines on one 110 circuit won't work,,,,you can put the DC on it's own circuit then run one for the TS and BS but only run one machine at a time,,,,lights should be on a dedicated circuit ,,,,air compressor should be on a dedicated circuit,,,


Mike,

I would only be running the DC, and either the TS, or BS on the 220 circuit, I bought a 20 amp breaker, but am now thinking that maybe i need a 30 amp one instead. Am I on the right track here? I only have 6 slots in my subpanel, one 220, 2 outlet circuits, and 1 lighting circuit. With one spare slot left.

Thanks for the reply,

Roger

[Roger Turnbough]

Mike,

I would only be running the DC, and either the TS, or BS on the 220 circuit, I bought a 20 amp breaker, but am now thinking that maybe i need a 30 amp one instead. Am I on the right track here? I only have 6 slots in my subpanel, one 220, 2 outlet circuits, and 1 lighting circuit. With one spare slot left.

Thanks for the reply,

Roger


Ok, just came back up from the shop, the TS draws 6.5amps, the DC draws 5.5amps, and the BS draws 5amps, so totalling them all up brings us to, 17 amps total. So a 20 amp circuit should do the trick correct? Im a carpenter by day, and a jack of all trades at all other times. Just dont want to burn my house down doing something stupid.

Thanks guys.

Roger

[Jim Becker]

If you are running a 220V circuit using #10 Wire, you MUST use a 30 Amp Breaker.

Not true, Kevin. You can put a 15 amp breaker on #10 wire. In fact, some folks will wire machine circuits up with #10 in case they need to increase the breaker size at a later date--they just need to change the breaker and the socket to appropriately rated units at that time and the cost difference to pre-install the larger wire is mininal. Over engineering the wire is fine and no problem with code. Under-engineering a breaker or wire is dangerous and can cause a fire.

To Roger, it's generally a good idea to place a 240v DC on a separate circuit from other machines. When you do put more than one 240 termination on a circuit (IF your local code allows it...some do not), you should use a junction box to branch to the outlets, and not daisy chain between them as is common to do with 120v circuits. This also makes adding or relocating an outlet easier at a later date when you shop needs change.

[Rob Russell]

...

If you are running a 220V circuit using #10 Wire, you MUST use a 30 Amp Breaker.



Kevin,

Sorry, but that's not correct. There is absolutely nothing in the NEC that would prevent you from running 10 wire and a 20 amp breaker. In fact, there are times when that is appropriate, for example if you were factoring in voltage drop for a long run of wire.

Roger,

It sounds to me as if you should install a larger subpanel before you really get into this. It's worth the time and effort to give yourself the extra breaker capacity. Just replace the 6 slot panel with a 12 or 20 slot panel. Make sure you get one with an isolated Neutral. The work you've done roughing in your circuits is still all good.

The proper term for your 120 volt circuits that share a neutral is a "multiwire" circuit. It is an NEC requirement now that all ungrounded [aka "hot"] conductors be opened simultaneously. In other words, you need to use a 2-pole, common trip circuit breaker. In the 99 NEC, it was a requirement that 2 devices on a single yoke (IOW, if you "split-wired" a receptacle) be opened at the same time. In the 2002 NEC the requirement was strengthened such that all hot conductors of a multiwire circuit need to be be opened at the same time regardless of whether the devices share a yoke. What this means to you is that you can't use (2) individual circuit breakers, even if you use handle ties. You need to use a 2-pole breaker which opens both hot legs even though only one may have caused the trip.

Rob

[Dick Howard]

Rob, can you give us references in the nec to the double breaker requirement you refer to. The only ones i find are in reference to hazardous locations. Dick in Emmett, Idaho

[Walt Pater]

Sorry for the $.02, but Kevin's right- a 220 line gets a 30 amp breaker, and #10 wire. Sure, you can use #10 for 110 lines, but under no circumstances should one ever run 12 or 14 wire from a 30 amp breaker.

[Jim Becker]

Sorry for the $.02, but Kevin's right- a 220 line gets a 30 amp breaker, and #10 wire. Sure, you can use #10 for 110 lines, but under no circumstances should one ever run 12 or 14 wire from a 30 amp breaker.

240v circuits can be 15, 20, 30, 40 or higher amperage ratings. Since the breaker protects the wire (not the load), it should be sized appropriately and not be greater than the wire can handle. The associated recepticals also need to be properly rated and should not be sized for less than the breaker amperate. The "general max" amperage for #10 wire in this application is 30 amps, but you can certainly use a smaller breaker if you want to. In my shop, all of my 240v circuits are 20 amp except one; the FS-350 required a 30 amp circuit and one was installed accordingly. The BS, Lathe, DC and TS all work just nicely on 20amp circuits.

[Rob Russell]

Rob, can you give us references in the nec to the double breaker requirement you refer to. The only ones i find are in reference to hazardous locations.



Dick - be happy too. One of the things I firmly believe in is "if you're gonna quote 'the code', you'd better be able to cite it."

From the 99 NEC (all I have at work), section 210-4 Multiwire Branch Circuits, (b) Dwelling Units: "In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated."

Note that this is the 99 NEC and only applies to multiple devices on the same yoke. An example of that is where you "splitwire" a receptacle - one hot leg for the top outlet and the other hot leg for the bottom outlet, shared neutral.

I don't have the '02 NEC here, but it is my understanding that the requirement for "simultaneous disconnect" applies to the whole circuit now, not just if you have yokes sharing the hot legs.




... but under no circumstances should one ever run 12 or 14 wire from a 30 amp breaker.



I'm probably going to regret opening this can of worms, but I'm going to anyway.

There ARE circumstances where it is appropriate, and allowed, under the NEC to use a conductor size that seems too small for the breaker. Those circumstances, however, are very specific and apply to circuits dedicted to motors. In those cases, there is a very specific process you follow to 1) determine conductor gauge based on the motor's FLA (Full Load Amp) rating as specified by the NEC tables and 2) determine the overcurrent and short circuit protection (those can be different devices). In some cases, you can end up with a combination of conductor and overcurrent protection that seems inappropriate based on our normal use of "Branch Circuits".

I will agree with Walt's statement, in the context it was used e.g., that all of the circuits we're talking about for our workshops are really "Branch Circuits" and not the circuits for Motors. If you're really interested in seeing how complicated it can get to spec motor circuits, the section is titled "Motors, Motor Circuits, and Controllers". In the 99NEC it's Article 430.

Rob

[Dick Howard]

Rob, Your right about the shared yoke. I didnt read far enough. A double breaker is not required in a residencial unit if there is no shared yoke tho. I checked this with a state elect inspector. Dick in Emmett, Idaho

[Rob Russell]

Rob, Your right about the shared yoke. I didnt read far enough. A double breaker is not required in a residencial unit if there is no shared yoke tho. I checked this with a state elect inspector. Dick in Emmett, Idaho

Dick,

Many states haven't adopted the 2002 NEC yet - Connecticut is one of them. However, in the '02 code, it is my understanding that the disconnect requirement was strengthened to cover the multiwire circuit in its entirety, not just of you had yokes sharing hot legs.

Even when/if a state adopts a version of the NEC, they can (and often do) amend/modify the code to suit their purposes.

Personally - using a 2-pole common trip breaker is the safest way to wire the multiwire circuit and how I'd do it - code or not.

Rob

[Paul Smith]

Rob,

Just for my own education, are you saying that you can use a double pole (ie 220 V) breaker to run two separate 110V circuits sharing the same neutral line? In other words, run a 3 plus ground line (red, black, white, ground) from a double pole breaker, using black for a hot, red for a hot, and white for both neutrals? If so, what are the gauge requirements for the wire? Would a 20 amp breaker still require only 12 ga wire, or should it go to 10 ga???

Just looking for some clarity for my own befuddled mind. Thanks

[Rob Russell]

Rob,

Just for my own education, are you saying that you can use a double pole (ie 220 V) breaker to run two separate 110V circuits sharing the same neutral line? In other words, run a 3 plus ground line (red, black, white, ground) from a double pole breaker, using black for a hot, red for a hot, and white for both neutrals? If so, what are the gauge requirements for the wire? Would a 20 amp breaker still require only 12 ga wire, or should it go to 10 ga???

Just looking for some clarity for my own befuddled mind. Thanks

Paul,

Exactly as you have described, with 12 gauge wire fed/protected by a 20 amp breaker, is a "multiwire branch circuit".

The reason you only need the neutral to be the same gauge as the 2 hot conductors is the subtractive effect of the phases. Remember that your 2 hot legs are 180 degrees out of phase with each other. If you are drawing 10 amps on your black conductor and 7.5 amps on the red conductor, the net current flowing back through the white/neutral conductor is only 2.5 amps.

The most you could ever have flowing back through the neutral is full load on 1 leg (say 20 amps on the red) with nothing on the other leg. In that case, you'd have 20 amps flowing back through the neutral. Continuing with that example, if you started using 5 amps on the black leg, the net current flowing back through the white/neutral would drop to 15 amps.

FYI, the 2-pole breaker needs to be a "common trip" breaker, which most are. It just means that both poles need to open if 1 trips the breaker.

Rob (unlicensed, DIY-electrician)

[Kevin Beck]

I was originally going to wire my shop (garage) using a multiwire branch circuit but ran into a problem with ground fault protection. If your outlets require GF protection (mine did) you have two choices with a multiwire circuit:

1) Use GF outlets only
2) Use a 220V GF breaker

Either of these choices was more expensive than using two separate 110V breakers in my situation.

Kevin (unlicensed, DIY-electrician)

[Rob Russell]

I was originally going to wire my shop (garage) using a multiwire branch circuit but ran into a problem with ground fault protection. If your outlets require GF protection (mine did) you have two choices with a multiwire circuit:

1) Use GF outlets only
2) Use a 220V GF breaker

Either of these choices was more expensive than using two separate 110V breakers in my situation.

Kevin (unlicensed, DIY-electrician)

Your point is quite valid. There is another permutation of this.

Use a 220v breaker.
Split the neutral and feed (2) GFI receptacles, each with its own neutral. Use the load side of the GFI recpetacles to feed down-circuit outlets.
Continue your wiring, either split-wiring your outlets or putting in quad outlets where each yoke is on one leg.

This would give you GFI protection as you need, but allow you to cluster the receptacles in the quad outlets. It means that, if the breaker tripped - all wiring in the quad outlets would be dead which is what you'd want.

Rob

[Chris Padilla]

14 AWG 5.47 8.21 (1.63 mm or 64.08 mil, just a *skotch* bigger than a 1/16 inch!)

12 AWG 8.70 13.06 (2.05 mm or 88.81 mil)

10 AWG 13.84 20.76 (2.59 mm or 101.90 mil)

08 AWG 22.01 33.01 (3.26 mm or 128.49 mil, just a hair bigger than an 1/8 inch!)


The first number is a conservative amp rating based on 750 circulare mil per amp and the second one is considered the maximum allowable current (based on 500 circulare mil per amp) and absolutely should not be exceeded.

The numbers in parentheses is the diameter of the wire in millimeters and thousandths of a inch (mil).

Just some numbers if you need them or were curious.

Chris

http://members.roadfly.com/agent99/AWG.doc contains a whole Word file listing way more than you could possibly care about for wiring...might be of interest for some of you

[Rob Russell]

The first number is a conservative amp rating based on 750 circulare mil per amp and the second one is considered the maximum allowable current (based on 500 circulare mil per amp) and absolutely should not be exceeded.


Chris



Chris,

I firmly disagree with the numbers posted in that document.

The NEC is quite specific about allowable conductor ampacities. For example, stating that you need to run 10 gauge conductors to carry a 20 amp load flies in the face of the research, review and approval process of the NFPA and all the engineers involved with that organization.

There is a lot more to determining the ampacity of a conductor than its cross-section. For example, did you know that most of the current flows along the surface of the conductor, not the inside? That was something I learned last year.

That table of numbers is interesting, but I really believe that it could cause more confusion than it's worth. The problem it could cause is people might actually take that "max amps" value, believe it and use oversized conductors for their wiring.

Using oversized conductors for wiring won't hurt anything - as long as you size your boxes and wire nuts appropriately and understand what the minimum bending radius is for #10 or #8 wire.

Stuffing #10 into a box that's too small will cause problems. Frankly, if you ran #10 to a typical split-wired kitchen outlet, it won't fit into an 18 cubic inch box - you need to go to a 4" box.

It seems to me that posting links to documents like that table may be interesting because of the "curiousity" factor they generate. However, I'd really shy away from posting a link to such a table and making statements like these are numbers that "absolutely should not be exceeded" or similar.

Rob (Addy protocol - experienced, amateur, DIY-electrician)

[David Blangger]

You should also follow Jim on running 240v instead of 220....your cabinet saw will thank you for it.

[Chris Padilla]

Chris,

I firmly disagree with the numbers posted in that document.

The NEC is quite specific about allowable conductor ampacities. For example, stating that you need to run 10 gauge conductors to carry a 20 amp load flies in the face of the research, review and approval process of the NFPA and all the engineers involved with that organization.

There is a lot more to determining the ampacity of a conductor than its cross-section. For example, did you know that most of the current flows along the surface of the conductor, not the inside? That was something I learned last year.

That table of numbers is interesting, but I really believe that it could cause more confusion than it's worth. The problem it could cause is people might actually take that "max amps" value, believe it and use oversized conductors for their wiring.

Using oversized conductors for wiring won't hurt anything - as long as you size your boxes and wire nuts appropriately and understand what the minimum bending radius is for #10 or #8 wire.

Stuffing #10 into a box that's too small will cause problems. Frankly, if you ran #10 to a typical split-wired kitchen outlet, it won't fit into an 18 cubic inch box - you need to go to a 4" box.

It seems to me that posting links to documents like that table may be interesting because of the "curiousity" factor they generate. However, I'd really shy away from posting a link to such a table and making statements like these are numbers that "absolutely should not be exceeded" or similar.

Rob (Addy protocol - experienced, amateur, DIY-electrician)
Rob,

All good points and while I am no electrician, I am a EE. You are right, however...stuffing 10 AWG wire into a small box would be exceedingly difficult. I am not the author of that document but it seemed to make sense to me. Now I am not so sure. :confused:

If you took my short list of 14 - 8 AWG, how would the NEC adjust the numbers I posted?

Keep in mind that what you learned about current flowing mostly in the outer skin of the conductor is highly frequency dependent. It is call the skin effect and from this, you can calculate a skin depth (1/sqrt(pi*f*permeability*conductivity); for copper, use 66.1/sqrt(f) to get the answer in mm) to which the current will penetrate a conductor it is flowing in. At 60 Hz, the skin depth is 8.6 mm so unless you are running something like AWG 00 and larger, for the most part all of the current actually flows throughout the entire cross-sectional area so keep that in mind--if you have data contrary to this, I'd love to see it. If you are talking high-speed stuff on a PCB (stuff I design running several 100 MHz and above), then you are 100% correct and the current tends to push to the outer area of the conductor due to lower inductance. At 100 Hz it is 6.6 mm and at 500 Hz it is 3 mm so the harmonics of 60 Hz will penetrate less and less into the conductor and thereby flow more towards the outer shell. At the frequencies I work at, say 100 MHz, it is 6.6 um (micrometers, 1 um = 0.001 mm) and at 10 GHz, it is 0.66 um.

Chris

[Ken Salisbury]

For a long period of time I have seen wiring questions asked on many different forums. They almost always result in an electrical engineering debate revolving around various specifications, parameters, etc, etc. I personally do not respond to these posts because you can't make an electrical enginneer out of someone in one or two easy lessons :D. We EE's (MSEE here) shouldn't try to do that, much less get into debates about various federal and state rules, regulations, specifications, etc

My answer to these wiring questions (if I were to answer) would always be the same: "Check with someone you know who is a licensed electrician/contractor in your area. If you don't know one, maybe a mutual friend knows one."

Get a simple answer to a simple question (something an engineer is not trained to do) which was: "Can I use this single common wire to go across each outlet in the box? Or do I need to pull an extra common (one for each circuit?) These will be put in on 20 amp breakers, with 12ga wire."
Just a senile old man's 2¢ worth :)

[Rob Russell]

If you took my short list of 14 - 8 AWG, how would the NEC adjust the numbers I posted?



Let's assume the following:

THHN (copper) or similar which has the same ratings as the conductors in NM cable (aka "Romex).
Short runs (no compensation for voltage drop based on long runs.
No derating based on bundling too many conductors together.
Temperature ratings of 75 degrees C for the terminal connections. That's a typical rating for a residential circuit breaker or device (switch, receptacle, etc.).
Ambient temperature of 30 degrees C/86 degress F.

14 AWG - 20 amps (although can't use a breaker larger than 15 amps)
12 AWG - 25 amps (although can't use a breaker larger than 20 amps)
10 AWG - 35 amps
8 AWG - 50 amps

Reference: 99NEC, Table 310-16.




Keep in mind that what you learned about current flowing mostly in the outer skin of the conductor is highly frequency dependent. It is call the skin effect and from this, you can calculate a skin depth (1/sqrt(pi*f*permeability*conductivity); for copper, use 66.1/sqrt(f) to get the answer in mm) to which the current will penetrate a conductor it is flowing in. At 60 Hz, the skin depth is 8.6 mm so unless you are running something like AWG 00 and larger, for the most part all of the current actually flows throughout the entire cross-sectional area so keep that in mind--if you have data contrary to this, I'd love to see it. If you are talking high-speed stuff on a PCB (stuff I design running several 100 MHz and above), then you are 100% correct and the current tends to push to the outer area of the conductor due to lower inductance. At 100 Hz it is 6.6 mm and at 500 Hz it is 3 mm so the harmonics of 60 Hz will penetrate less and less into the conductor and thereby flow more towards the outer shell. At the frequencies I work at, say 100 MHz, it is 6.6 um (micrometers, 1 um = 0.001 mm) and at 10 GHz, it is 0.66 um.



I'm no EE and totally defer to your expertise on this. The electrical forum I lurk on has sparky's who routinely work with 250, 350 and 500 kcmil wire - so that would apply for them.




You should also follow Jim on running 240v instead of 220....your cabinet saw will thank you for it.



Actually - 220, 230 and 240 all refer to the same thing. If you take a multimeter and check the voltage in your house, you'll probably discover that it's 125/250.

110 is usually the "minimum" voltage that a device will be certified to run on.

The only difference would be if you're talking 3-phase 120/208 vs the 120/240 my phase convertor will generate. In that case, there is a difference between the HP the 3-phase motors will put out between 208 and 240 volts.

Rob

[Chris Padilla]

For a long period of time I have seen wiring questions asked on many different forums. They almost always result in an electrical engineering debate revolving around various specifications, parameters, etc, etc. I personally do not respond to these posts because you can't make an electrical enginneer out of someone in one or two easy lessons :D. We EE's (MSEE here) shouldn't try to do that, much less get into debates about various federal and state rules, regulations, specifications, etc

My answer to these wiring questions (if I were to answer) would always be the same: "Check with someone you know who is a licensed electrician/contractor in your area. If you don't know one, maybe a mutual friend knows one."

Get a simple answer to a simple question (something an engineer is not trained to do) which was: "Can I use this single common wire to go across each outlet in the box? Or do I need to pull an extra common (one for each circuit?) These will be put in on 20 amp breakers, with 12ga wire."
Just a senile old man's 2¢ worth :)

Ha! :D Threads (or hijacking thereof) often have a 'natural' progression on forums away from the original question and we all get the opportunity to interject our thoughts and sometimes the original inquiry is lost.

Personally, I learned A LOT reading this thread as I have some ideas to rewire my own garage being a DIY electrician myself but having no formal training as such. From my own point of view, I am glad the thread went where it did but that is a purely selfish statement.

I guess in engineering there is always the very first answer to just about ANY question: "Well, it depends on...." And from there, simplicity might be lost. I think it was Einstein that said to make things as simple as possible...but not too simple.;)

Chris

[Ken Salisbury]

Personally, I learned A LOT reading this thread as I have some ideas to rewire my own garage being a DIY electrician myself but having no formal training as such. From my own point of view, I am glad the thread went where it did but that is a purely selfish statement.;)
Chris

I am glad you learned a lot and i am sure others did also. For some folks however, too much information can be very dangerous like causing shop fires :D :D

[Ron Meadows]

As licensed electrician and holder of an MSEE....this is why I avoid, at all costs, threads like these.

The simplist answer to electrical questions on the internet is to involve a local electrician who is familiar with both the local, state, and NEC codes regarding the question at hand. Home wiring isn't difficult, but can lead to property, and in worst case circumstances human damage. The few dollars that you save by doing it yourself may end up costing you in the long run.


YMMV,

Ron