Rewiring garage Subpanel for 220volts, need advice.

[zxcvbob]

I drew a picture (sort of.) Two hot wires and a ground. Tap into the existing circuit and add a couple of new outlets. Turn it into a 20A branch circuit.

But you don't run a dust collector with it, or any of the other power tools, so you'd still be OK with the existing 20A circuit. Some popular

230A welders require a 50A circuit.

6/3wg cable if you want to put in a subpanel fed through a 50A or 60A breaker. If you can get by with a 30A subpanel, you can use 10/3wg cable. The "wg" part means "with ground", because you need 4 conductors. I'm not sure, but I think you can still buy large 3 conductor cables without a ground, so I said wg just to be safe.

Bob

[Mark or Sue]

main panel to the

as many receptacles on

another 240V 20A circuit.

them and keep daisy

existing 240V 20A circuit

each circuit so you're

Can you list the equipment you have and the motor nameplate amps at 240V for each? If so, we should be able to tell you what can run together on the same circuit. I would expect the dust collector to draw its nameplate amps. Saws, jointers, planers, etc only draw their rated current when cutting wood. If the motor amps used simultaneously on the same circuit add up to 20, things should work. Keeping that sum at 16 to 18 would be better though.

going to have enough

three cables should fit

and you're still

When you run multiple wires together, you have to derate the amount of current they carry because heat from one wire heats the other wires too. This is true whether you're stuffing a bunch of wire in a conduit, or running bundles of cable. With cable labeled "NM-B" (which is what Romex made after

1985 will indicate), you can run up to 9 current carrying wires in a bundle before #12 can't carry 20 amps anymore. Should you need more than 4 cables to the same location, you just run two separate bundles (say 3 cables and 2 cables) spaced a few inches apart so heat from one doesn't add to the other. This works anyway, because you don't want a hole larger then 1" in your 2x4 studs so that you can keep the wires 1.25" from the face of each stud. You won't get more than 4 cables in a 1" hole.

-- Mark Kent, WA

[John Hines]

A friends garage has the 2Hp DC on a 15 amp 220 circuit, and his 3hp saw on a 20 amp 220, on a 60 amp sub-panel in the remote garage.

I'd suggest putting in a 60 amp sub-panel, then the controls (breakers) will be in your shop, which makes things safer when you can see that nobody is flipping breakers on behind your back.

One thing to note, with this arrangement, there is no flicker or noticeable effects, in the house, based on what is done in the shop.

GFCI's work fine with woodworking tools, never had a problem with trips in my basement shop.

Again, a sub-panel will allow you to have 220 circuits and 120 for tools and lights and tv/radio whatever.

Flexible conductor wire is much easier to pull. No problems pulling 4 #6 wires through 3/4 rigid (thicker for underground) conduit. (I pulled a full rated ground cause I'm a belt and suspenders man when it comes to not getting shocked).

Big problems trying to pull 3 stranded and one solid #6, in another application inside, you know, unified ground stuff. yuck go with stranded.

[John Hines]

Or an Edison style circuit, which uses the common neutral, and allows full current on each side of the outlet.

I did this in a old house I rewired, where the owner went with central ac after I worked to pull 220/30amp to the upstairs bedroom for a window unit. Installed 20 amp outlets in an edison circuit, and told the owner it is heavy duty, this is where you'd plug in a steam cleaner or something like that.

[zxcvbob]

I didn't think you could use solid #6 in conduit? I'm about to pull three #6's in a 3/4" EMT conduit for the service entrance conductors to my detached garage; I'd rather use two #6 THHN stranded wires and one #6 bare solid copper but I thought the code book says anything larger than #10 had to be stranded if used in a raceway, except where specifically allowed elsewhere in the code (and I couldn't find anywhere else that mentioned it)

I have enough solid #6 in my odd-and-ends box to do the job, but I'll have to buy the insulated stranded #6 for the hot conductors. Plus it is real obvious which conductors are hot and which are grounded at the ends of the conduits without having to put white tape on one of the wires.

When I talked to the inspector a couple of months ago, he didn't think you could use a bare wire in conduit, but the code book specifically says you can use it for a grounded conductor.

Bob

[Mark or Sue]

I think you are correct, although I don't know the section that mandates this either.

There are limits to this, and you can only use bare neutrals where specifically allowed by the code. Otherwise we could use the a bare wire for clothes dryer, range, and feeder neutrals, but I know this is not allowed. I'm not convinced you can use a bare neutral in this application unless you are tapping your service conductors prior to your main disconnect.

I would encourage you to run a 4 wire feeder to this structure anyway unless you know you'll never want phone, CATV, network, or other cables or metal pipes going to that building. The 4th equipment grounding wire can certainly be bare or green, but may need to be stranded because of its size.

-- Mark Kent, WA

[zxcvbob]

specifically allowed by the code.

neutrals, but I know

application unless you are

you know you'll never

building. The 4th equipment

because of its size.

I'm using triplex overhead wire between my house and the garage's service conduit. I'm reusing the abandoned old service entrance conductors at the house to feed the triplex, so there is no 4th wire unless I want to pull new wires through the old 3/4" conduit -- I don't know what kind of bends and/or pull boxes might be in the 50 year-old conduit, but they would be inaccessible. I also don't think you can put four #6's in a 3/4" conduit without exceeding its maximum "fill", but I'd have to look it up.

BTW, I'm backfeeding the old service conductors through a 60A 2-pole breaker for my overcurrent protection, and the service panel in the garage only holds 6 switches so it doesn't need a disconnect.

If I ever do have to run telephone or gas or CATV to the garage, I'll bury it, and I'll redo the 60A feeder with four #6 wires in a 1" rigid conduit in the same trench.

Bob

[John Hines]

I don't know if meets code, this wasn't an inspected job, I was helping the home owner, who bought the wire.

In this case, it isn't a conductor, but rather tieing the ground stake driven in by the main box, to the water service piping, into a unified ground, above and beyond the EMT that connects the two panels.

[John Hines]

specifically allowed by the code.

neutrals, but I know

application unless you are

you know you'll never

building. The 4th equipment

because of its size.

That makes the remote system like a service in and of itself, requiring a ground rod.

Again, I install a 4 wire feed, so one of the wires is an earth safety conductor (green), and not carrying a load.

I figure at worst, the inspector would require a derating to 50 amps (new breakers).

[Tom Horne]

Use Quadplex and tie the messenger to the old service mast with a lug or grounding clamp. The Aluminum Clad Steel Reinforced (ACSR) messenger cable that supports the other three conductors of the quadplex then serves as the Equipment Grounding Conductor (EGC). If the original service mast for your home is discontinuous between the panel and the service head then you will have to bond around any gaps.

Remember that you have to build a Grounding Electrode System at the detached garage consisting of a minimum of two eight foot ground rods spaced at least six feet apart.

-- Tom H

[zxcvbob]

The grounded conductor in the old service entrance is not insulated, so I don't think I can use it for a neutral and the old service mast as a ground

-- so I can't tell if the raceway is continuous back to the service panel or not because the grounded conductor inside will be shorted to the raceway. I'm gonna attach the messenger wire of the 3plex to the bare conductor and the insulated wires to the old insulated wires (obviously) and the messenger wire will be my neutral *and* my equipment ground.

Two electrodes? I thought I only needed one 5/8" x 8' ground rod for a 60A feeder to a separate building. (I think I'll ask the inspector if I need a second electrode before I buy the grounding wire, in case I need an unspliced conductor long enough to reach both ground rods.) Is this a new rule? When I wired my old garage 10 years ago using the exact same method I only used one electrode and the inspector thought it was just fine.

Hey, I just thought of something. Maybe I can use 4plex and attach the messenger wire to the grounded service entrance conductor of the *new* house service. It might look kind of weird, but I think the grounded service entrance conductor or the service entrance raceway can be used as an equipment ground. The old service mast and the new one are about 18 inches apart, and there's a big insulator right between the two for the messenger wire for the garage to clamp onto. I think I need to dig up my code book and study it before I ask the inspector any stupid questions.

Thanks, regards, Bob

[Tom Horne]

Your best approach is to use the existing raceway and repull it using an insulated #6 THWN neutral. The code allows up to five compact stranded THWN conductors in a 3/4" rigid conduit so you could even add a bare stranded number eight equipment grounding conductor to the raceway if you wanted to. You may not tie any of the conductors to the garage into the service entrance wires because that connection would be on the utility side of the service disconnecting means and because the US NEC requires that all conductors of a circuit be in the same raceway or cable.

As for the grounding electrode system the code language has changed so that if the first rod does not have an impedance of 25 ohms or less a second rod is required. Since the equipment to measure the impedance of grounding electrodes cost 1000 dollars and up most of us just install two rods and let it eat. The Grounding Electrode Conductor does need to be continuous between electrodes (rods) but it does not have to be continuous from the second rod all the way back to the service disconnecting means. Since the acorn clamps are only listed to terminate a single conductor it is easier to keep the conductor continuous.

-- Tom

[John Hines]

AFAIK, a cheap and easy way to test a ground system, is that it should be able to light up a 100w bulb when connected between hot and ground.

If the ground resistance is too high, the bulb won't light up fully. I may be wrong on the bulb size (maybe a 60w?), but the idea behind the test is valid.

[Tom Horne]

If you can get the inspector to accept your field expedient test than more power to you. I test my grounds as a matter of course and I rarely get less than twenty five ohms with two rods let alone just one. I have driven sectional rods to depths of twenty five feet without getting less than twenty five ohms. Your light bulb test will test the total impedance of the earth return pathway but that does not tell you anything specific about the impedance of the rod in question. The assumption that the impedance of the Multi Grounded Neutral (MGN) of the power company's distribution network is effectively zero may or may not be acceptable to the inspector.

As far as what bulb size an impedance of twenty five ohms with a voltage of 120 would produce a current of 4.8 amps. 4.8 amps times 120 volts is

476 watts of power. That is a heck of a lot more than one light bulb. If you can flow enough current through the ground rod to open a five ampere fuse than the total impedance of the circuit is less than twenty four ohms so I guess that the demonstration of the ground rods ability to blow a five ampere fuse would prove an impedance of less than twenty five ohms. That does not mean that test will be acceptable to the inspector. In general it is simpler to drive two rods and be done with it but I never claimed that it is best practice.

-- Tom Horne

[William]

Rewired and tested my 1HP Crapsman table saw today from 110/14amps to 220/7amps. It's more powerful running in 220volts and it started without hesitation. I also turn on my compressor with the TS running and it did not trip the circuit. I guess it's safe for me to run both at the same time.

I guess I will be starting to pull the two 12/2's from the main panel to the garage sometime soon and complete everything before Spring.

Thanks everyone for the help. I wish everyone here a Happy and safe New Year!

Thanks again!

[Anthony Diodati]