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Discussion Starter · #1 · (Edited)
I've got a 220V line coming from a 50A breaker in my garage's subpanel. I use this for a welder. I would like to add two 110V 20A outlets to that line. Because of some space and location restrictions I've come up with this plan, and would like to know if everything is OK with it:

I want to route the 220 to the welder outlet first. From there go to a small, 70A, breaker/load center. That will have two 20A breakers that route down to two 20A 110V receptacles.

The 220V receptacle is a 3-prong 50A outlet with only one terminal per wire. Would it be OK to use that receptacle box, assuming it's large enough, as a junction box to tie together the incoming line, 220 receptacle lead, and breaker panel feed? And what would be "large enough"? And can the 110V receptacles share the same box (separate from the 220 box)?

I think I have the basic requirements under control; no wires or circuits can be overloaded without tripping a breaker somewhere. The 50A breaker is GFI, since this is a garage. But are there any subtle problems that could be safety issues?

Thanks.
 

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Is this an attached or dettached garage? If it is attached, then you need a 6/3 wground cable to take to the subpanel first.
from there run the 50 amp welding receptacle and the other receptacles
The breaker feeding the subpanel does not need to be GFCI.
Seperate the ground and neutral in the subpanel.
If it is a dettached, then other rules must be followed and we can give a link.
 

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Discussion Starter · #3 ·
Is this an attached or dettached garage? If it is attached, then you need a 6/3 wground cable to take to the subpanel first.
It's an attached garage. I already had the 6/3 with ground going to the welder receptacle. I'm hoping to use that line and just wire in the new panel and outlets.

I used GFI to feed the welder since I often have water on the floor if it rains hard, or during a big snow melt. Would the GFI get in the way because of the two 110 circuits, though?
 

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Discussion Starter · #5 ·
You can use that line, but you must go to the panel first.
Thanks. Does that mean I need a separate breaker in the new panel for the welder outlet? Or can I just connect the welder outlet from that panel. That would essentially be using the panel as a junction box. I would worry that someone later would expect the 220 outlet to be dead if the 110 breakers are thrown, but it would be live all the time unless the breaker in the existing sub-panel, or a breaker up the line to the mains, were thrown.

The panel I was planning to use is just a simple 2-ckt breaker / load center.
 

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That depnds on what the instructions for the welder will tell you.
Some only need a 30 and some need a 60, and some are inbetween.
You also only need 2 hots and a ground for the welder if it has a 3 prong plug.
 

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Discussion Starter · #9 ·
That depnds on what the instructions for the welder will tell you.
The welder is a 50A. Actually it could take higher, but I don't run it that high. That's been set up and running for quite a while, though.

My question was more about hanging a 50A breaker on a line that already has a 50A breaker. I don't see it being a problem. If I go over current, I would expect only one of them to trip, but it would be kind of a race condition on which one decides to trip. What I don't know, though, is if there are any code restrictions on having two breakers of the same amperage on one line.

Basically, my configuration now is I have a 60A breaker in the main panel that feeds the sub-panel in my garage access area. In that sub, I have some 110 circuits for the rest of the garage and access area, plus a 50A, 220V breaker that only goes to one 220V outlet in the garage (the welder outlet), about 25 feet away. It's that line I want to tap two 110V outlets off of.
 

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My question was more about hanging a 50A breaker on a line that already has a 50A breaker. I don't see it being a problem. If I go over current, I would expect only one of them to trip, but it would be kind of a race condition on which one decides to trip. What I don't know, though, is if there are any code restrictions on having two breakers of the same amperage on one line.
I don't think there's any problem with it. I've seen it done all the time at least. It can be a hassle to figure out which one tripped, but it's not a safety issue.
 

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Discussion Starter · #12 ·
A followup and more questions:

I finally got to wiring the new garage sub-panel and have run into a problem. The breaker feeding this box is a 50A 220V GFI. I got this under the impression that I needed GFI for anything in the garage. I have since found out that I don't need it for 220V, but there it is.

The new sub trips the GFI. It looks like connecting the ground from the main panel to the neutral causes the trip. So is this working the way it should? Might something be miswired in the 50A GFI?

I was thinking of just swapping breakers, putting the GFI in the garage panel. I know GFI isn't needed there for the 220V, but it wouldn't hurt. However, I want to run a couple 110V circuits from that box, and would lose the GFI to them, which is required. I'm trying to make the best use of what I have, without another trip to the store, so any ideas? Can I keep the garage panel, at least the 110V circuits, on a GFI circuit somehow?

And that brings up a question about GFI in general. I've read that 220V breakers sense a difference in current between the two hots, since the neutral is rarely used on 220V appliances. But that doesn't seem to be the case. I ran a sander on one of the 110V circuits, which would have put a load on one of the GFI's hot lines, and no tripping. So how do the 220V GFI breakers work?

--Marc
 

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Neutral tied to ground should trip the GFI. You never tie the neutral and ground together in an attached garage sub panel (and very rarely in a detached situation). You will need a ground bus bar for your subpanel to separate the grounds and neutrals.

Also, you will need a standard 50 amp 2 pole breaker upstream of this subpanel, and either GFCI outlets for your 110 circuits or GFCI breakers in the sub panel for those 2 circuits.

You can use the 50amp GFCI breaker in the subpanel for your welder, however as you have realized its not required or nessecary.
 

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To clarify what theatretch said; Neutral tied to ground downstream of the GFCI should trip the GFCI. So like he said, you are probably incorrectly bonding neutral to ground in the sub.

So how do the 220V GFI breakers work?
A 120/240 GFCI has three terminals... it measures the net current between both hots and the neutral, and detects a difference, just like any other GFCI. If there are mixed loads, say 5 amps on hot1 and 10 amps on hot2, then it will see 5 amps on the neutral (in phase with H2) and everything still cancels, as long as there isn't a ground fault.

Also note on terminology that GFI sometimes refers to 30ma+ equipment ground fault protection, not 6ma personnel ground fault protection which is usually called GFCI. Probably not an issue but something to keep in mind for clarity sake.
 

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Discussion Starter · #15 ·
Thanks to both of you for clearing that up and educating me. First, I always thought GFI and GFCI were interchangeable. And it now makes sense how the GFCI breaker works. Learn something new every day.

On the garage sub, do I need to sink a ground rod for the new ground bus bar, or do I tie the buss to the ground wire from the main? This is an attached garage, if that makes a difference.

--Marc
 

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Also note on terminology that GFI sometimes refers to 30ma+ equipment ground fault protection, not 6ma personnel ground fault protection which is usually called GFCI. Probably not an issue but something to keep in mind for clarity sake.
Gigs, GFI and GFCI are generally interchangeable. What you describe is GFPE, Ground Fault Protection of Equipment. Some engineers may use GFI and GFCI differently, but among the field electricians, GFI is contextual, sometimes referring to a receptacle or breaker, and sometimes applied to GF protected service equipment.
 

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Gigs, GFI and GFCI are generally interchangeable. What you describe is GFPE, Ground Fault Protection of Equipment
You are right that they are used interchangeably often, but it seems that GFI=equipment (30ma) GFCI=personnel (6ma) is getting some traction.

http://www.mikeholt.com/mojonewsarchive/AFCI-HTML/HTML/AFCI_Questions_and_Answers~20030301.htm

Dual listed AFCI/GFCI circuit breakers are designed to protect against ground faults of 6 mA or more, short circuits, overloads, and arcing line-to-neutral faults.

Dual listed AFCI/GFI circuit breakers are designed to protect against ground faults in excess of 30 mA, short circuits, overloads and arcing line-to-neutral faults.
So I think to avoid any confusion we should probably stop using GFI when we mean GFCI.
 

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The gfci should not be a problem.
The GFCI main will be a problem. A 120V load will be an unbalance ind it will trip.

Use a regular breaker at the source panel and install the 240v GFCI for the welder at the sub. Install separate GFCI protection for the 120V circuits also.

Atached garage doesn't need ground rods.

The white/neutral bus needs to be isolated from the enclosure. The ground bus needs to be attached to the enclosure.

A lot of small panels have buses on borh side which can be separated by removing a jumper piece that connects the two.

If not, just get a ground bus kit and screw it to the enclosure and remove any bonding jumper that may connect the neutral bus to the enclosure.
 

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Discussion Starter · #20 ·
OK, everything works now. Here's my followup, in case someone else asks the same questions.

I installed the bus bar for the new, separate, ground. FYI, Home Depot and Lowes calls them "ground bars". And elsewhere on the net they're called grounding bars, buss bars, busbars, and bussbars. My 220V feed to the garage was already a 4-wire. The box's ground/neutral bar was not connected to the case. It came with a grounding screw that threads through the bar into the panel, in case you want to tie ground to the case. Obviously, I left this off.

I found conflicting information on using a GFCI as a main breaker to sub-panels. Some say OK, some say don't. I went with the easier/cheaper option of leaving the GFCI in as the upstream breaker. This is working fine. I'm going to try putting a 10K resistor between the 110V hot and ground to see if the GFCI trips, but I suspect it will.

220/221, I think you're mistaken on a 110V load unbalancing the GFCI. I think Gigs had it right when he said that the GFCI breaker compares all currents to the neutral. Technically, I believe it sums up the currents and expects zero, as the phases cancel each other out. I hooked up my compressor to one of the 110's and it cranked up just fine, while the welder was running and not.

So thanks all for the advice and education.

--Marc
 
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