Need advice on adding 220V to the workshop

Alex Dron

Alex Dron

Joined
Feb 24, 2007
Messages
328
Hi,
I'm thinking of new grinder and really want to get 2HP VFD this time, but looks like it almost exclusively offered wired for 220V. Well, I saw new KMG-TX and they say it runs on 110V too, but I'm a bit reluctant to be one of the first users of that new grinder and it is probably not that efficient on 110 source.

So, I wonder if I can safely add 220 outlet in my workshop. The shop is fed by a 10/3 wire coming from AC breaker box (30A fuse), 2 conductors (red and black) are hot, the other 2 (white and copper) have the same source - they are connected together at the AC breaker box. I use Red and Black as 2 independent sources to build 2 lines of 110V outlets to distribute the load - one I use for grinder (15A max) and one for heavy duty shop vac in my dust collection system (10A).
As I understand to get 220 outlet I need both hot wires plus neutral white. My question is, once I add 220 outlet, can I still use existing 110 built on the same power source? I.e. for a shop vac which is 10A rated, lights, small power tools etc.
 
Is that 10/3 wire coming into your shop feeding a sub panel, or are you just wire nutting each leg into your 110 runs? (this is bad, I hope not, and that I'm just misinterpreting)

Not knowing the distance from your source panel to your shop it's hard to speculate 10/3 is capable of carrying 30a, but assuming it is, the ideal way to do this would be to put another breaker box in your shop, fed by the 10/3. Using single pole breakers in that sub panel to feed your 110 and a double pole single throw breaker for whatever 220 outlet you want to run.

The problem is that even if 10/3 is sufficient for 30a at whatever distance, you'll run the very real risk of drawing more than 30a if you're running multiple 110 circuits and the new 220 circuit simultaneously, tripping the breaker in your house or wherever that panel is.

So can you add 220 and keep your 110? Yes. Can you run them all at the same time? Doubtful without pulling heavier wire to feed your shop and a bigger breaker in your source panel.
 
It is 25 ft between AC breaker and my shop. I have a breaker box on my side with single pole breakers for each 110 line. Yes I was going to put a double pole breaker in that box for 220 outlet. What is a typical draw for 2hp grinder running on full speed? If it is below 20A I should be fine, I guess. All my other equipment runs below 10A total.
 
Fit a subpanel at the end of your 30amp 10-3 circuit.
Your proposed 240V grinder should draw little over 6A.
That leaves you 18A for each 120V circuit.
 
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Sounds like you already have a subpanel in your garage?
A 15 to 20 amp 2 pole breaker will be more than enough. I'd run some 12 gauge wire, 2 hots and a ground (not a neutral). I assume you're running conduit? If you're running some 12/2 romex, then just wrap some red tape around the white wire on the outlet side to indicate both wires are hot. Or better yet, run some 12/3 and just tuck the neutral back into the box. That way you'll have a neutral available if you ever need to change the outlet to a 4 prong, and there won't be any confusion about hots and neutrals.
 
It is a standalone shed, 10/3 wire from house A/C breaker box running in ground conduit 25 ft long ends up with shed's breaker box (or subpanel) that enough space for few more breakers.
My only concern is that white wire and copper ground are connected at the A/C breaker box. So even though 10/3 conduit comes with 4 wires, 2 of them are essentially from the same source - ground panel on A/C box.
 
Wire everything properly and let the breakers worry about overdraw (that's their job).

Alex Dron said:
My only concern is that white wire and copper ground are connected at the A/C breaker box.
Click to expand...

Why is that your concern? This is the correct wiring. Coming from the street, you have two hots and a ground. Once the ground comes into your main box, the ground is branched into two redundant/duplicate lines - one we call 'ground' and one we call 'neutral'. The neutral lines in your house are basically an 'extra' ground. What I just wrote is an oversimplification, but that's the basic idea.
 
Alex Dron said:
It is a standalone shed, 10/3 wire from house A/C breaker box running in ground conduit 25 ft long ends up with shed's breaker box (or subpanel) that enough space for few more breakers.
My only concern is that white wire and copper ground are connected at the A/C breaker box. So even though 10/3 conduit comes with 4 wires, 2 of them are essentially from the same source - ground panel on A/C box.
Click to expand...

Yes, you're ground and neutral buses on your MAIN panel should be bonded, or in other words, ground and neutrals on a main service panel are essentially connected/going the the same place (though in practice, common and ground wires should always be connected to separate buses, and never mixed inside the panel).

You're subpanel likely has (or hopefully HAD) a bonding strap that connects the neutral and ground bus bars in the sub panel. This should be removed, or rather, the neutrals and grounds in a sub panel should NOT be bonded at the sub-panel. The neutral bus bar is typically insulated from the sub panel case, the ground bus is not (it should have continuity with the case). Since it's an exterior/separate building, I believe you're also required to have a separate grounding rod running to your ground bus as well. All grounds and neutrals connected inside your sub-panel will go to each respective bus, they just won't be bonded in the subpanel.
 
Thank you guys. Came from a different country, and the US way of having neutral and ground in the same outlet as a separate wires but bonded at the main panel is difficult to comprehend. I know neutral should be connected to ground "only at the service panel", but what is counting as a service panel? PG&E distribution box on the street? Main house breaker box? Would A/C box in my case count as a such, which is also about 25 ft away from main house panel? Was afraid I'm doing something totally wrong.
Anyways, now when I talked myself into 2HP grinder, the only thing left is to choose the right one :)
Without breaking the bank...
 
P.Brewster said:
Edit to add: this link explains the 'why' http://www.esgroundingsolutions.com...eutral-and-the-ground-wire-in-the-main-panel/
Click to expand...
Overall thats not bad explanation of concept, excepting proofreading was in order before publishing...
"If the current flowing on a grounded conductor is higher than an amp, and you are not in a high-voltage (600V+) environment, it typically indicates a erroneous neutral-to-ground bond somewhere"
Current on a grounded conductor two wire circuit must be equal to current on its ungrounded companion.
Ok, pedantic.
Sorry, used to teach this stuff, I spot these kind of errors quickly. ’Grounding conductor’ and ’grounded conductor’ are NOT the same thing.
Given the high stakes of electrical errors, makes me nuts unless I point it out.
 
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knife to a gunfight said:
Yes, you're ground and neutral buses on your MAIN panel should be bonded, or in other words, ground and neutrals on a main service panel are essentially connected/going the the same place (though in practice, common and ground wires should always be connected to separate buses, and never mixed inside the panel).

You're subpanel likely has (or hopefully HAD) a bonding strap that connects the neutral and ground bus bars in the sub panel. This should be removed, or rather, the neutrals and grounds in a sub panel should NOT be bonded at the sub-panel. The neutral bus bar is typically insulated from the sub panel case, the ground bus is not (it should have continuity with the case). Since it's an exterior/separate building, I believe you're also required to have a separate grounding rod running to your ground bus as well. All grounds and neutrals connected inside your sub-panel will go to each respective bus, they just won't be bonded in the subpanel.
Click to expand...
This must be what it's like for other people to read Knife Steel Nerds. How do so many electricians work alone when they have to drive a neutral bus and a ground bus at the same time?
 
The "main" panel is where the main disconnect is. That would be the breaker connected to the utility entrance. Might not be a distribution panel. Might be just a breaker. Depending on your configuration and where you live, this might me outside on a utility pole or in your one and only distribution panel. The advice given here is good, but I can see where it would be pretty confusing to the person not familiar with electrical theory and code. Contact the AHJ in your area (that would be your code inspector) and ask him for advice. Most of these folks will tell you what they want to see. Do it right. Pull a permit and avoid a dangerous situation later.
 
Read that few times, I think I understand now I have illegal neutral-to-ground bond at A/C subpanel. It is 50 y.o. house, not sure when the A/C was added.

Here is my A/C panel. Incoming conduit has only 2 black and one ground, no neutral. Am I in trouble? Should I pull the neutral from main house breaker box to this one?

20181008_143800.jpg
 
Is it a sub panel or simply an ac disconnect? It is code in most places to have an ac disconnect within X feet of the unit. You are then stealing power from it to run to a subpanel. Do you have the ability to run a new line from your breaker box to the shed? Realizing in an old house, things are often hmmmmm
 
It is probably a "disconnect" as it located next to A/C unit and have that quick disconnect fuse. Yes, my workshop is stealing power from it. I don't work in the shop when A/C is on, because it is dead hot in the shed in summer anyways and impossible to work.
I =could= run a new line from main house breaker box but only if it is absolutely necessary. Lots of work and time for me, or lots of money (contractors are very expensive here in San Jose). Kind of on budget now, just paid for new workshop shed and now facing another 3K for a new grinder

Just to clarify, I was not the first who ran that conduit from A/C box to the shed. There was an old shed when I bought the house wired this way, and conduit is properly buried - I only replaced the older wire in it (was 12AWG) to new 10/3
 
Ahhh... I guess I misunderstood. That does apear to simply be a fuse box / disconnect for your Air Conditioner. If I were you, I would strongly consider running a separate sub panel for your shed. You really shouldn't be using your disconnect ground conductor as a return path for your 110 shop circuit(s). Does it work? Yes. Will it make your house explode? Probably not. Is it up to code? No.

What size is the buried conduit that supplies the disconnect? If it's 1/2" you'll want to run another conduit, BUT, if it's 3/4", you can potentially run 4 more 10AWG conductors through it to feed a seperate 30 amp sub panel. You'll probably want to run an additional j-box just before the disconnect, just so there's room to route the new conductors to the sub panel as necessary.

Worst case, you could fish one more conductor from the main to the disconnect to give you a neutral for your 110VAC circuits, but technically, your A/C should be on a dedicated circuit. I suppose you could also replace your disconnect with a subpanel, so that you can at least disconnect power to your A/C while running power to your shed, but pig tailing into it the way it is now is really not ideal.
 
Pardon me, should have been more clear, yes A/C = air conditioner. For some reason I never though it could be interpreted other way.
Anyways, thanks Andrew - I got the point. Need to fish a neutral conductor to a disconnect box at least. This is for 110 only.
And 220 doesn't need a neutral - only 2 hot and 1 ground, right?
And my next project would be to run a separate conduit from the main house box.

(Offtopic) speaking of a 220 grinder, leaning towards KMG-TX after all. They have it in stock and shipping now. By price/value/availability I don't see any alternative at the moment. Loved TAG 101 but it is discontinued and who knows when new model comes, NRT have 7 week lead time and $400 over KMG-TX, and TW-90 is even more expensive and there is also wait list.
 
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