I have a 240 circuit in my shop to run the tablesaw and planer. This is a 20A circuit, 2 hot, neutral, and ground in a pvc conduit.
I want to run some lights but don’t want to run another conduit from the panel just for this. What is the downside of using one of the hot lines and the neutral from this 240 circuit?
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Replies
The only downside is reduced capacity for your tools and dimming lights when they start
If you use an electronic ballast and fluorescent lights your lights wont dim when you start the saw or planer.....
Unless the saw and planer have 3HP or more motors, you likely wont even notice it with less than 5 ea 8 ft fluorescent lights - split the lights between the 120 V sides.
BTW, didja know that most of the electronic ballasts rated 277V (cheap on ebay cause nobodythinks they can use them) will work just fine off 240 V. Most anyway, the ones with an isolation xfmr ok, but ya gotta takem apart to looksee..
Single phase 277v is common in commecial lighting circuits. That is 277v to ground.
240v residential wiring is 120v each leg to ground and the 240v is phase to phase.
Don't think I have ever seen 240v single phase in residential wireing, but then I'm primarily a commercial electrician.
277v to ground
yep, that is the type I'm using, work just fine on .... that is why I put in the disclaimer for electronic, although I have used a few old magnetic ballasts that way in sheds. Just gotta check the ones you use with a megger to be sure the white wire is isolated from the case and not grounded. Although every one I've ever tried was isolated.
good point though, probably would not recommend installing in anyone's house but your own due to somebody coming along later and replacing with a non-isolated ballast.....
E-ballast
The newer electronic ballast are 120v/277v smart ballast. The olde ones are one or the other. You wire the new one per the schematic on the ballast with hot and neutral to hot and neutral, the ballst figures out the voltage.
Magic?
This is one of those things that separates the pros from the hacks - and the ignorant. It's not so much 'what's wrong' as it's all about the correct way to do things.
(This is also the exact situation that lies behind the instructions I give for running power to a shed, etc.)
You've 'outgrown' your shop once already; why not take the time now to do it right, and ease your future needs as well?
Step #1 is to remove that existing 240v. circuit - assuming you ran the smallest possible wire and used the smallest possible breaker to feed it. If the wire is "oversize," then maybe you can re-direct it, and use it for something new: a sub-panel in the shop.
I wouldn't want a shop panl fed with less than #8 wire, and would really prefer at least #6. This allows you to feed the panel with at least 40 amps- enough for some real work.
At this new panel, you would have properly sized breakers for each tool and can easily add circuits for lights and receptacles.
Now .. for 'what's wrong' with your 'gee, I think it will work' idea ....
The first issue is where you will tie into the circuit. It's pretty rare for there to be ebough slack in the cable to properly make a splice in an accessible box. Ever notice all those 'violation' pics of hackwork at the electrical forums? There are countless pictures of 'flying splices' (no box used) and boxes where the wires inside are barely long enough for the wire nuts to grab them (another violation). Then there are the splices buried under the drywall, pegboard, or otherwise made inaccessible.
Then there's the matter of circuit protection. If the tool is on a 30 amp breaker, so will your 15-amp receptacles ... another violation.
Maybe you've loked at the saw nameplate, and think "gee, it says it only needs 7 amps, so there's plenty of power left on that 20-amp circuit." Wrong. That 7-amp motor might need as much as 40 amps in the first few moments of start-up. If youi already have all sorts of stuff biting into the power available from the 20-amp breaker, Start the saw, and pop goes the breaker. Now you'll be tempted to 'fix' things by simply using a bigger breaker .... who needs rules, anyways?
That leads to the REAL issue with your idea: conflicting theories. Receptacles are an exception to the way we do things; we add them willy-nilly for our convenience, without regard for what they might power. In electric work, our practice is to use the smallest breaker that will power the machine. The idea is so that the breaker will trip as soon as possible if there's a problem. By combining the two circuits on one breaker, you've just tried to mix oil with water, code-wise.
To sum it up: stop improvising and do it right.
There may be some theoretical code issue with regard to the mix of outlets on the circuit (I'm not a code lawyer), but electrically what you want to do is not a problem. Since the main is 20A, if you keep all the wire #12 or larger there's no problem with overcurrent protection.
As to being unbalanced, nothing's ever perfectly balanced. The feed coming into your house is 240V, and then it's split into 120V circuits. Certainly no one ever goes around turning on and off lights in pairs just to make sure they load both sides of the line identically. Of course if you try you can set up a situation (a couple of big electric heaters, eg) that will unbalance the line enough to measure/notice, but not enough to cause any real problems.
Keep in mind that using a 240V circuit to feed multiple 120V circuits actually reduces voltage drop problems vs using separate 120V circuits.
I think you know this as you're not new here.............
but there are a couple posters that have the personality of a postage stamp. While their expertise should be enough, they sometimes have to interject the "you don't know squat" right off the bat. It's a shame as the knowledge on this board has been limited somewhat by the changeover caused migration. Admittedly there's always been a certain amount of unqualified answering going on but usually there's a counterbalance of substantiated information.
Best of luck picking through the maze.
>>>Thanks for the
>>>Thanks for the insults.
I didn't see any.
And when someone, a pro electrician no less, takes the time to key in a multi-paragraph response of cogent advice, I think you ought not to get snippy.
You asked for advice, he delivered it in frank, but well informed terms.
Other than a tripped breaker kills the light?
I wouldn't do it. Mostly because even though light circuits are on a breaker, I have never seen one tripped.
Equipment breakers do trip.
I'm not sure I want to loose the lights, and the tool power all at once.
I had my shop wired so the tool circuits and receptacles are on a relay/contactor (not sure what it's really called), so that if the power drops out, and comes back on the tools stay off. But, the lights and heat will come back on.
I apologize for everything - and nothing!
Sometimes folks see a thread, and wonder if they can apply an idea to their situation. A proper answer will provide enough information that folks can understand some of the thought behind the answer.
Code lawyer? Sure, there's always the 'but it's ONLY code' argument. Well, there's no helping someone who insists on reinventing the wheel.
Search this forum, and you will find many, many threads where someone wants to 'create' 120 where they ran a 240 circuit. Oddly enough, do a further search, and a year back you'll find that same person insisting "but I only want ...," as they go about doing things in as minimalist a way as possible.
Usually they don't want to have to dig up the 300ft. of cable they ran to the pump house and run new cable - though its' hard to feel any sympathy when they were told to run pipe. Or, they don't want to open up walls and such.
Yet, I am puzzled by the resistance to running a new circuit. Most garages and shops have open walls - and if the panel is there, what's so hard about running a new circuit?
Otherwise, the proper way is to have the 240 circuit feed a sub-panel, and to then feed your lights, receptacles, and saw from their separate breakers in the new panel. Put the saw on the same circuit as the light, and you've given yourself on either working 'hot' on the saw, or working in the dark.
I am perplexed by those who insist upon the finest materials, best tools ... then schlock together a 'shop' in as poor a manner as they can devise. Forget the rulebook- there's no substitute for good design.
Thank you, Scott, for your kind words. Yes, I am an electrician by trade. Perhaps not the best ... but I am terrified by the thought of all those worse than I!
Well, I'm not disagreeing at all to what you said, just that you seem to be a little harsh in making your point. I worked on a house where the back porch light and some other stuff was connected to one leg on a dryer circuit. It had two 30 amp screw in fuses on the circuit. What a mess.
AE
Love that last comment.
Fits me to a tee also.
I get the criticism
of being too harsh in correcting the semi-competent guesswork hack posts that some frequently produce here. Don't back down or compromise, you just might save someone's life or property by insisting that "almost right" is never good enough. Keep it up!
My business involves renovating more often than not, older poorly maintained and hacked up residential buildings. The electrical work I have seen is very scary. You are right to be terrified of all those worse than you. They, unfortunately outnumber you by 1000 to 1. I cannot in good concience allow my tennants to live in unsafe conditions, so I rip out and replace all substandard work. It costs me a little more up front, but ethics, safety and piece of mind, as well as practical functionality, trump being cheap, always.
I guess I'll put in gas lights.
Probably the best thing to do is to put in a small subpanel. Probably not totally code-kosher, with only a 20A feed and a few other picky details regarding outbuilding power, but as safe as one could hope for. Then you can at least have the saw and lights on separate breakers, allowing circuits to be serviced, etc (though the breakers would be as large as the "main" back in the house, so they wouldn't really provide protection against "lights out", etc).
What are you doing for lights now?
So this is a new shop with new wire and you want to "bootleg" off of a dedicated circuit to run some lights? You're being penny wise and pound foolish. Dumb idea. Run some more wire.