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Thread: Electrical code question

  1. #1
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    Electrical code question

    I tried to get an account to access the electrical code in the sticky above, but no go...
    Does the code require me to have each 220V machine on a separate circuit with a separate breaker? Or can I double up machines not used together, (say a tablesaw and bandsaw), on a single 220V breaker? I do this routinely with my 110V machines - just plug them into the nearest outlet.

  2. #2
    Doesn't mean its code, but when my electrician wired my shop, he put all the 220's on one circuit. He said anything 3HP or under if you're using one machine at a time.

    Now I have a dedicated 200A service, but at the time I was working off a 60A feed from the house.

  3. #3
    It is obviously OK if the wire is large enough for all the 220V tools to be running at the same time. But that may not be what you plan. I don't think the NEC says you cannot have multiple outlets off a 220V circuit and a quick google indicates other agree with that. But I did not dig out my copy and look.

    If you put two 20A 220V tools on a 20 or 30 amp circuit, you will need to be sure they do not both run at the same time. That would overheat the wire unless the breaker tripped. Two 15A on a 30 amp circuit would not be an issue, however.

    So I say what you plan seems fine but you need to add up the 220V loads and compare it to the wire/breaker size. If the total load is less than the wire can handle you are clearly safe. If not, you need to think about whether they could all run at the same time. If so, you probably should get another circuit. Depending totally on the breaker isn't a great plan since they sometimes malfunction. You could also have issues with starting load if the total running current is within the capacity of the circuit but the startup draw is no. You need to look at the startup draw, not just the running current draw in other words. You could possibly avoid a trip by starting one at a time but that is cutting it too close IMHO. Electricity is very handy but can be a bit dangerous. Best to be at least a little conservative.

  4. #4
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    For residential, the NEC does not specify a max # of receptacles on a circuit as I recall.

    So as above, as long as you're not over current limit on the circuit, and you have appropriately sized wiring.. you are good.
    ~mike

    happy in my mud hut

  5. #5
    Code-wise, I believe you're fine. Obviously dust collector, compressor, and anything else automatic or likely to run at the same time should be on a separate circuit. I think an inspector would actually enforce that if they were inspecting a building designed as a workshop.

    Bruce

  6. #6
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    Quote Originally Posted by Josko Catipovic View Post
    I tried to get an account to access the electrical code in the sticky above, but no go...
    Does the code require me to have each 220V machine on a separate circuit with a separate breaker? Or can I double up machines not used together, (say a tablesaw and bandsaw), on a single 220V breaker? I do this routinely with my 110V machines - just plug them into the nearest outlet.
    Code may not specify a limit but your local electrical inspector might (if it will be inspected.) I put multiple 220v outlets on one breaker since I'll use just one at a time.

  7. #7
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    Quote Originally Posted by John K Jordan View Post
    Code may not specify a limit but your local electrical inspector might (if it will be inspected.) I put multiple 220v outlets on one breaker since I'll use just one at a time.
    I always love arguing with inspectors. It's fun.
    ~mike

    happy in my mud hut

  8. #8
    Quote Originally Posted by mike stenson View Post
    I always love arguing with inspectors. It's fun.

    Sure it's fun, but remember they have a MAGIC PEN. It determines whether you get power or not. Over my working life, I battled a couple of inspectors. Score was inspectors 1, me 20+. When working in a new to me town, first day, local inspector and I would have lunch. In discussion of project, I would always ask what gives him the most problems. You can rest assured it was perfect on job. Some times inspectors do have to be reminded of the rules. Last permit required job I did was designed by a PE. Job specified 1/2 " galvanized bolts. Code called for 5/8" galvanized bolts. Had to remind inspector that drawings had a PE's seal on them, so he was over ruled. No hard feelings on either's part. Once pouring a concrete floor, had a set of "gang studs" carrying mico-lam beam for second floor. Footing was 2' X 3', so I built up a pier using three 8X8X16 masonry blocks, which would be filled with concrete as part of floor pour. Inspector said he didn't think it would carry the weight safely Took a rainy day, and schooled him. Masonry units have a bearing strength of 2000PSI per nominal face size. Each block would support 2000# X 16 X 2, or 64,000 pounds, times three for a total of 192,000 pounds. Because I was pouring them solid, bearing strength went up to almost three quarters of a million pounds. Asked what bearing strength did they use for soil, and was told 2000 # per square foot. So footing they approved would hold 2 X 3 X 2000#, or 12,000 pounds, while my pier would hold almost 3/4 million pounds. Poured my floor the next day. As for loads on circuit, the size of wire determines that, not the number of outlets.

  9. #9
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    Yeah, the key is to be right. It helps to have cred as well. Most importantly, it needs to be professional. Being antagonistic does no good.

  10. #10
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    Putting multiple receptacles on one circuit is definitely allowed and you can plug in as many items as you’d like. As long as wire sizes, receptacles and all wiring devices are wired appropriately with the proper sized breaker you’re fine according to NEC. Another item to help with this understanding is a continuous load is defined as operation greater than 3 hours continuously. I don’t think I’ve ever ran any of my equipment continuously for 3 hours. If you’re a production shop this is likely different. Intermittent loads are allowed to have breakers sized at 100% as opposed to 80% continuous operation. A caveat is that motor loads are considered continuous.
    I always assume the 80% rule to be conservative.
    I think your concern isn’t the NEC but practical nuisance trips. Woodworking machinery is typically motor loads. Dedicated motor load circuits have a number of rules to follow per NEC (some may surprise you how you can actually use smaller wiring and such. It requires proper thermal protection overloads in addition to breakers. Likely the equipment for a personal shop this protection is built into the equipment/motor).
    So the main thing is just to make sure you’re not going to cause yourself grief. A few hours wiring up a separate circuit can be time well spent. Additionally, if you do find an issue you didn’t think of then it’s fixable since usually shops are fairly easy to add a circuit assuming your panel is in or near your shop.
    Last edited by Eric Arnsdorff; 06-17-2020 at 7:57 AM.

  11. #11
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    One additional item in reference to the voltage. Europe as well as other parts of the world use 230 VAC for residential power. That is the lowest they use. The 220/230 VAC voltage doesn’t present any additional hazard per se.

  12. #12
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    If it's an inspected job, as a non-professional I would make the powers-that-be happy. Pick your battles.

  13. #13
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    It doesn't matter (from a code perspective) what you plug in to a circuit; that's outside the scope of the code. Hard wired installations are different, but that wasn't the OP''s question. Typically when you get inspected nothing at all is plugged in to the circuits. The inspector is not going to be checking in on you twice a week to make sure you haven't put your toaster and waffle iron on one outlet.

    What matters is that the wire (and other components) are sized to match the breaker on the circuit, that's about the only thing the inspector cares about with respect to loads in a shop.

    From a practical perspective I put large loads that may run simultaneously with other machines (eg DC, compressor, air conditioner) on dedicated circuits and other machines on shared circuits in my one-person shop.

  14. #14
    As others have posted, the NEC does not regulate the number of machines plugged into a 220/240/250VAC circuit.
    In a one man shop where you are the only one using a 220 volt machine, one circuit with multiple outlets is fine. The issue is when you add a 220 dust processor, or have another person in the shop using a second 220 machine.
    If you are able, install 2 more dedicated 220 circuits than you'll need.
    220 outlets are available with either one or 2 (duplex) outlets. Use the duplex version and split wire with the top outlet on one circuit and the bottom on another.
    Last edited by Billy Merrill; 06-18-2020 at 11:47 AM.

  15. #15
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    Yea, if I'm not mistaken, the limits on a 240v circuit to one endpoint tend to be for certain appliances in a residential setting. General purpose circuits...like in our shops...are more flexible. While my current shop setup "primarily" has dedicated circuits for my machinery, several have multiple outlets on them because of my rearranging things over time. It was easier to run from a j-box to a new location than to move an entire circuit. If I ever build a new shop, I'll probably have less physical circuits with multiple outlets for those machines that it's practical to share in a one-person operation. DC, CNC, compressor and HVAC would all still have dedicated circuits for obvious reasons.
    --

    The most expensive tool is the one you buy "cheaply" and often...

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