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Thread: Electric disconnects

  1. #1
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    Electric disconnects

    Hi folks,

    Has anyone here installed a disconnect switch which serves a series of outlets or machines?

    I'm looking to run a subpanel for the machines in my shop and would like to install an appropriate disconnect switch between the main panel and the subpanel.

    Any recommendations?

  2. #2
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    You don't necessarily need the disconnect, you could have a main breaker in the subpanel. But code would dictate depending on the location of the subpanel. Same building, close to an exit, etc.

    Otherwise any disconnect is fine as long as it is appropriately sized for the amperage.

  3. #3
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    I believe that a breaker isn't supposed to be used as a regular "disconnect"...they are not meant for constant on/off cycles. The OP is going to be better served with a true disconnect switch to "drop power tool" power in his shop. I've never installed them, but it should be pretty straight forward...the disconnect needs to be rated for a minimum of what the feed to the sub-panel is built to. It may need to be sourced from an electrical supply house to get one that's a lockable switch rather than a pull-disconnect like is typical for an HVAC setup.
    --

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

  4. #4
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    Quote Originally Posted by Jeff Bartley View Post
    Hi folks,
    Has anyone here installed a disconnect switch which serves a series of outlets or machines?
    I'm looking to run a subpanel for the machines in my shop and would like to install an appropriate disconnect switch between the main panel and the subpanel.
    Any recommendations?
    The best answer to your question would be from the electrical inspector, assuming you plan to have it inspected.

    I didn't provide a separate disconnect on any of the sub panels I've installed. Do you plan on disconnecting often or just for emergency? The industrial electrical supply where I buy all my electrical supplies does have some heavy duty disconnect switches made for that.

    I did install disconnect switches for two 5amp motors, one for the cyclone and a separate one for the air compressor.
    I used this one: https://www.amazon.com/Leviton-MS302.../dp/B002MPQ51O
    This is a heavy-duty switch.

    If you decide on separate disconnect switches don't make the mistake of getting this cheaper 30 amp switch: https://www.amazon.com/gp/product/B000HEIVZK . I bought one only to discover it will not work as a 5 hp motor starter/disconnect. Although advertised as 30A-120/277V the switch is labeled: "MOTOR LOADS OF 24 FULL LOAD AMPS. MAX. AND 2 H.P. MAX". Although not indicated, the wire connection appears to be limited to 10 ga, another problem for my 5hp motors circuits.

    I won't use a breaker as a routine disconnect although I know people who do and have done so for years. I wouldn't hesitate to use it for occasional and emergency use.

    JKJ

  5. #5
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    Every heavy industrial shop I've ever seen ONLY used the breakers to turn on/off all the shop lighting in the place. On in the morning, off at night. Of course, this is the single phase 277v on a 480/277v system so they are quality breakers bolted in place.

  6. #6
    If you're not going to be switching it off and on every time you go and leave the shop, but just occasionally, such as when you go on vacation, a breaker will work fine for you. Get a subpanel with a "main breaker" sized appropriately to your feeder wire (or larger). So if you have a 50 amp breaker in your main panel (feeding your subpanel), you can put a 50 amp (or larger) "main breaker" in your subpanel.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  7. #7
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    Oglesby,Il.
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    Not the most relevant but I recently installed a disconnect switch for a gentleman’s shop sub panel that fed the woodworking machines solely for the purpose of killing the power to all of them for safety....he has 4 grandsons that are very curious and like to nose around grandpas stuff.....it’s always locked out when he isn’t in the shop...
    I can sure make a mean pile of Saw Dust !!!

  8. #8
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    I put two disconnects off my meter base when I upgraded to 400amp in 2013. One for the house and one for the new shed. That way when It came to do electric in 2014 for new shed I did not have to call for a meter disconnect.
    Glad its my shop I am responsible for - I only have to make me happy.

  9. #9
    I've got a subpanel just above the main panel in the shop that feeds all the 240V machines and the 120V outlets that are for machines. It is controlled by the 60A breaker in the lower right hand part of the main panel. That way I can drop all the power to the machines with one switch while leaving on the power to the lights, heater, fridge, AC, etc. I did it originally to be able to make the shop safer when the my kids or the Cub Scouts were out there, but now I kill the power to the machines every time I leave the shop for the day. It just feels more secure.

    The only thing the electrical inspector wasn't thrilled with was the height of the machine subpanel, but he was OK with it since those breakers were still accessible and would not likely be used often. He actually liked the idea of the subpanel and said something about wanting to put one in his shop.

    panel.jpg

  10. #10
    What is the purpose of the disconnect? Safety when changing tooling, peace of mind when you leave, fire risk?

    Just curious. You can certainty use a disconnect to shut a whole panel down, or single circuit. Not the cheapest method depending on voltage and amperage though.

  11. #11
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    Martin, there are a lot of folks with "home shops" (and even small pro shops sometimes) that prefer to have a way of totally shutting power to machinery for safety reasons...grandkids/children might be just one example. I believe that in general, this is the context of the reason for OP's question.
    --

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

  12. #12
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    Quote Originally Posted by Jim Becker View Post
    Martin, there are a lot of folks with "home shops" (and even small pro shops sometimes) that prefer to have a way of totally shutting power to machinery for safety reasons...grandkids/children might be just one example. I believe that in general, this is the context of the reason for OP's question.
    Jim has it, I want to be able to shut down all power to the machines, partly because I have kids, and partly so I can throw a switch and know that everything is off.

    The other reason for a disconnect is for the line that feeds a phase converter and the 3-phase panel. I don't want the phase converter to be on all the time.

    What's interesting is that the switch boxes the electrician gave me are just breaker housings, not the type that looks like an over-sized wall switch. I wonder if there's an advantage in one over the other?

    I've been enjoying this part of my shop build, I actually now think it might be fun to be an electrician (no offense to any electricians, I just never thought I'd enjoy the work as much as I have)!

  13. #13
    I first got the idea from the scenery shop of the local PBS station. Back when I was in college, I was helping the old "Newton's Apple" show with a river flood model we built at the research lab I worked at. The scenery shop had a safety switch that killed the power to all the machines, probably for liability/insurance reasons. When I saw it, I thought to myself, that is a really good idea; I will put one of those in when I build a shop some day.

    I like to kill the power when I leave for the day in case I left on the compressor or something else that runs intermittently. It is nice to know everything is off when you leave and be able to do it with one easy switch.

  14. #14
    Quote Originally Posted by Jim Becker View Post
    Martin, there are a lot of folks with "home shops" (and even small pro shops sometimes) that prefer to have a way of totally shutting power to machinery for safety reasons...grandkids/children might be just one example. I believe that in general, this is the context of the reason for OP's question.
    I get it, I was just curious what the reason was as it wasn't stated in the original post. If it were me, I'd just throw a disconnect in front of a sub panel. Put everything I wanted to kill in that sub panel like he was thinking. I just didn't know the purpose.

  15. #15
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    Quote Originally Posted by Martin Wasner View Post
    If it were me, I'd just throw a disconnect in front of a sub panel. Put everything I wanted to kill in that sub panel like he was thinking. I just didn't know the purpose.
    That's what he wants to do...he's just seeking input from others who have done it.
    --

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

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