Replies

1. 
   Stumper | Aug 30, 2006 08:04am | #1

   I'm not sure why you would need so much ampacity. If you plan on having more than one large machine working at once, then add all the potential machine amperage draw that you will be running at one time and then size your panel/conductor accordingly. For my own use, I have a branch circuit from the main panel that has a capacity of 40 amps. My dust collector and compressor are the two biggest draws so I put each of them on separate 220VAC circuits. All the rest of the 220VAC machinery are on the same circuit but not on the circuit with either the dust collector or compressor. The 110VAC machinery is plugged into two separate circuits and then I also have two separate circuits for lighting. For about 95% of the time, I'm the only person using machinery, but even on the rare occasion that there has been more than one person, I've yet to trip a CB. The one exception was when I was using an electrical heater, a treadmill, and a large TV on the same 20A circuit at the same time!
   There are some other factors to consider as far as conductor size is concerned; distance being the main one--the longer the distance, the larger the conductor needs to be to avoid unnecessary voltage drop. Seems to me that there has been an article in FWW on this very topic published not too long ago--it's worth a look!

   Good luck,

2. 
   jackplane | Aug 30, 2006 03:47pm | #2

   60A is plenty for a shop that size. Unless you plan to work there with help, and have machines constantly running, you should have no problem.

    

3. 
   Rennie | Aug 30, 2006 04:00pm | #3

   One caution, and I may not be correct in this - Check with the local inspector.

   I seem to remember that the number of circuits you have in a panel is limited by the overall amperage available at the panel. In other words, you may be able to have a greater number of circuits (depending on the individual amperage rating for each) available in a 100 amp panel than a 60 amp panel. This will be important if you plan to have individual circuits for your major tools and several circuits for lighting, bench power, etc.

   Determine how many circuits (including amperage requirements) you will need, add a couple more for future expansion, and then see if you fall within the allowable limits. Frankly, telling the inspector you don't plan on running more than one machine at a time will probably not interest him/her at all. Having 10 breakers totaling 240 amps in a 60 amp panel will.

   Rennie

   A man is a fool if he drinks before he reaches the age of 50, and a fool if he doesn't afterward.
   Frank Lloyd Wright

1. 
   ron123 | Aug 30, 2006 05:48pm | #4

   I thought that you can take a panel that is rated for 150 amps, and replace the main breaker with a 60 amp breaker.  This would give you lots of spaces, but still never be in danger of overloading the feeder wires. 

   Does this sound correct?

   - Ron

1. 
   Rennie | Aug 30, 2006 05:54pm | #5

   Not sure about that, but I do think you are limited to the total amperage of all individual breakers as a ratio to your main. Assuming your shop would not have anything less than 20a breakers, in a panel with a 60a main you might be limited to 6 or 8 breakers @ 20a each. Number of spaces available really has little to do with it as the spaces are useless if you max out the main with fewer breakers than will fit in the panel.

   I wish I could remember the ratio - I think it's around 200%, but I can't remember. It's been several years since I wired my shop.Rennie

   A man is a fool if he drinks before he reaches the age of 50, and a fool if he doesn't afterward. Frank Lloyd Wright

1. 
   mudman | Aug 30, 2006 07:22pm | #7

   I reciently had my shop inspected when the buisiness park I am in was incorperated into the city. I asked the inspectors about the relationship of sizing the service supply, the panel capacity, the number of circuits, and their total wattage (or amperage). He explained that the residential formula I am familular with:

   (pick the heating or cooling system <which ever is higher> and add to that any other continously supplied circuits <things that are hard wired like the pool equipment, water heaters, venting systems, etc.>, then add to that %50 of the remaining general lighting, kitchen, and outlet circuits, multiply all that by 10% and you get the minimum panel rating)

   dosent apply to comercial aplications, like wood shops. He said larger instalations must be engineered by a master electrician versed in comercial/ industrial enviroments, and smaller instalations like mine, are aproved if the inspector thinks it is OK. He told me that one of my sub panels (60 amp, 24 spaces, 13 circuits, with most of my machinery on it) was borderline. Since it is a sub panel and the main panel, which is 200 amps, has most all of the general lighting and climate controll circuits he was OK with it. He also said if I ever triped the sub panel breaker I need to upgrade the supply to it. Which is obvious to me.

   My point to all this is that the final say in these small industrial and home based shop installations is what the inspectors say it is. And that varies from day to day, inspector to inspector, and municipality to municipality. Also the residential formula has a got all kinds of flex in it. I see all the time in 4,000 sqft + homes that the supply comes nowhare near what the formula I was tought gives.

    Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

1. 
   Rennie | Aug 30, 2006 07:39pm | #8

   varies from day to day, inspector to inspector, and municipality to municipality

   Amen.Rennie

   A man is a fool if he drinks before he reaches the age of 50, and a fool if he doesn't afterward. Frank Lloyd Wright

2. 
   jackplane | Aug 30, 2006 06:31pm | #6

   If need be, you can install piggyback breakers-for example double up 2 20 amps where 1 20 amp breaker used to be, as they are half size of standard.