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Old 12-09-2012, 10:18 PM   #1
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Dedicated circuits?


I am building a wood shop and have a table saw and dust collector. They are 110/220. I will be wiring them for 220. They pull 13 amps each at 110 and 6.5 at 220. Together at 220 they will pull 13 amps.

A lot of people say they should both be on their own dedicated circuit. What is the benefit? Why not just put them both on one 20 amp 220 circuit as combined they will be far below 80% of the 20 amp draw?

Unless there is some benefit I would rather run one line and save space in the box and only use one double pole breaker.

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Old 12-09-2012, 10:22 PM   #2
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Dedicated circuits?


The equipment specs may require a dedicated circuit.

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Old 12-09-2012, 10:59 PM   #3
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Dedicated circuits?


Can you elaborate? What specs would make a dedicated circuit a requirement?
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Old 12-09-2012, 11:00 PM   #4
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Dedicated circuits?


Read the instruction manuals that came with the equipment.
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Old 12-10-2012, 12:33 AM   #5
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Dedicated circuits?


If it were my shop, I wouldn't think twice about putting both on a 20 amp circuit. It'll easily handle the load.

The only potential problem would be the table saw is rated for 6.5 amps, but cutting a 2X with a dull blade will make it pull more like 15 or 20 amps when it lugs down. The motor overload should trip before the breaker, but it might not.

No big deal, just reset it and start up again.

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Old 12-10-2012, 12:57 AM   #6
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Dedicated circuits?


Quote:
Originally Posted by Troy32 View Post
I am building a wood shop and have a table saw and dust collector. They are 110/220. I will be wiring them for 220. They pull 13 amps each at 110 and 6.5 at 220. Together at 220 they will pull 13 amps.

A lot of people say they should both be on their own dedicated circuit. What is the benefit? Why not just put them both on one 20 amp 220 circuit as combined they will be far below 80% of the 20 amp draw?

Unless there is some benefit I would rather run one line and save space in the box and only use one double pole breaker.

Troy...I understand what your trying to do.....and as a fellow woodworker, I too have a lot of stuff in the garage....

As everyone said, no requirement to have a dedicated ckt.....

But...one that never changes....is change.....your power tools wear out....you upgrade....etc.

One of the things you will notice if you tie them together is that you will get a slight power drop on the saw when the dust collector kicks in.....even though the current draw for the saw is a little over 6 amps....when the saw kicks in, your going to get enough voltage drop on the total ckt to notice.

Personally....I wouldn't do it.....yea, it's a bit more work to run another ckt....but in the long run, it will be more flexible.
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Old 12-10-2012, 08:55 AM   #7
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Dedicated circuits?


More for the sake of future expansion and your mention of saving space in the box (panel) I would recommend running an 8-3 gauge or 6-3 gauge cable for 40 or 55 amps respectively. You can avoid installing a subpanel in the shop now provided you use at most a 20 amp (double) breaker back at the panel.

Usually the tool instructions for any one tool won't call for a breaker less than 20 amps. What you need to be aware of is startup amps. The breaker will take a few seconds of a little over 20 amps without tripping. But if one tool draws over 20 amps all by itself for that few seconds, having the other already running at its 6-1/2 amps may be enough to trip the breaker immediately.
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Old 12-10-2012, 09:25 AM   #8
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Dedicated circuits?


Thanks for the info so far. All good points. I already have the wire and breakers etc to run 2 dedicated circuits and it is not much more work. My question is more of a theoretical one. I always like to know the reasoning for what I am doing.

While working on the wiring i Just began to question why you would use 2 20 amp circuits over 1 30 or 40amp circuit. My GUESS was that using a table saw that drew 7 amps you would have little protection for the machine. In other words a 40 amp breaker would let a lot of amperage go through the machine before the breaker cut off. A 20 amp would trip sooner with less amperage hopefully not causing damage to the machine.

I understand the breakers main function is to protect the wiring but I would assume if matched to the machines amp draw it would also protect the machine.

Again I am not trying to argue one way or the other just like to understand the benefits and draw back of all options.

Thanks
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Old 12-10-2012, 09:33 AM   #9
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Originally Posted by AllanJ View Post
More for the sake of future expansion and your mention of saving space in the box (panel) I would recommend running an 8-3 gauge or 6-3 gauge cable for 40 or 55 amps respectively. You can avoid installing a subpanel in the shop now provided you use at most a 20 amp (double) breaker back at the panel.

Usually the tool instructions for any one tool won't call for a breaker less than 20 amps. What you need to be aware of is startup amps. The breaker will take a few seconds of a little over 20 amps without tripping. But if one tool draws over 20 amps all by itself for that few seconds, having the other already running at its 6-1/2 amps may be enough to trip the breaker immediately.
I was considering running a sub panel but decided against it. I actually have a spare panel I could use with the breakers in it. Previous owner was an electrician and he left a lot of stuff in garage I just have a small shop in my basement and only I will work with the tools so I will never use more then one tool and the dust collector at one time. I will run 3 total circuits of 12/2 which cost $75 for a 250 fooft roll.

I definitely understand the 'slippery slope' aspect of wood working and upgrading. It is an unfinished basement and the panel is 50 feet from the farthest point in the basement so it is not a big deal to rerun the electric if I ever decide to really go crazy with some bigger machines. If I was finishing the walls etc I would definitely go with the sub panel.
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Old 12-10-2012, 11:10 AM   #10
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Dedicated circuits?


Quote:
Originally Posted by Troy32 View Post
While working on the wiring i Just began to question why you would use 2 20 amp circuits over 1 30 or 40amp circuit. My GUESS was that using a table saw that drew 7 amps you would have little protection for the machine. In other words a 40 amp breaker would let a lot of amperage go through the machine before the breaker cut off. A 20 amp would trip sooner with less amperage hopefully not causing damage to the machine.
You are correct.

The appliance (tool, etc.) also has a maximum circuit amperage rating. Unless a higher rating is indicated this maximum is usually 20 amps.

The power plug shape and size can be used to infer the appliance amperage rating if that is not stated in the instructions.

So you may not connect the saw or air cleaner with 20 amp rating to a 30 or 40 amp feed from the panel without a subpanel in between with a 20 amp breaker for the circuit actually feeding that tool.

By the way, receptacles are also rated for different amperages and you may not put, say, a 20 amp receptacle on a 30 amp circuit. (You may use or intermix 15 and 20 amp receptacles on a 20 amp circuit with a minimum of two (round) single 15s or one duplex 15 or one 20 altogether.)
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Last edited by AllanJ; 12-10-2012 at 11:17 AM.
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Old 12-10-2012, 11:53 AM   #11
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Dedicated circuits?


Thanks for the confirmation. I will use the dedicated circuits like I originally planned. I just feel better knowing why it is a better choice.

Thanks for everyones help.
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Old 12-10-2012, 12:32 PM   #12
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Dedicated circuits?


Right! By using a dedicated circuit and a lower amperage breaker, you not only protect the wiring, but can also limit damage to the equipment in the case of a malfunction with that equipment. Or become aware of a malfunction with certain equipment if it suddenly starts drawing more amperage and is tripping the breaker.
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Old 12-10-2012, 01:42 PM   #13
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Dedicated circuits?


Another good point. Keep you from continuing to use a machine that is malfunctioning.

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