How safe is this power configuration? - Router Forums
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post #1 of 23 (permalink) Old 06-13-2014, 07:51 PM Thread Starter
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Default How safe is this power configuration?

I have a regular 2 socket, 15 amp outlet in my garage. I need to run my miter saw and shopvac at the same time, the saw draws 15A and the shopvac 8.5A.

I've currently been running them off one outlet through a 50 foot 14AWG extension cord with a 3 way splitter at the end. The other socket is running to a power strip by an extension cord that is powering by workbench light.

I know very little about electricity and it's boundaries, how bad is my current set up? What risks are there with this?

-Zach

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post #2 of 23 (permalink) Old 06-13-2014, 08:53 PM
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Obviously, Zach, if both devices are a full load amps(FLA) you will trip the breaker if it is 15A. The miter saw will rarely hit the full 15A rated though. As you likely only run the miter saw a few seconds at a time, you may well get by with the situation.

That said, there would be less chance of tripping the breaker if both unit ran on separate circuits.

If both units ran at FLA for any period of time, and the breaker doesn't trip, then there is a likelyhood of overheating the wire and even possibly causing a fire.

I have found that hand tools are the best choice when I want to make mistakes at a slower rate of speed.

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post #3 of 23 (permalink) Old 06-13-2014, 09:41 PM Thread Starter
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While it hasn't tripped the breaker yet, the lights do dim briefly when i run the saw, even if only the saw is plugged into the outlet. At what point does the saw actually hit 15 amps?

I don't have another receptacle (outlet) near the saw, i may have to have an electrician put one in.

Is it OK to power the saw over an extension cord like that provided its the right gauge?

-Zach

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post #4 of 23 (permalink) Old 06-13-2014, 10:31 PM
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With extension cords, heavier gage is better. I would look for a 12 ga cord for that saw over that distance. Current is a unit of 'electron flow', so you want as big of a pipe (conductor) as possible, and as short of a run as necessary. Using a long light gage extension cord could cause the impedance in the circuit to effect the power available at the tool... again, try visualizing filling your bathtub with a very long, skinny garden hose. The pressure (voltage) at the end will drop, and that could cause damage to your tools, or the electrical circuit. It's probably not going to be the case with the tools you are describing, but it's up to you if it is worth the risk of using the 50 footer when a 25 footer would do.

Start up is when current draw is usually highest. Make sure the vacuum is running before starting the saw, so you aren't hitting the circuit with both starting currents at the same time.

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post #5 of 23 (permalink) Old 06-14-2014, 09:12 AM
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Zach...You are getting good information here. Having been a master electrician for past 36 years I would suggest you get an electrical contractor to give you a bid on adding some additional circuits, not just outlets. The lights dimming is a dead give away as to the existence of a real problem. Be sure to ask other residents in the home if other lights ever get brighter or dimmer when you start the saw. If so, I would really wait till you get the problems fixed before doing any large projects. As far as cords go...larger size and shorter is better!
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post #6 of 23 (permalink) Old 06-14-2014, 09:29 AM
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I use master/slave switches on my saw and router tables which are programmable. when the saw is switched on there is a three second delay before the dust collector comes on, this ensures that the initial surges of the two tools don't co-inside and allows the saw to reach full speed before the Dust collector comes on. When the saw is switched off the dust collector runs for a further six seconds to collect residual dust. Because the router picks up speed almost instantly I only have a half second delay before the Dust collector comes on and it carries on for five seconds. The unit is in the far left corner of the saw bench.
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post #7 of 23 (permalink) Old 06-14-2014, 09:53 AM Thread Starter
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Thanks guys, super helpful.

I found an old kill-a-watt meter and tried it out on the setup, here are the results.

Miter saw only
Startup (Peak): 18A
Saw running: 7.5A
Saw cutting: 10A

Shop vac only
Startup (Peak): 12A
Running: 8.4A

Saw and Shop vac:
Shopvac running and then starting saw (peak): 21.6A
Both running: 16A
Both running and saw cutting: 18A

I notice the saw bogs down a bit while cutting and both are running, seems perhaps the motor isn't getting the juice it needs?

I think the answer is clear, I need to get one on another circuit. I thought these were interesting and wanted to share.

-Zach

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post #8 of 23 (permalink) Old 06-14-2014, 11:14 AM
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A 15 amp is typically wired with 14 gauge and I consider 14 gauge for lighting or walls that use very little draw like some of my living room circuits .
As mentioned your past the edge . I would have felt better if it was wired with 12 gauge which is a 20 amp circuit .

In the future I will need 90amps worth of circuits just to run my home theatre , and that's not including running the vacuum

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post #9 of 23 (permalink) Old 06-14-2014, 11:24 AM
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One other thing to keep in mind is a lack of current is very hard on equipment , motors and electronics etc . I'm sure Harry would agree
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post #10 of 23 (permalink) Old 06-14-2014, 02:21 PM
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An another good move would be to rewire the table saw to run 220v so it would not bog down at all and the motor would last a lot longer. Having an electrician come and locate the outlets so no extention cords are needed would be ideal!

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