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Question for the electricians

Discussion in 'General Signmaking Topics' started by mark in tx, Aug 10, 2012.

  1. mark in tx

    mark in tx Very Active Member

    Oct 25, 2005
    Harker Heights, Texas
    Been having an interesting issue with electric in the shop.

    I am running a shop vac and a panel saw on the same circuit. Nothing else on the circuit.
    Turn on shop vac, then saw, poof! circuit breaker blows.

    Replaced the outlets, they were very old, everything worked fine for 2 weeks.

    Today, turned on shop vac, then saw. Poof! Circuit breaker tripped.

    hmmm.....now is the time to try crazy things.

    I plugged the panel saw into a 100 foot extension cord, changed nothing for the shop vac and everything works.

    Can't remember enough of my high school shop class, but if I remember right, the extension cord induces more resistance, which increases the load on the circuit. Which should actually make the circuit more prone to overload and trip the breaker.
    But I'm getting the opposite effect here.

    Any ideas from the smart people?

  2. Gino

    Gino Premium Subscriber

    Jun 7, 2006
    Sounds like you have a short somewhere in one of the cords.... or perhaps both. It touches, then it doesn't.

    Be sure your breaker is the correct size. Also, how or why are you certain these two items are the only thing on this particular circuit ??

    If the receptacle was indeed as old as you claimed, I would think there might be something along the way which branches off to another room or set of receptacles.... possibly where something is running more often.
  3. ellsmako

    ellsmako Member

    Apr 21, 2010
    not really helpfull for your question,... but,... maybe get another circuit put in.
    Whats the rating of the breaker you are using.?
    Could be a tired breaker,

    Saw will draw a spike compared to the shop vac. when the motor starts.
  4. Steve G.

    Steve G. Member

    Tripping is cause by drawing too much or too quick. Could be many things.

    Saw or shop vac could be going bad. Breaker could be bad, or more likely, Loose connection at breaker. (I've seen that multiple times)

    Adding the 100' cord is opposite of what you stated. Saw will not draw as much current because of the resistance, Therefore less / slower current flowing through and not tripping breaker, but the lower current supply would be detrimental to saw in the long run.

    I would Check connections at breaker and or change out breaker.
    Obviously, DO NOT open the panel if you are not qualified.
  5. Hicalibersigns

    Hicalibersigns Member

    Apr 8, 2011
    Ditch the 100 ft. cord unless you want to replace the motor on the saw. Most common outlet circuits are 15 amp circuits. The saw and the vac combined are probably right at that limit. Thing is, when you fire up a motor there is something called inrush current. So, a motor that will draw 2 amps running might have a 20 amp inrush current for just a few milliseconds. So if you have one or the other running and fire up the other one the inrush is tripping your breaker. Save yourself a lot of trouble and move one to another circuit, or spend a few bucks and hire an electrician if you don't have another circuit available.
  6. Cross Signs

    Cross Signs Active Member

    Mar 30, 2006
    Clearwater FL
    I had something similar at my old shop. Table saw and shop vac would trip the breaker. But. If I powered on the saw first, let it run for a few seconds and then switched on the vac. It would run both fine. The vac draws less power on initial startup. Of course when your running that close to the outside of the envelope, If I was cutting something heavy or ripping some wet pressure treated lumber the breaker would trip.
  7. mark in tx

    mark in tx Very Active Member

    Oct 25, 2005
    Harker Heights, Texas
    Told you it has been a long time since high school, but yes, the cord would mitigate the spike.
    It is a 20 amp circuit.

    Going to look at the breaker itself next.

    Thanks for the help!
  8. ThinkRight

    ThinkRight Active Member

    Nov 13, 2011
    Atlanta Ga
    What he said .
  9. Stealth Ryder

    Stealth Ryder Very Active Member

    Jul 16, 2009
    The Circuit Breaker...
  10. Mosh

    Mosh Major Contributor

    Oct 19, 2009
    Commercial shop we run 50 amp breakers on our saws and heavy stuff....how heavy is the cord? There are cords and there are heavy cords...."A Christmas Story" comes to mind....
  11. John L

    John L Very Active Member

    Apr 28, 2007
    Its either too much amperage through a breaker (too much on the circuit, under sized wire gauge, undersized breaker rating, too long of a wire run, etc etc etc) ... or a ground fault (bad equip, shorted or loose wires, bad breaker, etc etc etc).

    If nothing seems out of whack from a quick look around (burnt smells, hot wiring, melted stuff, loose connections, etc) I'd start by reading the plates on equip, then check their actual amp draw with an inductive ammeter. Compare this to the size of breaker, size of wire, and length of wire that makes up your circuit to the equip. Also check the amps moving through the wire as it leaves the breaker. Many times people think that the equip is causing the trouble and theres a whole string of lights, outlets, etc tapped off the same circuit or something.

    It's impractical to thoroughly cover electricity here. A good electrician might be your best bet. Good luck, be careful.
  12. signage

    signage Major Contributor

    Oct 5, 2005
    :goodpost: It could be any number of things, like said above.
  13. LittleSnakey

    LittleSnakey Member

    Jan 12, 2008
    Main problem is that the total of the 2 devices you are trying to run is more than 20a.
    Either run them on separate circuits or run one at a time.

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