Wire an auto switch using two feeds.

[mchoms]

I registered as a DIY because it looked like the best option for my situation but am not really a DIY because I always hire an electrician so I will not be doing the work, however my electrician did not know how this could be done. She is extremely busy so I said I would check on the internet.

I want to use a 15 amp Miter saw and and a 12 amp dust extractor at the same time using an auto-switch. I have two available 20 amp circuits (normally with no to very little load on them) but neither can handle all the current by itself. Especially since the vacuum and saw will start at the same time.

Will I be able to use an auto-switch somehow? Is there a product that will work for this? Is there a way this could be wired to work? Or am I stuck having to remember to turn on the vacuum (I never do)?

Your answer can be technical because I teach electrical safety to licensed electricians and my own training is in nuclear physics (30 years in nuclear power). I just prefer to have my close friend, a licensed electrician, do the work.

If there is a better forum for this please let me know.

 

[Lucien Nunes]

I can see some products designed with this in mind, that have separate input power cords for the tool power and extractor power. Just as an example there is this:

Automated Vacuum Switch : Amazon.co.uk: DIY & Tools

Automated Vacuum Switch : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

I'm in the UK where all our domestic power is 230V but we do use 110V tools on construction sites for added safety. This is an equivalent product available over here:

Dust extractor automatic switch 110v 2x 16A

Simply plug a power tool into the left socket, and a vacuum/dust extractor into the right socket. When the power tool turns on, the vacuum is automatically switched on. The vacuum turns off 30 seconds after the power tool, to allow time for the tubing to clear. 230v, max combined load 13A. IP66...

toughleads.co.uk

So I think you will find something suitable that does not require any modifications to your shop wiring.

 

[mchoms]

I can see some products designed with this in mind, that have separate input power cords for the tool power and extractor power. Just as an example there is this:

Automated Vacuum Switch : Amazon.co.uk: DIY & Tools

Automated Vacuum Switch : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

I'm in the UK where all our domestic power is 230V but we do use 110V tools on construction sites for added safety. This is an equivalent product available over here:

Dust extractor automatic switch 110v 2x 16A

Simply plug a power tool into the left socket, and a vacuum/dust extractor into the right socket. When the power tool turns on, the vacuum is automatically switched on. The vacuum turns off 30 seconds after the power tool, to allow time for the tubing to clear. 230v, max combined load 13A. IP66...

toughleads.co.uk

So I think you will find something suitable that does not require any modifications to your shop wiring.

Thank you! The IVAC do not appear to be available in the US. Amazon said it could not ship the Ivac to the US but the Tough Leads appears to be the better option anyway since they use robust contactors instead of relays. I will contact them and see if they can ship to the US. I doubt the plugs will be compatible but that is an easy fix I can do myself. Might even be able to find converters without having to do any wiring at all.

 

[mchoms]

Update. I found the IVAC two power imput autowitch on US Amazon . So problem solved. I have to check and see if they use mechanical relays. If they do I will need to switch them out with solid state relays that can handle 20 amps. I guess I would just wait until the original relays fail.

 

[Lucien Nunes]

OK cool, hope it works out.

So it doesn't sound like you'll be needing the UK-made unit but I should have added a bit of an explanation about how they would differ from a USA-market equivalent. Our construction-site 110V (and it is 110, not 120) is actually 55-0-55V centre-tapped to ground, supplied from a small transformer near the point of use (like your 120-0-120 makes 240V, except that we can't and don't draw any current at 55V because like an old NEMA 10-30 3-prong dryer outlet there's no official neutral in the circuit, only safety ground.) Therefore the contruction of our 110V equiment tends to be a bit different. Everything must be double-pole switched and fused because both wires are technically hots. Such equipment should be absolutely fine on your 120V hot and neutral too, I'm just mentioning it for completeness. I expect the units are designed to handle 120V as the voltage from the small construction site transformers can be quite variable, but might be worth checking.

 

[mchoms]

OK cool, hope it works out.

So it doesn't sound like you'll be needing the UK-made unit but I should have added a bit of an explanation about how they would differ from a USA-market equivalent. Our construction-site 110V (and it is 110, not 120) is actually 55-0-55V centre-tapped to ground, supplied from a small transformer near the point of use (like your 120-0-120 makes 240V, except that we can't and don't draw any current at 55V because like an old NEMA 10-30 3-prong dryer outlet there's no official neutral in the circuit, only safety ground.) Therefore the contruction of our 110V equiment tends to be a bit different. Everything must be double-pole switched and fused because both wires are technically hots. Such equipment should be absolutely fine on your 120V hot and neutral too, I'm just mentioning it for completeness. I expect the units are designed to handle 120V as the voltage from the small construction site transformers can be quite variable, but might be worth checking.

I assume the last sentence was about US 120 volts since you don't have that and you re right that there is considerable fluctuation in the voltage. In fact of the ones I have measured, 115 volts is the most common. But I have observed as much as 10 volt differences sometimes. But I have never had a problem with tools that use 120 volts in the US.

Thanks for the clarification. I had no idea that England (and I assume Europe) had such a different electrical system. I thought it was just the voltage difference. Good to know!

I was actually considering building my own switch using an Arduino, a current sensor and solid state relay. But then, when I saw I could buy one, "lazy" kicked in and I decided not to (even though I have about a dozen Arduino clones and most of the other components)! I even considered making a wireless device that would start the vacuum like a remote when the saw was turned on. Same components with addition of a transmitter and receiver. Then reality reared its ugly head and I realized I would never have time for that much more complicated project and it would never get done. The new switch is now ordered from Amazon!

Thanks for your help!!