Shop power question

[CantologyLLC]

Hi all, sorry to have to share the sad state of my man cave, but I need help.
Bought the upgrade 1hp 120v spindle for my Desktop and finally got a little time to install and begin the learning curve. Can start it from the SB control screen and after a call to SB support I now understand the relationship between freq displayed on VFD and Rpm. However, when I try to warm up the spindle, after about 6 min. the VFD reads "Lu" and it shuts down. From the docs this code must be "Lv" for low voltage. My 'shop' has a single line coming from a 20 amp breaker in my home breaker box. When supplemented with a 12ga extension cord from my back deck, this has been 'enough' The VFD apparently requires 18A so I finally need to get serious about power to my shop. I dont have real big power needs - vac pump, lights, shop vac, laptop, and SB when cutting. So my question is, what should I ask an electrician for? A full 200A box for my tiny shop? And I could understand if the spindle tripped the breaker, but this low voltage code has me wondering about quality as well as quantity.
Thanks for any light you can shed - I'm a dim bulb when it comes to elect.

[bleeth]

You can probably solve it all with an 80 amp sub-panel for what you described.
In my shop (which is industrial) I have an 80 Amp sub by the bot that runs 5HP spindle, SB controller, computer, regenerative blower, Holzer Edgebander, and a small dustvac. It does depend on how much service you already have at the main.

[dana_swift]

Will.. your existing circuit has two halves.

The feed from your existing breaker box to the outlet. Then the feed from your outlet through that extension cord to your router. I am highly suspicious of the extension cord or the plug wiring.

First thing to do is measure the voltage at the outlet with everything off. Lets call that V(off). It should read 120 volts within about 5.

Then set the spindle to warm-up and again measure the voltage at the outlet. Lets call that V(warm).

If VWarm is less than one volt lower than VOff, your house wiring is just fine. That would leave the extension cord.

If they are more than one volt different, check the voltage at an outlet on ANOTHER circuit on the same phase. (A house usually has two seperate supply feeds, or "phases".) Do the lights in the house dim when the spindle is started? If so, you need to look at the supply adequacy for the house.

When was your house/shop built? After 1960? If so, its very unlikely your shop wiring is inadequate. Presuming it was built up to the national electric codes of the time.

Last question- how long is your extension cord? 5ft, 100ft? That would make a big difference.

The tables show 12ga wire has a resistance of 0.001588 ohms per foot. Lets guess its a 20 foot cord. And the house has 30 feet of 12ga solid wire. The circuit requires 2 conductors, so the effective length of 12ga wire is:

(20 + 30) * 2 = 100 feet of wire.

The total resistance would be 0.1588 ohms. Running 18 amps would make a voltage drop of:

V = amps * ohms
V = 18 * .1588
V = 2.8v volts drop. That is already getting to be a fair amount.

Now if it was a 100 foot cord:
(100 + 30) * 2 = 260 feet of wire.
Ohms = 0.001588 * 260 = .4128 ohms
V = 18 * .4128
V = 7.43 volts drop.

That is about what it would take for a spindle to complain.

Presuming the extension is not that long, the plug wiring is the next suspect. Warmup the spindle until it shuts down. Are any of the plugs warm to the touch? If they are barely warm, that is ok, but if they are "warm" that is bad, and if they are "very warm".. you just found the problem.

See if that helps run down the trouble..

D

[CantologyLLC]

Thanks guys! Dana, the extension cord is 50' and used to power my chip collection vac and a shop vac which is only used when the bot is not cutting. Both are switched from within the shop but this circuit is outside the shop, physically and electrically. But your point about dimming the house lights is noted. The SB is powered from one of several outlets supplied from the house main panel. House is about 15 yrs old. I'll check the voltages as you explained and see what I can learn. And be looking into a sub panel if it's marginal.

[bleeth]

Well; there is the generally practical answer that will likely work without you needing to become an electrical technician and there is the answer that requires you to learn a huge amount of electrical theory about electricity. You now have them both. Frankly, since I have successfully wired everything from Yachts to houses to industrial shops and have never gone to the extent of uber-analysis that Dana has laid out I think that his post has what I commonly refer to as "too much information" but coincidentally, since I know from whence he speaks, I recognize that it is also quite accurate.
The wiring sizing needs as well as the current ability of your existing main panel to run a shop sub-panel should be at-hand knowledge on the part of your electrician from a five or ten minute lookover of what you have. Your basic question is self evident that you aren't an experienced electrician. Call a few for consultation and get some quotes. Remember that, for example, you don't need to understand why your car won't start on cold mornings, but simply recognize that you need a mechanic to check it out.
Since you stated that you are running everything from one 20 amp breaker I can tell you that isn't enough regardless of wire size and distance. If any electricians disagree and can prove it I'd be "shocked".
A 50 foot 12GA cord loses a more power than you may think by the time you are at the end. Dana will likely concur.

[dana_swift]

Dave- I don't intend to provide too much info. I can provide much more, I promise you.

There is a problem. How does somebody figure out exactly where the problem is so they fix the right one? Everything has ratings, most people never bother to look at the ratings of wire. Wire is not rated in amps. Its rated in ohms per distance. The insulation is rated for volts and temperature. Rules of thumb handle 95% of the situations. The ratings handle the other 5%. A problems indicates something is out of the ordinary.

If the wire was the problem (as it appears to be), what wire would fix the problem? How can a person know in advance so they don't have to go buy the next larger wire gauge (10 gauge in this case) then discover that may still show the problem and waste money? Then go buy 8 gauge, etc.

The calculation is short. I provided a worked example so somebody has the option to examine their case, and figure out what the correct wire is before making the mistake of buying the next several wire gages to find out what is adequate by experiment.

Something that impresses me about the shopbot community is the breadth of knowledge available. I am not a wizard about coatings for instance, and having people that will share the insides and outs saves me money because I can go directly to a working result. Thanks everyone.

If my information is more than any reader cares to know, ignore it. Those that value it, you are welcome.

[donclifton]

My 4hp HSD spindle pulls 2 amps per leg. You can't go by the nameplate on the spendle. When you change the feq you change the Amp. Thats runing at 1800 rpm fully loaded.
Don Clifton

[chiloquinruss]

Will, slightly different subject but related: I live in southern Oregon and when I put my shop in I had them add the EXTRA service to the HOUSE and not the shop. It required upgrading the main panel at the HOUSE with a dual breaker setup. I then wired the SHOP into the new panel at the house. The reason was a second meter base on the shop would have caused me to pay COMMERCIAL rates for the shop power. Having a SINGLE meter base but a split power panel saves on electricity costs. Russ

[bruce_taylor]

If your going to have an electrician add a service you should have them add as much as they can at the time without adding to much money, If you have a 200 amp service at your house ou can add up how much your house uses and have them drop 80 to 100 amp sub back to the shop that will work for what you need, I had 400 amp put in 200 amp house and 200 amp shop really nice to have plenty with the old 60 amp I would blow breakers and always had to watch power usage. Only your electrician can tell you what can be done with your situation.

[CantologyLLC]

A little follow-up: I bought a Fluke 113 (idiot-proof) multimeter and found that power to my shop outlets is steady 120-121v. Same with my extension cord from the deck (rather surprised by that as the run for that circuit is all the way across the garage and house footprints to a GFI in the kitchen, then 10' to the outside wall then 50' to the side of the shop. This only powers a chip collection vac, and has done so for 1+ years.)
Then, with only lights on, I plugged the multimeter leads into the other outlet of the duplex the bot is plugged into, and ran the spindle through a warm up seq. for about 8 min. Voltage moved around a lot, but stayed north of 119.8 the whole time. Then I stopped the spindle and started setting up to get some work done. A few minutes later I heard the snap sound that the VFD makes when it switches off, looked over and saw the dreaded "Lv" on the display!!! Grrrrrr.... So I pressed reset. It doesn't come back to life for 3-4min. In fact, when this unit first gets power, it looks dead for 3-4min every time - so is that normal? Anyway, I plugged the meter back in and then just watched. Sure enough, after about 5 min the VFD did its low voltage thing with the meter reading 120.4! Spindle was not on. In fact, only the lights were on. So... I'm thinking that either this VFD is DOA or my power is somehow screwy. I did experiment and find that I can't run my Gast vac table pump while VFD is on so I've started requesting quotes from electricians. And I'll give SB support a call on Monday.
I'll be getting a new panel out there, no matter what. It's the VFD that concerns me now.