Shop Electrical Caution

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BClemens
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Location: Gloucester, VA (Sassafras)

Shop Electrical Caution

Post by BClemens »

We had a new shop constructed about a year ago and along with the local county building permit came stipulations about the shop wiring. This required hiring a licensed electrical contractor to do all of the wiring in the entire shop - everything. That was expensive but we passed the final county inspection - the goal. The power company set up a meter and turned on the power.

Now with that came dealing with the electrical contractor and what he is required to do. Most all machine shop equipment is 220 VAC. There are two types of 220 VAC: three wire and four wire. Three wire is most commonly used in household appliances like a cloths drier - all three wire with the big three 'prong' plug. The problem with that in a shop is that you cannot take 110 VAC from it because there is no neutral - only two legs of 220 and a ground. The add-on power feeds on mills is 110 VAC powered so each of those on a machine must be plugged in to a 110 VAC outlet - NOT taken from the 220 VAC that runs the motor on the machine. I've seen that done... DANGEROUS!

When you take 110VAC from a three wire 220 VAC system you have no neutral. You have one leg of 110 and a ground. If you happen to fulfill the rest of the circuit for the 110 VAC you are electrocuted. Since there was no neutral, you supplied the path and a circuit WILL find a path!

So; either take 110 VAC from a four wire system (with neutral) or power any and all 110 VAC circuits to a dedicated 110VAC wall outlet and not from a box on the side of the machine with power going to the motor with only three wires!!

Some will say what difference does it make because neutral and ground are tied together in the main electrical panel at the main power inlet. The difference is that you are either dealing with 220 or 110 VAC. Both legs of 220 are balanced or cancel each-other for the neutral, all you need is ground. 110VAC without a neutral has no 'balance' so can deliver 110 VAC to any source that can make that balance. An accidental short circuit through you with 110 VAC without a neutral can and probably will be a lethal dose of 220 VAC sufficient to kill in an instant.

I hate lectures because most are nap time (joking!) but the electrician that wired our shop gave me some eye openers with his. I'm guilty of doing exactly what I'm telling not to do. I'm lucky and got away with it but all of my machines are now either four wire or add-ons are powered from their own 110 outlet. He convinced me! I hope you all can and will take heed with this...life is precious and fragile enough without such a needless risk...!!

BC
Last edited by BClemens on Thu Mar 25, 2021 7:54 pm, edited 1 time in total.
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NP317
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Re: Shop Electrical Caution

Post by NP317 »

My shop has 3-wire 220 Vac, and 110 Vac.
Every 220 Vac outlet has a separate 110 Vac outlet next to it.
We planned ahead...
RussN
BClemens
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Re: Shop Electrical Caution

Post by BClemens »

220 VAC four wire feeding a machine is very convenient because you can power everything on the machine; power feeds, dro, coolant pumps and etc. without each having its own wire feed cord to an outlet. That convenience is tempting to do the one leg 110 and ground trick - which is to be avoided. That's the caution - and a very common mistake (according to a certified electrician) and I'm only relating this...

BC
curtis cutter
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Re: Shop Electrical Caution

Post by curtis cutter »

I am curious, what comes into your shop panel? Is it single phase with two legs of 120 volts each and a neutral and a ground?

Is it a three phase power supply with no neutral to the panel?
Gregg
Just let go of it, it will eventually unplug itself.
BClemens
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Re: Shop Electrical Caution

Post by BClemens »

The residential line here is single phase, so only two legs of 120, a neutral and a ground - four wire. They call it 220 VAC single phase here and not 240 VAC although you can read 130 VAC on a "110" outlet from hot to neutral or ground.

I use 3 phase motors and phase converters - VFD's. Much more efficient than 220 single phase motors - with the added benefit of speed control too!

BC
curtis cutter
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Re: Shop Electrical Caution

Post by curtis cutter »

I am no electrical expert by any stretch of the imagination but I am curious, what comes in to your shop panel?

Is it single phase with two legs of 120 volts each and a neutral and a ground? Or is it a three phase power supply with no neutral to the panel?
Gregg
Just let go of it, it will eventually unplug itself.
John Hasler
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Re: Shop Electrical Caution

Post by John Hasler »

Neutral is always carried to all panels.
BClemens
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Re: Shop Electrical Caution

Post by BClemens »

John Hasler wrote: Thu Mar 25, 2021 9:58 pm Neutral is always carried to all panels.
Not with three wire 220 VAC John. Only two legs of 120 and ground. Clothes driers and Portable AC units only use three wire circuits. Neutral is only carried to 120VAC outlets for stable 120 Volts. That is what I'm talking about - three wire 220VAC is not safely splittable to 120VAC without neutral.

BC
John Hasler
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Re: Shop Electrical Caution

Post by John Hasler »

Gregg asked about your shop panel. Neutral is always carried to all panels so far as I know. It is not always carried to all outlets. It may be legal under some circumstances to carry only L1 and L2 to single point of load breakers.

BTW what you describe is more often called two wire 220 because there are only two current-carrying conductors. The non-current-carrying green safety ground is presumed to always be present.
BClemens
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Re: Shop Electrical Caution

Post by BClemens »

Hey John, The electrician that wired this shop building gave me this data as we were discussing how we wanted the shop wired. There were individual dedicated outlets for specific machines and when I told him how the Bridgport was wired he very stoutly alerted me of what this post is about. We had chosen a location for that mill which included splitting off 120 VAC for the power feeds and DRO - that's when he told us that ordinarily 220VAC is "three wire" and that it included no neutral so 120VAC could NOT be split off and why. He referred to it as "three wire" and he may well have been talking about the wire cable that he would need to run from the panel to the outlet. He said "four wire" outlets which include neutral would need four wire cable. Referring to the outlet - if it has three terminals - it would be "three wire" 220VAC, - if the outlet has four terminals - it would be a "four wire" 220VAC outlet. That was my understanding and having to pay him $11,000 to wire the shop gave him some credibility with me and especially the county code compliance and building inspection office...

The Bridgeport has its own panel and magnetic breakers manage the load circuits and it is split in that panel to 120VAC outlets for accessories with their own individual included breakers - point is the 220 was split down to 120VAC - and required "four wire" 220. The CNC machine is 220 VAC also but the old shop had the 220 "three wire" split for the computer and BOB - probably why under certain circumstances it would occasionally miss steps. Anyhow it hasn't missed a step since using "four wire" 220 in the new shop.

The main panel has all four - two 120VAC load lines, a neutral and a ground. But it can be wired through duplex breakers to an outlet as required - three wire 220 or four wire 220. 120VAC outlets wired through a single breaker to standard or heavy duty outlets - hot(120VAC), neutral and ground.
BC
Last edited by BClemens on Fri Mar 26, 2021 8:34 am, edited 1 time in total.
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liveaboard
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Re: Shop Electrical Caution

Post by liveaboard »

$11,000!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I did my own.
Might be up to local code... probably.
They're not as strict here, for non-commercial properties at least.
BClemens
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Re: Shop Electrical Caution

Post by BClemens »

liveaboard wrote: Fri Mar 26, 2021 8:29 am $11,000!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I did my own.
Might be up to local code... probably.
They're not as strict here, for non-commercial properties at least.
I was under the gun with the county... wish I could have done it myself but they required a "certified" electrical contractor.
BC
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