Equipment Grounding

[wareagle]

We work mostly alone, and getting electrocuted really isn't the result we are trying to attain in our shops!

This is a big one! Every machine (well, almost every one) we use requires electricity to operate. Is your machine properly grounded? Here is something to think about....

This past week my crew worked on a piece of equipment that had a fault in the motor. The machine was a punch press and the operator complained of feeling a slight tingle everytime he touched the machine. Our visual inspection revealed that the unit was placed on rubber vibration pads, and not directly on the floor. The second thing we noticed was that the machine was feed power through a rubber cord. The technician that worked the call immediatly checked the voltage from the machine to a nearby source of ground and found that the machine was energized! The voltage from the machine to ground was 278 volts! (This unit is 3 phase 480V) Once that was discovered, he turned off the power and checked the wiring in the motor. One of the leads was bare and against the case of the motor. The rubber cord feeding the machine had three conductors in it, and each was a phase wire, so the unit was not grounded. After the cord was changed and the machine was grounded, the problem was gone. Disaster avoided; this time.

I present this to you to think about the machines and electrical system in your shop. Is your system and equipment properly grounded? The operator in the above scenario was lucky! If he would have become a pathway, then an accident would have happened, most likely resulting in a very nasty shock if not death.

If you are unsure of your grounding, then check it out, or have a qualified electrician check it for you. The money and time spent will be less that a hospital stay or funeral!



Remember this - the problem with getting killed is that you stay dead for such a long time!

 

[wareagle]

After some thought, I felt that this topic needed a fresh look. Safety is the first thing we all should consider in our shops, and this topic is a very important topic in that we use electricity in our shops for just about all of our equipment.

The following has been copied from the post GFI Q in the Q&A section.

There is some terminology to understand on electrical systems if you see it, and I will refer to the terms below again, so there is a test <wink>.

First, there are ungrounded conductors which are your "hot" wires. These are the wires that have the voltage on them (not that this means the others won't have some).
Second, you have a grounded conductor, which is the neutral wire. This wire carries the unballanced load of the ungrounded conductors, which means there is current (amps) on the neutral, but very little or no voltage. WARNING: This wire WILL KILL YOU if you get between it and and a return pathway to the source.
Third, you have a grounding conductor, which is your ground wire. It's sole purpose in life is to present a pathway to carry fault currents back to the source of power.

With that knowledge, understanding what the different jobs of each conductor are will become easier. For equipment grounding, it is absolutly essential to have a COMPLETE pathway back to the power source to have a safe electrical system. Earth ground here does not cut it. The circuit breaker or fuse will not open the circuit at the voltages we are dealing with in a residential application.

Why? The earth has a typical resistance of 25 ohms. Take an ungrounded conductor that is energized and ground it to earth. The circuit breaker or fuse will not open the circuit. Do a little ohms law calculation: Take your voltage and divide it by the resistance, and this will give you the current. As follows:

110 volts / 25 ohms = 4.4 amps
220 volts / 25 ohms = 8.8 amps

As you can see, these values are not close enough to the rating of a 15A or 20A breaker to open the circuit under a fault condition. Take the same numbers, and then put the human body in the circuit. It takes less than one amp to incapacitate and kill a human being!

As you can see, it is very important to ground your machinery and to make sure your electrical system is in proper working order.

The use of this information is at your own risk! The responsibility to thoroughly understand the proper methods of installing and maintaining electrical systems should not be taken lightly. If one is in doubt, has questions, or concerns, then consult the expertise of a qualified electrician. The above is for informational purposes only, and the author is not liable for any use of the above information.

 

[1Kenny]

Very good topic. The little lathe I got a few months ago only had a two prong plug on it. First thing I did was install a new switch and wires with a ground. Last month my other lathe was getting an intermitent start and I found a couple of wires with copper showing so it got all new wires. Bad wires are not even worth a wet pant leg.

 

[J. Tranter]

What gauge wire should you use for plugs on equipment?

 

[tattoomike68]

I notice my box has a big ground rod way deep in the ground. I have a hot tub next to my box and I know its eating 30$-40$ by itself.

my basement has some grounds hooked to my water pipes, It must be OK as the guys who put the gas furnace in did it.

just so you folks in the UK and europe know we all have 220vac here in the states but it on our baseboard heater, clothes dryers, stoves, ovens, and water heaters.

The little stuff is 110vac and the big stuff is 220vac+.

I know 220vac is better but we dont use it where we dont need it.

I dont need a 220vac clock radio/alarm or a shaver so 110 does the job just fine for the little stuff.

Thats my opinion and I may be an idiot so take it for what it is worth, please educate me why 220vac everything is better?

 

[1Kenny]

12 gage for most 110 vac motors 1 1/2 horse motors or under.

 

[tattoomike68]

I am an electrical idiot, I want to learn. I am not afaid at all.

Anyone know a site for super basic electrical? I can read.. ;D

 

[1Kenny]

Most of the time I just look at the drawing on the motor, switch or relay and make my own print. Haven't found any basic books that explains everything.

The advantage of 220 vac is cost. 110 vac costs the most to use. 220 vac is half the cost of 110. My mill runs on 220 and one lathe is 110/220 the other is 110 only but I have them both on 110.

 

[Bogstandard]

Mike,
Notice it was not me on about the voltage rates, all I know is that when you stick your fingers into a socket, it hurts and you get that burning flesh smell, (if you are a masochist, please don't try it, it might be the last thing you do).
To me it is just electric string and wiggly amps, so I get my mate to do it for me (he knows less than me, but he is now more resistant to the shocks).
I am only joking of course.
If you don't know what it is all about, don't play around with it, you just might get a bit more than curly hair. Get someone who knows what he is doing, or a professional.

BE SAFE.

John

 

[gilessim]

Well I'm sorry for my misunderstanding of the american voltages, I've now learnt something, in the UK ,on construction sites we are required by law to use 110 vac power tools on site with a 110 vac transformer, this being a bit of a drag because we had to have 2 sets of power tools,1 at 110 and 1 at 240v ,the idea for this being that 110 is much safer.

If you stick your fingers in a socket, it obviously does hurt, but you are only getting a shock across your fingers ,the current taking the shortest route, when I said about holding a pos. in one hand and a neg. in the other (I also said don't try it!) I meant to say that, as the body is 70%+ water and therefore a very good conductor, you are effectively making a short circuit and that should in theory flip a circuit breaker, it could just be long enough to stop your heart though!.

In the UK ,when you have your house rewired ,or a new one, the electricity company come round and check the circuits and the earth (not everywhere has earth return, if you have a pole, the resistance has to be less than 8 ohms,you are much more likely to do yourself harm grabbing a pos. and the earth, this being the reason for earth protection!) If there are problems with the wiring, they won't hook you up to the mains!.

It is always better to be safe than sorry, if you have a badly earthed motor, you can also end up with a burnt out motor or much worse. if you don't have the possibility to check the wiring yourself, get an electrician to check it, it shouldn't cost much and they have all the gear to do it, sorry for any misunderstandings....Giles

 

[shred]

I am an electrical idiot, I want to learn. I am not afaid at all.

Anyone know a site for super basic electrical? I can read.. ;D

Basic residential wiring info is scattered all around the net.. I've yet to find one good spot for it, but start with Wikipedia for the basics.
About 90% of the time the answer to any electrical question is "go look in chapter X of the NEC", the recent versions of which aren't available online.

AC is somewhat tricky and counter-intuitive if all you've ever messed with is batteries and light bulbs.

 

[1Kenny]

One thing that is going on here in the US is the newer houses are being wired with 14 gage wire. The smaller wire won't carry the same amperage in a garage as the larger 12 gage. The lights are on a different circut breaker than the wall plugs but the wall plugs are still wired with 14 gage. On some newer buildings even the re-bar in the concrete is being grounded.

If you have ever been shocked you may have noticed your body joints will hurt. The electricity jumps between the ball and socket of the bones which is why your arm and shoulder will be in pain. I was hit by a secondary lighting strike in the early 80s and was blown back over 6'. Now I make sure I am inside during storms.

 

[wareagle]

What gauge wire should you use for plugs on equipment?

For general circuits (non-motor loads):
15A = #14 Copper
20A = #12 Copper
30A = #10 Copper
40A = #8 Copper
50A = #6 Copper
100A = #3 Copper

For 120V motor loads:
1/4HP = #14
1/2HP = #14
3/4HP = #12
1HP = #12
1 1/2HP = #10
2HP = #10
3HP = #8

For 220V motor loads:
1/2HP = #14
3/4HP = #14
1HP = #14
1 1/2HP = #14
2HP = #14
3HP = #14
5HP = #12
7 1/2HP = #10

It is up the the individual to determine the suitability of this information for the applied application. The above information is for reference only, and any electrical installation should be performed by a qualified electrician.

Best practice for shop equipment is to use #12 copper wire for all of the 15A & 20A general purpose circuits.
_________________________________________________

Grounding is a very misunderstood topic, even for professional electricians, so don't feel bad if this is a little confusing.

tattoomike68, The reason that water pipes are grounded is to keep the potentials the same between the plumbing systems and the electrical systems. The water lines are not used for a grounding electrode to earth. The reason for this is there are many locations where there is copper water line in the slab, but is converted to plastic underground. Also, the copper connections in water lines are not rated to carry fault currents, however they will in the real world.

If I wasn't totally clear, the purpose of the grounding conductor (ground wire) is to carry fault currents back to the power source so the overcurrent protection device (fuse or circuit breaker) can open the circuit in the event of a fault.

 

[Cedge]

Here in the US the houses are wired at 220 V single phase from the mains to the breaker box. It's then split inside the breaker box where two legs are "hot" and the third leg is "common" which serves as the return/ground circuit. Heavy appliances get wired for the full 220 volts. I once had an incoming underground line short when one "hot" leg couldn't withstand the years of abrasion from a stone. The strange part was that half the house had power while half didn't. It took me a few minutes to figure that one out...LOL. Single phase power is the norm for residential use and its expensive to get residential 3 phase power service... if you can get it at all. Many opt for a rotary phase converter when they need 3 phase in a residential setting.

When my company was still in in operation, we had multiple service circuits so that we could deal with a broad spectrum of power requirements. It was common to see industrial motors rated for 208, 220, 230, 240, 400, 440, 460, 480, 600 and 660 (incoming mains) volts, all 3 phase. You could cover a number of those ratings with the 10% variance rule, but you never knew what you'd be wiring into a circuit from one day to the next. We had 230 440 and service throughout the shop, with 660 volts available at the box, plus the standard 220 volt single phase and 110 volt single phase. The ground on that building was a buried 4ft square copper plate with a 1.5 inch diameter copper rod attached to reach the mains box.

I was by the old place last week and noticed that the local copper bandits had spotted the ground rod and it is now missing in action. If they only knew about that plate they left in the ground...LOL They've found a few dead ones in the local power transfer stations of late, along with a few fried fingers left by the lucky ones.

Steve

 

[Bogstandard]

Just going off topic slightly here.
Due to China and India sucking up all the world supplies of scrap copper and the price is going sky high, maybe now would be a good time to stock up on some of the copper based alloys from your usual cheap sources, as without doubt, they will eventually start to rise in price as the copper shortage hits. I have enough stock in now maybe for about ten years of small engine building, but I will still be looking for the good stuff, even if just for investment.
Now a little nearer to topic.
A few years ago, I worked for a small American company in the UK, and when I came to install their unique machinery I had to get specialists in to rewire them all, due to what looked like copper wiring, but I am sure it was an ali/copper alloy and the only way to join it was by physical means (crimping), solder just 'blobbed' on the surface.
Do you think that maybe with this shortage of copper, this crappy type of wiring might reappear?

John

 

[shred]

Just going off topic slightly here.
Due to China and India sucking up all the world supplies of scrap copper and the price is going sky high, maybe now would be a good time to stock up on some of the copper based alloys from your usual cheap sources, as without doubt, they will eventually start to rise in price as the copper shortage hits. I have enough stock in now maybe for about ten years of small engine building, but I will still be looking for the good stuff, even if just for investment.
Now a little nearer to topic.
A few years ago, I worked for a small American company in the UK, and when I came to install their unique machinery I had to get specialists in to rewire them all, due to what looked like copper wiring, but I am sure it was an ali/copper alloy and the only way to join it was by physical means (crimping), solder just 'blobbed' on the surface.
Do you think that maybe with this shortage of copper, this crappy type of wiring might reappear?

John

It may be too late many places.. around here people steal air conditioners and even live wires (couple guys got fried not long ago) to get the copper to sell it to the junkman. The electrical guy at the hardware store had to move all wire up out of reach because so much was getting swiped off the shelves.

I was just thinking about the Al wire coming back the other day.. I would hope not-- it's an issue here if a house has Al wiring in it, though many do... knocks a few thousand off the price at sale time, even if it was terminated correctly. But, you still can buy Al-wiring-compatible plugs and switches at the big-box hardware store, so it's not gone far.

 

[Cedge]

John
It' pretty much too late on the copper front. I need a piece of brass for the little water pressure engine. Strangely, I have bronze and copper enough to last for quite a while, but a decent source of scrap yard brass has been elusive. There is a local supplier who sells drops and ends so I gave him a call last week to inquire about getting 18" of 1.5 inch 360 grade (free cutting) brass round bar. I was glad we were not face to face when he gave me the price. Sticker shock would have surely been etched on my mug. I think I'm onto a source for the metal I need, but will have to be patient until it comes available. Since it will be free, i can afford a lot of patience for what new would have cost. The last scrap yard brass I bought was priced at $2.50/pound which is double what I paid 12 months ago... for bronze.

A number of years back, the mobile home industry won approval to use aluminum wiring in trailer, prefab and modular home construction. It didn't take but a few years for the approval to be withdrawn. Fires jumped in frequency to the point insurance companies wouldn't touch a manufactured home. Between improper wiring techniques and the wire oxidizing, the danger of waking up dead, one morning, was pretty high.

It never became as prevalent in stick built housing but enough exist to make buyers and bankers beware.

Steve

 

[wareagle]

There is nothing wrong with aluminum wire. The utility companies use aluminum for overhead and underground power lines, with few problems. The actual problems are with the way the terminations are made. Aluminum, as we all know, has a high rate of expansion and contraction with changes in temperature. This causes the terminations to loosen up after time, and then the connection develops a high resistance, which builds up heat, the heat then increases the resistance, which creates more heat, then the resistance goes up, then that resistance builds more heat, and then you have a run away cycle that will result in a failure or more likely a fire.

Would I want aluminum wire in my house? No, not really. However, if it is installed properly with the properly rated devices and terminations, then aluminum is a safe system. It does require more frequent maintenance than copper does, but as long as the system is maintained, it is just fine.

The other drawback to aluminum wire is it is has a lower melting point than copper. If you were to have a connection get to the melting temperature of the aluminum (or copper for that fact), then the wire will come free and will usually short out and create more problems. If there is a problem that creates this amount of heat, there will be damage, and will usually be extensive.

Rule of thumb: If you smell any electrical type odors, hear arcing in switches, have plugs that won't hold the cords, or circuit breakers that are tripping for no apparent reason, have lights that dim and brighten for no apparent reason (ie. A/C coming on, compressor starting, etc.), then it is time to consult a qualified electrician to assess and correct the situation. Odds are, the cost of the electrician will be less than the insurance deductible is when the place catches fire. That doesn't take into consideration the risk to life (BIG ONE) or the huge headache of dealing with the losses, paperwork, and everything else that comes with dealing with a fire event.

 

[Circlip]

Surprised the Brit contingent hasn't mentioned this one but not only is it advisable to have MCB's (miniature circuit breakers -automatic fuses) but also ELCB'S (earth leakage circuit breakers) If you put yourself between live and earth, these things break the power instantly, so it's not fries with everthing, and oh, Tattoomike68, PLEASE get someone to put a cover on that socket, It makes me flinch just looking at a picture of it