Lathe electrically "hot" due to VFD? WTF?

Ignoramus15569 wrote:


I'll bet you don't. I'd hook a long wire to a water pipe and measure between it and the VFD. If you're getting zapped, I'll bet there's at least a 40 volt AC difference between the water pipe and the VFD chassis.
Follow the ground wire back to the service entrance measuring the voltage. See if it drops to zero at some point. Be sure your multimeter is set to AC volts.

Pretty much. Florescent lights with old style magnetic ballasts would do the same thing. The frame of the light can float up from ground enough to give you a good tingle if not grounded.

Try to find an open ground first.

Good plan. Let us know what you find.

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"Jim Stewart" wrote...

Good so far, but a separate ground wire from the lug to the lathe would be a good idea.

If you've had a long dry spell the ground resistance can increase a lot - I sometimes have to water mine (as part of the 3-monthly check I do on my shed electrics) to get a safe resistance...
If you want / need to measure it, get a low-voltage transformer and attach one side of the low volts winding to the earth rod, other to a "roving" earth rod that you hammer into the earth and water (or if the local elec. co, provide one, use that) - do this in a number of spots at least 20-30 yards away and measure the AC voltage and the current into the rod, V/I will give you the resistance, check your local electrical code for the minimum value - to save the transformer for next time you may need a bulb in series with the low volts if the earth is any good - DAMHIK ;)

Dunno about VFDs (mine is on a *short, thick* cable to a pair of local earth spikes), but when I play with the ham radio (which has high frequencies buzzing about, although a few octaves above VFD frequencies) I find the house earth is too long for satisfactory earthing and I have RF on the equipment cases... for a narrow range of frequencies a 1/4 wavelength wire (insulated at the far end) works to absorb it, being a dead short at the right frequency - not easy to do for a *variable* frequency drive, tho! The VFD output is a chopped square wave, so has some pretty high-frequency components at fairly high voltages that can be a problem to shield effectively and can't be filtered easily (the magic smoke leaks out of the VFD if the HF impedance is too low) - one of the reasons that cable choice is important when installing 'em.

High-resistance in the ground circuit would be my first thought, too
Dave H.
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Jim Stewart wrote:

Even metal water pipe can be a poor ground, and if you have much current flowing it will damage the pipe at the joints.
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Michael A. Terrell wrote:

I didn't mean to imply that he should bond the VFD to the water pipe. Just to use it as a ground reference while he looks for an open in the house and machine grounds.
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Jim Stewart wrote:

If the joints are corroded, it isn't a good reference. It can get you killed when you don't read enough voltage to bother you, when it is much higher. Also, with a VFD there may be a lot of harmonics on the neutral and running a wire to a water pipe won't show them.
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On 10/27/2010 12:25 PM, Ignoramus15569 wrote:

Your safety ground system, somewhere, has a problem. it COULD be the ground for the lathe is bad, or it could be the entire ground for the whole house is going out. this is quite common. Our ground went out somev time ago, but fortunately, the whole feeder went out in the same event, so we lucked out and didn't fry all the 120 V stuff in the house. Our neighbor was not so fortunate, and a bunch of electronics got fried.
So, basically, trust NOTHING, assume NOTHING.

These are most likely NOT the problem. Turn the VFD and lathe on, and then just keep working back to the panel. You need a real ground reference, but as I said above, you can't trust anything. You may have to drop a bar in the ground to get a real reference. But, you may be able to hook an extension cord to a known-good outlet somewhere else in the house, and then use the ground terminal on it with a meter to probe around to find the open ground connection.
In many wood homes, you can have a totally screwed up ground system, and have NO IDEA anything is wrong. But, if all your other machines are OK (I would NOT go around testing them with the bare feet and wet finger technique!) then it is just something on the lathe. If your safety ground is tied THROUGH the VFD, that is a definite possible culprit there. Could be a misunderstanding of what terminal is what, or just a bad connection. And, just because you have one continuous "wire" from here to there, don't be absolutely SURE there is solid copper all the way. As I said, trust NOTHING!
Jon
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On 10/27/2010 12:25 PM, Ignoramus15569 wrote:

Hmm, I didn't read this carefully before. Do NOT make safety ground connections through anything aluminum and not expressly designed for wire termination. Aluminum instantly builds an oxide layer, and that can be quite a good insulator. Anodized aluminum can withstand several thousand volts, and some anodized aluminum cannot be distinguished from plain. But, anything bolted to aluminum sheet or whatever cannot be trusted to carry a safety ground over time. Make a copper wire connection for your safety ground, with terminal lugs approved for electrical connections.
I'm just guessing here, but this could be it. It also could be that your VFD case is isolated from the inner safety ground frame, so you grounded the VFD, but not the plate.
Jon
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Further to this discussion, and not in response to any particular post, Plumbers are not great fans of cold water pipes being used as electrical grounds. And for good reason. If there is a ground fault, and the pipe is carrying any current, and a plumber has to cut the pipe to do a plumbing repair, that current tries to pass through the plumber.
Also, any plastic pipe in the system obviously has to be bypassed with wire, though it ususlly isn't, resulting in bad (no) grounds downstream of the plastic.
IMO, if you are going to use the cold water pipe as your ground connection, you really ought to do it right at the point where it enters the building, before any plumbing connections (which could corrode and develop high resistance.
I'm getting ready to replace my service entrance, and there will be multiple ground rods.
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On another note, if you dond find an actual mising or broken ground
wire, and the conclusion is that the potential difference is due to
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On Thu, 28 Oct 2010 09:44:08 -0700 (PDT), rangerssuck

When I re-wired my previous house, I moved the service panel to directly below the kitchen. Since I had a good supply of salvaged, bare, #6 stranded wire, I ran that from the incoming water line through the service ground lug the and further on to connect both hot and cold feeds and the copper drain at the kitchen sink. The inspector thought that the drain line grounding was such a good idea, I gave him an extra ground clamp and enough wire to modify his own home system.
He told me the story of the guy that wired his rec. room much more cheaply than anyone else. Investigation revealed that all his wire was 300 ohm twin lead. Gerry :-)} London, Canada
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"Gerald Miller" wrote...

Here in the UK that's compulsory, known as "supplemental bonding" of basically all metalwork that could be touched in "special locations", i.e. kitchens, bathrooms... Some "electricians" go to town and have ugly cables appearing from floors to bond the central heating radiators and handrails too, rather than make an effort and lift a floorboard :( We're not allowed to use the water supply pipe as a protective earth (ground) though, as a lot of homes now have plastic incoming pipework!
Is electrical work as tightly regulated in the US as it is here? We've had new laws ("statutory instruments" that don't go before a vote in Parliament) inflicted on us that pretty much outlaw DIY electrical work beyond replacing an existing switch, light fitting, socket or piece of damaged cable etc. (and not even that in the bathroom and kitchen!), the local council building control office have to be informed and handed inspection certificates (produced by members of an "approved scheme" who often refuse to certify anyone else's work or charge almost as much as having them do the work from start to finish) etc. - of course, this has resulted in "old colours" cables selling at a premium as the new laws came in after a change of cable core colours and another result is that more and more people are tripping over overloaded extension cables... The law (Part P of the Building Regulations) was put in force after a politician's son-in-law screwed a metal shelf in through a cable in the wall without checking for cables first, and his wife died from touching that and her dishwasher, so it got blamed on the contractor - no avoiding stupidity I guess, however hard Nanny tries to legislate, the only law you can really count on is Darwin's...

Friends of mine bought a falling-down farmhouse in La Belle France a few years ago, and discovered the wiring was mostly bell-wire (that you'd use to connect a doorbell button) - nice when they plugged in a 3KW heater and wondered what the burning smell was! A rewire was one of the first steps in the rebuild, and done to the same standard they've applied to the rest of the building - damn near perfect :)
Dave H.
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You have quite insane gun control too, now people cannot own guns and cannot install receptacles, pretty weird country I would say.
i
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You might feel it's an unneccessary issue, Ig... so you apparently believe you should have that freedom (assuming that you believe you're intelligent enough to do work like this),
..and yet, your lathe has probably had a ground fault for all this time.
An earth ground is a single conductor.. how hard can it be?
When wiring anything that's line powered.. a replacement receptacle or a major piece of equipment, the first connection I make is to a known good earth ground. The earth ground doesn't get disconnected until the equipment is taken out of service, with all power conductors removed (bare ends cut off or capped with wire nuts).
Everyone doing any electrical work should know how little electrical current it takes to disrupt normal heart rhythm. This info is included in NEC manuals and numerous other sources.
--
WB
.........


"Ignoramus1553" <ignoramus1553@NOSPAM.1553.invalid> wrote in message
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"Wild_Bill" wrote...

Agreed, safety is important, I've gone a bit over the top for my shed/workshop, 100mA time-delayed RCD ( = Residual Current Device, see below) on the armoured cable from the house, another (30mA instantaneous) for everything but the lights so I won't be left in the dark with spinning machines, separate circuit breakers for each machine and the local outlets, but a lot of people will be using 25 yards or more of trailing extension cable across the garden and through puddles if they want to use anything electrical beyond the confines of the house: this is perfectly legal but bloody dangerous, rather than having a properly-wired fixed installation which would be very much safer but which they currently aren't permitted to install - anyone with an ounce of sense will find out how to do it properly (there are plenty of resources online), anyone without... well, maybe they should be shooed out of the gene pool before they drown someone else ;)
As for Iggy's ground fault - could be an existing fault and nothing to do with him and his electrical work, lucky he found it now and not when a *major* fault occured! I've seen quite a few horrors installed by "approved electricians" and some really excellent jobs by DIYers - one that comes to mind was aluminium cables terminated to brass connectors, first sign of damp and they start to corrode, resistance goes up and it overheats, up in smoke goes the junction box, possibly followed by the house... That was a "professional" installation too :(
I have an electrical + electronic engineering cert. that took 3 years post-college and several years practical experience on everything from 20KV transmitter supplies to 100HP servomotor systems but according to the regulations here I'm not a "competent person" to work on electrics in my own home, unlike a guy straight out of school (where he failed all his courses) who's done a one-week course on testing *and has paid a huge amount for membership* in one of the "approved bodies" who run the certification scheme and lobbied (mostly in the newspapers) for the change in the law. Makes you think, eh?
Part of the current regulations here that I approve of is whole-installation 30mA RCD protection, so the power will disconnect in a few milliseconds if there's any more than a 30mA current difference between phase and neutral - but even that won't save those who put themselves between phase and neutral without earthing themselves! Against stupidity the gods themselves contend in vain...
Dave H.
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Here in the U.S. we generally refer to similar devices as GFCI ground fault circuit interrupter. They are available in several versions for installing into walls to protect branches of receptacles, and required most places for receptacles near sinks (bath, kitchen, laundry, circuits near swimming pools) or receptacles near exit doors where cords might be used for outdoor equipment, also permanent outdoor locations (also available built into extension cords and power cords of equipment primarily used outdoors - electric pressure washers, for example).
http://en.wikipedia.org/wiki/Residual-current_device
There are also GFCI versions for installing directly into service panels (mains power feed boxes).
One thing that's worse than excessive use of extension cords, is cheap morons that never throw them away when the cords become damaged or develop worn out receptacles. In addition to that issue, too many folks don't have any understanding of wattages or current.
I can tell you're a real maverick, Dave.. you used yards, instead of meters, heh.
Yep, your regulators not accepting your certifications and experience for not being adequate for fairly simple electrical work, reminds me of the sig quote that's used by Wes (I think), about a guy's right to have a weapon to protect important pople in his job.. but not able to keep a weapon in his home to protect himself and his family.
Double standards have long been becoming the norm, twisted as that is.
Yep, there are essentially no safety devices that are 100% effective.. circuit breakers don't detect fires from hot conductors, etc.
Even isolation transformers can't protect someone from electrocution from fatal voltage potentials within the piece of isolated equipment.
Folks were generally safer when they were very superstitious and afraid of electrical power. Of course, they had to suffer lots of injuries from wandering around in the house in the dark, and possibly oil lamp fires. But they wouldn't risk getting killed instantly by the mysterious "fire on a wire".
There were lots of rural folks in this country using gasoline-powered washing machines (outdoors, I suppose) just a couple of generations ago.
--
WB
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"Dave H." <hopefuldave_doesnt_eat_spiced snipped-for-privacy@hotmail.com> wrote in message
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Wild_Bill wrote:

And the expression 'tit in the wringer' came from those old wringer type washing machines, Ouch :)
John
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wrote:

I remember my aunt having a gasoline powered washer with a length of flexible exhaust hose out trough a hole in the kitchen wall. My grand father used to threaten to get an exhaust hose for my Grandmother every time she would have an "intestinal event". Gerry :-)} London, Canada
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The fact that Iggy had a ground fault does not mean Iggy is not competent. The ground fault may have been in wiring which had been done before Iggy bought his house.
But Iggy may now see the wisdom of not trusting others to do competent work. The house I now own was built about twenty years before I bought it.. After I bought the place, I checked every outlet to see if it was correctly wired. I found about five outlets that were not correctly wired. I suspect the incorrect wiring was done when the place was built. Why the errors were not found during the original inspection is a mystery.
Most of the places I have lived, allow the owner to do wiring and plumbing to his own residence. This has more to do with how much political power the unions have than anything. Wiring is not rocket science.
Dan
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Like you stated, wiring isn't rocket science, but then many other things aren't rocket science either.
The part about "known good earth ground" got snipped.
***When wiring anything that's line powered.. a replacement receptacle or a major piece of equipment, the first connection I make is to a known good earth ground.***
He may or may not be an intelligent electrician, but he's had his children and wife living in that house. So who is responsible for confirming that the electrical system is safe? Realtor, gubmint, seller, inspector, non-existent contractor etc.
The thing is, none of those other people sleep in that house, and they'll all just point their fingers at each other, eventually assigning blame to who ever makes the best scapegoat. The other people's responsibility most likely ended with the sale of the house.. and that leaves only one other person.
The responsibility ends up being the homeowner's.
I think the majority of home fires are determined to have been caused by "faulty wiring". There hasn't been a lot of wire being sold that doesn't meet specifications. Realistically, many home fires are caused by improper installations or misused circuits and/or misused electrical equipment.
A person can buy or find free information WRT safe, proper wiring practices, so there aren't many reasons why wiring should be done improperly, but one reason is arrogance (which is essentially choosing to be ignorant).
I've seen a lot of horrible electrical work.. including a spliced & taped romex junction (no wire nuts with a branch meeting a run, adding 12 to 14ga) hanging free inside a wall without a box.
People are stupid, but add tighter-than-a-frog's-ass cheap to stupid, and they'll perform feats that are difficult to imagine, by anyone with the slightest amount of common sense (which needs to be renamed uncommon sense, as it seems to be fairly scarce nowadays).
--
WB
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< snipped-for-privacy@krl.org> wrote in message
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wrote:

http://www.moonbattery.com/archives/2008/03/britain_starts.html
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Most ridiculous.
i
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