Electrical Problem

[Glenn Kotnik]

I know many of you on this forum have a strong background in electrical power and wiring so I hope someone can help me troubleshoot this situation before I loose any more equipment. I built my workshop about 8 years ago. The power company put in completely new 200 amp service for the shop, separate from our house and on a new account. I have quite a few power tools and machines, both 120v and 240v. Ground is via an 8Â’ copper coated steel rod just outside the workshop. A couple of years ago I also put in a 240v surge protector which is mounted next to the load center so I can always see the green lights are on. The protector has 2 wires, one connects to each side. Until yesterday I had zero electrical problems in the shop. Then in the morning I used my 120v Mirka palm sander which is powered from an electronic control box. It ran fine but then I shut it off and 1/2 hour later tried to use it again it ran for about one second and that was it, dead. Power to the box but no output. Seemed very odd to me but I thought it had gotten old and just failed from old age. In the afternoon I was running my lathe and using my 5hp Super Gorilla dust collector, 240v single phase. and it ran fine. Shut it off for awhile and turned it on again but there was only a click in the magnetic starter switch box and the big Gorilla was dead. Climbed up with my multimeter and took the lid off the wire box. Zero volts between the white and black wires after I pressed the start button. I did find 123v between white and ground, zero between black and ground. Then I took the cover off the magnetic starter switch and smelled something burnt. The black wire from coming in from the 240v outlet had gotten very hot where it connects to the switch and in fact started to melt the plastic side of the switch. I checked the voltage at rhe outlet and it is 246v. The surge protectors at the load center and in various outlets show the green light glowing so I assume my ground is ok. Called Gorilla reach support and he agrees that something caused the black side of the switch to short out.
So I have to assume something is wrong with my power, it would be too big a coincidence for both units to fail on the same day if there werenÂ’t a problem. But where do I go from here? I did see the power company putting in new poles and wires over the past few days.

[Paul F Franklin]

The first thing I would check (power off at main) is that all the neutral connections in your panel are clean and tight, especially the one coming from the meter. A poor neutral connection is one of the few things that could be wrong inside your shop that can cause overvoltage conditions on 120 volt loads. Of course a surge from outside could be a problem. Also make sure your neutral is bonded to the ground in the service panel (and only in the service panel).

A bad neutral leg connection in the meter base or in the feed from the utility can also cause the same kind of problems; the utility will usually check this if you tell them you are having problems.

I will say that 9 times out of 10, in my experience, when a single connection burns up, it did so because it was loose. A loose connection gets hot, and it gets worse over time until it fails. Unfortunately, it's usually impossible to confirm this once something has burned up.

[Eric Arnsdorff]

The 0V between ground and black and 120 V between white and ground sounds like you’ve lost a leg somewhere. I’m going to assume the black and white wires are being used for the hot legs. The white wire should be marked with a black marker (typically black electrical tape). It doesn’t sound like the neutral was pulled with the 240V wire which is fine but just confirming.
You mentioned where the ground goes to the grounding rod which is good but has little to do with the proper operation of your electrical circuits. More important for normal operation is the ground makes it to the neutral bus only at the service entrance panel.
My guess is your tools are being under-voltaged which would lead to overheating, high amperage and failures. I don’t think the issue is coming from surges. You should have ~240 VAC between the hot legs and ~120 VAC from either hot leg yo ground. I wonder if you have a loose connection that when loaded is not capable of delivering the current (likely arcing) and causing the under voltage. I’d start at the panel checking each connection is good (no insulation under the screw, etc.) and work out to the outlet.

[Glenn Kotnik]

Thank you both for your ideas, it gives me a way to start troubleshooting. I will go thru the load center and check all connections. As I recall it is the type where ground comes in and connects to a terminal of its own and if the power company wants white and ground bonded then you screw in a bolt which connects neutral to ground. IÂ’ll check this. The only place where there is an unusual ground is the DRO display on my 240V vertical mill. The display has a ground terminal on the back and the instructions say to connect this with a separate wire to ground. Since the mill is only a few feet from the service panel I ran a wire from the ground screw to a screw on the cover of the panel.

The tech guy at Oneida said something has shorted in the magnetic starter switch. The connection fried so there no way to determine if it was loose. The power from the 20A double ganged breakers in the panel go to a wall receptacle near the Gorilla, then a cord with a plug on it comes out of the magnetic starter switch and plugs in. This is the way it was supplied to me. So so as far as I know there was no way to pull the neutral all the way thru.
IÂ’ll reply again when IÂ’ve checked everything, thanks for your help.

[John K Jordan]

... The power from the 20A double ganged breakers in the panel go to a wall receptacle near the Gorilla, then a cord with a plug on it comes out of the magnetic starter switch and plugs in. This is the way it was supplied to me. So so as far as I know there was no way to pull the neutral all the way thru.
...

230 volt motors of the type usually used in dust collectors don't need a neutral, just a ground and two hot conductors. You only need a neutral if the machine needs 120 for something.

Some things that can cause a conducting wire to overheat:
- Too small wire gauge for the motor current and wire length. The voltage drops and the motor tries to pull more current. The higher current can make the wire hot. The heat increases the resistance in the wire lowering the voltage further. (thermal runaway) Usually the motor windings are damaged before the wiring.
- A poor connection somewhere in the circuit. Like the too-small wire, the increased resistance at the connection can cause heat, reduce voltage, and increase current draw from the motor. Could be anywhere but usually it's at the burned spot.
- A component failure or shorted conductors somewhere on the circuit (switch, junction box, even the motor itself)

Something I do with electrical connections, especially in vehicles and trailers but also elsewhere: use a smear of dielectric grease. This can keep humidity and such from causing corrosion and compromising the connection.

I'm not familiar with your dust collector. The 5hp ClearVue I use and other big motors often use a contactor (relay) instead of a magnetic starter switch for a robust and remote way to switch on the 240v power.
After you replace the switch and/or contactor you might put a volt meter on the motor and verify the voltage while the motor is running. I also like to put a clip-on amp meter around one of the conductors somewhere on the line and see how much current the motor is actually pulling (I usually do this in the breaker panel box since the individual wires are accessible.)

The main breaker panel connected to the service entrance needs the ground bonded with common. The ground is not bonded in a sub-panel.

Caveat: I've been wiring for almost 50 years but I am not an electrician (except in Mexico) and I don't keep up with the codes so I don't know if things have changed since I wired my houses and shops.

JKJ

[Glenn Kotnik]

What I’m thinking is the switch somehow developed a short which caused the black wire to fry and created an open connection in the black leg. You mention that a loose wire causes lower voltage and causes the motor to draw more current. Obviously this is not Ohm’s law so does this occur because the motor is an inductive load rather than a resistive load?
I’m not an electrical engineer so I don’t know much about this, although my father had a master’s degree in EE from Case Western and was chairman of the EE dept at a Reliance Electric plant. Later they were acquired by Baldor and ironically, both names appear on the name plate on my motor.

I’ll attach a photo of my service box, the BI passed it without problems. The two big black wires coming in the bottom are the 240v hot wires from the meter base. The multi conductor wire on the left connected to the left bus is neutral. The single large copper wire connected to the bus on the right is the ground.
Also, the readout for my DRO is shown in the other photo. The green wire goes from the display ground terminal to a screw on the service box. The instructions with the DRO say to connect this ground terminal to an “earth ground”. The power to the display has no ground, only two wires.


Thanks everyone.

[glenn bradley]

I know things vary widely with geography but your inspector was pretty relaxed for around here. Un-insulated neutral? No colored tape markings? That would be a revisit here. Something skipped by almost every sparky I have ever worked with is torquing the lugs. An experienced sparky can get in the ball park by feel but they are tightened a LOT more than one might think. Your surge protector is supposed to shunt excessive voltage to ground so spikes should not be your problem if it is working correctly. Was the Mirka plugged into the same line that is being used for one side of the DC? That would be a no-no. The DC should have its own circuits. If your "black" side of the service panel is all being effected you would see misbehavior at every circuit (outlet or whatever). If the lights are on that panel do they work as expected? Just trying to narrow things down a bit.

[Julie Moriarty]

Some thoughts...

One leg on the 240v circuit heated up and then went dead? Amperage is usually the culprit when wire insulation melts because most insulation is rated at 600v. If you had a direct short across the two legs, the breaker would have tripped. (or should have) So there was a demand for higher amps in that one leg which makes me wonder what was creating that demand.

You mentioned the POCO was working on some overhead lines nearby when this happened. If there was a drop in voltage on one leg of your service while your machine was running, it's possible the other leg could have seen a higher current demand. There could have been something in your starter wiring that tried to make up for the imbalance and it fried. A bad transformer could cause undervoltage and maybe the POCO was working on that. One job I was on the temp transformer (3ph) lost a leg. Of the two reaming legs, one was about 50v, the other was close to 200v.

As for your panel, I'm not a big fan of landing grounds and neutrals on the same bus. You service entrance (usually at the meter) should have the neutral bonded to ground but the fact you have a separate ground coming into the panel, means they may have made the panel the service entrance.

I isolate the neutral bus bars from the panel tub and install separate ground bus bars. I realize a lot of homes where NM wiring is permitted land grounds and neutrals on the same bus but I've seen too many incidents where strange things have happened when grounds and neutrals bond after the service entrance.

[Glenn Kotnik]

When I built my workshop in 2013 REMC put in a new transformer at the base of the pole and brought 240v service to the workshop in an underground conduit. They gave me a meter base to install and told me to get an electrical permit at the city building. City told me I don’t need a permit and I should just install the base. I connected the base to the load center which I installed inside the workshop. I put in the ground rod and also connected that to the panel. I don’t know of any other grounds. So I assume this is the service entrance. The dust collector has its own breakers. The DC manual says the magnetic switch has an “overload breaker” in it. It apparently tripped but I don’t know what caused that. There is no sign of wires on the output side of the switch or in the box to the motor over heating. Just the incoming black wire and the small melted area on the side of the switch where the black wire connects. When I turn the switch on the breaker inside the switch immediately trips. So faulty switch? Coincidence that the Mirka sander went out just a couple of hours before?
‘I’ve never had any problems with lights or any other circuits. I put in plenty of breakers and circuits when I built the place. A couple of years ago I put in the surge protector just because we have had problems with surges in our house. One thunderstorm blew out my computer and the cable modem. I discovered that the cable company installer had “grounded” their surge protector at the box to a schedule 80 conduit.
‘I talked to Oneida and ordered a new starter switch. When it arrives I’ll install it and measure voltage in both legs at the switch and at the motor.
I donÂ’t know what else to do except keep my fingers crossed.

[John K Jordan]

.... and measure voltage in both legs at the switch and at the motor. ...
I don't know what else to do except keep my fingers crossed.

Another thing to do is measure the lengths of wiring runs and double check the conductor sizes. An online voltage-drop calculator might be helpful, such as this one: https://www.southwire.com/calculator-vdrop
If I remember correctly, the target non-commercial voltage drop is 3% or less. When I built my shop I went for overkill and sized my underground feed and each circuit wiring in the shop to limit voltage drop to 1% at projected full load. This required larger size conductors than normally installed. (I hate it when lights dim when a load cuts in.) If your wiring is pushing the boundaries and voltage drop is high enough to contribute to the switch failure, it could happen again.

When you measure voltage be sure to do it with the motor is running under full load. For a cyclone dust collector full load is when blast gates are open. You can ignore startup transients typical with large motors.

BTW, from the last time I dug into the code I think two ground rods were required, perhaps at least 8' apart, to provide a better ground. Also, if the building has a concrete floor or footings the ground should be connected to the rebar as well (difficult if already constructed!)

The sander incident is suspicious but there is a reason for the word "coincidence" exists in the English language!

Again, I'm not an electrician. It might be money well spent to pay for an electrician or ask an inspector to look at your wiring and grounding. Or at least an acquaintance with some experience can contribute a second pair of eyes!

JKJ

[Robert Engel]

Call an electrician. This is not something to mess around with.

[Tom M King]

Bad ground somewhere at the beginning of the system.

[Dan Rude]

I would think that what Julie Moriarty said, might be closer to the truth. I worked at a college when we lost a 3-Phase leg (I was teaching Basic Electricity/Electronics at the time it was a good teaching moment.), most of the motors that were on that circuit had damage either in the controller or the motor. I would at a minimum contact your power company about it. Dan

[John Lifer]

Not to cast dispersion on your electrical panel, but you have a 50 amp breaker at top left wired with what looks like 12 gauge wire. You need 8 gauge wire for that breaker. And you have at least 2 30 amp breakers with maybe same 12 gauge wire. (should be 10 gauge) You WILL burn or even melt the wires before you would get a trip at those breakers. Wire must be equal to the breaker or larger. Now that isn't your issue here, but could possibly the breaker might should have tripped if it was right size.... And I'm cringing at that bare ground too.

[John K Jordan]

Not to cast dispersion on your electrical panel, but you have a 50 amp breaker at top left wired with what looks like 12 gauge wire. You need 8 gauge wire for that breaker. And you have at least 2 30 amp breakers with maybe same 12 gauge wire. (should be 10 gauge) You WILL burn or even melt the wires before you would get a trip at those breakers. Wire must be equal to the breaker or larger. Now that isn't your issue here, but could possibly the breaker might should have tripped if it was right size.... And I'm cringing at that bare ground too.

As I mentioned, I'm not an electrician (except in Mexico) but my understanding is the wire gauge needed for any circuit depends on two things - the maximum sustained amperage and the length of the wire. Not accounting for both can be a mistake. For example, a wire correctly sized for a short run may not be enough for a very long run. Do the calculations. For these reasons and more I ran 8 and 6 gauge from 50amp breakers to several places in my shop.

I repeat, get someone qualified to evaluate this.

I once worked on lights and wiring in a large building at a children's camp in the central highlands of Mexico. I found a water heater wired with 14ga wire strung across the wooden rafters in the attic space for well over 100ft. The circuit was fed by a 50amp breaker!!, a fire waiting to happen. Electrical supplies were not available in that area - the nearest was a 5 hr drive and there was no guarantee wire or breaker could be found there. It was several years before I could get back there with the proper supplies. Several years of worrying...

Wiring in that part of Mexico was the worst I've ever seen. I saw stores where bare copper wires carrying 110v were stapled about 3" apart to concrete block walls. This was where even little kids wandering around had access. Yikes.

JKJ