Stinger Leg

Philip--

I believe you need a new electrician. It sounds to me like your electrical panel is connected to a three-phase source (in other words, three hot legs and one neutral). Virtually all homes in the USA are single-phase (two hot legs and one neutral placed in the middle between them). However, commercial facilities often are three phase. There are four ways that three phase power can be supplied, but two of these are very unlikely to be used at the voltages you are using (corner ground delta and ungrounded delta).

Usually, three phase has the neutral right in the middle between the phases (picture a triangle with each phase or hot conductor at a corner and the neutral a dot at the very center). This is called a Wye or "Y" type of power distribution, with the same voltage from each hot to the neutral and somewhat less than twice this voltage from any one hot to another hot. Typical USA voltages are 208/120V or 480/277V. The other is given different nicknames in different areas--high leg, wild leg, stinger leg. It is a delta with the midpoint between two legs being the neutral (picture a triangle as before, but move the neutral down and place it on the middle of the bottom line). Between any two hot legs you have 240V, but voltages from neutral to hot are not the same! They will be 120V, 208V, and 120V. If the wiring was done correctly, the high leg is called the "B" phase and is marked with orange colored tape on the incoming wires. The voltage numbers I mentioned above are the typical or "nominal" ones we use in descriptions, but power companies often run higher than this (such as Wye of 220/127 or delta of 127V, 220V, 127V)

The reason I said to get a new electrician is because with three phase power, you cannot add the voltages from neutral to each hot leg as regular numbers (120+208 is 328 in single phase but not three phase). That is because the AC voltages are rising and falling 120-degrees out of phase with each other, so they are never both at a peak simultaneously. Look back to your delta triangle and you will see that the 120 and 208 volt lines are 90 degrees apart, a right-angled 30-60-90 degree triangle. Trigonometry tells you that the lengths of the sides are related as: short side is 1, hypotenuse is 2, and long base side is square-root of 3 or 1.732. Therefore, if the diagonal (hypotenuse) is 240, the short side is 120, and the longer side is 208.

If you had those fans wired on 360V, like your electrician claimed, they would have been adding their own smoke to your greenhouse, instead of just air.

Your post asks about the "stinger" leg, which I discussed above. But it also asks why the wire to the fan was burning out. I assume that the wire used was a typical extension-cord type of cable, a rubber or plastic jacket and three wires inside colored black, white, and green. Most commonly this type of cable is rated for modest amounts of use and is only insulated for 300volts. If my assumptions are correct, embossed into its jacket or printed on it will be a string of letters such as SJT or SJO or SJTO or even SJTOW. It will also tell the size or gauge of wire and the voltage rating for its insulation. I suggest that you try rewiring a few fans, using a cable with a higher voltage rating (600V). It will not have the "J", and often not have the "T" either. Therefore you would be using SO or SOW. (These letters have meanings--S is service cord, O is oil resistant, W is water resistant, T is thermoplastic instead of rubber, and J is junior size insulation).

Your problem can be because of vibration. If only a short section of the wire is being vibrated continuously when the fan is running, the individual wire strands within each conductor can eventually be flexed enough to become hardened and then break. This forces the electrical load to flow through a conductor whose size is ever-decreasing. At some point, the current flow at this bottle neck point starts heating up the wire to the point where it overheats and burns the insulation. To fix this, you would need to either decrease the amount of vibration or increase the length of cable the vibration is being passed along (so the magnitude of the bending caused by the vibration is lower at any section of the cable and thus making the amount of work-hardening of the wire strands much less). If vibration is causing the problem you have seen, it will probably be worse for some fans than others, and you will only be seeing the burned-out cables on certain fans (and these same ones will be felt to vibrate more than others). To cure the vibration you can remove the fan blades and have a machine shop balance them.

I hope this rather long post has helped--John M. (master electrician since 1979)

Oops--if the fans came from Holland, and were with pre-wired cables, their cables most likely were with insulation colored brown, blue, and yellow with a green stripe. John M.

John,

Great post!

Greg

Look on page 3

http://www.behlman.com/applications/AC%20basics.pdf

Why would anyone import fans from holland for the USA, with hundreds of fan makers here and no warranty problems or imprt problems

If you look at the original post, he says he is in California. That should explain why they imported from Holland.

Yes, I see that now ;)

I do not mean to be a killjoy buuuuut;

Has anyone found out if the fans motors are fifty cycle versus sixty cycle?, as this is even more important.

Actually Guys, if you read the post, the only Holland import is Phillip. He doesn't mention the origin of the fans.

About half way through the original post. Philip does say that fans are from Holland. So the 50/60 HZ question is a very good question - unless they were specifically made for export to America or some other 60 Hz place, they are most likely 50Hz.

If the electrician did not read the name plate to authenticate 50/60 cycle its his fault as the power feed will have to be converted for 50 cycle

Oops. You are correct Sled about both the origin of the fans and the operating frequency.

I disagree. The original post says 50/60 cycle. This implies that they are made for use at either frequency. This is a fairly common practice. If the fan were with a purely 50 cycle motor, then the thing to watch is the voltage/frequency ratio. Since he also says he is using them on a supply which has a variable voltage, I suspect that a problem may have been missed in my original answer as well as in everyone's posts since then.

When the voltage is reduced, frequency is unchanged. If the fan tries to run at its full speed, this causes a significant increase in current draw. If this was overheating the cable to the fan, where it is placed in the moving air stream (assuming it is not a belt-driven fan) the air flow would keep the wire cooler, so the heat damage would be found along the portion of the wire that was nearer where it connected to the building's wiring. If, however, Philip is using components as specified by or supplied by the fan manufacturer, then any such problem has been investigated and should not be significant. A simple inquiry to the manufacturer may help with this. Philip--could you enlighten us here?

John M.

The main reason why we import from Holland is because the greenhouse industry there is somewhat more advanced then here. This is all caused by the fact that have to do it with less area less sun and energy prices being double as high as here. The price on these fans is a lot lower than fans with the same quality/efficiency you can buy here. We pretty much import complete greenhouses, 4-6 mil btu boilers, unit heaters, shading system etc. These particular fans came from a company in Canada though. They again buy them in Holland and had never before a problem with the cables. They can run on both 50 and 60 htz. The cables are the 220V type with a molted on plug, the type with the prongs a little bit more appart . The strange thing is that there is no molted material nor any residue from vibrating/rubbing. It just seems like wherever the cable touches the protective grid material just disappears. I am all for buying American build but first I need to find out what is happening here. Could it be that the frequancy control unit could not handle two hot legs with one being higher than the other?

Philip--

Good response. I applaud your reasoning. Your last question raises a very good point. If this is a problem with the controller, then you could verify this quickly by looking at the number of failures. If your fans are running on only two hot legs (single phase fans), then only 1/3 of them will be connected to the two legs with lower voltages to neutral. Therefore you would have as much as a 67% failure rate. More importantly, you would have no failures on the units connected to the two legs with lower voltages to neutral.

Question--you say "frequency control unit". If this is an SCR type of speed control, it doesn't change the frequency, just the applied voltage. If it is a true VFD (much higher cost), then it changes the voltage and frequency simultaneously. Have you asked the manufacturer of the controller? What is the motor current at different settings of the "frequency controller"? Also, what is the voltage? Finally, many digital multimeters also allow one to measure the frequency, so what is this at different settings? All this will help to find the problem. It is hard to diagnose something from a distance, but we are trying.

John M.

Just a thought here. It sounds like you might be running into a Delta 3 phase setup.

Unlike a typical 3 phase distribution Delta uses the transformer to create the 3 phase loade balance. in Delta one phase is always going to be 230v to ground or neutral. Ife the fans are 3 phase or 2 phase then the load should balance. If they are supposed to have a single 110v supply then this could be the problem.

Go to Google, ask for "Stinger leg", and then to Behlman´s "Basic AC Power Source Configurations" wher you will find the info you are looking for.

On the Behlman information "240 V split phase Delta", the Voltage between Dog Leg and Phase B is "208 V ca, and not 180 V ca.

Best regards,

Arturo Pérez

I am not an engineer but I have run into a problem like this before. It occured on a large 3 phase motor with a variable frequency drive. The problem was the motor overheated on the drive yet the motor was well within its normal current range. The solution was that the motor was not rated for a variable frequency drive and the harmonics generated in the windings caused extra heat to build up in the frame and windings. The motor was replaced with one engineered for that type of drive and the problem disapeared.

Hi Philip. I found this page http://ecmweb.com/mag/electric_stumped_code_17/ I'm sure it 'll help you

Regards

Guillermo Alvarez-Torres