I can nay get the power Captain!

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sooo…

I didn’t get to play with my current set of centrifuges on Friday, because the chiller had quit…but it had quit in a manner we’ve seen before, and one that points to a problem with our 3-phase power if I’m reading it correctly.

Chiller states it will draw max 26A, yet repeatedly (three times in the last few months) according the the tech I talked to, we’ve had them burn out one leg AT the (30A 250V twistlock) wall socket/plug interface.

to me this says one leg is low voltage…but I’m a biologist and the only formal electrickery I’ve had was back in high school.

I tried playing with one of the fuges anyway, because I don’t need cold to figure out spray patterns or appropriate spin speeds (ok, I do, but I can get close)…and the thing kept throwing LU.

quick check of the fine manual reveals LU == Low Voltage! (why U not V?!?)

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yes, there are other excuses for that particular error, but combined with the chiller on the same sub-panel pulling too many amps on one leg, I’m not sure there is a whole lot of point chasing those down.

not sure what it is about my whirled, but it seems that I’m plagued by “I can nay get the power” wherever I go…

Anyone able to suggest other options? How hard is this gonna be to track down?

Rumor has it the pro’s will be in tomorrow to at least address the wall socket the chiller took out…will I have any trouble convincing them it’s a low voltage problem? (Nah dude, it’s the POS chiller!)

seems like sag under load to me…is that gonna make it harder to solve?

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Honestly 26 amps continually is asking a lot of a 30 amp circuit.
Is the same leg of power at fault each time? Its also likely that you have a faulty breaker or loose connection which is causing hi amp load on the one circuit
Hope all goes well, an amp meter at the panel is where I would start

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I’ve seen them burn up because of bad install before

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I can’t confirm it’s the same leg, but it’s not always the same circuit.

Centrifuge throwing low voltage errors was on different circuit than chiller. Pretty sure it’s on the same sub panel, but there are three in the room, so I’m not certain (and haven’t poked at it because the pros will be back tomorrow).

One prong on the plug was blackened and melted, as was the socket. Tech says he’s seen the same phene repeatedly (different chillers)

My initial response was “unbalanced three phase”…given the fuge throwing “low voltage”, I’m unclear what else it could be.

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Them?!?

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Twist lock

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Fair enough. Might even be repeatable if the same clown is failing to secure the conductors on each one they install. I’ll put that on the list.

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I’ve serviced a few… if they are not torqued enough it will cause this

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I’ve had to replace entire panels etc because idiots forget to torque shit down…never move on without completing task In Hand 100%

Heat is the enemy

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Does the exposed copper connected into twist lock get charred?

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I though I had pictures. I don’t. Will take a look tomorrow.

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Power quality is my company’s specialty! It sounds like voltage imbalance. Under load within 3% is acceptable but closer to 1% is ideal. This is an easy test at the run contractor for a tech. This could be caused by a loose connections or amperage imbalance in one of the feed panels. Refrigeration nameplate are usually circuit ampacity which would include the 125% continuous calc for a circuit.

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yep. that’s certainly the explanation that makes the most sense to me.

you’re not located in Eugene are you? How does your company differentiate itself from the run of the mill sparky? (what am I looking for if the electricians we generally use can’t figure this out?)

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Sorry I’m in Iowa. We mainly focus on electrical safety - NFPA 70E and electrical maintenance NFPA 70B. Power quality falls under 70B.

We have the training, experience, and proper equipment to diagnose and identify these types of issues. More often than not these problems don’t get fixed they just get worked around and the issues are mostly due to bad electrical system design.

Check the voltage phase to phase (all 3) at the unit while running. If your system is 208 volts all 3 should be within 6 volts of each other. Check the amperage. Move to the circuit breaker do the same. If the numbers are about the same check the panel mains if the numbers are still about the same start turning stuff off in the panel. If everything is off but your voltage is still off the problem is further up the system.

If its fine at the circuit breaker check the circuit. Look for loose connections, check for insulation failure-disconnect the equipment and check amperage on the wire or megger the circuit if your electrician has access to one.

If turning everything off in the panel corrects the voltage imbalance look for patterns in breaker layout. If you have a lot of 2 poles make sure they are not all on the same 2 phases. Last summer I was on a call where for some reason the HVAC contractor installed all single phase AC units. There was about 6 or 8 of them and the electrician who installed the circuits thought it would be handy to install the corresponding 1 pole AHU breakers adjacent to each 2 pole AC breaker. When it got hot out 2 of the phases were about 100 amps more than the 3rd.

If the amp readings don’t seem to be off as much as the volt reading then you likely have a harmonic issue causing a voltage phase shift. You would need a Power Quality Analyzer to know this. Not many sparkys have one. Before I got mine the electrical supplier had one for rent. These go on the sytem for a day or 2 and do a recording. Anything with a DC power supply can cause this type of issue. Welders, VFDs, UPSs, computers, and even LED lighting.

Get to know your electrical system. Do you share a utility transformer with your neighbor(s)? If you do what is their power use? Could they have any of the above? Could they be part of the problem? What is your service main/distribution panel? Do all feeder panels originate from there or do you have a series of feeder panels chained together?

Hit me with specifics and I can try to help you. I can even get on a call to walk through some of this with you or your sparky.

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Have you tried throwing a clamp-on meter and checking the draw on the 3 legs? It should be the same, especially if it’s only powering a motor drive? Is the leg in question powering the rest of the controls circuit/anything else of substantial draw? Is you voltage to ground the same on each leg?

If the drive is drawing uneven power with the same voltage on each leg, your drive is fucked. Based on the fact that you’re not throwing OCPD, it sounds more like an arc at the receptacle that is causing you to lose the leg, not the other way around.

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Twist locs aren’t great connectors to use on our equipment, especially with as many high amp startup and resistive loads we tend to use in our labs. I’ve seen them have problems at 50% of nameplate load coming from a well balanced source. Any good quality electrical connector meant to carry a load should have more than one screw or fastener to hold pressure on the wire, I’ve yet to see a twistloc style fitting that did. This isn’t the only hedge against failure but a loose connection causes heat that isn’t easily dissipated, which increases resistance, which causes more heat, until you’ve got a charred mess you have to fix before your equipment will run again

IMO pin and sleeve are what you should be using for any load over 20 amps. Almost every one I’ve seen had two screws to clamp the wire and while they’re more expensive and not as easily gotten from the big box stores, their failure rate is significantly lower even when running higher amps relative to the nameplate rating.

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So many times I have gone to a place and had this issue. It runs havoc with my instruments for sure!

I started having people do electrical checks at each junction and also confirmation at each panel. I now include verification of the wire sizing during these checks as well. And if there are any transformers - I run a monitor overnight to verify there are no issues with capacitance or conditioning (I’m looking for consistent volts and amps, with minimal frequency changes if any…).

A couple of places I was able to remedy an issue with the broader area grid (our downstep was old and janky) by using a transformer with power conditioner (grainger and others carry them semi cheaps). It was a lot faster and cheaper to go with a conditioner than it was finding and fixing the actual sag.

I’ve also seen people have decent success using UPS for this kind of stuff (though for a fuge…that’s a big UPS…)

100% of the time my Installation Qualification includes this electrical verification - in new buildings I do a 72-hr check to make sure I’m not seeing weird fluctuations. Its just got to be or I cannot be certain that my equipment and instruments are performing as intended.

Heck - one time I found that the entire HVAC 3-phase was wired backwards… leading to all of the fans turning the wrong way. This had been going on for YEARS - once it was fixed, their air balance issues went away.

Sure hope you can resolve this issue at your location and its not a year long endeavor to find your solution.

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VFD is generating the three-phase.
it’s being fed by two 116V legs.
202V when combined.
199V for 15sec or so before drive throws Low Voltage error.
one 116V leg drops to 115V, the other to 114V

Electricians came and went, and only bothered to swap wall outlet. gonna try and catch them tomorrow. if they hadn’t just added a dozen new circuits (mixture single phase and 3-phase), I wouldn’t have connected the two problems. it’s possible they’re not connected, but that’s not what the voices in my head are telling me. might have convinced the boss this morning. thought he got it Friday. amazed by the number of folks that pay for my damn opinion, then just ignore it. clearly I’m not charging them enough.

so it really could be two separate issues…

I’ve got two more fuges I should be able to repeat the error on if it really is a facility issue. I’m also gonna go take a picture of the mains…we’ve got a LOT of power coming in. it would not surprise me at all if the web that has been built up over the years is starting to show emergent behavior.

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How are you measuring this? L1-N for your “combined” legs? What voltage is to neutral isn’t relevant unless this VFD is also drawing from your neutral.
202 is low for a 208V system and awful for a 230V system, 199 is even worse.

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What’s the part number on that drive? I had this issue once when I wasn’t getting quite enough juice out of a RPC. There may be a parameters to allow the drive to run with a slightly lower input voltage than it would like. What’s the nominal input voltage?

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