Help! Not sure if this is allowed by codes, UL 508a Experts?

[meternerd]

One thing to keep in mind....many, single phase conditions are on the primary side of the transformer. On a typical 3 PH Wye or Delta system, a motor can continue to operate both starting and running with one primary phase missing. This is because most pad-mount transformer use common core windings, where the core is shaped like double-H and the induced voltage in the missing phase will be enough to keep the motor operating. But...voltages will be unbalanced and motor overheating will probably occur. I've seen quite a few instances where a KWH meter showed odd phase voltages which turned out to be blown primary fuses, but the pump station continued to run. That's why we install phase monitors that trip on phase current or voltage imbalance. Overloads don't always provide protection.

 

[XxaudioholicxX]

Thanks guys, good discussion. Disconnect means is external and being provided in the field. From what I can gather, there are branch circuits they want running if a circuit breaker trips. Basically if one breaker trips, the other parts of the circuit are still running - not sure why they would want that and have other branch circuits using the same protection as the motor... It is a poor design, they should have run the motor on a separate branch with its own protection. Fortunately, this is not my project but a co-workers, he just stumped me with the UL part of it.

I am going to suggest the use of a 3 pole breaker, but the question was, is it considered legal under UL and I could not find anything backing it up that it wasn't - will have to ask the inspector next time he is in. NEC 240.15 and NFPA 7.2.3 were the only codes I could find that address this. Since NEC is law binding, I would think even though it is not mentioned in UL, it is still illegal because it is in the NEC. That being said the best practice, at least in my opinion, is to follow the most stringent code out of the three, that way your covered no matter how you slice it.

 

[SceneryDriver]

neither the code nor UL508a would allow its use as a disconnecting means.

Agreed, but not really my point. When I design panels, I try to think about what the next person would likely expect when they open the panel. It's the same idea as installing a contactor such that power enters the terminals on top, and exits the terminals on the bottom.

Absolutely nothing wrong with flipping that contactor so that the Line terminals are on the bottom and the Load terminals on the top. The electrons don't care, and it meets code because the Line and Load labels are followed. That said, it's about what you (or someone else) would likely expect when working on a panel. Someone might somewhat reasonably infer power usually enters the top terminals on a contactor, and that circuit breaker off = no voltage to motor.

Granted, that should always be verified with a meter, and possibly reference to the documentation but we all know that doesn't always happen. Whether or not it's code enforceable or not, three single-pole breakers for a three phase motor is a poor design choice. I know the code isn't meant to be a design guide, but not all good ideas are code enforceable (I believe that saying is someone's signature on this forum).


SceneryDriver