I recently was at a building that had a two phase monitors, a very old mercury switch phase monitor and a newer solid state phase monitor. I thought it was a pretty cool picture to show a older device that provided phase protection next to a newer device that provides phase protection.
[new phase monitor on the left old mercury switch on the right]
Phase monitors are also required on all traction elevators in the State of Illinois[with exception of City of Chicago] – Starting 1/1/15.
Traction elevators – State of Illinois – Phase monitors required 1/1/15
Traction elevators – City of Chicago – Strongly encouraged
Hydraulic elevators – Everywhere – Strongly encouraged
The National Electrical Code (NEC) specifies that elevators driven by poly-phase
AC motors must be prevented from starting when there is a phase reversal or phase failure condition present. The reversal of three phase voltage can lead to a sudden change in direction, which could lead to a disastrous hazard when the transportation of people is involved. A phase failure could lead to a sudden or uncontrolled stop, which is another possible hazardous condition
14% of all motor failures can be attributed to single phasing
30% of motor failures can be attributed to electrical over loading
The electrical code suggests all elevator systems should have a phase monitor device which would shut an elevator down if the following conditions occur
1. Phase reversal
2. Phase loss
3. Under voltage
Phase monitors can be found in elevator motor drives[traction elevators], solid state starters[hydraulic elevators] or purchased as a component
[Motor drive with phase protection - Traction elevators - Magnatek]
[Siemens soft start with phase protection - Hydraulic elevators]
[This is a stand alone phase monitor - Traction or hydraulic elevators - Diversified Electronics]
In summary, basic but critical voltage and phase monitoring for applications involving transporting people or heavy equipment such as escalators or elevators is not only imperative, but mandated by the NEC[on new installations]. A simple monitor doesn't cost a fortune, but should something go wrong, failure to provide one can be quite costly in liability claims.
Information used from – Carlo Gavazzi automation components – www.gavazzionline.com