Noway2
Electrical
- Apr 15, 2005
- 790
I am working on a project to replace a steam meter panel (enclosure) and the project sponsor wants it to be built to UL508A. He is also telling me that the max available fault current at the building transformers where these will be installed is 65KA and he wants the panel to have a rating greater than that. There are two things / questions that are causing me some hesitation and confusion about this requirement.
Background and description:
The steam meter will consist of a PLC, HMI, power supply, possibly a HART to (Modbus ?) converter and connect to a Rosemount V-Cone transmitter via a 4-20mA + HART line. The panel will be powered by 120Vac and will have a GFCI service outlet inside the cabinet so that the technicians can plug in their HART communicator. The PLC will also communicate to a SCADA system via standard Ethernet.
Questions / request for sanity check.
1) As the panels are 120Vac, and I am going to assume that the buildings are either 208Vac or 480Vac 3-phase that this pretty much precludes the meter being potentially subject to (receiving) that level of fault current because I would expect this meter to be downstream of a distribution panel and likely a transformer (except for possibly 120/208 wye) and don't think that it would ever be "service entrance" equipment, but who knows. Making a panel like this, Service Entrance would create a lot of expense requiring a suitable disconnect and door latching mechanism.
2) If this equipment is NOT going to be service entrance would it not be a violation to have a larger sized protection device down stream of a smaller protection device, as this circuit would become a feeder rather than a branch circuit. The power requirements of the PLC system would be minimal, call it a couple of amps maximum (and that is likely at the DC power supply level). Does anyone even make service entrance rated devices for circuits that small or would this necessitate a larger entrance circuit and then a transformer to step down the voltage and / or capacity?
Background and description:
The steam meter will consist of a PLC, HMI, power supply, possibly a HART to (Modbus ?) converter and connect to a Rosemount V-Cone transmitter via a 4-20mA + HART line. The panel will be powered by 120Vac and will have a GFCI service outlet inside the cabinet so that the technicians can plug in their HART communicator. The PLC will also communicate to a SCADA system via standard Ethernet.
Questions / request for sanity check.
1) As the panels are 120Vac, and I am going to assume that the buildings are either 208Vac or 480Vac 3-phase that this pretty much precludes the meter being potentially subject to (receiving) that level of fault current because I would expect this meter to be downstream of a distribution panel and likely a transformer (except for possibly 120/208 wye) and don't think that it would ever be "service entrance" equipment, but who knows. Making a panel like this, Service Entrance would create a lot of expense requiring a suitable disconnect and door latching mechanism.
2) If this equipment is NOT going to be service entrance would it not be a violation to have a larger sized protection device down stream of a smaller protection device, as this circuit would become a feeder rather than a branch circuit. The power requirements of the PLC system would be minimal, call it a couple of amps maximum (and that is likely at the DC power supply level). Does anyone even make service entrance rated devices for circuits that small or would this necessitate a larger entrance circuit and then a transformer to step down the voltage and / or capacity?