I have a couple of questions regrading the National Electrical Code:
1) Consider a power measuring device that is intended to be installed into a residential 120V branch circuit, protected by a single 15 A or 20 A circuit breaker. The device would be installed into a conduit outlet box on the load side of the breaker to measure the power loads on the outlet receptacles or lights connected to the branch circuit. The device has two neutral terminals with a 12 AWG copper wire connected between them to sense the load currents. This device would be wired in series with the neutral (grounded) conductor for the branch circuit. The live (ungrounded) conductor of the branch circuit would have a common connection on this device.
Based on Section 300-13(b) of the NEC (NFPA 70), this device could not be used in a multi-wire branch circuit, since the removal of the device would interrupt the continuity of the grounded conductor. However, I cannot find any requirements that would prohibit the use of this device in a single phase branch circuit, protected by one circuit breaker. Since the resistive loss in the neutral circuit through this device would be negligible, would this device comply with the NEC?
My guess is yes, that it meets the NEC code requirements for this branch circuit. Any comments?
2) Consider the same power measuring circuit installed into a direct plug-in (NEMA 5-15P) with a single outlet receptacle (NEMA 5-15R) or into an outlet strip with a 16 AWG power cord with several outlet receptacles. Assuming that the measuring circuit is provided with a suitable fuse for overcurrent protection, are the outlet receptacles required to be protected by a 15 A fuse or circuit breaker in the device or can they rely on the circuit breaker for the branch circuit for overcurrent protection?
The UL product standard for this device is UL 3111-1 (Electrical Measuring and Test Equipment), which is harmonized with IEC 61010-1, requires an overcurrent protector to be fitted within the equipment for all devices connected to the mains supply (9.6.2). There are no US deviations in this standard that would allow the circuit breaker to provide this protection, so based on this I would assume that a 15 A circuit breaker of fuse would be required for the NEMA 5-15R receptacles. I would also assume that a 20 A overcurrent protector would be required for a NEMA 5-20R outlet receptacle.
However, the UL product standard for household appliances (UL 60335-1) does have a US deviation to a similar requirement for overcurrent devices (19.1, Note 2) that states the "The PROTECTIVE DEVICE in the fixed wiring does not provide the necessary protection." However, the US deviation states "The circuit protection device is permitted to provide necessary protection". If I am interpreting this correctly, a household appliance in the USA could rely on the panel breaker for overcurrent protection. Any comments?
Thanks in advance for anyone willing to wade through this and send me a response.
Richard A. Meyette. PE [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
