I was looking at the released datasheet for the Enphase IQ-series inverters
yesterday and I noticed the following entries which are non-existent in both the preliminary datasheet for the IQ-series inverters and in the datasheets for Enphase' previous products:
Enphase IQ 6 and IQ 6+ Microinverters Datasheet wrote:Overvoltage class DC port: II
Enphase IQ 6 and IQ 6+ Microinverters Datasheet wrote:Overvoltage class AC port: III
Even though I have designed and tested lightning-suppression equipment in the past, I had not hear of this type of rating. An internet search revealed this National Instruments webpage
which has the following to say:
National Instruments white paper on Isolation and Safety Standards for Electronic Equipment wrote:The amount of insulation required in the isolation barrier depends on several factors:
- Working Isolation Voltage (voltage across the isolation barrier) -- larger isolation voltages require more insulation.
- Transient Voltage (temporary voltage spikes across the isolation barrier) -- insulation strong enough to withstand the normal working voltages of the circuit can break down under large transients. Therefore larger transients will require more insulation.
- Air Pollution -- insulation can be reduced by contaminants in the air. Dirtier environments require more insulation.
- Single-Fault Current Path -- if the insulation breaks down, can the shorted current go through a human body? If so, a larger amount of insulation is required.
The IEC has covered these issues in Section 6 of the IEC 1010 standard. The commission has defined things such as overvoltage categories, pollution degrees, and double insulation.
That page also includes a table indicating the transient voltage which must be withstood for each overvoltage class. The National Instruments webpage
also lists these descriptions for IEC "installation categories":
National Instruments white paper on Isolation and Safety Standards for Electronic Equipment wrote:Category II -- Energy-consuming equipment to be supplied from the fixed installation.
Examples: Appliances, portable tools, and other household and similar loads. Measurement equipment intended to measure the voltage levels of these loads must be rated at this overvoltage category.
Category III -- In fixed installations and for cases where the reliability and the availability of the equipment is subject to special requirements.
Examples: Switches in fixed installation and equipment for industrial use with permanent connection to the fixed installation; measurement equipment intended to measure the voltage levels of these fixed installations must be rated at this overvoltage category.
I suppose what is implied by all of this is that BOTH the DC section AND the AC section of the new IQ 6 and IQ 6+ inverters are galvanically isolated from something (the metal tab on the unit?) and have the following minimum insulation breakdown voltages: DC section: 500V, AC section 4000V (or is it 2500V?). And I suppose the transient is common-mode on top of the two wires connected to each section.
Is this the proper understanding of what those specifications mean? If not, what then is meant by "overvoltage class"? Also, is this new requirement something that comes about because of the elimination of both the ground and the neutral wires in these new inverters?