CSA 22.2 No. 14 and MOV

[patm72]

Can anyone help me shed some light on the following claim found in CSA 22.2 No. 14 (2008) paragraph 4.15.2 regarding MOV's as overvoltage protection devices? Where does it come from?

Surge suppressors of the metal oxide varistor type are not considered to be acceptable overvoltage protection for
equipment and circuits that operate in the primary circuit.

It is found at the bottom of a paragraph about spacing, in fine prints. For the record, a "Primary Circuit" is defined as:
"wiring and components that are conductively connected to the supply circuit".

And a "Secondary circuit" is "wiring and components connected to a circuit, where power is limited by a transformer, rectifier, voltage divider, or similar device that derives power from a primary circuit, and where the short-circuit limit between conductors of the secondary circuit or between conductors and ground is 1500 V•A or less." (so I clearly deal with a Primary circuit).

I was intending to use a MOV type SPD for protecting my electrical equipment (a VFD) from overvoltages. The VFD's could not have these or any other sort of OVP built-in, so now what? The manufacturer "enforces" the use of a choke and EMI filter in front of the VFD to meet CSA 22.2 No. 14 (note that no equivalent of this is applicable in NEC). An EMI filter is quite bulky compared to the SPD's we use all the time.

Thanks.

 

[davidbeach]

MOVs are only suitable for transient overvoltage (microseconds to a few milliseconds) and they are not suitable for protection against any sort of sustained overvoltage.

 

[LionelHutz]

IF you're looking at CSA 22.2 No. 14 then you should be looking to list a product to meet that standard. So, ask the accreditation agency engineer that you're working with. I suspect it simply means your product must survive the required testing without the MOV protecting it (the surge/impulse testing) but you could still install the MOV in the finished product if you want.

You are talking about a VFD manufacturer and internal protection in the VFD. For that, you should be following the harmonized C22.2 No. 274 or 61800-5-1 standard which is specific for VFDs.

Of course the NEC doesn't contain the equivalent to #14. The CEC would be comparable to the NEC. The CED is the code telling you how to install a piece of listed industrial control equipment (equipment already listed to #14). Comparable standard to #14 would be ones like UL508 or UL508A.