Surge Protection Device Ratings

[msimms]

I have an application where a 208/120V rated SPD is being used on a 400/230V (European) application. Reading NEC 285.3 (3) it states "Where the rating of the SPD is less than the maximum continuous phase-to-ground power frequency voltage available at the point of application". Talking to various vendors, some have stated that 208/120V rating would preclude use at the higher voltage application (120V vs. 230V), but others have stated that the MCOV (maximum continuous operating voltage) rating may allow these SPDs to be used at these higher voltages. In my case, the device has an MCOV of 550/275V.

Can someone confirm if the MCOV is means to allow a lesser system voltage rated SPD to be used if the nominal operating voltage falls within the MCOV range, or is this to account for fluctuations in the system voltage? Does an SPD 'rating' per the NEC refer solely to its nominal system voltage rating, or does it also account for the MCOV as part of its 'rating?

Thanks.

 

[tortuga]

Did you mean a 600/347v type 2 rated?
Either way MCOV will allow a lesser voltage, MCOV is a maximum.

See the UL whitebook on Surge Protective Devices (VCCA) and UL 1449.

Voltage Protection Rating (VPR) A rating selected from a list of pre-
ferred values as given in Table 63.1 of ANSI/UL 1449 and assigned to
each mode of protection. The value of the VPR is determined as the near-
est highest value taken from Table 63.1 to the measured limiting voltage
determined during the transient-voltage surge suppression test using the
combination wave generator at a setting of 6 kV, 3 kA.

 

[paulengr]

MCOV is the critical parameter. If system nominal voltage exceeds it the surge arrester will fail in seconds.

Generally you want MCOV at least 10% above the nominal voltage or 440 V in your case. So say it’s 430 and during a plant outage the transformer output increases to 435 V. It is within the voltage range allowable by standards (+10%) but now the SPD fires (435 exceeds 430) so it shorts to ground. Typically the fuse in the device opens and it no longer does anything.

 

[msimms]

Did you mean a 600/347v type 2 rated?
Either way MCOV will allow a lesser voltage, MCOV is a maximum.

See the UL whitebook on Surge Protective Devices (VCCA) and UL 1449.

No, 400/230V is the voltage; this is a European application which is the nominal voltage here for Type 1 & 2 SPD installation but the contractor here is electing to use SPDs from the states. Instead of electing to use SPDs that are rated 480/277V, they've chosen to use lesser voltage rated ones in order to meet VPR and other requirements. I've also read up on the UL1449 and the use of the lower rated SPDs is to meet VPR ratings that align with NFPA 780.

MCOV is the critical parameter. If system nominal voltage exceeds it the surge arrester will fail in seconds.

Generally you want MCOV at least 10% above the nominal voltage or 440 V in your case. So say it’s 430 and during a plant outage the transformer output increases to 435 V. It is within the voltage range allowable by standards (+10%) but now the SPD fires (435 exceeds 430) so it shorts to ground. Typically the fuse in the device opens and it no longer does anything.

Understood, but wouldn't I be more concerned about phase to ground based on the code requirement then? In this case, a 230V L-G with an MCOV at 275V (about 20% above nominal). There are swings of incoming utility voltage as much as 10% so that is relevant here. I guess I'm still having a hard time understanding why have a ratings at nominal voltages if the MCOV can be a safety net that seems to allow their use. Or am I just overthinking it at this point?

 

[tom baker]

Leviton has great tech support give them a call, ask for a product recommendation.

 

[msimms]

Leviton has great tech support give them a call, ask for a product recommendation.

Thanks, I'll give them a call.