Overcurrent Protection for SPD's

[Ken Clark]

NEC Article 280 and 285 discuss the locations and connection means for surge arresters and surge suppressors. Neither article references NEC Article 240 - Overcurrent Protection of circuits. Since SPD's are considered a "no load" device, do they still require overcurrent protection when being connected directly to the bus of a panel board?

 

[A/A Fuel GTX]

How do you intend to make the connection to the buss if not through an OCPD? I always have used circuit breakers to make the connection.

 

[Ken Clark]

On rare occassions, the only option is to connect to the line side lugs or feed through lugs of a panel board if all circuits are being used. NEC does not appear to reference Article 240 in the Article 285 - TVSS. Would that dictate that no OCPD is required?

 

[lj]

OCP on TVSS

OCP on TVSS

I have searched for OCP requirements for my own Type 2 TVSS application but, like you, I can find no reference to OCP in NEC 285. However, NEC 230.82(8) says OCP and a disconnecting means are required if the Type 2 TVSS is connected to the line side of the service disconnecting means. Has anyone else identified an NEC requirement for OCP on a Type 2 TVSS that is installed on the load side of the service main? Thanks.

 

[acrwc10]

The OCP protects more then the equipment attached to it, it also protects conductors, How are you going to manage that with out a fuse or breaker ?

 

[Pierre C Belarge]

Did you see 285.21(A)?
It does reference 230.82.


The general rule in the NEC is for the SPD to be on the load side of at least the service overcurrent device, or have it's own OCPD.



Here is some info from the UL White Book, 2008

SURGE PROTECTIVE DEVICES
(VZCA)
GENERAL
This category covers surge protective devices (SPDs) designed for
repeated limiting of transient voltage surges as specified in the standard on
50 or 60 Hz power circuits not exceeding 1000 V and designated as follows:

Type 1 ? Permanently connected SPDs intended for installation
between the secondary of the service transformer and the line side of
the service equipment overcurrent device, as well as the load side,
including watt-hour meter socket enclosures and intended to be
installed without an external overcurrent protective device.

Type 2 ? Permanently connected SPDs intended for installation on the
load side of the service equipment overcurrent device, including SPDs
located at the branch panel.

Type 3 ? Point-of-utilization SPDs, installed at a minimum conductor
length of 10 m (30 ft) from the electrical service panel to the point of
utilization, e.g., cord-connected, direct plug-in, receptacle type and
SPDs installed at the utilization equipment being protected. The distance
(10 m) is exclusive of conductors provided with or used to attach
SPDs.

 

[topgone]

I have searched for OCP requirements for my own Type 2 TVSS application but, like you, I can find no reference to OCP in NEC 285. However, NEC 230.82(8) says OCP and a disconnecting means are required if the Type 2 TVSS is connected to the line side of the service disconnecting means. Has anyone else identified an NEC requirement for OCP on a Type 2 TVSS that is installed on the load side of the service main? Thanks.

The catch in 230.82 . . . "If suitable, overcurrent protection and disconnecting means are provided."
The fact is, you don't want your OCP to trip off leaving your pricey equipment unprotected from transients! IMO, it is not "suitable" to provide OCP to your equipment that will open the SPD circuit on spurious values. A disconnecting means however must be provided for servicing purposes of the SPD.

 

[lj]

OCP on TVSS

OCP on TVSS

All of you have good points. I certainly don't want the SPD to trip off line unecessarily. However, I think 230.82 might not apply to my situation since the SPD is a Type 2 TVSS to be connected to the load side of the service main, not to the line side. Nevertheless, it seems an OCPD is needed to comply with NEC 240.4. I will need to use the 10' tap rule from NEC 240.21.(B)(1), because there is no space for another breaker on the bus (it's a service-entrance-rated automatic transfer switch). Thanks for your advice.

 

[don_resqcapt19]

These are not Chapter 4-8 installations...all of the rules in Chapters 1-4 apply.
Correction:
These are not Chapter 5-8 installations...all of the rules in Chapters 1-4 apply.

 

[jim dungar]

... because there is no space for another breaker on the bus (it's a service-entrance-rated automatic transfer switch). Thanks for your advice.

Too bad. TVSS leads should be kept as short as possible and in a straight line. And yes, there are TVSS devices that can be direct connected to bus bars, they use the main device for protection but they are usually not very "fancy" or large.