surge arrester

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Right, but this website uses one general term: surge protection device (SPD) . HoweNEC has 2 separate sections. One is for surge arrester and the other is for transient voltagr surge suppresspr. What would be the difference between tye two?
 
NEC article 280 is for surge arresters, and article 285 is for transient voltage surge suppressors. What would be the difference between the two?
 
timm333 said:
NEC article 280 is for surge arresters, and article 285 is for transient voltage surge suppressors. What would be the difference between the two?
Click to expand...
Read all of the words...

280.1 Scope. This article covers general requirements, installation
requirements, and connection requirements for surge
arresters installed on premises wiring systems over 1 kV.
Click to expand...
285.1 Scope. This article covers general requirements, installation
requirements, and connection requirements for
SPDs [surge arresters and transient voltage surge suppressors
(TVSSs)] permanently installed on premises wiring
systems 1 kV or less.
Click to expand...

They are not the same, can you spot the difference?

By the way I'm not being as condescending as it seemed when I re-read my post just now, I think we've all done this sort of thing at one time or another. At least I know I have...
 
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Jref, yes I see that article 280 is for >1kV, and article 285 is for <=1kV. So it is clear that article 280 will apply for switching surges. Switching surges originate internally within the structure, for example from switching of inductive loads.

IEEE recommends (as attached) that the arresters for switching surges should be used for extra high voltages (>242 kV). However in practice, arresters for switching surges are used for much less voltage, as low as 2.4 kV.

Is it worthwhile to use the arresters for switching surges for circuits of 2.4 kV, or should they only be used for the extra high voltage of >242 kV?
 

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  • IEEE Surge 9.pdf
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timm333 said:
Jref, yes I see that article 280 is for >1kV, and article 285 is for <=1kV. So it is clear that article 280 will apply for switching surges. Switching surges originate internally within the structure, for example from switching of inductive loads.
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Was that a typo or are you confused?
The division is not based on the expected magnitude of the surge voltage in an unprotected system. It is based on the nominal operating voltage of the system.
....on premises wiring systems over 1 kV
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280 will apply for switching surges inside your building only if your distribution voltage or load voltage inside the building is >1kV, and even then only if the devices are installed on the medium voltage portion of the system.

I would say just the opposite, namely that unless you have an internal medium voltage system, including perhaps very large motors, the Article 280 devices will affect primarily utility operations.
The inductive surges at turn off on a 4kV motor can be very high, but AFAIK they would be handled by the motor controller itself and you would not have to rely on external devices.
 
No not confused, actually I believed that switching surges occurred only for nominal voltages above 1kV, so I said that for switching surges only article 280 will apply (not 285 because 285 is for nominal voltage below 1kV).

My other question is still unanswered, why do IEEE say (in attachment above) that switching surges should are prominent only for extra high nominal voltages of (>242 kV), while we know that large medium voltage motors can generate switching surges too.
 
timm333 said:
No not confused, actually I believed that switching surges occurred only for nominal voltages above 1kV, so I said that for switching surges only article 280 will apply (not 285 because 285 is for nominal voltage below 1kV).

My other question is still unanswered, why do IEEE say (in attachment above) that switching surges should are prominent only for extra high nominal voltages of (>242 kV), while we know that large medium voltage motors can generate switching surges too.
Click to expand...

Possibly because the excerpt you posted seems to be talking about switching surges in terms of a disconnect in a substation rather than in a motor controller.
For higher voltage distribution or transmission substations, the switching surges become a more acute problem at higher voltages where it is hard to increase insulation withstand voltage, even though they may still occur at lower voltages.
Nothing there that is directly relevant to motor loads at the branch circuit level.
But if you do have MV motor loads and want to incorporate surge mitigation, you would have to use arresters (280) rather than SPDs (285).
 
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