How do TVSS and Circuit Breakers (thermal-magnetic) interact with each-other?

Question

In EU you can find thermal-magnetic circuit breakers all other the places in buildings and it's not uncommon to have daisy chains of them (meaning a main panel will have one, which is connected to another secondary panel which has another one, etc).

First of all I am not whether having daisy chaining of breakers increase surge protections (against lightning or shorts)?

Also, say we have a TVSS in the mix now (e.g. one found in a UPS), what is the electrical relationship between that and the breakers? Do the breakers add protection or do they subtract it to the efficiency of the TVSS? Or does it not matter at all?

Thanks a lot!

Answer 1

Breakers are for overcurrent. TVSS is for overvoltage. They protect against different aspects of different things. They have nothing to do with each other.

Lightning already traveled thousands of feet through the air. The little air gap in a circuit breaker isn't going to do anything to stop the lightning even if it were fast enough, which its not.

Series breakers don't increase protection (in that protection doesn't increase by stacking breakers). They just let you tailor protection for different parts of the system. Each breaker is protecting something known at the time of installation in the system from igniting, but downstream current-handling capability and loads are unknown and could be much smaller. So if you want to protect specifically for those loads you add breakers that trip sooner in series specifically for that load. It also lets only part of the system trip without bringing down everything, and allows you to shutdown part of the system for maintenance without bringing down the whole system.

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In your example, you have a main panel leading to a secondary panel. Just one secondary panel? Or multiple secondary panels? If multiple secondary panels, the current capability of those panels is probably less than the main panel which means the main panel would have a larger breaker since it must carry all the current, while the secondary panels have smaller breakers since they only carry a fraction of the current running through the main panel.

So if something goes wrong downstream of the secondary panel, only that panel trips and it trips at a value low enough to protect that panel. If it was the main panel that had to trip, the secondary panel would be long gone and on fire since the main panel would only trip if the secondary panel passed the same current that the main panel was expected to trip at.

If something goes wrong within the main panel or itself or after the main panel but before the secondary panel, then the main panel trips. The breakers secondary panels could have never protected against that something happening upstream of them.

Answer 2

This current breaker is an essential part of the Transient Voltage Surge Suppressor or “Surge Protective Device” or (SPD) as the generic new name.

When a lightning transient triggers the TVSS in 10 microseconds or less, the follow-on current is huge. Depending on the phase the instant short circuit current is so high, that it must dissipate the transient Joules until the breaker can trip, otherwise it will detonate material and melt conductors.

Thus speed of the breaker is important to ensure the part selected is compatible with the trip time duration. The TVSS is much faster than gas tubes which are sometimes used with fuses.