Surge Protective Device at the point of service connected through a branch bkr, overcurrent req'd ?

bdn2004 · Dec 5, 2022

Looking at a proposed electrical design....they've got an SPD connected right at the new switchboard through a branch circuit breaker.
I'm thinking perhaps this just for disconnection means.... but they used a #6 wire on a 100A trip. #6 is too small for a 100A circuit breaker normally. But if it's just just used for disconnection - is this necessarily wrong ? And perhaps it's a tap rule exception, and the HPI cable has a higher ampacity ?

unclebob · Dec 5, 2022

This SDP module should be installed right into the switchgear. 8 feet distance is too large and protection is lost. Our manufacturer states a max cable length of 14 in! And we use 30 A breakers. Not much current flows into this, only high voltage transient surges.

TugboatEng · Dec 5, 2022

If it's a MOV type surge protector, it goes into a short circuit mode during the surge. They are limited on the amount of energy they can dissipate. It should have a protective breaker or else the suppressor can fail incandescently during longer duration faults. Ideally, the surge suppressor will cause a trip of the main breaker to protect both itself and the equipment.

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Surge Protective Device at the point of service connected through a branch bkr, overcurrent req'd ?

bdn2004

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TugboatEng

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